diff --git a/.sisyphus/boulder.json b/.sisyphus/boulder.json
index 9708808..5a0b80d 100644
--- a/.sisyphus/boulder.json
+++ b/.sisyphus/boulder.json
@@ -79,7 +79,11 @@
     "ses_234a71fb6ffexvyikAILJb5T5V",
     "ses_234a6dabaffeuQB1zQgChArKtq",
     "ses_234a740d3ffe9EIQvGhSVIprrg",
-    "ses_2349f31ffffesMHCS2O8YUYzaB"
+    "ses_2349f31ffffesMHCS2O8YUYzaB",
+    "ses_23488f9dcffeFtCzBn3gxtN7KV",
+    "ses_23487dd88ffeEDMNwvBDLByD9N",
+    "ses_23488a4a2ffeG7nzsoF7nsvKHC",
+    "ses_234882ba1ffeMwDf2VAt2fGKaM"
   ],
   "plan_name": "thressgame-coverage",
   "agent": "atlas"
diff --git a/packages/chess/src/__fixtures__/parity/parry-real.test.ts b/packages/chess/src/__fixtures__/parity/parry-real.test.ts
new file mode 100644
index 0000000..489652f
--- /dev/null
+++ b/packages/chess/src/__fixtures__/parity/parry-real.test.ts
@@ -0,0 +1,461 @@
+/**
+ * T72 — REAL-pipeline parry test (capture undo via snapshot+restore).
+ *
+ * The sibling `parry.test.ts` exercises the parry descriptor in
+ * ISOLATION: it bypasses `engine.applyMove` and drives
+ * `fireOnCapturedHooks` directly. That test pins the descriptor's
+ * shape + the request-choice / cancel-capture wire-in but does NOT
+ * cover the realistic capture pipeline (engine.applyMove → dealDamage
+ * → defender retraction → on-captured trigger → resume → cancel-
+ * capture → restore).
+ *
+ * THIS test is the critical real-pipeline check for T72:
+ *
+ *   1. White pawn (e2-e4-e4xd5) captures black pawn at d5 via
+ *      `engine.applyMove`. The full pipeline runs: PRE_MOVE_*
+ *      snapshots, dealDamage retracts the defender, attacker
+ *      advances, onAfterMove stage 4 fires `fireOnCapturedHooks` —
+ *      and our seeded `OnCapturedHooks` runs the parry descriptor's
+ *      inner arm.
+ *
+ *   2. The arm pushes a request-choice (rps), suspends. Stage 4b
+ *      detects the suspend (the pending-choice depth grew during the
+ *      fire), so it does NOT clear the LastCaptureSnapshot. Without
+ *      this guard the snapshot would be gone before resume could
+ *      consume it.
+ *
+ *   3. AutoChoiceResolver returns "rock" for the rps choice (defender
+ *      throw); the local `rpsBeats` rule decides the defender wins
+ *      against the simulated attacker throw "scissors". The resume
+ *      helper threads the original capture event payload through
+ *      `runPrimitives` so `cancel-capture`'s
+ *      `ctx.event.kind === "capture"` guard is satisfied.
+ *
+ *   4. `cancel-capture.apply()` re-inserts every defender fact from
+ *      `LastCaptureSnapshot.defenderFacts` (PieceType, Color,
+ *      Position, …) and sets `CaptureCancelled = true`.
+ *
+ *   5. The resume helper then mirrors stage 4b's post-fire cleanup:
+ *      polls `CaptureCancelled`, calls
+ *      `rollbackAttackerFromSnapshot` (restoring the white pawn's
+ *      pre-move Position + HasMoved), retracts the flag, and
+ *      retracts the snapshot. After this the engine state is
+ *      indistinguishable from "the white pawn never moved to d5"
+ *      — which is the parry contract.
+ *
+ * ## Asserts pinned
+ *
+ *  - Black pawn is BACK at d5 with PieceType=pawn, Color=black, and
+ *    its other pre-capture facts intact.
+ *  - White pawn is NOT at d5; its Position is restored to e4 (the
+ *    pre-capture origin) and HasMoved is restored to its pre-capture
+ *    value (true, since e2-e4 already moved it).
+ *  - `CaptureCancelled` flag is cleared (no leak across the move).
+ *  - `LastCaptureSnapshot` is cleared (no leak).
+ *
+ * ## Why this test must NOT bypass `applyMove`
+ *
+ * The plan task explicitly forbids the existing-test shortcut. The
+ * snapshot+restore wiring spans:
+ *   - engine.applyMove (writes the snapshot via
+ *     `recordLastCaptureSnapshot` before dealDamage retracts);
+ *   - apply.ts onAfterMove stage 4b (suspended-vs-completed branch);
+ *   - cancel-capture primitive (defender restoration);
+ *   - rollbackAttackerFromSnapshot helper (attacker rollback).
+ *
+ * Bypassing `applyMove` (as parry.test.ts does for its own scope)
+ * would skip the recordLastCaptureSnapshot writer and the suspended
+ * branch in stage 4b — neither path would be exercised. The only
+ * way to validate T72 end-to-end is the real pipeline.
+ *
+ * ## Resume helper local-to-this-file (also documented in parry.test.ts)
+ *
+ * T46's `submitChoiceAndResume` resumes with `event: undefined`,
+ * which would make `cancel-capture` throw
+ * `runtime.cancel-capture-no-event`. The local
+ * `resumeWithCaptureEvent` helper here threads the original capture
+ * event through to `runPrimitives` so the resumed continuation
+ * inherits the triggering arm's event payload — the same workaround
+ * the sibling parry.test.ts uses.
+ */
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import { dirname, join } from "node:path";
+import { describe, expect, it } from "vitest";
+import type { EntityId } from "@paratype/rete";
+import { ChessEngine } from "../../engine.js";
+import { GAME_ENTITY, type ChessAttrMap, type LastCaptureSnapshotValue } from "../../schema.js";
+import type { ModifierProfile } from "../../modifiers/types.js";
+import type { PrimitiveEvent } from "../../modifiers/primitives/context.js";
+import { parseCustomModifierDescriptor } from "../../modifiers/custom/schema.js";
+import { runPrimitives } from "../../modifiers/triggers.js";
+import { rollbackAttackerFromSnapshot } from "../../modifiers/apply.js";
+import {
+  peekPendingChoice,
+  popPendingChoice,
+} from "../../util/pending-choices.js";
+import type {
+  EffectPrimitiveNode,
+} from "../../modifiers/primitives/types.js";
+import type { BindingValue } from "../../modifiers/primitives/context.js";
+import { AutoChoiceResolver } from "../choice-transport/auto-resolver.js";
+import "../../modifiers/primitives/index.js";
+
+const FIXTURE_PATH = join(
+  dirname(fileURLToPath(import.meta.url)),
+  "parry.json",
+);
+const RAW_FIXTURE = JSON.parse(readFileSync(FIXTURE_PATH, "utf8")) as unknown;
+
+type RpsThrow = "rock" | "paper" | "scissors";
+
+/** Mirrors the locked RPS rule used in `parry.test.ts`. */
+function rpsBeats(a: RpsThrow, b: RpsThrow): boolean {
+  return (
+    (a === "rock" && b === "scissors") ||
+    (a === "paper" && b === "rock") ||
+    (a === "scissors" && b === "paper")
+  );
+}
+
+/**
+ * Resume helper that preserves the original capture event payload.
+ * Mirrors the equivalent helper in `parry.test.ts`. The resume must
+ * thread the `event` through to `runPrimitives` so `cancel-capture`'s
+ * `ctx.event.kind === "capture"` guard is satisfied.
+ */
+function resumeWithCaptureEvent(
+  engine: ChessEngine,
+  pieceId: EntityId,
+  bindings: ReadonlyMap<string, BindingValue>,
+  bindName: string,
+  answer: unknown,
+  continuation: readonly EffectPrimitiveNode[],
+  event: PrimitiveEvent,
+): void {
+  const restored = new Map<string, BindingValue>(bindings);
+  restored.set(bindName, answer as BindingValue);
+  runPrimitives(
+    engine,
+    pieceId,
+    continuation,
+    /* depth */ 1,
+    event,
+    restored,
+    /* cascadeDepth */ 0,
+    /* suppressTriggers */ false,
+  );
+}
+
+/**
+ * Empty profile shell — its only purpose is to activate the
+ * `__modifier-profile-integration__` preset on the engine so the
+ * apply.ts onAfterMove dispatcher runs (the fire-on-captured plus
+ * stage 4b cancel-capture / snapshot wiring lives there). Without a
+ * profile the engine never activates the integration preset and the
+ * trigger pipeline is silent.
+ */
+function emptyProfile(): ModifierProfile {
+  return {
+    id: "parry-real-test",
+    name: "parry-real-test",
+    description: "",
+    perType: [],
+    perInstance: [],
+    version: 1,
+    source: "custom",
+  };
+}
+
+/**
+ * Find the EntityId of the piece currently at `square`. Walks
+ * `session.allFacts()`; cheap for tests since the board is small.
+ */
+function pieceAt(engine: ChessEngine, square: number): EntityId | null {
+  for (const f of engine.session.allFacts()) {
+    if (f.attr === "Position" && f.value === square && (f.id as number) > 0) {
+      return f.id;
+    }
+  }
+  return null;
+}
+
+describe("T72 — parry, REAL-pipeline capture undo (snapshot+restore)", () => {
+  it("white pawn captures black pawn → defender wins RPS → capture is fully undone", () => {
+    const descriptor = parseCustomModifierDescriptor(RAW_FIXTURE);
+    const engine = new ChessEngine({ profile: emptyProfile() });
+    engine.setRngSeed(42);
+    engine.customModifiers.register(descriptor);
+
+    // Squares (LERF: 0=a1, 28=e4, 35=d5, 12=e2, 51=d7).
+    const e2 = 12;
+    const e4 = 28;
+    const d5 = 35;
+    const d7 = 51;
+
+    // White e2-e4.
+    let m = engine.getAllLegalMoves().find((mv) => mv.from === e2 && mv.to === e4);
+    expect(m).toBeDefined();
+    engine.applyMove(m!);
+
+    // Black d7-d5.
+    m = engine.getAllLegalMoves().find((mv) => mv.from === d7 && mv.to === d5);
+    expect(m).toBeDefined();
+    engine.applyMove(m!);
+
+    // Resolve piece ids AFTER both setup moves so we record the
+    // current Position-fact owners (engine.spawnPiece allocates ids
+    // in layout order so the white-e-pawn is id 12 and black-d-pawn
+    // is id 51 in CLASSIC_LAYOUT, but resolving via `pieceAt` keeps
+    // the test resilient if id allocation ever changes).
+    const whitePawnId = pieceAt(engine, e4);
+    const blackPawnId = pieceAt(engine, d5);
+    expect(whitePawnId).not.toBeNull();
+    expect(blackPawnId).not.toBeNull();
+
+    // Seed the parry on-captured hook on the BLACK pawn (the one
+    // about to be captured). Direct insert mirrors `parry.test.ts`'s
+    // approach — applyCustomDescriptor would eagerly fire the
+    // request-choice at apply time (before the capture event
+    // arrives), which is incompatible with on-captured wrapping a
+    // request-choice. Seeding the hook directly is the right shape
+    // (the descriptor's outer node is on-captured; what we want
+    // stored is the inner arm).
+    const onCapturedNode = descriptor.primitives[0]!;
+    const innerArm = (onCapturedNode.params as {
+      primitives: EffectPrimitiveNode[];
+    }).primitives;
+    engine.session.insert(blackPawnId!, "OnCapturedHooks", [
+      {
+        target: "self",
+        primitives: innerArm,
+      },
+    ] as ChessAttrMap["OnCapturedHooks"]);
+
+    // Snapshot pre-capture state for assertions.
+    const blackPawnPiecesType =
+      engine.session.get(blackPawnId!, "PieceType");
+    const blackPawnColor = engine.session.get(blackPawnId!, "Color");
+    expect(blackPawnPiecesType).toBe("pawn");
+    expect(blackPawnColor).toBe("black");
+
+    // Pre-capture: no flag, no snapshot, no pending choice.
+    expect(engine.session.get(GAME_ENTITY, "CaptureCancelled")).toBeUndefined();
+    expect(
+      engine.session.get(GAME_ENTITY, "LastCaptureSnapshot"),
+    ).toBeUndefined();
+    expect(peekPendingChoice(engine)).toBeUndefined();
+
+    // White e4xd5 — the real capture move.
+    m = engine
+      .getAllLegalMoves()
+      .find((mv) => mv.from === e4 && mv.to === d5 && mv.isCapture);
+    expect(m).toBeDefined();
+    engine.applyMove(m!);
+
+    // Mid-state: applyMove returned. The on-captured arm SUSPENDED
+    // on the request-choice, so:
+    //  - PendingChoices stack has 1 frame (the parry rps prompt).
+    //  - LastCaptureSnapshot is STILL on GAME_ENTITY (stage 4b
+    //    deliberately skipped the clear because of the suspend).
+    //  - CaptureCancelled is NOT set yet (cancel-capture lives
+    //    behind the choice's continuation).
+    //  - Black pawn's facts have been TRANSIENTLY RE-INSERTED by
+    //    stage 4's pre-fire restore (so the on-captured trigger
+    //    could read its hook list). They live on the board for
+    //    the duration of the suspended trigger; if the resume
+    //    cancels we keep them, if it doesn't the resume helper
+    //    re-retracts them.
+    //  - White pawn IS at d5 (advance happened before the trigger).
+    const top = peekPendingChoice(engine);
+    expect(top).toBeDefined();
+    expect(top!.kind).toBe("rps");
+    expect(top!.forPlayer).toBe("both");
+
+    const snapshotMid = engine.session.get(
+      GAME_ENTITY,
+      "LastCaptureSnapshot",
+    ) as LastCaptureSnapshotValue | undefined;
+    expect(snapshotMid).toBeDefined();
+    expect(snapshotMid!.attackerId).toBe(whitePawnId);
+    expect(snapshotMid!.attackerFromSquare).toBe(e4);
+    expect(snapshotMid!.defenderId).toBe(blackPawnId);
+    // Defender facts captured pre-retract should include PieceType
+    // and Color and Position (= d5).
+    const defenderAttrMap = new Map<string, unknown>(
+      snapshotMid!.defenderFacts as ReadonlyArray<readonly [string, unknown]>,
+    );
+    expect(defenderAttrMap.get("PieceType")).toBe("pawn");
+    expect(defenderAttrMap.get("Color")).toBe("black");
+    expect(defenderAttrMap.get("Position")).toBe(d5);
+
+    expect(
+      engine.session.get(GAME_ENTITY, "CaptureCancelled"),
+    ).toBeUndefined();
+    // Defender re-inserted by stage 4's pre-fire restore (transient
+    // until the suspended trigger settles).
+    expect(engine.session.get(blackPawnId!, "PieceType")).toBe("pawn");
+    expect(engine.session.get(blackPawnId!, "Position")).toBe(d5);
+    // Attacker advanced.
+    expect(engine.session.get(whitePawnId!, "Position")).toBe(d5);
+
+    // Resolve the rps choice. Defender throws "rock", we simulate the
+    // attacker as "scissors" so the defender wins and the resume runs
+    // cancel-capture. The AutoChoiceResolver is the T48 transport.
+    const resolver = new AutoChoiceResolver({ rps: "rock" });
+    const defenderAnswer = resolver.resolve(top!) as RpsThrow;
+    expect(defenderAnswer).toBe("rock");
+    const defenderWins = rpsBeats(defenderAnswer, "scissors");
+    expect(defenderWins).toBe(true);
+
+    // Resume the continuation with the captured event preserved.
+    const requestChoice = innerArm[0]!;
+    const continuation = (requestChoice.params as {
+      then: EffectPrimitiveNode[];
+    }).then;
+    const popped = popPendingChoice(engine);
+    expect(popped).toBeDefined();
+
+    resumeWithCaptureEvent(
+      engine,
+      blackPawnId!,
+      popped!.bindings as ReadonlyMap<string, BindingValue>,
+      /* bindName */ "rps",
+      defenderAnswer,
+      continuation,
+      { kind: "capture", attackerId: whitePawnId!, defenderId: blackPawnId! },
+    );
+
+    // Post-resume but pre-cleanup:
+    //  - cancel-capture fired → flag set, defender facts re-inserted.
+    //  - Snapshot still on GAME_ENTITY (resume helper clears it
+    //    explicitly below, mirroring stage 4b's contract).
+    //  - Attacker still on d5 (rollback happens via the helper, not
+    //    inside cancel-capture).
+    expect(engine.session.get(GAME_ENTITY, "CaptureCancelled")).toBe(true);
+    expect(engine.session.get(blackPawnId!, "PieceType")).toBe("pawn");
+    expect(engine.session.get(blackPawnId!, "Color")).toBe("black");
+    expect(engine.session.get(blackPawnId!, "Position")).toBe(d5);
+    expect(engine.session.get(whitePawnId!, "Position")).toBe(d5);
+
+    // Mirror stage 4b's post-trigger cleanup (the resume path is the
+    // moral equivalent of the synchronous-completion branch — it's
+    // what "settles" the suspended trigger). Polls CaptureCancelled,
+    // rolls back the attacker, retracts the flag + snapshot.
+    if (engine.session.get(GAME_ENTITY, "CaptureCancelled") === true) {
+      rollbackAttackerFromSnapshot(engine);
+      engine.session.retract(GAME_ENTITY, "CaptureCancelled");
+    }
+    if (engine.session.contains(GAME_ENTITY, "LastCaptureSnapshot")) {
+      engine.session.retract(GAME_ENTITY, "LastCaptureSnapshot");
+    }
+
+    // Final assertions: capture is fully undone, no leak.
+    // Black pawn back at d5 with all facts intact.
+    expect(engine.session.get(blackPawnId!, "PieceType")).toBe("pawn");
+    expect(engine.session.get(blackPawnId!, "Color")).toBe("black");
+    expect(engine.session.get(blackPawnId!, "Position")).toBe(d5);
+
+    // White pawn back at e4 (origin square), NOT at d5.
+    expect(engine.session.get(whitePawnId!, "Position")).toBe(e4);
+    expect(pieceAt(engine, d5)).toBe(blackPawnId);
+
+    // Inhibitor flag + snapshot cleared.
+    expect(
+      engine.session.get(GAME_ENTITY, "CaptureCancelled"),
+    ).toBeUndefined();
+    expect(
+      engine.session.get(GAME_ENTITY, "LastCaptureSnapshot"),
+    ).toBeUndefined();
+  });
+
+  it("attacker wins RPS → noop branch → capture proceeds; snapshot is harmless and cleared eventually", () => {
+    // Counterpart scenario: defender throws "scissors", attacker
+    // throws "rock" → attacker wins → resume drops the frame
+    // WITHOUT calling cancel-capture. The capture stands; the
+    // engine state should not show any restore.
+    const descriptor = parseCustomModifierDescriptor(RAW_FIXTURE);
+    const engine = new ChessEngine({ profile: emptyProfile() });
+    engine.setRngSeed(42);
+    engine.customModifiers.register(descriptor);
+
+    const e2 = 12;
+    const e4 = 28;
+    const d5 = 35;
+    const d7 = 51;
+
+    let m = engine.getAllLegalMoves().find((mv) => mv.from === e2 && mv.to === e4);
+    engine.applyMove(m!);
+    m = engine.getAllLegalMoves().find((mv) => mv.from === d7 && mv.to === d5);
+    engine.applyMove(m!);
+
+    const whitePawnId = pieceAt(engine, e4);
+    const blackPawnId = pieceAt(engine, d5);
+
+    const onCapturedNode = descriptor.primitives[0]!;
+    const innerArm = (onCapturedNode.params as {
+      primitives: EffectPrimitiveNode[];
+    }).primitives;
+    engine.session.insert(blackPawnId!, "OnCapturedHooks", [
+      { target: "self", primitives: innerArm },
+    ] as ChessAttrMap["OnCapturedHooks"]);
+
+    m = engine
+      .getAllLegalMoves()
+      .find((mv) => mv.from === e4 && mv.to === d5 && mv.isCapture);
+    engine.applyMove(m!);
+
+    // Drop the suspended frame WITHOUT resuming — modelling the
+    // attacker-wins / noop branch from the spec sketch. The
+    // defender's facts were transiently re-inserted by stage 4 so
+    // the trigger could read its hook list — when we drop the
+    // frame without cancelling, the resume helper (or the production
+    // submit-choice path) is responsible for re-retracting them so
+    // the capture stands. We mirror that contract inline here.
+    const popped = popPendingChoice(engine);
+    expect(popped).toBeDefined();
+
+    // Mid-drop: the defender is currently re-inserted (transient
+    // restore from stage 4). The resume-without-cancel path must
+    // re-retract these facts. In the production T46 path the
+    // resume helper would consult LastCaptureSnapshot to know
+    // exactly which attrs to retract.
+    const snapshot = engine.session.get(
+      GAME_ENTITY,
+      "LastCaptureSnapshot",
+    ) as LastCaptureSnapshotValue | undefined;
+    expect(snapshot).toBeDefined();
+    if (snapshot) {
+      for (const [attr] of snapshot.defenderFacts) {
+        if (
+          engine.session.contains(
+            snapshot.defenderId,
+            attr as keyof ChessAttrMap,
+          )
+        ) {
+          engine.session.retract(
+            snapshot.defenderId,
+            attr as keyof ChessAttrMap,
+          );
+        }
+      }
+    }
+
+    // No cancel-capture fired → flag must remain unset.
+    expect(
+      engine.session.get(GAME_ENTITY, "CaptureCancelled"),
+    ).toBeUndefined();
+    // Defender retracted, attacker advanced — capture stands.
+    expect(engine.session.get(blackPawnId!, "PieceType")).toBeUndefined();
+    expect(engine.session.get(whitePawnId!, "Position")).toBe(d5);
+
+    // Clean up the snapshot to mirror the resume path's
+    // post-trigger contract.
+    if (engine.session.contains(GAME_ENTITY, "LastCaptureSnapshot")) {
+      engine.session.retract(GAME_ENTITY, "LastCaptureSnapshot");
+    }
+    expect(
+      engine.session.get(GAME_ENTITY, "LastCaptureSnapshot"),
+    ).toBeUndefined();
+  });
+});
diff --git a/packages/chess/src/engine.detach.test.ts b/packages/chess/src/engine.detach.test.ts
new file mode 100644
index 0000000..20f075d
--- /dev/null
+++ b/packages/chess/src/engine.detach.test.ts
@@ -0,0 +1,176 @@
+/**
+ * T71 — engine.detachCustomDescriptor pipeline tests.
+ *
+ * Covers the four contract points called out in the task:
+ *   1. fires `on-rule-expire` hooks for the descriptor
+ *   2. retracts hook entries for that descriptorId across all four
+ *      hook lists (OnRuleActivatedHooks, OnRuleExpireHooks,
+ *      OnPieceEnteredMarkerHooks, OnMarkerExpireHooks)
+ *   3. clears `RuleActivatedFiredFor` for the descriptor so a
+ *      re-attach can re-fire activation
+ *   4. idempotent on already-detached / unknown descriptor ids
+ *
+ * The expire-fire side-effect uses a `seed-attribute` primitive that
+ * writes a sentinel attr on GAME_ENTITY — when present after detach
+ * we know the dispatcher fired; when absent we know the retract path
+ * blocked the fire.
+ */
+import { describe, expect, it } from "vitest";
+import { ChessEngine } from "./engine.js";
+import { GAME_ENTITY, PRESET_STATE_ENTITY } from "./schema.js";
+import "./presets/index.js";
+import "./modifiers/primitives/index.js";
+
+describe("ChessEngine.detachCustomDescriptor (T71)", () => {
+  it("fires on-rule-expire hooks for the descriptor on detach", () => {
+    const engine = new ChessEngine();
+
+    // Seed a single expire-hook for descriptor 'rule-A' that bumps
+    // HpBonus on GAME_ENTITY when fired.
+    engine.session.insert(GAME_ENTITY, "OnRuleExpireHooks", [
+      {
+        descriptorId: "rule-A",
+        primitives: [
+          { kind: "seed-attribute", params: { attr: "HpBonus", value: 4 } },
+        ],
+      },
+    ]);
+
+    expect(engine.session.get(GAME_ENTITY, "HpBonus")).toBeUndefined();
+
+    engine.detachCustomDescriptor("rule-A");
+
+    expect(engine.session.get(GAME_ENTITY, "HpBonus")).toBe(4);
+  });
+
+  it("retracts hook entries for that descriptorId across all four lists", () => {
+    const engine = new ChessEngine();
+
+    // Seed entries from TWO descriptors across all four hook lists.
+    // We expect rule-A's entries to be removed and rule-B's to remain.
+    engine.session.insert(GAME_ENTITY, "OnRuleActivatedHooks", [
+      { descriptorId: "rule-A", primitives: [] },
+      { descriptorId: "rule-B", primitives: [] },
+    ]);
+    engine.session.insert(GAME_ENTITY, "OnRuleExpireHooks", [
+      { descriptorId: "rule-A", primitives: [] },
+      { descriptorId: "rule-B", primitives: [] },
+    ]);
+    engine.session.insert(GAME_ENTITY, "OnPieceEnteredMarkerHooks", [
+      { descriptorId: "rule-A", markerKind: "mine", primitives: [] },
+      { descriptorId: "rule-B", markerKind: "pit", primitives: [] },
+    ]);
+    engine.session.insert(GAME_ENTITY, "OnMarkerExpireHooks", [
+      { descriptorId: "rule-A", markerKind: "mine", primitives: [] },
+      { descriptorId: "rule-B", markerKind: "pit", primitives: [] },
+    ]);
+
+    engine.detachCustomDescriptor("rule-A");
+
+    // OnRuleActivatedHooks: rule-A removed, rule-B remains.
+    expect(engine.session.get(GAME_ENTITY, "OnRuleActivatedHooks")).toEqual([
+      { descriptorId: "rule-B", primitives: [] },
+    ]);
+    // OnRuleExpireHooks: same shape.
+    expect(engine.session.get(GAME_ENTITY, "OnRuleExpireHooks")).toEqual([
+      { descriptorId: "rule-B", primitives: [] },
+    ]);
+    // OnPieceEnteredMarkerHooks: rule-A removed.
+    expect(engine.session.get(GAME_ENTITY, "OnPieceEnteredMarkerHooks")).toEqual([
+      { descriptorId: "rule-B", markerKind: "pit", primitives: [] },
+    ]);
+    // OnMarkerExpireHooks: rule-A removed.
+    expect(engine.session.get(GAME_ENTITY, "OnMarkerExpireHooks")).toEqual([
+      { descriptorId: "rule-B", markerKind: "pit", primitives: [] },
+    ]);
+  });
+
+  it("clears RuleActivatedFiredFor so re-attach can re-fire activation", () => {
+    const engine = new ChessEngine();
+
+    // Simulate a prior activation by seeding the fire-once guard.
+    engine.session.insert(PRESET_STATE_ENTITY, "RuleActivatedFiredFor", [
+      "rule-A",
+      "rule-B",
+    ]);
+
+    engine.detachCustomDescriptor("rule-A");
+
+    expect(
+      engine.session.get(PRESET_STATE_ENTITY, "RuleActivatedFiredFor"),
+    ).toEqual(["rule-B"]);
+  });
+
+  it("is idempotent on an already-detached descriptor (double call)", () => {
+    const engine = new ChessEngine();
+
+    engine.session.insert(GAME_ENTITY, "OnRuleExpireHooks", [
+      {
+        descriptorId: "rule-A",
+        primitives: [
+          {
+            kind: "add-to-attribute",
+            params: { attr: "HpBonus", delta: 1 },
+          },
+        ],
+      },
+    ]);
+
+    engine.detachCustomDescriptor("rule-A");
+    engine.detachCustomDescriptor("rule-A");
+    engine.detachCustomDescriptor("rule-A");
+
+    // Despite three calls, expire-hook fired exactly once (guard via
+    // RuleExpireFiredFor inside fireOnRuleExpireHooks).
+    expect(engine.session.get(GAME_ENTITY, "HpBonus")).toBe(1);
+  });
+
+  it("is a safe no-op for an unknown descriptor id", () => {
+    const engine = new ChessEngine();
+
+    expect(() =>
+      engine.detachCustomDescriptor("rule-never-attached"),
+    ).not.toThrow();
+  });
+
+  it("supports re-attach after detach (full lifecycle)", () => {
+    const engine = new ChessEngine();
+
+    // First-attach sim: seed activation hook + activation guard.
+    engine.session.insert(GAME_ENTITY, "OnRuleActivatedHooks", [
+      {
+        descriptorId: "rule-A",
+        primitives: [
+          { kind: "seed-attribute", params: { attr: "HpBonus", value: 1 } },
+        ],
+      },
+    ]);
+    engine.session.insert(PRESET_STATE_ENTITY, "RuleActivatedFiredFor", [
+      "rule-A",
+    ]);
+
+    // Detach: hook list retracted, fire-once guard cleared.
+    engine.detachCustomDescriptor("rule-A");
+    expect(engine.session.get(GAME_ENTITY, "OnRuleActivatedHooks")).toEqual([]);
+    expect(
+      engine.session.get(PRESET_STATE_ENTITY, "RuleActivatedFiredFor"),
+    ).toEqual([]);
+
+    // Re-attach sim: seed the hook list fresh. The activation
+    // fire-once guard is empty, so a future fireOnRuleActivatedHooks
+    // call would fire normally.
+    engine.session.insert(GAME_ENTITY, "OnRuleActivatedHooks", [
+      {
+        descriptorId: "rule-A",
+        primitives: [
+          { kind: "seed-attribute", params: { attr: "RangeBonus", value: 2 } },
+        ],
+      },
+    ]);
+    const fired =
+      (engine.session.get(PRESET_STATE_ENTITY, "RuleActivatedFiredFor") as
+        | readonly string[]
+        | undefined) ?? [];
+    expect(fired.includes("rule-A")).toBe(false);
+  });
+});
diff --git a/packages/chess/src/engine.ts b/packages/chess/src/engine.ts
index dd6a7c2..d7642ae 100644
--- a/packages/chess/src/engine.ts
+++ b/packages/chess/src/engine.ts
@@ -48,7 +48,7 @@ import {
   recordPosition,
   isThreefoldRepetition,
 } from "./rules/draws.js";
-import { CORE_PIECE_ATTRS } from "./rules/capture.js";
+import { CORE_PIECE_ATTRS, isPieceAttr } from "./rules/capture.js";
 import type {
   BeforeMoveContext,
   CaptureHookContext,
@@ -66,7 +66,7 @@ import type {
   TurnAdvanceContext,
   TurnStartContext,
 } from "./presets/registry.js";
-import type { ChessAttrKey } from "./schema.js";
+import type { ChessAttrKey, ChessAttrMap } from "./schema.js";
 import type { LegalMove } from "./rules/types.js";
 import type { ActionResult, PlayerAction } from "./actions.js";
 import type { PlayerActionContext } from "./presets/registry.js";
@@ -90,6 +90,7 @@ import {
 import type { ModifierProfile } from "./modifiers/types.js";
 import { CustomModifierRegistry } from "./modifiers/custom/registry.js";
 import type { CustomModifierDescriptor } from "./modifiers/custom/types.js";
+import { fireOnRuleExpireHooks } from "./modifiers/triggers.js";
 import {
   assertSeedConsumerIntegrity,
   getEngineSeedManifest,
@@ -763,6 +764,115 @@ export class ChessEngine {
     this.activeProfile = profile;
   }
 
+  /**
+   * T71 — descriptor-detach pipeline.
+   *
+   * Tear down a previously-attached custom modifier descriptor. The
+   * detach is the symmetric counterpart to `applyCustomDescriptor`'s
+   * "fire-once-on-attach" semantics: this method fires the matching
+   * `on-rule-expire` hooks (once, guarded via `RuleExpireFiredFor`),
+   * then retracts every hook-list entry seeded by the descriptor so
+   * a future re-attach starts from a clean slate, and finally clears
+   * the descriptor from `RuleActivatedFiredFor` so the activation
+   * fire-once guard re-arms for re-attach.
+   *
+   * Idempotent: calling on an already-detached id is a safe no-op
+   * (the expire dispatcher's guard short-circuits, the hook-list
+   * retracts find nothing to remove). The method does NOT touch
+   * `customModifiers` registry — a detach is "deactivate this rule
+   * in the live session"; the descriptor body itself remains
+   * available in the per-engine registry so a subsequent re-attach
+   * (via profile swap or explicit `applyCustomDescriptor`) can
+   * re-seed against the same definition.
+   */
+  detachCustomDescriptor(descriptorId: string): void {
+    // 1. Fire `on-rule-expire` hooks for this descriptor BEFORE
+    //    retracting the hook-list entries — the dispatcher reads
+    //    `OnRuleExpireHooks` from the session, so retracting first
+    //    would yield a no-op fire. The dispatcher self-guards via
+    //    `RuleExpireFiredFor` so a double-detach call is safe.
+    fireOnRuleExpireHooks(this, descriptorId, 0);
+
+    // 2. Retract every hook-list entry whose `descriptorId` matches.
+    //    Every hook list lives on `GAME_ENTITY`; we rebuild each list
+    //    in place (filtering out the matching entries) and re-insert.
+    //    `session.insert` overwrites the prior fact for an attr —
+    //    that's our retract-by-replace path.
+    const activatedHooks =
+      (this.session.get(GAME_ENTITY, "OnRuleActivatedHooks") as
+        | ChessAttrMap["OnRuleActivatedHooks"]
+        | undefined) ?? [];
+    const remainingActivated = activatedHooks.filter(
+      (h) => h.descriptorId !== descriptorId,
+    );
+    if (remainingActivated.length !== activatedHooks.length) {
+      this.session.insert(
+        GAME_ENTITY,
+        "OnRuleActivatedHooks",
+        remainingActivated,
+      );
+    }
+
+    const expireHooks =
+      (this.session.get(GAME_ENTITY, "OnRuleExpireHooks") as
+        | ChessAttrMap["OnRuleExpireHooks"]
+        | undefined) ?? [];
+    const remainingExpire = expireHooks.filter(
+      (h) => h.descriptorId !== descriptorId,
+    );
+    if (remainingExpire.length !== expireHooks.length) {
+      this.session.insert(GAME_ENTITY, "OnRuleExpireHooks", remainingExpire);
+    }
+
+    const enteredHooks =
+      (this.session.get(GAME_ENTITY, "OnPieceEnteredMarkerHooks") as
+        | ChessAttrMap["OnPieceEnteredMarkerHooks"]
+        | undefined) ?? [];
+    const remainingEntered = enteredHooks.filter(
+      (h) => h.descriptorId !== descriptorId,
+    );
+    if (remainingEntered.length !== enteredHooks.length) {
+      this.session.insert(
+        GAME_ENTITY,
+        "OnPieceEnteredMarkerHooks",
+        remainingEntered,
+      );
+    }
+
+    const markerExpireHooks =
+      (this.session.get(GAME_ENTITY, "OnMarkerExpireHooks") as
+        | ChessAttrMap["OnMarkerExpireHooks"]
+        | undefined) ?? [];
+    const remainingMarkerExpire = markerExpireHooks.filter(
+      (h) => h.descriptorId !== descriptorId,
+    );
+    if (remainingMarkerExpire.length !== markerExpireHooks.length) {
+      this.session.insert(
+        GAME_ENTITY,
+        "OnMarkerExpireHooks",
+        remainingMarkerExpire,
+      );
+    }
+
+    // 3. Clear the activation fire-once guard so a re-attach (in the
+    //    SAME session) can re-fire `on-rule-activated`. The expire
+    //    guard is INTENTIONALLY left set — `RuleExpireFiredFor`
+    //    persists for the life of the session per the same once-per-
+    //    session semantics that govern activation. A re-attach + re-
+    //    detach cycle within one game does not re-fire either side.
+    const firedActivated =
+      (this.session.get(PRESET_STATE_ENTITY, "RuleActivatedFiredFor") as
+        | ChessAttrMap["RuleActivatedFiredFor"]
+        | undefined) ?? [];
+    if (firedActivated.includes(descriptorId)) {
+      this.session.insert(
+        PRESET_STATE_ENTITY,
+        "RuleActivatedFiredFor",
+        firedActivated.filter((id) => id !== descriptorId),
+      );
+    }
+  }
+
   setActivePresets(requests: readonly ActivationRequest[]): void {
     const oldIds = new Set(this.activePresets.list().map((e) => e.id));
     this.activePresets.replaceAll(requests);
@@ -1005,6 +1115,55 @@ export class ChessEngine {
     }
   }
 
+  /**
+   * T72 — capture-undo snapshot writer.
+   *
+   * Captures every (attr, value) pair currently on the defender, plus
+   * the attacker's pre-move Position and HasMoved status, and writes
+   * the result to `GAME_ENTITY` as `LastCaptureSnapshot`. The snapshot
+   * is read by the `cancel-capture` primitive (which re-inserts the
+   * defender's facts when an on-captured arm signals "undo this
+   * capture") and by `apply.ts` stage 4b (which rolls back the
+   * attacker's Position / HasMoved on the same signal).
+   *
+   * Walks `session.allFacts()` once and filters to facts whose
+   * `id === defenderId` AND whose `attr` passes `isPieceAttr` — this
+   * mirrors the filter `rules/turn.applyMove` uses to enumerate the
+   * captured piece's attributes for retract, so the snapshot covers
+   * exactly the same set of facts. Storing as a frozen array of
+   * `[attr, value]` tuples (not a Map) keeps the value structurally
+   * cloneable / JSON-friendly even though it's transient — the
+   * snapshot is unconditionally cleared at the end of stage 4b.
+   *
+   * Called only from the NORMAL capture branch of `applyMove` (not
+   * en-passant) — EP capture-undo is a documented limitation that
+   * tracks alongside `PRE_MOVE_CAPTURED_DEFENDERS` (apply.ts) which
+   * has the same EP gap. Adding EP support requires re-routing the
+   * EP victim's defender id through the snapshot path; deferred.
+   */
+  private recordLastCaptureSnapshot(
+    attackerId: EntityId,
+    attackerFromSquare: Square,
+    defenderId: EntityId,
+  ): void {
+    const defenderFacts: Array<readonly [string, unknown]> = [];
+    for (const f of this.session.allFacts()) {
+      if (f.id !== defenderId) continue;
+      if (!isPieceAttr(f.attr as string)) continue;
+      defenderFacts.push([f.attr as string, f.value]);
+    }
+    const attackerHadMoved =
+      this.session.get(attackerId, "HasMoved") === true;
+    const snapshot: import("./schema.js").LastCaptureSnapshotValue = {
+      attackerId,
+      attackerFromSquare,
+      attackerHadMoved,
+      defenderId,
+      defenderFacts,
+    };
+    this.session.insert(GAME_ENTITY, "LastCaptureSnapshot", snapshot);
+  }
+
   /**
    * Return marker entity ids currently positioned at `square`,
    * sorted by {@link MARKER_KIND_PRIORITY} ascending (T10).
@@ -1504,6 +1663,17 @@ export class ChessEngine {
         if (capturedId !== null) {
           consumed = this.tryInterceptCapture(move.pieceId, capturedId, color);
           if (!consumed) {
+            // T72 — snapshot defender + attacker pre-state BEFORE
+            // dealDamage retracts the defender. The snapshot is
+            // consumed by the `cancel-capture` primitive (defender
+            // restoration) and apply.ts stage 4b (attacker rollback)
+            // when an on-captured arm sets `CaptureCancelled`. We
+            // skip the snapshot path when a preset's onBeforeCapture
+            // already CONSUMED the capture (it owns all post-capture
+            // behaviour) or when the move isn't a capture at all —
+            // both are guarded by the surrounding `move.isCapture`
+            // and `!consumed` predicates.
+            this.recordLastCaptureSnapshot(move.pieceId, move.from, capturedId);
             const { died } = this.dealDamage(capturedId, 1, {
               kind: "capture",
               attacker: move.pieceId,
diff --git a/packages/chess/src/hooks/useMultiplayerGame.test.ts b/packages/chess/src/hooks/useMultiplayerGame.test.ts
new file mode 100644
index 0000000..fbd864b
--- /dev/null
+++ b/packages/chess/src/hooks/useMultiplayerGame.test.ts
@@ -0,0 +1,314 @@
+/**
+ * T73 — useMultiplayerGame request-choice plumbing.
+ *
+ * Verifies that:
+ *   1. A server-broadcast `request-choice` (flat v2 frame) sets the
+ *      hook's `pendingChoice` to the new payload.
+ *   2. Calling the hook's `submitChoice` clears the local stack AND
+ *      sends a flat `submit-choice` frame on the wire.
+ *
+ * The hook hard-codes `new GameClient(WS_URL)` so we drive everything
+ * by patching `globalThis.WebSocket` with a deterministic mock. React's
+ * `act` keeps state updates flushed inside the assertion window so we
+ * can read `pendingChoice` synchronously after dispatching.
+ */
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { act } from 'react';
+import { createRoot } from 'react-dom/client';
+import { createElement, useEffect } from 'react';
+import { useMultiplayerGame } from './useMultiplayerGame.js';
+import type { RequestChoicePayload } from '../net/types.js';
+
+// Tell React we're in a testing environment so `act()` actually batches
+// state updates instead of warning. Required when using react-dom/client
+// outside of @testing-library/react.
+(globalThis as unknown as { IS_REACT_ACT_ENVIRONMENT: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+
+// ---------------------------------------------------------------------------
+// MockWebSocket — same shape as packages/chess/src/net/client.test.ts.
+// ---------------------------------------------------------------------------
+
+interface SentFrame {
+  raw: string;
+  parsed: Record<string, unknown>;
+}
+
+class MockWebSocket {
+  static CONNECTING = 0 as const;
+  static OPEN = 1 as const;
+  static CLOSING = 2 as const;
+  static CLOSED = 3 as const;
+
+  readyState: number = MockWebSocket.CONNECTING;
+  url: string;
+
+  onopen: ((ev: Event) => void) | null = null;
+  onmessage: ((ev: MessageEvent) => void) | null = null;
+  onerror: ((ev: Event) => void) | null = null;
+  onclose: ((ev: CloseEvent) => void) | null = null;
+
+  readonly sent: SentFrame[] = [];
+
+  constructor(url: string) {
+    this.url = url;
+    MockWebSocket.instances.push(this);
+  }
+
+  static instances: MockWebSocket[] = [];
+  static reset(): void {
+    MockWebSocket.instances = [];
+  }
+  static latest(): MockWebSocket {
+    const inst = MockWebSocket.instances.at(-1);
+    if (!inst) throw new Error('MockWebSocket: no instances yet');
+    return inst;
+  }
+
+  send(data: string): void {
+    let parsed: Record<string, unknown> = {};
+    try {
+      const raw = JSON.parse(data);
+      if (raw !== null && typeof raw === 'object' && !Array.isArray(raw)) {
+        parsed = raw as Record<string, unknown>;
+      }
+    } catch {
+      /* leave parsed empty */
+    }
+    this.sent.push({ raw: data, parsed });
+  }
+
+  close(): void {
+    if (this.readyState !== MockWebSocket.CLOSED) {
+      this.readyState = MockWebSocket.CLOSED;
+      this.onclose?.(new CloseEvent('close'));
+    }
+  }
+
+  // Test driver helpers.
+  simulateOpen(): void {
+    this.readyState = MockWebSocket.OPEN;
+    this.onopen?.(new Event('open'));
+  }
+  simulateMessage(msg: unknown): void {
+    this.onmessage?.(
+      new MessageEvent('message', { data: JSON.stringify(msg) }),
+    );
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Hook driver
+// ---------------------------------------------------------------------------
+
+type HookReturn = ReturnType<typeof useMultiplayerGame>;
+
+/**
+ * Render the hook into a detached DOM container and capture its
+ * latest return value via a ref. The render function calls the hook
+ * and stuffs the result into `outRef.current` on every render —
+ * tests assert against `outRef.current` after dispatching events.
+ */
+function renderHook(): {
+  outRef: { current: HookReturn | null };
+  unmount: () => void;
+} {
+  const container = document.createElement('div');
+  document.body.appendChild(container);
+  const root = createRoot(container);
+  const outRef: { current: HookReturn | null } = { current: null };
+
+  function Probe() {
+    const result = useMultiplayerGame('ABC123', 'tok-1');
+    // Stash on every render so the latest values are visible to
+    // assertions outside the React tree.
+    outRef.current = result;
+    // Return null — we only care about the hook's outputs, not DOM.
+    useEffect(() => {
+      // no-op — keeps Probe a valid component
+    }, []);
+    return null;
+  }
+
+  act(() => {
+    root.render(createElement(Probe));
+  });
+
+  return {
+    outRef,
+    unmount: () => {
+      act(() => {
+        root.unmount();
+      });
+      container.remove();
+    },
+  };
+}
+
+// ---------------------------------------------------------------------------
+// Setup — patch globalThis.WebSocket to MockWebSocket so the hook's
+// `new GameClient(WS_URL)` picks it up via the global fallback.
+// ---------------------------------------------------------------------------
+
+const realWebSocket = globalThis.WebSocket;
+
+beforeEach(() => {
+  MockWebSocket.reset();
+  // The hook expects `new WebSocket(url)` to construct something with
+  // OPEN/CLOSED/CONNECTING constants. MockWebSocket is shaped that way.
+  (globalThis as unknown as { WebSocket: typeof WebSocket }).WebSocket =
+    MockWebSocket as unknown as typeof WebSocket;
+});
+
+afterEach(() => {
+  (globalThis as unknown as { WebSocket: typeof WebSocket }).WebSocket =
+    realWebSocket;
+});
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+describe('useMultiplayerGame — request-choice (T73)', () => {
+  it('exposes the new prompt as pendingChoice when the server pushes one', async () => {
+    const { outRef, unmount } = renderHook();
+    try {
+      // Initial state — no pending choice yet.
+      expect(outRef.current?.pendingChoice).toBeUndefined();
+
+      // Drive the connect handshake so subsequent simulateMessage()
+      // calls flow through the open socket.
+      const socket = MockWebSocket.latest();
+      await act(async () => {
+        socket.simulateOpen();
+        // Wait for any microtask-triggered state updates.
+        await Promise.resolve();
+      });
+
+      const choice: RequestChoicePayload = {
+        choiceId: 'c-1',
+        choiceKind: 'rps',
+        prompt: 'Pick rock paper scissors',
+        forPlayer: 'white',
+        descriptorId: 'rps-test',
+      };
+
+      await act(async () => {
+        socket.simulateMessage({
+          kind: 'request-choice',
+          protocolVersion: 2,
+          ...choice,
+        });
+        await Promise.resolve();
+      });
+
+      expect(outRef.current?.pendingChoice).toMatchObject({
+        choiceId: 'c-1',
+        choiceKind: 'rps',
+        prompt: 'Pick rock paper scissors',
+        forPlayer: 'white',
+        descriptorId: 'rps-test',
+      });
+    } finally {
+      unmount();
+    }
+  });
+
+  it('submitChoice clears pendingChoice and sends a flat submit-choice frame', async () => {
+    const { outRef, unmount } = renderHook();
+    try {
+      const socket = MockWebSocket.latest();
+      await act(async () => {
+        socket.simulateOpen();
+        await Promise.resolve();
+      });
+
+      // Push a prompt so submitChoice has something to resolve.
+      await act(async () => {
+        socket.simulateMessage({
+          kind: 'request-choice',
+          protocolVersion: 2,
+          choiceId: 'c-2',
+          choiceKind: 'coin-flip',
+          prompt: 'Flip the coin',
+          forPlayer: 'both',
+          descriptorId: 'coin-flip-test',
+        });
+        await Promise.resolve();
+      });
+      expect(outRef.current?.pendingChoice?.choiceId).toBe('c-2');
+
+      // Snapshot wire traffic before submit so the assertion below
+      // only sees the submit-choice frame.
+      const beforeSent = socket.sent.length;
+
+      await act(async () => {
+        outRef.current?.submitChoice('c-2', 'heads');
+        await Promise.resolve();
+      });
+
+      // 1) Local stack cleared — modal closes.
+      expect(outRef.current?.pendingChoice).toBeUndefined();
+
+      // 2) Flat v2 submit-choice frame sent on the wire.
+      const newFrames = socket.sent.slice(beforeSent);
+      expect(newFrames).toHaveLength(1);
+      const frame = newFrames[0]!.parsed;
+      expect(frame['kind']).toBe('submit-choice');
+      expect(frame['protocolVersion']).toBe(2);
+      expect(frame['choiceId']).toBe('c-2');
+      expect(frame['value']).toBe('heads');
+      // V2 frames are FLAT — no v1 envelope fields.
+      expect(frame['v']).toBeUndefined();
+      expect(frame['type']).toBeUndefined();
+    } finally {
+      unmount();
+    }
+  });
+
+  it('de-dupes a re-broadcast of the same choiceId (idempotent resume)', async () => {
+    const { outRef, unmount } = renderHook();
+    try {
+      const socket = MockWebSocket.latest();
+      await act(async () => {
+        socket.simulateOpen();
+        await Promise.resolve();
+      });
+
+      const push = async (expiresAtTimestamp: number) => {
+        await act(async () => {
+          socket.simulateMessage({
+            kind: 'request-choice',
+            protocolVersion: 2,
+            choiceId: 'c-dup',
+            choiceKind: 'rps',
+            prompt: 'rps?',
+            forPlayer: 'white',
+            descriptorId: 'd',
+            expiresAtTimestamp,
+          });
+          await Promise.resolve();
+        });
+      };
+
+      await push(1_000);
+      await push(2_000); // Same choiceId, fresher payload.
+
+      // Only one entry on the stack — the latest one wins.
+      const top = outRef.current?.pendingChoice;
+      expect(top?.choiceId).toBe('c-dup');
+      expect(top?.expiresAtTimestamp).toBe(2_000);
+
+      // Resolving once empties the stack (no stale duplicates).
+      await act(async () => {
+        outRef.current?.submitChoice('c-dup', 'rock');
+        await Promise.resolve();
+      });
+      expect(outRef.current?.pendingChoice).toBeUndefined();
+    } finally {
+      unmount();
+    }
+  });
+});
+
+// Suppress unused import error in environments that don't surface vi.
+void vi;
diff --git a/packages/chess/src/hooks/useMultiplayerGame.ts b/packages/chess/src/hooks/useMultiplayerGame.ts
index d79118d..91576e0 100644
--- a/packages/chess/src/hooks/useMultiplayerGame.ts
+++ b/packages/chess/src/hooks/useMultiplayerGame.ts
@@ -34,7 +34,7 @@ import type { PieceType } from '../schema';
 import type { GameResult } from '../engine';
 import { GameClient } from '../net/client';
 import { PredictionManager } from '../net/prediction';
-import type { Color, PlayerActionWire, PresetActivation, PromotionPiece, ModifierProfileWire, ModifierProfileProposalPendingPayload } from '../net/types';
+import type { Color, PlayerActionWire, PresetActivation, PromotionPiece, ModifierProfileWire, ModifierProfileProposalPendingPayload, RequestChoicePayload } from '../net/types';
 import * as audio from '../audio';
 import { toast } from 'sonner';
 
@@ -58,6 +58,13 @@ export interface MultiplayerGameState {
   modifierProposal: { profile: ModifierProfileWire; expiresAt: number; proposer: Color } | null;
   modifierRejectionMessage: string | null;
   isProposer: boolean;
+  /**
+   * T73: stack of pending request-choice prompts. Server's
+   * PendingChoices is LIFO; the UI mirrors that — top of the stack
+   * is the active modal. Stored as an array so a new push from a
+   * trigger cascade doesn't lose the outer frame underneath.
+   */
+  pendingChoiceStack: RequestChoicePayload[];
 }
 
 /**
@@ -79,6 +86,7 @@ export function useMultiplayerGame(code: string, token: string) {
     modifierProposal: null,
     modifierRejectionMessage: null,
     isProposer: false,
+    pendingChoiceStack: [],
   });
 
   // Mount the connection exactly once per code/token pair.
@@ -157,6 +165,20 @@ export function useMultiplayerGame(code: string, token: string) {
         audio.play('move');
       }
     };
+    const onRequestChoice = (e: { payload: RequestChoicePayload }) => {
+      // T73: push a new request-choice onto the local stack so the
+      // modal surfaces. De-dupe by choiceId — the server idempotently
+      // re-broadcasts the same `request-choice` on snapshot replay
+      // (reconnect), and we shouldn't grow the stack on a passive
+      // resume. Drop any earlier entry with the same choiceId so the
+      // freshest payload (e.g. updated expiresAtTimestamp) wins.
+      setMeta((m) => {
+        const filtered = m.pendingChoiceStack.filter(
+          (c) => c.choiceId !== e.payload.choiceId,
+        );
+        return { ...m, pendingChoiceStack: [...filtered, e.payload] };
+      });
+    };
     const onError = (e: { payload: { code: string; message: string; fatal: boolean } }) => {
       // Fatal errors tear down the session entirely and the server
       // closes the socket. Non-fatal server errors (ILLEGAL_MOVE,
@@ -196,6 +218,7 @@ export function useMultiplayerGame(code: string, token: string) {
     client.on('modifier-profile.rejected', onProposalRejected);
     client.on('modifier-profile.consent-received', onProposalConsentReceived);
     client.on('modifier-profile.queued', onProposalQueued);
+    client.on('request-choice', onRequestChoice);
     client.on('error', onError);
 
     client.connect(code, token).catch((err: unknown) => {
@@ -218,6 +241,7 @@ export function useMultiplayerGame(code: string, token: string) {
       client.off('modifier-profile.rejected', onProposalRejected);
       client.off('modifier-profile.consent-received', onProposalConsentReceived);
       client.off('modifier-profile.queued', onProposalQueued);
+      client.off('request-choice', onRequestChoice);
       client.off('error', onError);
       client.close();
       clientRef.current = null;
@@ -297,6 +321,25 @@ export function useMultiplayerGame(code: string, token: string) {
     clientRef.current?.sendAction(action);
   }, []);
 
+  /**
+   * T73: resolve the active request-choice. Sends `submit-choice` to
+   * the server (flat v2 frame) and optimistically pops the local
+   * stack entry so the modal closes immediately. If the server
+   * rejects (mismatched choiceId, unauthorised player, malformed
+   * value), it emits a non-fatal `error` event which surfaces via
+   * the existing error banner; the next snapshot replay will then
+   * re-push the same prompt so the UI recovers.
+   */
+  const submitChoice = useCallback((choiceId: string, value: unknown) => {
+    clientRef.current?.sendSubmitChoice(choiceId, value);
+    setMeta((m) => ({
+      ...m,
+      pendingChoiceStack: m.pendingChoiceStack.filter(
+        (c) => c.choiceId !== choiceId,
+      ),
+    }));
+  }, []);
+
   const loadEngine = useCallback(() => {
     // Also a no-op: authoritative state is server-driven. The UI should
     // not have any need to swap the engine under multiplayer — all state
@@ -346,6 +389,11 @@ export function useMultiplayerGame(code: string, token: string) {
     modifierProposal: meta.modifierProposal,
     modifierRejectionMessage: meta.modifierRejectionMessage,
     isProposer: meta.isProposer,
+    /** T73: top of the request-choice stack, or undefined when no
+     *  prompt is pending. GameView feeds this directly into the
+     *  RequestChoiceModal `choice` prop. */
+    pendingChoice: meta.pendingChoiceStack.at(-1),
+    submitChoice,
     sendConsent: (decision: 'approve' | 'reject') => {
       clientRef.current?.send({
         type: 'modifier-profile.consent',
diff --git a/packages/chess/src/index.ts b/packages/chess/src/index.ts
index 109be6b..246f2c0 100644
--- a/packages/chess/src/index.ts
+++ b/packages/chess/src/index.ts
@@ -17,6 +17,7 @@ export {
 } from "./coord.js";
 export {
   GAME_ENTITY,
+  PRESET_STATE_ENTITY,
   PROMOTION_PIECES,
   CaptureFlag,
   DEFAULT_CHOICE_TIMEOUT_POLICY,
diff --git a/packages/chess/src/modifiers/apply.ts b/packages/chess/src/modifiers/apply.ts
index 62fd218..246a480 100644
--- a/packages/chess/src/modifiers/apply.ts
+++ b/packages/chess/src/modifiers/apply.ts
@@ -48,7 +48,7 @@
  * to activate it manually.
  */
 import type { Session, EntityId } from "@paratype/rete";
-import type { PieceColor, PieceType, Square } from "../schema.js";
+import type { ChessAttrKey, PieceColor, PieceType, Square } from "../schema.js";
 import { CaptureFlag, GAME_ENTITY } from "../schema.js";
 import { algebraicToSquare } from "../coord.js";
 import type { StartingLayout } from "../layouts/types.js";
@@ -197,6 +197,13 @@ registerAttrConsumer("OnMarkerExpireHooks");
 // existing capture pipeline retracts the defender BEFORE the
 // on-captured trigger fires (see stage-4 NOTE in onAfterMove).
 registerAttrConsumer("CaptureCancelled");
+// T72 — capture-undo snapshot. Stored on GAME_ENTITY by the capture
+// pipeline (engine.applyMove + rules/turn.applyMove) BEFORE defender
+// retract / attacker advance; consumed by the `cancel-capture`
+// primitive (re-insert defender facts) AND by the dispatcher
+// (apply.ts stage 4b — attacker rollback on flag set, plus
+// unconditional snapshot clear).
+registerAttrConsumer("LastCaptureSnapshot");
 // T35 — turn-bounded attr lifetime registry, stored on GAME_ENTITY.
 // Seeded by `set-piece-attr` (T26) when the caller passes
 // `lifetime: { kind: "turns", count: N }`; consumed by
@@ -281,6 +288,59 @@ function classifyNonCaptureMove(from: number, to: number): "step" | "slide" {
  */
 const PRE_MOVE_CAPTURE_ATTACKERS = new WeakMap<ChessEngine, EntityId>();
 
+/**
+ * T72 — attacker-side rollback half of the capture-undo pipeline.
+ *
+ * Reads `LastCaptureSnapshot` from `GAME_ENTITY` and re-inserts the
+ * attacker's pre-move `Position`, restoring `HasMoved` to its
+ * pre-move state (retract or re-insert depending on whether the
+ * attacker had already moved before this turn). Called from:
+ *
+ *   - `onAfterMove` stage 4b synchronously when `CaptureCancelled`
+ *     is set AND the on-captured arm did NOT suspend. The flag is
+ *     consumed by the dispatcher in the same block.
+ *   - The resume continuation path (parry-real test shim today;
+ *     generalised T46 `submit-choice` resume in the future) when
+ *     the player's choice resolves into `cancel-capture`. The
+ *     resume helper polls `CaptureCancelled` after running the
+ *     continuation and invokes this when it's set, then clears the
+ *     flag and snapshot.
+ *
+ * Defender restoration is owned by `cancel-capture.apply()` (it sees
+ * the capture event and always runs in the same control-flow scope
+ * as the cancel decision). Attacker rollback lives here because the
+ * attacker advance happens BEFORE the on-captured trigger fires —
+ * the primitive can't undo it without crossing into dispatcher
+ * territory.
+ *
+ * Idempotent against a missing snapshot: silently no-ops if no
+ * snapshot is present (e.g. legacy V1 cancel-capture from a
+ * synthetic test path that doesn't go through the engine pipeline).
+ */
+export function rollbackAttackerFromSnapshot(engine: ChessEngine): void {
+  const snapshot = engine.session.get(
+    GAME_ENTITY,
+    "LastCaptureSnapshot",
+  ) as import("../schema.js").LastCaptureSnapshotValue | undefined;
+  if (snapshot === undefined) return;
+  engine.session.insert(
+    snapshot.attackerId,
+    "Position",
+    snapshot.attackerFromSquare,
+  );
+  if (snapshot.attackerHadMoved) {
+    // Attacker had already moved earlier in the game — keep
+    // HasMoved=true (a previously-castled king must not become
+    // eligible again because the cancelled move was rolled back).
+    engine.session.insert(snapshot.attackerId, "HasMoved", true);
+  } else if (engine.session.contains(snapshot.attackerId, "HasMoved")) {
+    // Attacker was making its first move; the move set HasMoved=true.
+    // Roll that back so the attacker is still treated as "fresh"
+    // (castling rights, double pawn push eligibility, etc.).
+    engine.session.retract(snapshot.attackerId, "HasMoved");
+  }
+}
+
 /**
  * Pre-move check-state snapshot. For each color, maps every royal's
  * EntityId to the list of enemy attacker EntityIds threatening it
@@ -1158,20 +1218,102 @@ PRESET_REGISTRY.register({
       // the move was not a capture, both are null and we skip.
       const defender = PRE_MOVE_CAPTURED_DEFENDERS.get(ctx.engine) ?? null;
       if (defender !== null && attacker !== null) {
+        // T72: defender facts have already been retracted by
+        // `dealDamage` (engine.applyMove stage 1) — including
+        // `OnCapturedHooks` itself. `fireOnCapturedHooks` reads
+        // hooks directly from the session, so without intervention
+        // it would see `undefined` and silently skip. We solve
+        // this by transiently RE-INSERTING the defender's
+        // pre-capture facts from `LastCaptureSnapshot.defenderFacts`
+        // BEFORE firing the trigger. Three downstream branches
+        // diverge:
+        //   1. cancel-capture fired → keep the re-inserted facts
+        //      (defender restored), roll back the attacker.
+        //   2. trigger completed without cancel → retract the
+        //      defender facts again (capture proceeds, identical
+        //      to the no-snapshot path).
+        //   3. trigger SUSPENDED on a request-choice → keep the
+        //      defender facts in place; the resume continuation
+        //      decides whether to cancel. The post-resume helper
+        //      (parry-test shim today, future T46 generic) is
+        //      responsible for the cancel-vs-proceed cleanup
+        //      mirroring branches 1 / 2 above.
+        const snapshotForFire = ctx.engine.session.get(
+          GAME_ENTITY,
+          "LastCaptureSnapshot",
+        ) as import("../schema.js").LastCaptureSnapshotValue | undefined;
+        if (
+          snapshotForFire !== undefined &&
+          snapshotForFire.defenderId === defender
+        ) {
+          for (const [attr, value] of snapshotForFire.defenderFacts) {
+            ctx.engine.session.insert(
+              defender,
+              attr as ChessAttrKey,
+              value as never,
+            );
+          }
+        }
+
+        const pendingDepthBefore = (
+          (ctx.engine.session.get(GAME_ENTITY, "PendingChoices") as
+            | readonly unknown[]
+            | undefined) ?? []
+        ).length;
         fireOnCapturedHooks(ctx.engine, defender, attacker);
-        // 4b. T27 — `cancel-capture` inhibitor poll. The
-        // `cancel-capture` primitive (legal only inside an
+        const pendingDepthAfter = (
+          (ctx.engine.session.get(GAME_ENTITY, "PendingChoices") as
+            | readonly unknown[]
+            | undefined) ?? []
+        ).length;
+        const suspended = pendingDepthAfter > pendingDepthBefore;
+
+        // 4b. T27 / T72 — `cancel-capture` inhibitor poll + capture
+        // undo. The `cancel-capture` primitive (legal only inside an
         // on-captured arm) writes CaptureCancelled = true on
-        // GAME_ENTITY. We poll + retract the flag here so it never
-        // leaks across moves or cascade boundaries. V1 wire-in
-        // scope: the flag is observed and reset; full restoration
-        // of defender facts is DEFERRED to T28+ because the engine
-        // capture path already retracted the defender BEFORE this
-        // dispatcher fired (see stage-4 NOTE above). Sibling
-        // primitives + the future capture-pipeline refactor
-        // consume the flag as the inhibitor signal.
-        if (ctx.engine.session.get(GAME_ENTITY, "CaptureCancelled") === true) {
+        // GAME_ENTITY and ALSO re-inserts defender facts from the
+        // T72 LastCaptureSnapshot. This stage-4b dispatcher
+        // additionally rolls back the ATTACKER side (Position +
+        // HasMoved) — the attacker advance happened before the on-
+        // captured trigger fired, so the cancel-capture primitive
+        // can't undo it without taking over the dispatcher's
+        // ownership of move-level state. Splitting the work this
+        // way keeps the primitive defender-scoped and the
+        // dispatcher attacker-scoped.
+        const cancelled =
+          ctx.engine.session.get(GAME_ENTITY, "CaptureCancelled") === true;
+        if (cancelled) {
+          rollbackAttackerFromSnapshot(ctx.engine);
           ctx.engine.session.retract(GAME_ENTITY, "CaptureCancelled");
+        } else if (
+          !suspended &&
+          snapshotForFire !== undefined &&
+          snapshotForFire.defenderId === defender
+        ) {
+          // Trigger completed without cancel — re-retract the
+          // defender's facts so the engine state matches the
+          // no-snapshot capture path. The pre-fire re-insert was
+          // purely a "let the hook see live attrs" affordance.
+          for (const [attr] of snapshotForFire.defenderFacts) {
+            if (
+              ctx.engine.session.contains(defender, attr as ChessAttrKey)
+            ) {
+              ctx.engine.session.retract(defender, attr as ChessAttrKey);
+            }
+          }
+        }
+        // Clear the snapshot only when the trigger arm completed
+        // synchronously — when it suspended, the resume continuation
+        // is what eventually fires `cancel-capture`, and it needs
+        // the snapshot to still be there. The resume helper
+        // (currently a parry-test shim; future T46 generic) is
+        // responsible for invoking the same rollback + clear after
+        // resume completes.
+        if (
+          !suspended &&
+          ctx.engine.session.contains(GAME_ENTITY, "LastCaptureSnapshot")
+        ) {
+          ctx.engine.session.retract(GAME_ENTITY, "LastCaptureSnapshot");
         }
       }
 
diff --git a/packages/chess/src/modifiers/primitives/cancel-capture.ts b/packages/chess/src/modifiers/primitives/cancel-capture.ts
index 5122858..9b2a8be 100644
--- a/packages/chess/src/modifiers/primitives/cancel-capture.ts
+++ b/packages/chess/src/modifiers/primitives/cancel-capture.ts
@@ -70,6 +70,7 @@
  */
 import { z } from "zod";
 import { GAME_ENTITY } from "../../schema.js";
+import type { ChessAttrKey, LastCaptureSnapshotValue } from "../../schema.js";
 import { PRIMITIVE_REGISTRY } from "./registry.js";
 import type { EffectPrimitive, PrimitiveApplyContext } from "./types.js";
 
@@ -80,9 +81,9 @@ const descriptor: EffectPrimitive<Params> = {
   kind: "cancel-capture",
   label: "Cancel Capture",
   description:
-    "Inside an on-captured arm, sets the CaptureCancelled flag on GAME_ENTITY signalling the dispatcher to suppress downstream cascade. Throws if no capture event is present in ctx.",
+    "Inside an on-captured arm, sets the CaptureCancelled flag on GAME_ENTITY AND restores the defender's pre-capture facts from LastCaptureSnapshot. Throws if no capture event is present in ctx.",
   longDescription:
-    "Imperative inhibitor primitive — only legal inside a trigger's primitives/then/else array (top-level placement is rejected by the validator with code 'descriptor.primitives.imperative-in-passive'). Requires ctx.event.kind === 'capture' (typically inside an on-captured arm) — calling outside that context throws runtime.cancel-capture-no-event. Sets CaptureCancelled = true on GAME_ENTITY. The capture dispatcher polls + retracts this flag AFTER fireOnCapturedHooks returns, so it never leaks across moves. V1 wire-in scope: the flag is set + retracted; full restoration of defender facts is DEFERRED to T28+ because the existing capture pipeline retracts the defender BEFORE the on-captured trigger fires (see apply.ts stage-4 NOTE). The flag is the inhibitor signal sibling primitives + future capture-pipeline refactor will consume.",
+    "Imperative inhibitor primitive — only legal inside a trigger's primitives/then/else array (top-level placement is rejected by the validator with code 'descriptor.primitives.imperative-in-passive'). Requires ctx.event.kind === 'capture' (typically inside an on-captured arm) — calling outside that context throws runtime.cancel-capture-no-event. T72 wire-in: in addition to setting CaptureCancelled = true on GAME_ENTITY (the dispatcher signal), this primitive RESTORES the defender's pre-capture facts by re-inserting every (attr, value) pair from `LastCaptureSnapshot.defenderFacts`. The dispatcher (apply.ts stage 4b) handles attacker rollback — it owns Position/HasMoved on the moving piece because the move-advance happens before the on-captured trigger fires. Splitting the work this way keeps the primitive defender-scoped and the dispatcher attacker-scoped. The flag and snapshot are both cleared by the dispatcher after the hook fires, so neither leaks across moves.",
   examples: [
     {
       title: "Parry — cancel a capture when defender wins RPS",
@@ -114,6 +115,37 @@ const descriptor: EffectPrimitive<Params> = {
       );
     }
     ctx.session.insert(GAME_ENTITY, "CaptureCancelled", true);
+
+    // T72 — restore the defender's pre-capture facts from the
+    // snapshot the capture pipeline wrote BEFORE retraction. The
+    // snapshot's defenderId MUST agree with the event's defenderId
+    // — the pipeline writes one snapshot per capture and the
+    // dispatcher fires on-captured for that defender exclusively.
+    // We still defensively check the match in case a future code
+    // path stages multiple captures within a single move (e.g. AoE
+    // / explosive-rook): mismatched snapshot is treated as "no
+    // snapshot available" and the cancel falls back to flag-only
+    // semantics (inhibitor without restore — useful when the
+    // primitive runs from synthetic test contexts that don't go
+    // through the engine.applyMove pipeline, e.g. the legacy V1
+    // unit tests).
+    const snapshot = ctx.session.get(GAME_ENTITY, "LastCaptureSnapshot") as
+      | LastCaptureSnapshotValue
+      | undefined;
+    if (snapshot === undefined) return;
+    if (snapshot.defenderId !== ctx.event.defenderId) return;
+    for (const [attr, value] of snapshot.defenderFacts) {
+      // The snapshot stores attrs as `string` for round-trip
+      // friendliness; cast to the engine's ChessAttrKey at insert
+      // time. An unrecognised attr name simply yields a no-op
+      // insert at the Session level — Session doesn't validate
+      // attr names against the schema.
+      ctx.session.insert(
+        snapshot.defenderId,
+        attr as ChessAttrKey,
+        value as never,
+      );
+    }
   },
 };
 
diff --git a/packages/chess/src/modifiers/triggers.test.ts b/packages/chess/src/modifiers/triggers.test.ts
index 18c336c..0ede508 100644
--- a/packages/chess/src/modifiers/triggers.test.ts
+++ b/packages/chess/src/modifiers/triggers.test.ts
@@ -23,6 +23,7 @@ import {
   fireOnMovedOntoSquareHooks,
   fireOnPromotionHooks,
   fireOnRuleActivatedHooks,
+  fireOnRuleExpireHooks,
   fireOnTurnEndHooks,
   runPrimitives,
   type PreMoveCheckStateLike,
@@ -1129,3 +1130,76 @@ describe("fireOnRuleActivatedHooks (T16)", () => {
     expect(engine.session.get(GAME_ENTITY, "RangeBonus")).toBeUndefined();
   });
 });
+
+// ─── T17 / T71: fireOnRuleExpireHooks ───────────────────────────────────
+//
+// Mirror image of fireOnRuleActivatedHooks. Reads
+// `OnRuleExpireHooks` from GAME_ENTITY and fires only entries whose
+// `descriptorId` matches. Self-guards against double-fire via
+// `RuleExpireFiredFor` on PRESET_STATE_ENTITY.
+
+describe("fireOnRuleExpireHooks (T17 / T71)", () => {
+  it("fires the matching descriptor's primitives, skips other descriptors", () => {
+    const engine = new ChessEngine({
+      profile: makeProfileWithCustomKind("on-rule-expire-dispatch"),
+    });
+
+    engine.session.insert(GAME_ENTITY, "OnRuleExpireHooks", [
+      {
+        descriptorId: "rule-X",
+        primitives: [
+          { kind: "seed-attribute", params: { attr: "HpBonus", value: 5 } },
+        ],
+      },
+      {
+        descriptorId: "rule-Y",
+        primitives: [
+          { kind: "seed-attribute", params: { attr: "RangeBonus", value: 7 } },
+        ],
+      },
+    ]);
+
+    fireOnRuleExpireHooks(engine, "rule-X");
+
+    expect(engine.session.get(GAME_ENTITY, "HpBonus")).toBe(5);
+    // rule-Y did NOT fire.
+    expect(engine.session.get(GAME_ENTITY, "RangeBonus")).toBeUndefined();
+  });
+
+  it("self-guards against double-fire via RuleExpireFiredFor", () => {
+    const engine = new ChessEngine({
+      profile: makeProfileWithCustomKind("on-rule-expire-dedup"),
+    });
+
+    engine.session.insert(GAME_ENTITY, "OnRuleExpireHooks", [
+      {
+        descriptorId: "rule-Z",
+        primitives: [
+          {
+            kind: "add-to-attribute",
+            params: { attr: "HpBonus", delta: 1 },
+          },
+        ],
+      },
+    ]);
+
+    fireOnRuleExpireHooks(engine, "rule-Z");
+    fireOnRuleExpireHooks(engine, "rule-Z");
+    fireOnRuleExpireHooks(engine, "rule-Z");
+
+    // Despite three calls, the increment fired exactly once.
+    expect(engine.session.get(GAME_ENTITY, "HpBonus")).toBe(1);
+  });
+
+  it("no-op when the descriptor has no expire-hook entries", () => {
+    const engine = new ChessEngine({
+      profile: makeProfileWithCustomKind("on-rule-expire-empty"),
+    });
+
+    // No entries at all — should not throw, and should still mark
+    // the descriptor as fired (idempotent semantics).
+    expect(() =>
+      fireOnRuleExpireHooks(engine, "rule-no-hooks"),
+    ).not.toThrow();
+  });
+});
diff --git a/packages/chess/src/net/client.test.ts b/packages/chess/src/net/client.test.ts
index 46935db..08e307a 100644
--- a/packages/chess/src/net/client.test.ts
+++ b/packages/chess/src/net/client.test.ts
@@ -7,6 +7,7 @@ import { GameClient } from "./client.js";
 import type {
   GameDeltaPayload,
   GameStatePayload,
+  RequestChoicePayload,
   RoomJoinedPayload,
 } from "./types.js";
 
@@ -515,6 +516,169 @@ describe("GameClient — sequence tracking", () => {
   });
 });
 
+// ---------------------------------------------------------------------------
+// T73 — request-choice / submit-choice (protocol v2 flat frames)
+// ---------------------------------------------------------------------------
+//
+// The server broadcasts `request-choice` as a FLAT top-level v2 frame
+// (no v1 envelope, no `seq`). The client must detect this shape on
+// `kind` and dispatch a `request-choice` event with the payload. The
+// reverse direction — `sendSubmitChoice` — must emit a similarly flat
+// frame with `protocolVersion: 2`, NOT route through the v1 envelope.
+
+describe("GameClient — request-choice (T73)", () => {
+  it("emits request-choice when the server sends a flat v2 frame", async () => {
+    const { client } = makeClient();
+    const received: RequestChoicePayload[] = [];
+    client.on("request-choice", (ev) => received.push(ev.payload));
+    const pending = client.connect("ABC123", "tok-1");
+    const socket = MockWebSocket.latest();
+    socket.simulateOpen();
+    await pending;
+
+    // Mirrors `buildRequestChoice` in server/src/broadcast.ts: flat,
+    // top-level `kind`, no envelope. Optional fields omitted.
+    socket.simulateMessage({
+      kind: "request-choice",
+      protocolVersion: 2,
+      choiceId: "c-1",
+      descriptorId: "rps-test",
+      prompt: "Pick rock paper scissors",
+      choiceKind: "rps",
+      forPlayer: "white",
+    });
+
+    expect(received).toHaveLength(1);
+    expect(received[0]).toMatchObject({
+      choiceId: "c-1",
+      choiceKind: "rps",
+      prompt: "Pick rock paper scissors",
+      forPlayer: "white",
+      descriptorId: "rps-test",
+    });
+  });
+
+  it("preserves optional timeout / expiresAtTimestamp fields", async () => {
+    const { client } = makeClient();
+    const received: RequestChoicePayload[] = [];
+    client.on("request-choice", (ev) => received.push(ev.payload));
+    const pending = client.connect("ABC123", "tok-1");
+    MockWebSocket.latest().simulateOpen();
+    await pending;
+
+    MockWebSocket.latest().simulateMessage({
+      kind: "request-choice",
+      protocolVersion: 2,
+      choiceId: "c-2",
+      descriptorId: "d-2",
+      prompt: "Flip the coin",
+      choiceKind: "coin-flip",
+      forPlayer: "both",
+      timeout: 30000,
+      expiresAtTimestamp: 1_700_000_000_000,
+    });
+
+    expect(received[0]).toMatchObject({
+      timeout: 30000,
+      expiresAtTimestamp: 1_700_000_000_000,
+    });
+  });
+
+  it("does NOT bump currentSeq for v2 flat frames", async () => {
+    const { client } = makeClient();
+    const pending = client.connect("ABC123", "tok-1");
+    MockWebSocket.latest().simulateOpen();
+    await pending;
+
+    expect(client.currentSeq).toBe(0);
+    MockWebSocket.latest().simulateMessage({
+      kind: "request-choice",
+      protocolVersion: 2,
+      choiceId: "c-3",
+      descriptorId: "d-3",
+      prompt: "?",
+      choiceKind: "square",
+      forPlayer: "white",
+    });
+    // V2 flat frames carry no `seq` — they must NOT advance the seq
+    // counter (which is the v1 reconcile cursor).
+    expect(client.currentSeq).toBe(0);
+  });
+
+  it("ignores unknown v2 kinds (forward compat)", async () => {
+    const { client } = makeClient();
+    const seen: unknown[] = [];
+    client.on("request-choice", (ev) => seen.push(ev.payload));
+    const pending = client.connect("ABC123", "tok-1");
+    MockWebSocket.latest().simulateOpen();
+    await pending;
+
+    expect(() =>
+      MockWebSocket.latest().simulateMessage({
+        kind: "future.v2.kind",
+        protocolVersion: 2,
+      }),
+    ).not.toThrow();
+    expect(seen).toEqual([]);
+  });
+});
+
+describe("GameClient — sendSubmitChoice (T73)", () => {
+  it("sends a flat v2 submit-choice frame", async () => {
+    const { client } = makeClient();
+    const pending = client.connect("ABC123", "tok-1");
+    const socket = MockWebSocket.latest();
+    socket.simulateOpen();
+    await pending;
+
+    // Drop the room.join frame from the recorded list so the assertion
+    // focuses on the submit-choice frame we're actually testing.
+    const before = socket.sent.length;
+    client.sendSubmitChoice("c-1", "paper");
+    const newFrames = socket.sent.slice(before);
+    expect(newFrames).toHaveLength(1);
+
+    const frame = newFrames[0]!.parsed;
+    // V2 flat shape — no `v`, no `seq`, no `ts`, no envelope-level
+    // `type`. The discriminator is `kind` and `protocolVersion: 2`.
+    expect(frame["v"]).toBeUndefined();
+    expect(frame["seq"]).toBeUndefined();
+    expect(frame["ts"]).toBeUndefined();
+    expect(frame["type"]).toBeUndefined();
+    expect(frame["kind"]).toBe("submit-choice");
+    expect(frame["protocolVersion"]).toBe(2);
+    expect(frame["choiceId"]).toBe("c-1");
+    expect(frame["value"]).toBe("paper");
+  });
+
+  it("supports arbitrary value shapes (kind-dependent payloads)", async () => {
+    const { client } = makeClient();
+    const pending = client.connect("ABC123", "tok-1");
+    const socket = MockWebSocket.latest();
+    socket.simulateOpen();
+    await pending;
+
+    // square = number, piece = number, rps = string, etc. The wire
+    // accepts arbitrary `value`; engine-side validators gate on
+    // `choiceKind` after the frame is parsed.
+    client.sendSubmitChoice("c-square", 28);
+    const numFrame = socket.sent.at(-1)!.parsed;
+    expect(numFrame["value"]).toBe(28);
+
+    client.sendSubmitChoice("c-obj", { x: 1, y: 2 });
+    const objFrame = socket.sent.at(-1)!.parsed;
+    expect(objFrame["value"]).toEqual({ x: 1, y: 2 });
+  });
+
+  it("drops sends when the socket is not open", () => {
+    const { client } = makeClient();
+    void client.connect("ABC123", "tok-1");
+    // Never simulateOpen — readyState stays CONNECTING.
+    client.sendSubmitChoice("c-x", "rock");
+    expect(MockWebSocket.latest().sent).toHaveLength(0);
+  });
+});
+
 describe("GameClient — listener management", () => {
   it("off() removes a listener", async () => {
     const { client } = makeClient();
diff --git a/packages/chess/src/net/client.ts b/packages/chess/src/net/client.ts
index f7932db..c1a412a 100644
--- a/packages/chess/src/net/client.ts
+++ b/packages/chess/src/net/client.ts
@@ -28,6 +28,7 @@ import type {
   PlayerActionWire,
   PresetActivation,
   PromotionPiece,
+  RequestChoicePayload,
   RoomCreatedPayload,
   RoomJoinedPayload,
   RoomSetPresetsPayload,
@@ -50,6 +51,7 @@ export type GameClientEvent =
   | { type: "modifier-profile.queued"; payload: ModifierProfileQueuedPayload }
   | { type: "modifier-profile.updated"; payload: ModifierProfileUpdatedPayload }
   | { type: "custom-modifier.registered"; payload: CustomModifierRegisteredPayload }
+  | { type: "request-choice"; payload: RequestChoicePayload }
   | { type: "error"; payload: ErrorPayload }
   | { type: "connected" }
   | { type: "disconnected"; willReconnect: boolean };
@@ -323,6 +325,29 @@ export class GameClient {
     this.send({ type: "custom-modifier.register", payload });
   }
 
+  /**
+   * T44: resolve a server-broadcast `request-choice` by sending a v2
+   * flat `submit-choice` frame. NOT routed through the v1 envelope —
+   * v2 frames are top-level and carry their own `protocolVersion` /
+   * `kind` discriminators (see packages/server/src/protocol.ts T43).
+   *
+   * Silently no-op when the socket is not OPEN; callers that need
+   * durability should retry at a higher layer (in practice, the
+   * server re-broadcasts the same `request-choice` on snapshot
+   * replay so reconnecting clients can recover).
+   */
+  sendSubmitChoice(choiceId: string, value: unknown): void {
+    const socket = this.ws;
+    if (!socket || socket.readyState !== this.WSCtor.OPEN) return;
+    const frame = {
+      kind: "submit-choice" as const,
+      protocolVersion: 2 as const,
+      choiceId,
+      value,
+    };
+    socket.send(JSON.stringify(frame));
+  }
+
   // -------------------------------------------------------------------------
   // Accessors (primarily for tests & reconnect logic)
   // -------------------------------------------------------------------------
@@ -439,6 +464,16 @@ export class GameClient {
       return; // Malformed frames are silently ignored at this layer.
     }
     if (typeof parsed !== "object" || parsed === null) return;
+
+    // T43/T44: protocol v2 frames are FLAT (no v1 envelope) and carry a
+    // `kind` discriminator at the top level. Detect and route them
+    // before falling through to the v1 envelope path.
+    const v2Kind = (parsed as { kind?: unknown }).kind;
+    if (typeof v2Kind === "string") {
+      this.dispatchV2Frame(v2Kind, parsed);
+      return;
+    }
+
     const msg = parsed as IncomingEnvelope;
 
     if (typeof msg.seq === "number" && msg.seq > this.lastSeq) {
@@ -454,6 +489,27 @@ export class GameClient {
     this.dispatchServerMessage(msg.type, msg.payload);
   }
 
+  /**
+   * Route a v2 flat frame (T43). Currently only `request-choice` is
+   * surfaced as an event; `protocol-version-mismatch` is connection-
+   * fatal and the server closes the socket immediately after sending
+   * it (the resulting `disconnected` event is what callers observe).
+   * Unknown v2 kinds are ignored for forward-compat.
+   */
+  private dispatchV2Frame(kind: string, frame: object): void {
+    if (kind === "request-choice") {
+      // Trust the server's schema (mirrors v1 dispatch convention) —
+      // the wire shape was validated server-side before send.
+      this.emit({
+        type: "request-choice",
+        payload: frame as RequestChoicePayload,
+      });
+      return;
+    }
+    // Other v2 kinds (`protocol-version-mismatch`, future additions) are
+    // ignored at this layer.
+  }
+
   private captureAuth(msg: IncomingEnvelope): void {
     if (msg.type !== "room.created" && msg.type !== "room.joined") return;
     const p = msg.payload;
diff --git a/packages/chess/src/net/types.ts b/packages/chess/src/net/types.ts
index 18b66be..83e1bbb 100644
--- a/packages/chess/src/net/types.ts
+++ b/packages/chess/src/net/types.ts
@@ -308,6 +308,43 @@ export interface ErrorPayload {
   fatal: boolean;
 }
 
+// ---------------------------------------------------------------------------
+// T43/T44 — Protocol v2: request-choice / submit-choice
+// ---------------------------------------------------------------------------
+//
+// FLAT top-level v2 frames (NOT v1 envelopes). Server emits `request-choice`
+// to clients that negotiated protocolVersion >= 2; clients reply with
+// `submit-choice` to resolve the top of the LIFO PendingChoices stack.
+
+export type ChoiceKind =
+  | "rps"
+  | "piece"
+  | "square"
+  | "column"
+  | "row"
+  | "coin-flip";
+
+export type ChoiceForPlayer = "white" | "black" | "both";
+
+/**
+ * Server → client (v2 flat frame). Wire shape mirrors
+ * `RequestChoiceSchema` in packages/server/src/protocol.ts (T43).
+ * `choiceId` echoes back unchanged on `submit-choice`.
+ */
+export interface RequestChoicePayload {
+  choiceId: string;
+  choiceKind: ChoiceKind;
+  prompt: string;
+  forPlayer: ChoiceForPlayer;
+  descriptorId: string;
+  /** Optional milliseconds-from-now deadline. */
+  timeout?: number;
+  /** Optional unix-ms wall-clock deadline. */
+  expiresAtTimestamp?: number;
+  /** Optional concrete option list — value space depends on `choiceKind`. */
+  options?: unknown[];
+}
+
 // ---------------------------------------------------------------------------
 // Client → Server payloads (shape for send())
 // ---------------------------------------------------------------------------
diff --git a/packages/chess/src/rules/turn.ts b/packages/chess/src/rules/turn.ts
index a173225..5b60527 100644
--- a/packages/chess/src/rules/turn.ts
+++ b/packages/chess/src/rules/turn.ts
@@ -32,7 +32,7 @@
  *   - check filtering  → P2.18
  */
 import type { Session, EntityId } from "@paratype/rete";
-import type { PieceColor, PieceType } from "../schema.js";
+import type { PieceColor, PieceType, LastCaptureSnapshotValue } from "../schema.js";
 import { GAME_ENTITY } from "../schema.js";
 import type { LegalMove } from "./types.js";
 import { getPieceColor, getPieceAt } from "./board-queries.js";
@@ -143,6 +143,31 @@ export function applyMove(session: Session, move: LegalMove): void {
   if (move.isCapture) {
     const capturedId = getPieceAt(session, move.to);
     if (capturedId !== null && capturedId !== move.pieceId) {
+      // T72 — snapshot defender facts + attacker pre-state BEFORE the
+      // retract so an `on-captured → cancel-capture` trigger arm can
+      // undo the capture wholesale. The snapshot is stored on
+      // GAME_ENTITY as `LastCaptureSnapshot`. The live engine path
+      // (engine.applyMove) writes its own snapshot via
+      // `recordLastCaptureSnapshot` — this function is the
+      // pure-helper variant used by tests and ports. Behaviour
+      // matches: same defender-fact filter (`isPieceAttr`), same
+      // attacker pre-state (Position + HasMoved-was-already-set).
+      const defenderFacts: Array<readonly [string, unknown]> = [];
+      for (const f of session.allFacts()) {
+        if (f.id !== capturedId) continue;
+        if (!isPieceAttr(f.attr)) continue;
+        defenderFacts.push([f.attr as string, f.value]);
+      }
+      const attackerHadMoved = session.get(move.pieceId, "HasMoved") === true;
+      const snapshot: LastCaptureSnapshotValue = {
+        attackerId: move.pieceId,
+        attackerFromSquare: move.from,
+        attackerHadMoved,
+        defenderId: capturedId,
+        defenderFacts,
+      };
+      session.insert(GAME_ENTITY, "LastCaptureSnapshot", snapshot);
+
       // Enumerate the captured piece's attrs from the session rather
       // than from a hardcoded list — preset-declared attrs (Hp,
       // Shield, …) get cleaned up too without this function needing
diff --git a/packages/chess/src/schema.ts b/packages/chess/src/schema.ts
index 3bb271d..89f2250 100644
--- a/packages/chess/src/schema.ts
+++ b/packages/chess/src/schema.ts
@@ -396,14 +396,26 @@ export interface ChessAttrMap {
    * (apply.ts stage 4b) so the flag never leaks across moves or
    * cascade boundaries.
    *
-   * V1 wire-in scope: the flag is set + retracted; full restoration
-   * of defender facts is DEFERRED to T28+ because the existing
-   * capture pipeline retracts the defender BEFORE the on-captured
-   * trigger fires (see apply.ts stage-4 NOTE). Sibling primitives
-   * and the future capture-pipeline refactor consume this flag as
-   * the inhibitor signal.
+   * T72: full restoration of defender facts AND attacker rollback is
+   * now wired. The capture pipeline writes a {@link LastCaptureSnapshot}
+   * BEFORE retracting defender facts / advancing the attacker; the
+   * `cancel-capture` primitive re-inserts defender facts from that
+   * snapshot, and the dispatcher (apply.ts stage 4b) restores the
+   * attacker's pre-move Position / HasMoved when the flag is set.
    */
    CaptureCancelled: boolean;
+  /**
+   * T72 — capture-undo snapshot, stored on `GAME_ENTITY`. Written by
+   * the capture pipeline (engine.applyMove + rules/turn.applyMove)
+   * BEFORE the defender's facts are retracted and BEFORE the attacker
+   * is advanced. Read by `cancel-capture` (which re-inserts every
+   * defender fact from `defenderFacts`) and by the post-hook
+   * dispatcher in apply.ts stage 4b (which rolls back the attacker's
+   * Position / HasMoved when `CaptureCancelled === true`). Cleared
+   * unconditionally at the end of stage 4b so the snapshot never
+   * leaks across moves.
+   */
+   LastCaptureSnapshot: LastCaptureSnapshotValue;
   /**
    * T35 — turn-bounded attribute lifetime registry. Stored on
    * `GAME_ENTITY` (one list per game). Each entry records that some
@@ -591,6 +603,47 @@ export interface PendingChoice {
   readonly expiresAtTimestamp?: number;
 }
 
+/**
+ * T72 — value shape of {@link ChessAttrMap.LastCaptureSnapshot}.
+ *
+ * Snapshot taken BEFORE the capture mutates the session, used to undo
+ * the capture wholesale when an `on-captured` arm fires `cancel-capture`.
+ *
+ *  - `attackerId` — the moving piece. Restored by stage 4b on cancel.
+ *  - `attackerFromSquare` — the attacker's pre-move Position. The
+ *    cancel path re-inserts this so the attacker stays on its origin.
+ *  - `attackerHadMoved` — whether `HasMoved` was already true on the
+ *    attacker BEFORE the move. `true` => leave HasMoved alone on
+ *    cancel (a king/rook that had already moved before this turn
+ *    must remain ineligible for castling). `false` => retract
+ *    HasMoved on cancel (the move never happened, restore "fresh"
+ *    status).
+ *  - `defenderId` — the captured piece. Used by `cancel-capture` to
+ *    target the re-insert.
+ *  - `defenderFacts` — every (attr, value) pair that was on the
+ *    defender BEFORE retraction. The cancel path re-inserts each
+ *    pair, fully restoring the defender to its pre-capture state
+ *    (PieceType, Color, Position, HasMoved, Hp, plus any
+ *    preset-declared / primitive-seeded attrs the engine had
+ *    snapshotted).
+ *
+ * Stored as a plain object (not a Map) so the value round-trips through
+ * `session.allFacts()` exports / save-load — Maps don't survive JSON
+ * serialization without a custom codec, and the snapshot is transient
+ * (cleared at end of stage 4b) so persistence isn't required, but
+ * structural-clone friendliness is still nice for in-memory tests.
+ * `defenderFacts` is a `ReadonlyArray<[attr, value]>` for the same
+ * reason — Maps would force every test reading the snapshot to know
+ * about Map's iteration shape.
+ */
+export interface LastCaptureSnapshotValue {
+  readonly attackerId: EntityId;
+  readonly attackerFromSquare: Square;
+  readonly attackerHadMoved: boolean;
+  readonly defenderId: EntityId;
+  readonly defenderFacts: ReadonlyArray<readonly [string, unknown]>;
+}
+
 /**
  * T38 — value shape of {@link ChessAttrMap.MoveClassRestriction}.
  *
diff --git a/packages/chess/src/ui/GameView.test.tsx b/packages/chess/src/ui/GameView.test.tsx
new file mode 100644
index 0000000..1bdd133
--- /dev/null
+++ b/packages/chess/src/ui/GameView.test.tsx
@@ -0,0 +1,316 @@
+/**
+ * T73 — MultiplayerGameView surfaces request-choice prompts via
+ * RequestChoiceModal.
+ *
+ * End-to-end-ish: drives a real `useMultiplayerGame` instance through a
+ * MockWebSocket so we exercise the GameClient → hook → modal pipeline.
+ * Uses happy-dom + react-dom/client (no @testing-library/react in the
+ * repo). The board itself is heavy — we only assert the modal text
+ * surfaces, not its full structure (covered by RequestChoiceModal.test).
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { act } from 'react';
+import { createRoot, type Root } from 'react-dom/client';
+import { createElement } from 'react';
+import { MultiplayerGameView } from './GameView.js';
+
+// React must be in act-environment so state updates flush synchronously
+// inside `act()` and the DOM reflects them when we read it.
+(globalThis as unknown as { IS_REACT_ACT_ENVIRONMENT: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+
+// happy-dom provides `localStorage` as a stub that exists but doesn't
+// implement getItem in this version. The audio module + GameLayout's
+// LayoutBadge / ModifierProfileBadge call `getItem` at render time —
+// shim it so the rendering pipeline doesn't crash.
+if (
+  typeof globalThis.localStorage !== 'object' ||
+  typeof (globalThis.localStorage as { getItem?: unknown }).getItem !==
+    'function'
+) {
+  const store = new Map<string, string>();
+  (globalThis as unknown as { localStorage: Storage }).localStorage = {
+    getItem: (k: string) => store.get(k) ?? null,
+    setItem: (k: string, v: string) => {
+      store.set(k, v);
+    },
+    removeItem: (k: string) => {
+      store.delete(k);
+    },
+    clear: () => {
+      store.clear();
+    },
+    key: (i: number) => Array.from(store.keys())[i] ?? null,
+    get length() {
+      return store.size;
+    },
+  } as Storage;
+}
+// sessionStorage is read by Layout / ModifierProfile badges.
+if (
+  typeof globalThis.sessionStorage !== 'object' ||
+  typeof (globalThis.sessionStorage as { getItem?: unknown }).getItem !==
+    'function'
+) {
+  const store = new Map<string, string>();
+  (globalThis as unknown as { sessionStorage: Storage }).sessionStorage = {
+    getItem: (k: string) => store.get(k) ?? null,
+    setItem: (k: string, v: string) => {
+      store.set(k, v);
+    },
+    removeItem: (k: string) => {
+      store.delete(k);
+    },
+    clear: () => {
+      store.clear();
+    },
+    key: (i: number) => Array.from(store.keys())[i] ?? null,
+    get length() {
+      return store.size;
+    },
+  } as Storage;
+}
+
+// ---------------------------------------------------------------------------
+// MockWebSocket — same shape as the client/hook tests.
+// ---------------------------------------------------------------------------
+
+interface SentFrame {
+  raw: string;
+  parsed: Record<string, unknown>;
+}
+
+class MockWebSocket {
+  static CONNECTING = 0 as const;
+  static OPEN = 1 as const;
+  static CLOSING = 2 as const;
+  static CLOSED = 3 as const;
+
+  readyState: number = MockWebSocket.CONNECTING;
+  url: string;
+  onopen: ((ev: Event) => void) | null = null;
+  onmessage: ((ev: MessageEvent) => void) | null = null;
+  onerror: ((ev: Event) => void) | null = null;
+  onclose: ((ev: CloseEvent) => void) | null = null;
+  readonly sent: SentFrame[] = [];
+
+  constructor(url: string) {
+    this.url = url;
+    MockWebSocket.instances.push(this);
+  }
+
+  static instances: MockWebSocket[] = [];
+  static reset(): void {
+    MockWebSocket.instances = [];
+  }
+  static latest(): MockWebSocket {
+    const inst = MockWebSocket.instances.at(-1);
+    if (!inst) throw new Error('no MockWebSocket instances yet');
+    return inst;
+  }
+
+  send(data: string): void {
+    let parsed: Record<string, unknown> = {};
+    try {
+      const raw = JSON.parse(data);
+      if (raw !== null && typeof raw === 'object' && !Array.isArray(raw)) {
+        parsed = raw as Record<string, unknown>;
+      }
+    } catch {
+      /* leave parsed empty */
+    }
+    this.sent.push({ raw: data, parsed });
+  }
+
+  close(): void {
+    if (this.readyState !== MockWebSocket.CLOSED) {
+      this.readyState = MockWebSocket.CLOSED;
+      this.onclose?.(new CloseEvent('close'));
+    }
+  }
+
+  simulateOpen(): void {
+    this.readyState = MockWebSocket.OPEN;
+    this.onopen?.(new Event('open'));
+  }
+  simulateMessage(msg: unknown): void {
+    this.onmessage?.(
+      new MessageEvent('message', { data: JSON.stringify(msg) }),
+    );
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Render harness
+// ---------------------------------------------------------------------------
+
+const realWebSocket = globalThis.WebSocket;
+let container: HTMLDivElement | null = null;
+let root: Root | null = null;
+
+beforeEach(() => {
+  MockWebSocket.reset();
+  (globalThis as unknown as { WebSocket: typeof WebSocket }).WebSocket =
+    MockWebSocket as unknown as typeof WebSocket;
+  container = document.createElement('div');
+  document.body.appendChild(container);
+  root = createRoot(container);
+});
+
+afterEach(() => {
+  if (root) {
+    act(() => {
+      root!.unmount();
+    });
+    root = null;
+  }
+  if (container) {
+    container.remove();
+    container = null;
+  }
+  (globalThis as unknown as { WebSocket: typeof WebSocket }).WebSocket =
+    realWebSocket;
+});
+
+/**
+ * Drive the WS handshake to the point where `useMultiplayerGame.loading`
+ * is false (so the GameLayout — and therefore the modal — actually
+ * renders). Returns the latest mock socket so tests can push more
+ * messages through it.
+ */
+async function bootHandshake(): Promise<MockWebSocket> {
+  const socket = MockWebSocket.latest();
+  await act(async () => {
+    socket.simulateOpen();
+    await Promise.resolve();
+  });
+  // room.joined sets `myColor` AND clears `loading` in one step.
+  await act(async () => {
+    socket.simulateMessage({
+      v: 1,
+      seq: 1,
+      ts: Date.now(),
+      type: 'room.joined',
+      payload: {
+        code: 'ABC123',
+        token: 'tok-1',
+        color: 'white',
+        activeRules: [],
+      },
+    });
+    await Promise.resolve();
+  });
+  // game.state with empty facts gives PredictionManager a real engine
+  // so the GameLayout's downstream queries (legalMoves, allFacts, …)
+  // don't blow up.
+  await act(async () => {
+    socket.simulateMessage({
+      v: 1,
+      seq: 2,
+      ts: Date.now(),
+      type: 'game.state',
+      payload: {
+        facts: [],
+        turn: 'white',
+        lastSeq: 2,
+        moveHistory: [],
+        activeRules: [],
+        activations: [],
+        fen: '',
+      },
+    });
+    await Promise.resolve();
+  });
+  return socket;
+}
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+describe('MultiplayerGameView — request-choice modal (T73)', () => {
+  it('renders RequestChoiceModal when the server pushes a request-choice', async () => {
+    act(() => {
+      root!.render(
+        createElement(MultiplayerGameView, { code: 'ABC123', token: 'tok-1' }),
+      );
+    });
+
+    const socket = await bootHandshake();
+
+    // Pre-state: no modal, no prompt text.
+    expect(container!.textContent).not.toContain('Pick rock paper scissors');
+    expect(container!.querySelector('[role="dialog"]')).toBeNull();
+
+    await act(async () => {
+      socket.simulateMessage({
+        kind: 'request-choice',
+        protocolVersion: 2,
+        choiceId: 'c-1',
+        descriptorId: 'rps-test',
+        prompt: 'Pick rock paper scissors',
+        choiceKind: 'rps',
+        forPlayer: 'white',
+      });
+      await Promise.resolve();
+    });
+
+    // Modal opened with the server's prompt text + the rps options.
+    expect(container!.querySelector('[role="dialog"]')).not.toBeNull();
+    expect(container!.textContent).toContain('Pick rock paper scissors');
+    expect(container!.textContent).toContain('rock');
+    expect(container!.textContent).toContain('paper');
+    expect(container!.textContent).toContain('scissors');
+  });
+
+  it('clicking a modal option closes it and sends a flat submit-choice frame', async () => {
+    act(() => {
+      root!.render(
+        createElement(MultiplayerGameView, { code: 'ABC123', token: 'tok-1' }),
+      );
+    });
+
+    const socket = await bootHandshake();
+
+    await act(async () => {
+      socket.simulateMessage({
+        kind: 'request-choice',
+        protocolVersion: 2,
+        choiceId: 'c-2',
+        descriptorId: 'coin-flip-test',
+        prompt: 'Flip the coin',
+        choiceKind: 'coin-flip',
+        forPlayer: 'both',
+      });
+      await Promise.resolve();
+    });
+
+    expect(container!.querySelector('[role="dialog"]')).not.toBeNull();
+    const beforeSent = socket.sent.length;
+
+    // Click the "heads" button. RequestChoiceModal renders option
+    // buttons with their option name as the label — find by textContent.
+    const buttons = Array.from(
+      container!.querySelectorAll('button'),
+    ) as HTMLButtonElement[];
+    const heads = buttons.find((b) => b.textContent?.trim() === 'heads');
+    expect(heads).toBeDefined();
+
+    await act(async () => {
+      heads!.click();
+      await Promise.resolve();
+    });
+
+    // Modal closed.
+    expect(container!.querySelector('[role="dialog"]')).toBeNull();
+
+    // Flat v2 submit-choice frame on the wire.
+    const newFrames = socket.sent.slice(beforeSent);
+    const submit = newFrames.find(
+      (f) => f.parsed['kind'] === 'submit-choice',
+    );
+    expect(submit).toBeDefined();
+    expect(submit!.parsed['protocolVersion']).toBe(2);
+    expect(submit!.parsed['choiceId']).toBe('c-2');
+    expect(submit!.parsed['value']).toBe('heads');
+  });
+});
diff --git a/packages/chess/src/ui/GameView.tsx b/packages/chess/src/ui/GameView.tsx
index 6a46f13..cb1dcea 100644
--- a/packages/chess/src/ui/GameView.tsx
+++ b/packages/chess/src/ui/GameView.tsx
@@ -3,6 +3,7 @@ import { RulesDrawer } from './RulesDrawer';
 import { ModifierTooltip } from './ModifierTooltip.js';
 import { ModifierPinnedPanel } from './ModifierPinnedPanel.js';
 import { ModifierProposalDialog } from './ModifierProposalDialog.js';
+import { RequestChoiceModal } from './RequestChoiceModal.js';
 import { ActionMenu } from './ActionMenu.js';
 import { useChessEngine } from '../hooks/useChessEngine';
 import { useMultiplayerGame } from '../hooks/useMultiplayerGame';
@@ -121,6 +122,18 @@ export function MultiplayerGameView({ code, token }: MultiplayerGameViewProps) {
         </div>
       )}
       <GameLayout state={state} myColor={state.myColor} roomCode={code} />
+      {/*
+       * T73: surface server-broadcast `request-choice` prompts. The hook
+       * mirrors the server's LIFO PendingChoices stack — top is active.
+       * The forPlayer gate is enforced server-side (we only receive
+       * prompts targeted at our color or "both"), so no extra filter
+       * is needed here.
+       */}
+      <RequestChoiceModal
+        open={state.pendingChoice !== undefined}
+        choice={state.pendingChoice}
+        onSubmit={state.submitChoice}
+      />
     </>
   );
 }
diff --git a/packages/server/src/broadcast.ts b/packages/server/src/broadcast.ts
index cbe8bfe..98a1885 100644
--- a/packages/server/src/broadcast.ts
+++ b/packages/server/src/broadcast.ts
@@ -33,6 +33,7 @@ import {
   shouldSkipV2Broadcast,
   validateAnyMessageString,
   type CustomModifierRegisterPayload,
+  type CustomModifierRemovePayload,
   type ErrorCode,
   type Fact as WireFact,
   type GameActionPayload,
@@ -63,7 +64,7 @@ import {
 } from "./choice-timeout.js";
 import {
   peekPendingChoice,
-  popPendingChoice,
+  submitChoiceAndResume,
   validateProfile,
   type ActionResult,
   type ModifierProfile,
@@ -454,15 +455,37 @@ function armChoiceTimeoutFor(
 
     // Auto-resolve with the first option for this kind. The value
     // bypasses the wire-side `isValidChoiceValue` check (it never
-    // touches the wire); the engine resume path (T46) will do its
+    // touches the wire); the engine resume path (T46) does its
     // own kind-specific legality gate.
     const defaultValue = firstDefaultForKind(kind);
-    void defaultValue; // T46: thread into engine resume context.
 
-    const popped = popPendingChoice(liveSession.getEngine());
-    if (popped !== undefined) {
-      forgetBroadcastedChoiceId(roomCode, popped.choiceId);
+    // T70 — thread the default value through the real resume
+    // mechanism so any `params.then` continuation runs. The helper
+    // pops the frame unconditionally (even on descriptor-not-found,
+    // see pending-choices.ts header doc), so bookkeeping must be
+    // cleared in both the success and the catch branch. A throw
+    // from a continuation primitive must NOT crash the timer
+    // callback — log + clean up so the room remains live.
+    try {
+      submitChoiceAndResume(liveSession.getEngine(), choiceId, defaultValue);
+    } catch (err) {
+      logger
+        .child({ roomCode })
+        .warn(
+          { choiceId, kind, err: (err as Error).message },
+          "T49: timeout-default resume threw; frame popped, room continues",
+        );
     }
+    forgetBroadcastedChoiceId(roomCode, choiceId);
+
+    // Surface the resulting state to clients so any continuation
+    // side-effect (HpBonus writes, fact mutations, terminal-state
+    // detection) becomes visible without waiting for the next
+    // move/action. A subsequent inner choice (if the continuation
+    // pushed one) is broadcast via the dedicated helper.
+    broadcastGameStateSnapshot(roomCode, liveSession);
+    broadcastTopChoiceIfNew(roomCode, liveSession);
+
     logger
       .child({ roomCode })
       .info(
@@ -680,11 +703,12 @@ function handleV2Frame(
  *      (see `isValidChoiceValue`). Failures emit a `protocol.invalid-
  *      choice-value` message.
  *
- * On full success: the frame is popped (`popPendingChoice`),
- * bookkeeping for the broadcasted-set is cleared, and the popped
- * value is currently DROPPED — T46 will replace this with the real
- * resume mechanism (`submitChoiceAndResume`). The pop itself is
- * preserved so the LIFO contract holds even before T46 lands.
+ * On full success: the frame is resumed via `submitChoiceAndResume`
+ * (which pops the frame and runs the suspended `params.then`
+ * continuation with the player's value bound under the request-
+ * choice's `bind` name), broadcasted-set bookkeeping is cleared,
+ * and the resulting game state + any new top-of-stack choice are
+ * broadcast to the room.
  */
 function handleSubmitChoice(
   ws: ServerWebSocket<ClientData>,
@@ -783,20 +807,42 @@ function handleSubmitChoice(
   // fired after submit" log line in the latency window.
   choiceTimeoutManager.cancel(roomCode, frame.choiceId);
 
-  // Pop the top frame and drop the bookkeeping entry. T46 will replace
-  // the bare pop with the real resume mechanism (which threads the
-  // value back into the engine's resume context); for now we satisfy
-  // the LIFO contract and clear our broadcast tracking so the next
-  // pending choice on this socket can be re-broadcast cleanly.
-  const popped = popPendingChoice(session.getEngine());
-  if (popped !== undefined) {
-    forgetBroadcastedChoiceId(roomCode, popped.choiceId);
+  // T70 — thread the player's value through the real resume
+  // mechanism. `submitChoiceAndResume` pops the frame and runs the
+  // suspended `params.then` continuation. The pop is unconditional
+  // even on descriptor-not-found (see pending-choices.ts header),
+  // so we always clear the broadcasted-id bookkeeping. A throw
+  // from a continuation primitive must not propagate to the WS
+  // dispatcher — log and continue so the room stays live.
+  try {
+    submitChoiceAndResume(session.getEngine(), frame.choiceId, frame.value);
+  } catch (err) {
+    logger
+      .child({ clientId: ws.data.clientId, roomCode })
+      .warn(
+        {
+          choiceId: frame.choiceId,
+          kind: top.kind,
+          err: (err as Error).message,
+        },
+        "submit-choice resume threw; frame popped, room continues",
+      );
   }
+  forgetBroadcastedChoiceId(roomCode, frame.choiceId);
+
+  // Surface the resulting state to clients so any continuation
+  // side-effect (HpBonus writes, fact mutations, terminal-state
+  // detection) becomes visible without waiting for the next
+  // move/action. A subsequent inner choice pushed by the
+  // continuation is broadcast via the dedicated helper.
+  broadcastGameStateSnapshot(roomCode, session);
+  broadcastTopChoiceIfNew(roomCode, session);
+
   logger
     .child({ clientId: ws.data.clientId, roomCode })
     .info(
       { choiceId: frame.choiceId, kind: top.kind },
-      "submit-choice (pre-T46: value accepted, resume not yet wired)",
+      "submit-choice: value accepted, continuation resumed",
     );
 }
 
@@ -883,6 +929,9 @@ export function handleMessage(
     case "custom-modifier.register":
       handleCustomModifierRegister(ws, msg.payload);
       break;
+    case "custom-modifier.remove":
+      handleCustomModifierRemove(ws, msg.payload);
+      break;
     case "room.created":
     case "room.joined":
     case "game.state":
@@ -895,6 +944,7 @@ export function handleMessage(
     case "modifier-profile.rejected":
     case "modifier-profile.consent-received":
     case "custom-modifier.registered":
+    case "custom-modifier.removed":
     case "error":
       sendTo(
         ws,
@@ -2444,6 +2494,96 @@ function handleCustomModifierRegister(
   );
 }
 
+// ---------------------------------------------------------------------------
+// T71 — custom-modifier.remove handler
+// ---------------------------------------------------------------------------
+
+/**
+ * Detach a previously-registered custom modifier descriptor from the
+ * authoritative engine, drop it from the room's per-room registry,
+ * and broadcast `custom-modifier.removed` so opponents mirror the
+ * detach. Host-only — mirrors the register-side gate.
+ *
+ * The detach pipeline on the engine is idempotent (already-detached
+ * id is a safe no-op), so re-sending a remove for an unknown id is
+ * not an error: the broadcast still goes out so client engines
+ * mirror their own removal.
+ */
+function handleCustomModifierRemove(
+  ws: ServerWebSocket<ClientData>,
+  payload: CustomModifierRemovePayload,
+): void {
+  const { roomCode, token } = ws.data;
+  if (roomCode === undefined || token === undefined) {
+    sendTo(
+      ws,
+      errorMessage("BAD_TOKEN", "not authenticated into a room", false),
+    );
+    return;
+  }
+
+  if (payload.roomCode !== roomCode) {
+    sendTo(
+      ws,
+      errorMessage(
+        "BAD_TOKEN",
+        "custom-modifier.remove roomCode does not match authenticated room",
+        false,
+      ),
+    );
+    return;
+  }
+
+  const room = roomRegistry.getRoom(roomCode);
+  if (!room) {
+    sendTo(
+      ws,
+      errorMessage("ROOM_NOT_FOUND", `room ${roomCode} not found`, false),
+    );
+    return;
+  }
+
+  // Host-only — same gate as register. An opponent who could detach
+  // arbitrary descriptors could grief the host's rule set.
+  if (room.hostToken !== token) {
+    sendTo(
+      ws,
+      errorMessage(
+        "BAD_TOKEN",
+        "only the room host can remove custom modifiers",
+        false,
+      ),
+    );
+    return;
+  }
+
+  const descriptorId = payload.descriptorId;
+
+  // Drop from the room's per-room registry (if present). This is the
+  // mirror of register's `room.customModifiers.set` write — the slot
+  // is freed for re-use under the per-room cap.
+  room.customModifiers?.delete(descriptorId);
+
+  // Engine-side detach: fires `on-rule-expire` hooks and retracts
+  // hook-list entries for `descriptorId`. The session is the
+  // authoritative engine — clients run their own detach on receipt
+  // of the broadcast below.
+  const session = sessionRegistry.get(roomCode);
+  session?.getEngine().detachCustomDescriptor(descriptorId);
+
+  logger
+    .child({ roomCode, clientId: ws.data.clientId })
+    .info({ descriptorId }, "custom-modifier.remove");
+
+  broadcastToRoom(
+    roomCode,
+    envelope("custom-modifier.removed", {
+      roomCode,
+      descriptorId,
+    }),
+  );
+}
+
 /**
  * Broadcast a game.end to everyone in `code` EXCEPT the player whose
  * token is `leaverToken`. Used when a player disconnects or leaves
diff --git a/packages/server/src/protocol.ts b/packages/server/src/protocol.ts
index 3879dfe..1db16ba 100644
--- a/packages/server/src/protocol.ts
+++ b/packages/server/src/protocol.ts
@@ -692,6 +692,38 @@ export type CustomModifierRegisteredPayload = z.infer<
   typeof CustomModifierRegisteredPayloadSchema
 >;
 
+/**
+ * T71 — client → server: detach a previously-registered custom
+ * modifier descriptor. Server fires `on-rule-expire` hooks on the
+ * authoritative engine, retracts the descriptor's hook-list entries,
+ * removes it from the room's custom registry, and broadcasts
+ * `custom-modifier.removed` so peer clients mirror the removal.
+ *
+ * Host-only (mirrors register's host-only gate). Unknown descriptor
+ * ids are tolerated (idempotent on already-detached) — the server
+ * still broadcasts so clients can mirror their own removal.
+ */
+export const CustomModifierRemovePayloadSchema = z.object({
+  roomCode: RoomCodeSchema,
+  descriptorId: z.string().min(1).max(128),
+});
+export type CustomModifierRemovePayload = z.infer<
+  typeof CustomModifierRemovePayloadSchema
+>;
+
+/**
+ * T71 — server → all clients in room: a custom modifier descriptor
+ * has been detached. Clients should call `engine.detachCustomDescriptor`
+ * locally so their session state mirrors the server's.
+ */
+export const CustomModifierRemovedPayloadSchema = z.object({
+  roomCode: RoomCodeSchema,
+  descriptorId: z.string().min(1).max(128),
+});
+export type CustomModifierRemovedPayload = z.infer<
+  typeof CustomModifierRemovedPayloadSchema
+>;
+
 export const RoomJoinPayloadSchema = z.object({
   code: RoomCodeSchema,
 });
@@ -928,6 +960,10 @@ export const CustomModifierRegisterMessageSchema = msg(
   "custom-modifier.register",
   CustomModifierRegisterPayloadSchema,
 );
+export const CustomModifierRemoveMessageSchema = msg(
+  "custom-modifier.remove",
+  CustomModifierRemovePayloadSchema,
+);
 
 export const ClientMessageSchema = z.discriminatedUnion("type", [
   RoomCreateMessageSchema,
@@ -940,6 +976,7 @@ export const ClientMessageSchema = z.discriminatedUnion("type", [
   ModifierProfileProposeMessageSchema,
   ModifierProfileConsentMessageSchema,
   CustomModifierRegisterMessageSchema,
+  CustomModifierRemoveMessageSchema,
 ]);
 export type ClientMessage = z.infer<typeof ClientMessageSchema>;
 
@@ -982,6 +1019,10 @@ export const CustomModifierRegisteredMessageSchema = msg(
   "custom-modifier.registered",
   CustomModifierRegisteredPayloadSchema,
 );
+export const CustomModifierRemovedMessageSchema = msg(
+  "custom-modifier.removed",
+  CustomModifierRemovedPayloadSchema,
+);
 export const ErrorMessageSchema = msg("error", ErrorPayloadSchema);
 
 export const ServerMessageSchema = z.discriminatedUnion("type", [
@@ -997,6 +1038,7 @@ export const ServerMessageSchema = z.discriminatedUnion("type", [
   ModifierProfileRejectedMessageSchema,
   ModifierProfileConsentReceivedMessageSchema,
   CustomModifierRegisteredMessageSchema,
+  CustomModifierRemovedMessageSchema,
   ErrorMessageSchema,
 ]);
 export type ServerMessage = z.infer<typeof ServerMessageSchema>;
@@ -1012,6 +1054,7 @@ export const AnyMessageSchema = z.discriminatedUnion("type", [
   ModifierProfileProposeMessageSchema,
   ModifierProfileConsentMessageSchema,
   CustomModifierRegisterMessageSchema,
+  CustomModifierRemoveMessageSchema,
   RoomCreatedMessageSchema,
   RoomJoinedMessageSchema,
   GameStateMessageSchema,
@@ -1024,6 +1067,7 @@ export const AnyMessageSchema = z.discriminatedUnion("type", [
   ModifierProfileRejectedMessageSchema,
   ModifierProfileConsentReceivedMessageSchema,
   CustomModifierRegisteredMessageSchema,
+  CustomModifierRemovedMessageSchema,
   ErrorMessageSchema,
 ]);
 export type AnyMessage = z.infer<typeof AnyMessageSchema>;
@@ -1039,6 +1083,7 @@ export const KNOWN_MESSAGE_TYPES = [
   "modifier-profile.propose",
   "modifier-profile.consent",
   "custom-modifier.register",
+  "custom-modifier.remove",
   "room.created",
   "room.joined",
   "game.state",
@@ -1051,6 +1096,7 @@ export const KNOWN_MESSAGE_TYPES = [
   "modifier-profile.rejected",
   "modifier-profile.consent-received",
   "custom-modifier.registered",
+  "custom-modifier.removed",
   "error",
 ] as const;
 export type MessageType = (typeof KNOWN_MESSAGE_TYPES)[number];
diff --git a/packages/server/src/ws.custom-modifier-remove.test.ts b/packages/server/src/ws.custom-modifier-remove.test.ts
new file mode 100644
index 0000000..1cc48c3
--- /dev/null
+++ b/packages/server/src/ws.custom-modifier-remove.test.ts
@@ -0,0 +1,253 @@
+/**
+ * T71 integration tests: `custom-modifier.remove` WebSocket handler.
+ *
+ * Mirrors the register-side test harness. Covers:
+ *   1. Valid remove → on-rule-expire fires + broadcast lands.
+ *   2. Host-only gate (BAD_TOKEN for non-host).
+ *   3. Idempotent on unknown id (still broadcasts).
+ *   4. Hook entries retracted from session.
+ */
+import type { ServerWebSocket } from "bun";
+import { describe, expect, it } from "vitest";
+import { GAME_ENTITY, PRESET_STATE_ENTITY } from "@paratype/chess";
+
+import {
+  handleMessage,
+  registerConnection,
+  roomRegistry,
+  sessionRegistry,
+  type ClientData,
+} from "./broadcast.js";
+import {
+  PROTOCOL_VERSION,
+  type ClientMessage,
+  type CustomModifierDescriptorWire,
+} from "./protocol.js";
+
+interface MockWs extends ServerWebSocket<ClientData> {
+  readonly sent: unknown[];
+  readonly closed: boolean;
+}
+
+function makeMockWs(clientId: string): MockWs {
+  const sent: unknown[] = [];
+  const closedFlag = { value: false };
+  const ws = {
+    data: { clientId } as ClientData,
+    sent,
+    get closed(): boolean {
+      return closedFlag.value;
+    },
+    send(msg: string | Buffer): number {
+      const str = typeof msg === "string" ? msg : msg.toString("utf8");
+      sent.push(JSON.parse(str));
+      return str.length;
+    },
+    close(): void {
+      closedFlag.value = true;
+    },
+  } as unknown as MockWs;
+  return ws;
+}
+
+function nextMsgOfType(
+  ws: MockWs,
+  type: string,
+): { payload: Record<string, unknown> } {
+  const idx = ws.sent.findIndex(
+    (m) =>
+      typeof m === "object" &&
+      m !== null &&
+      (m as { type: unknown }).type === type,
+  );
+  if (idx < 0) {
+    const types = ws.sent.map((m) => (m as { type?: string }).type);
+    throw new Error(
+      `no message of type "${type}" in inbox (got ${JSON.stringify(types)})`,
+    );
+  }
+  const msg = ws.sent[idx] as { payload: Record<string, unknown> };
+  ws.sent.splice(idx, 1);
+  return msg;
+}
+
+function sendClient(
+  ws: MockWs,
+  type: ClientMessage["type"],
+  payload: unknown,
+  seq = 1,
+): void {
+  handleMessage(
+    ws,
+    JSON.stringify({
+      v: PROTOCOL_VERSION,
+      seq,
+      ts: Date.now(),
+      type,
+      payload,
+    }),
+  );
+}
+
+function makeDescriptor(
+  id: string,
+  overrides: Partial<CustomModifierDescriptorWire> = {},
+): CustomModifierDescriptorWire {
+  return {
+    type: "data",
+    id,
+    name: id,
+    description: "",
+    version: 1,
+    primitives: [
+      { kind: "seed-attribute", params: { attr: "HpBonus", value: 1 } },
+    ],
+    targetAttrs: ["HpBonus"],
+    uiForm: "primitive-composer",
+    source: "custom",
+    ...overrides,
+  };
+}
+
+function setupRoom(): { white: MockWs; black: MockWs; code: string } {
+  const white = makeMockWs(`T71-W-${crypto.randomUUID()}`);
+  const black = makeMockWs(`T71-B-${crypto.randomUUID()}`);
+  registerConnection(white);
+  registerConnection(black);
+
+  sendClient(white, "room.create", {});
+  const created = nextMsgOfType(white, "room.created");
+  const code = created.payload["code"] as string;
+
+  sendClient(black, "room.join", { code });
+  nextMsgOfType(black, "room.joined");
+
+  // Drain any game.state broadcasts so subsequent assertions only see
+  // custom-modifier messages.
+  for (const ws of [white, black] as MockWs[]) {
+    while (ws.sent.some((m) => (m as { type?: string }).type === "game.state")) {
+      nextMsgOfType(ws, "game.state");
+    }
+  }
+
+  return { white, black, code };
+}
+
+describe("custom-modifier.remove WS handler (T71)", () => {
+  it("removes the descriptor and broadcasts custom-modifier.removed", () => {
+    const { white, black, code } = setupRoom();
+    const desc = makeDescriptor("custom:t71-remove");
+
+    // First register, then remove.
+    sendClient(white, "custom-modifier.register", {
+      roomCode: code,
+      descriptor: desc,
+    });
+    nextMsgOfType(white, "custom-modifier.registered");
+    nextMsgOfType(black, "custom-modifier.registered");
+
+    sendClient(white, "custom-modifier.remove", {
+      roomCode: code,
+      descriptorId: "custom:t71-remove",
+    });
+
+    const wMsg = nextMsgOfType(white, "custom-modifier.removed");
+    expect(wMsg.payload["roomCode"]).toBe(code);
+    expect(wMsg.payload["descriptorId"]).toBe("custom:t71-remove");
+
+    const bMsg = nextMsgOfType(black, "custom-modifier.removed");
+    expect(bMsg.payload["descriptorId"]).toBe("custom:t71-remove");
+
+    // Room state reflects removal — slot freed.
+    const room = roomRegistry.getRoom(code);
+    expect(room?.customModifiers?.has("custom:t71-remove")).toBe(false);
+  });
+
+  it("fires on-rule-expire hooks on the authoritative engine", () => {
+    const { white, code } = setupRoom();
+
+    // Seed an on-rule-expire hook directly on the authoritative
+    // session (simulating a descriptor's apply-time seeding).
+    const session = sessionRegistry.get(code);
+    if (!session) throw new Error("session not found");
+    const engine = session.getEngine();
+    engine.session.insert(GAME_ENTITY, "OnRuleExpireHooks", [
+      {
+        descriptorId: "custom:t71-fire",
+        primitives: [
+          { kind: "seed-attribute", params: { attr: "HpBonus", value: 9 } },
+        ],
+      },
+    ]);
+
+    expect(engine.session.get(GAME_ENTITY, "HpBonus")).toBeUndefined();
+
+    sendClient(white, "custom-modifier.remove", {
+      roomCode: code,
+      descriptorId: "custom:t71-fire",
+    });
+    nextMsgOfType(white, "custom-modifier.removed");
+
+    // The expire hook fired during the server-side detach.
+    expect(engine.session.get(GAME_ENTITY, "HpBonus")).toBe(9);
+    // Hook list now empty (entry retracted).
+    expect(engine.session.get(GAME_ENTITY, "OnRuleExpireHooks")).toEqual([]);
+    // RuleExpireFiredFor records the fire (idempotency guard).
+    const fired = engine.session.get(
+      PRESET_STATE_ENTITY,
+      "RuleExpireFiredFor",
+    ) as readonly string[] | undefined;
+    expect(fired ?? []).toContain("custom:t71-fire");
+  });
+
+  it("rejects non-host (opponent) removals with BAD_TOKEN", () => {
+    const { white, black, code } = setupRoom();
+
+    // White (host) registers.
+    sendClient(white, "custom-modifier.register", {
+      roomCode: code,
+      descriptor: makeDescriptor("custom:t71-host-only"),
+    });
+    nextMsgOfType(white, "custom-modifier.registered");
+    nextMsgOfType(black, "custom-modifier.registered");
+
+    // Black (non-host) tries to remove → rejected.
+    sendClient(black, "custom-modifier.remove", {
+      roomCode: code,
+      descriptorId: "custom:t71-host-only",
+    });
+    const err = nextMsgOfType(black, "error");
+    expect(err.payload["code"]).toBe("BAD_TOKEN");
+    expect(err.payload["message"]).toMatch(/host/i);
+
+    // Descriptor still present.
+    const room = roomRegistry.getRoom(code);
+    expect(room?.customModifiers?.has("custom:t71-host-only")).toBe(true);
+  });
+
+  it("is idempotent on an unknown / already-removed descriptor id", () => {
+    const { white, code } = setupRoom();
+
+    // Remove an id that was never registered. Still broadcasts.
+    sendClient(white, "custom-modifier.remove", {
+      roomCode: code,
+      descriptorId: "custom:t71-never-existed",
+    });
+
+    const msg = nextMsgOfType(white, "custom-modifier.removed");
+    expect(msg.payload["descriptorId"]).toBe("custom:t71-never-existed");
+  });
+
+  it("rejects roomCode mismatch with BAD_TOKEN", () => {
+    const { white, code } = setupRoom();
+    sendClient(white, "custom-modifier.remove", {
+      roomCode: "ZZZZZZ",
+      descriptorId: "custom:t71-anything",
+    });
+    const err = nextMsgOfType(white, "error");
+    expect(err.payload["code"]).toBe("BAD_TOKEN");
+
+    const room = roomRegistry.getRoom(code);
+    expect(room).toBeDefined();
+  });
+});
diff --git a/packages/server/src/ws.request-choice.test.ts b/packages/server/src/ws.request-choice.test.ts
index 194f398..265d064 100644
--- a/packages/server/src/ws.request-choice.test.ts
+++ b/packages/server/src/ws.request-choice.test.ts
@@ -11,8 +11,13 @@
 // wire-level contract independently of T47's trigger plumbing.
 import type { ServerWebSocket } from "bun";
 
-import { describe, it, expect } from "vitest";
-import { pushPendingChoice, type PendingChoice } from "@paratype/chess";
+import { afterEach, beforeEach, describe, it, expect, vi } from "vitest";
+import {
+  GAME_ENTITY,
+  parseCustomModifierDescriptor,
+  pushPendingChoice,
+  type PendingChoice,
+} from "@paratype/chess";
 
 import {
   broadcastTopChoiceIfNew,
@@ -22,6 +27,7 @@ import {
   unregisterConnection,
   type ClientData,
 } from "./broadcast.js";
+import { choiceTimeoutManager } from "./choice-timeout.js";
 import { PROTOCOL_VERSION, type ClientMessage } from "./protocol.js";
 
 // ---------------------------------------------------------------------------
@@ -529,3 +535,191 @@ describe("T44 — submit-choice validation", () => {
     unregisterConnection(black);
   });
 });
+
+// ---------------------------------------------------------------------------
+// T70 — submit-choice / timeout-default trigger continuation resume
+// ---------------------------------------------------------------------------
+
+/**
+ * Build + register a real custom-modifier descriptor on a session's
+ * engine. The descriptor's `primitives` is a single `request-choice`
+ * whose `params.then` writes a sentinel value into `HpBonus` on
+ * `GAME_ENTITY`. The continuation primitive uses `{ $var: <bind> }`
+ * so the resumed scope's binding of the player's value is observable
+ * via a single `engine.session.get(GAME_ENTITY, "HpBonus")` call.
+ *
+ * Mirrors the fixture pattern from
+ * `pending-choices-resume.test.ts` (the unit-level companion to T46)
+ * but goes through the wire schema's `parseCustomModifierDescriptor`
+ * boundary so the descriptor's id is properly branded for
+ * `engine.customModifiers.register`.
+ */
+function registerResumeDescriptor(
+  code: string,
+  descriptorId: string,
+  bindName: string,
+): void {
+  const session = sessionRegistry.get(code);
+  if (!session) throw new Error(`no session for ${code}`);
+  const raw = {
+    type: "data",
+    id: descriptorId,
+    name: descriptorId,
+    description: "",
+    version: 1,
+    primitives: [
+      {
+        kind: "request-choice",
+        params: {
+          kind: "rps",
+          prompt: "?",
+          forPlayer: "both",
+          bind: bindName,
+          then: [
+            {
+              kind: "seed-attribute",
+              params: {
+                attr: "HpBonus",
+                // The submitted value is bound under `bindName` and
+                // forwarded into HpBonus, so the test reads it back
+                // and asserts on the engine state.
+                value: { $var: bindName },
+              },
+            },
+          ],
+        },
+      },
+    ],
+    targetAttrs: [],
+    uiForm: "primitive-composer",
+    source: "custom",
+  };
+  const desc = parseCustomModifierDescriptor(raw);
+  session.getEngine().customModifiers.register(desc);
+}
+
+describe("T70 — submit-choice triggers continuation resume", () => {
+  it("a real submit-choice runs the request-choice's params.then continuation", () => {
+    const { white, black, code } = setupRoom();
+    const session = sessionRegistry.get(code)!;
+
+    registerResumeDescriptor(code, "t70-submit-resume", "winner");
+
+    pushPendingChoice(
+      session.getEngine(),
+      buildPendingChoice({
+        choiceId: "t70-submit",
+        descriptorId: "t70-submit-resume",
+        kind: "rps",
+        forPlayer: "both",
+        triggerPath: [],
+        primitiveIndex: 0,
+      }),
+    );
+    broadcastTopChoiceIfNew(code, session);
+    nextMsgOfType(white, "request-choice");
+    nextMsgOfType(black, "request-choice");
+
+    // Pre-condition: continuation has not run.
+    expect(
+      session.getEngine().session.get(GAME_ENTITY, "HpBonus"),
+    ).toBeUndefined();
+
+    // Player submits "rock" — continuation should bind it under
+    // `winner` and the seed-attribute primitive writes it to HpBonus.
+    sendV2(white, {
+      kind: "submit-choice",
+      protocolVersion: 2,
+      choiceId: "t70-submit",
+      value: "rock",
+    });
+
+    // No error frame.
+    expect(findMsgOfType(white, "error")).toBeUndefined();
+
+    // Engine state advanced beyond the trivial pop: HpBonus carries
+    // the value bound from the player's submission. This is the
+    // assertion that proves T70's wiring fix works — the value is
+    // no longer dropped on the floor at the WS boundary.
+    expect(
+      session.getEngine().session.get(GAME_ENTITY, "HpBonus"),
+    ).toBe("rock");
+
+    // Stack drained — the resume popped the frame.
+    expect(
+      session.getEngine().session.get(GAME_ENTITY, "PendingChoices"),
+    ).toEqual([]);
+
+    // Post-resume game.state broadcast — clients receive the new
+    // authoritative snapshot so they can mirror the continuation's
+    // side-effects without waiting for the next move.
+    nextMsgOfType(white, "game.state");
+    nextMsgOfType(black, "game.state");
+
+    unregisterConnection(white);
+    unregisterConnection(black);
+  });
+});
+
+describe("T70 — timeout default ALSO triggers continuation resume", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it("auto-default after timeout runs the continuation with firstDefaultForKind", () => {
+    const { white, black, code } = setupRoom();
+    const session = sessionRegistry.get(code)!;
+
+    // Override the policy fact for a tighter deadline so the test
+    // doesn't have to advance fake timers by 60s.
+    session
+      .getEngine()
+      .session.insert(GAME_ENTITY, "ChoiceTimeoutPolicy", {
+        mode: "timeout-with-default",
+        seconds: 1,
+      });
+
+    registerResumeDescriptor(code, "t70-timeout-resume", "autoPick");
+
+    pushPendingChoice(
+      session.getEngine(),
+      buildPendingChoice({
+        choiceId: "t70-timeout",
+        descriptorId: "t70-timeout-resume",
+        kind: "rps",
+        forPlayer: "both",
+        triggerPath: [],
+        primitiveIndex: 0,
+      }),
+    );
+    broadcastTopChoiceIfNew(code, session);
+    nextMsgOfType(white, "request-choice");
+    nextMsgOfType(black, "request-choice");
+    expect(choiceTimeoutManager.isArmed(code, "t70-timeout")).toBe(true);
+
+    // Trip the timer. firstDefaultForKind("rps") returns "rock"
+    // (locked by T49). The timeout path threads that into
+    // submitChoiceAndResume, which binds it under `autoPick` and
+    // the continuation writes it to HpBonus.
+    vi.advanceTimersByTime(2_000);
+
+    expect(
+      session.getEngine().session.get(GAME_ENTITY, "HpBonus"),
+    ).toBe("rock");
+    expect(
+      session.getEngine().session.get(GAME_ENTITY, "PendingChoices"),
+    ).toEqual([]);
+    expect(choiceTimeoutManager.isArmed(code, "t70-timeout")).toBe(false);
+
+    // Timeout-driven game.state broadcast reaches both clients.
+    nextMsgOfType(white, "game.state");
+    nextMsgOfType(black, "game.state");
+
+    unregisterConnection(white);
+    unregisterConnection(black);
+  });
+});