feat(thressgame-coverage): Wave 8 (WS protocol v2 + suspended execution + request-choice)

- T43: WS protocol v2 schema; protocolVersion field; RequestChoice/SubmitChoice/ProtocolVersionMismatch messages; v1 backward-compat
- T44: server-side request-choice broadcast on push; submit-choice validation (kind/forPlayer/value-type); ordered LIFO matching
- T45: PendingChoices stack on GAME_ENTITY; pushPendingChoice/popPendingChoice/peekPendingChoice helpers; serializePendingChoice (Map<->Array roundtrip); MAX_CHOICE_DEPTH=8 enforced
- T46: submitChoiceAndResume(engine, choiceId, value); descriptor-by-id lookup; bindings restored; remaining primitives executed via runPrimitives from primitiveIndex+1
- T47: request-choice primitive; SuspendedExecution exception mechanism; dispatcher catches and stops sibling iteration; deterministic choiceId via session counter
- T48: AutoChoiceResolver test transport (answersByKind / answersById); drainPendingChoices LIFO walk
- T49: server-side choice timeout enforcement; auto-resolve to first-option-per-kind; disconnect handler (forfeit / pause)
- T50: ChoiceTimeoutPolicy on GAME_ENTITY (timeout-with-default | no-timeout); CreateGameRequest extended; default 60s

Tests: 2533 -> 2658 (+125). bun run check exit 0.

.sisyphus/notepads/visual-modifier-builder/learnings.md

@@ -671,3 +671,46 @@ Added BlockList wrapping BlockCard with dnd-kit for sorting. Added tests verifyi
   2. Depth-4 invalid (conditional -> on-move -> conditional -> add-to-attribute) triggering `descriptor.primitives.depth.exceeded`
   3. Mixed old/new kinds at depth 3 (on-captured -> conditional -> add-aura) valid
 - `bun test packages/chess/src/modifiers/custom/validate.test.ts` passes with 16 test cases.
+
+---
+
+## Path-based selection refactor + nested-editing + add-child button — 2026-04-21
+
+### Problem
+Nested BlockCards couldn't be selected/edited. BlockList recursion hardcoded `selectedIndex={null}` + `onSelect={() => {}}` (no-ops) because selection state was flat `number | null`. Also no visible affordance existed to add primitives inside an expanded trigger (user had to know "click parent → palette banner appears → click palette item").
+
+### Solution
+- Replaced `selectedIndex: number | null` with `SelectionPath = readonly number[]` throughout VisualBuilderPane / BlockList / BlockCard.
+- `[]` = no selection; `[0]` = top-level 0; `[0, 2]` = child 2 of top-level 0 (via `params.primitives`). Arbitrary depth supported.
+- Replaced `expandedIndices: Set<number>` with `expandedPaths: Set<string>` keyed by `path.join('.')` (avoids deep-set-equality ceremony).
+- 5 new pure path walkers in VisualBuilderPane.tsx: `getNodeAtPath`, `updateAtPath`, `removeAtPath`, `appendChildAtPath`, `reorderAtPath` + `pathStartsWith` helper.
+- Deleted redundant `handleNestedReorder` / `handleNestedRemove` — consolidated into path-based versions.
+- New BlockCard prop `onAddChildClick?: () => void` renders a dashed-violet "+ Add primitive inside" button at the bottom of the nested container. BlockList wires it to `() => onSelect(thisPath)` for container primitives only (checks `primitive?.childPrimitives !== undefined`).
+- Nested-container now renders even when children-list is empty — so empty triggers STILL show the add button.
+- Nested DnD id collision guard: `nodeIds` include `basePath.join('.')` so nested SortableContexts don't share IDs.
+- `handleSelect` auto-expands container primitives so the add-child button appears immediately.
+
+### Conditional `then`/`else` — documented as out of scope
+Path walker only traverses `params.primitives`. `conditional`'s separate `then`/`else` arrays are NOT selectable/editable in visual mode — same status as before this refactor. Comment in VisualBuilderPane.tsx:85-94.
+
+### Edge cases handled
+- Remove subtree containing selection → `pathStartsWith` clears selection
+- Remove cleans expandedPaths via key-prefix match
+- Reorder adjusts selection index if it pointed into the reordered list
+- "Add at top level instead" button → `setSelectedPath([])`
+
+### Verification
+- 27/27 visual-builder tests pass (up from 22, +5 new tests covering nested selection + add-child button)
+- `bun run check` → 166 files / 1957 tests pass
+- 0 lsp_diagnostics errors in modified files
+- No `as any`, no `@ts-ignore` introduced
+
+### Files touched
+- packages/chess/src/ui/visual-builder/VisualBuilderPane.tsx (+245 / -126 lines)
+- packages/chess/src/ui/visual-builder/BlockList.tsx (+86 / -49)
+- packages/chess/src/ui/visual-builder/BlockCard.tsx (+25 / -4)
+- packages/chess/src/ui/visual-builder/{BlockCard,BlockList,VisualBuilderPane}.test.tsx (updated for new prop shapes + new tests)
+
+### Pre-existing noise confirmed NOT caused by this work
+- `ParamField.snapshot.test.tsx` has 15 obsolete snapshots (T14 legacy) — untouched ParamField.tsx per user request
+- `CustomModifierEditor.mode-roundtrip.test.tsx` fails under `bun test` direct but passes under `bun run check` (vitest environment) — pre-existing localStorage mocking limitation documented at learnings.md:658