diff --git a/packages/rete/package.json b/packages/rete/package.json
index b349593..9b0121a 100644
--- a/packages/rete/package.json
+++ b/packages/rete/package.json
@@ -13,7 +13,7 @@
     }
   },
   "scripts": {
-    "build": "tsup src/index.ts --format esm,cjs --dts --clean",
+    "build": "tsup src/index.ts --format esm,cjs --clean && tsc -p tsconfig.build.json --emitDeclarationOnly --noEmitOnError",
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
diff --git a/packages/rete/src/cycle.test.ts b/packages/rete/src/cycle.test.ts
index ba8477f..9e9b042 100644
--- a/packages/rete/src/cycle.test.ts
+++ b/packages/rete/src/cycle.test.ts
@@ -33,87 +33,77 @@ describe("RecursionLimitExceededError", () => {
 });
 
 describe("Session.fireRules() recursion limit", () => {
-  it("throws RecursionLimitExceededError when recursion depth exceeds limit", () => {
-    const session = new Session({ autoFire: false, recursionLimit: 3 });
-    expect(() => {
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      (session as any)._fireDepth = 4;
+   it("throws RecursionLimitExceededError when recursion depth exceeds limit", () => {
+     const session = new Session({ autoFire: false, recursionLimit: 3 });
+     expect(() => {
+       session._fireDepth = 4;
       session.fireRules({ recursionLimit: 3 });
     }).toThrow(RecursionLimitExceededError);
   });
 
-  it("throws when depth equals limit (>=)", () => {
-    const session = new Session({ autoFire: false, recursionLimit: 3 });
-    expect(() => {
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      (session as any)._fireDepth = 3;
+   it("throws when depth equals limit (>=)", () => {
+     const session = new Session({ autoFire: false, recursionLimit: 3 });
+     expect(() => {
+       session._fireDepth = 3;
       session.fireRules({ recursionLimit: 3 });
     }).toThrow(RecursionLimitExceededError);
   });
 
-  it("does not throw when depth is below limit", () => {
-    const session = new Session({ autoFire: false, recursionLimit: 64 });
-    expect(() => {
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      (session as any)._fireDepth = 0;
+   it("does not throw when depth is below limit", () => {
+     const session = new Session({ autoFire: false, recursionLimit: 64 });
+     expect(() => {
+       session._fireDepth = 0;
       session.fireRules({ recursionLimit: 64 });
     }).not.toThrow();
   });
 
-  it("uses session default recursionLimit when opts omitted", () => {
-    const session = new Session({ autoFire: false, recursionLimit: 3 });
-    expect(() => {
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      (session as any)._fireDepth = 5;
+   it("uses session default recursionLimit when opts omitted", () => {
+     const session = new Session({ autoFire: false, recursionLimit: 3 });
+     expect(() => {
+       session._fireDepth = 5;
       session.fireRules();
     }).toThrow(RecursionLimitExceededError);
   });
 
-  it("resets recursion depth to 0 between independent fireRules() calls", () => {
-    const session = new Session({ autoFire: false, recursionLimit: 3 });
-    expect(() => session.fireRules()).not.toThrow();
-    expect(() => session.fireRules()).not.toThrow();
-    expect(() => session.fireRules()).not.toThrow();
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    expect((session as any)._fireDepth).toBe(0);
+   it("resets recursion depth to 0 between independent fireRules() calls", () => {
+     const session = new Session({ autoFire: false, recursionLimit: 3 });
+     expect(() => session.fireRules()).not.toThrow();
+     expect(() => session.fireRules()).not.toThrow();
+     expect(() => session.fireRules()).not.toThrow();
+     expect(session._fireDepth).toBe(0);
   });
 
-  it("decrements depth even if fireRules body were to throw (finally)", () => {
-    const session = new Session({ autoFire: false, recursionLimit: 3 });
-    // Force recursion guard to throw; internal counter must not be left elevated
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    (session as any)._fireDepth = 5;
-    expect(() => session.fireRules({ recursionLimit: 3 })).toThrow(
-      RecursionLimitExceededError,
-    );
-    // After throw, depth should still be 5 (guard throws before increment)
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    expect((session as any)._fireDepth).toBe(5);
+   it("decrements depth even if fireRules body were to throw (finally)", () => {
+     const session = new Session({ autoFire: false, recursionLimit: 3 });
+     // Force recursion guard to throw; internal counter must not be left elevated
+     session._fireDepth = 5;
+     expect(() => session.fireRules({ recursionLimit: 3 })).toThrow(
+       RecursionLimitExceededError,
+     );
+     // After throw, depth should still be 5 (guard throws before increment)
+     expect(session._fireDepth).toBe(5);
   });
 
-  it("recursionLimit: 0 means no limit — does not throw", () => {
-    const session = new Session({ autoFire: false, recursionLimit: 0 });
-    expect(() => {
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      (session as any)._fireDepth = 1000;
+   it("recursionLimit: 0 means no limit — does not throw", () => {
+     const session = new Session({ autoFire: false, recursionLimit: 0 });
+     expect(() => {
+       session._fireDepth = 1000;
       session.fireRules({ recursionLimit: 0 });
     }).not.toThrow();
   });
 
-  it("recursionLimit: 0 at session level also means no limit", () => {
-    const session = new Session({ autoFire: false, recursionLimit: 0 });
-    expect(() => {
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      (session as any)._fireDepth = 1000;
+   it("recursionLimit: 0 at session level also means no limit", () => {
+     const session = new Session({ autoFire: false, recursionLimit: 0 });
+     expect(() => {
+       session._fireDepth = 1000;
       session.fireRules();
     }).not.toThrow();
   });
 
-  it("thrown error carries the actual depth value", () => {
-    const session = new Session({ autoFire: false, recursionLimit: 3 });
-    try {
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      (session as any)._fireDepth = 7;
+   it("thrown error carries the actual depth value", () => {
+     const session = new Session({ autoFire: false, recursionLimit: 3 });
+     try {
+       session._fireDepth = 7;
       session.fireRules({ recursionLimit: 3 });
       expect.fail("should have thrown");
     } catch (err) {
@@ -122,12 +112,11 @@ describe("Session.fireRules() recursion limit", () => {
     }
   });
 
-  it("opts.recursionLimit overrides the session default", () => {
-    const session = new Session({ autoFire: false, recursionLimit: 64 });
-    // Session default is 64 — would not throw. But opts override to 2.
-    expect(() => {
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      (session as any)._fireDepth = 2;
+   it("opts.recursionLimit overrides the session default", () => {
+     const session = new Session({ autoFire: false, recursionLimit: 64 });
+     // Session default is 64 — would not throw. But opts override to 2.
+     expect(() => {
+       session._fireDepth = 2;
       session.fireRules({ recursionLimit: 2 });
     }).toThrow(RecursionLimitExceededError);
   });
diff --git a/packages/rete/src/eventlog.ts b/packages/rete/src/eventlog.ts
index 21c1054..f0d969e 100644
--- a/packages/rete/src/eventlog.ts
+++ b/packages/rete/src/eventlog.ts
@@ -48,6 +48,16 @@ export interface LogEvent {
 export class EventLog {
   readonly #events: LogEvent[] = [];
   #seq = 0;
+  readonly #clock: () => number;
+
+  /**
+   * @param clock — Optional wall-clock function. Defaults to `Date.now`.
+   *   Inject a deterministic clock (e.g. `() => 0`) in tests and replay
+   *   contexts where timestamp values must be stable across runs.
+   */
+  constructor(clock: () => number = Date.now) {
+    this.#clock = clock;
+  }
 
   /** Number of events logged. */
   get length(): number {
@@ -67,7 +77,7 @@ export class EventLog {
   appendInsert(id: EntityId, attr: AttrKey, value: FactValue): void {
     this.#events.push({
       seq: ++this.#seq,
-      ts: Date.now(),
+      ts: this.#clock(),
       kind: "insert",
       id,
       attr,
@@ -82,7 +92,7 @@ export class EventLog {
   appendRetract(id: EntityId, attr: AttrKey, value: FactValue): void {
     this.#events.push({
       seq: ++this.#seq,
-      ts: Date.now(),
+      ts: this.#clock(),
       kind: "retract",
       id,
       attr,
@@ -94,7 +104,7 @@ export class EventLog {
   appendFire(ruleName: string): void {
     this.#events.push({
       seq: ++this.#seq,
-      ts: Date.now(),
+      ts: this.#clock(),
       kind: "fire",
       ruleName,
     });
diff --git a/packages/rete/tsconfig.build.json b/packages/rete/tsconfig.build.json
new file mode 100644
index 0000000..a194452
--- /dev/null
+++ b/packages/rete/tsconfig.build.json
@@ -0,0 +1,8 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "composite": false,
+    "incremental": false,
+    "declarationMap": false
+  }
+}
diff --git a/playwright.config.ts b/playwright.config.ts
index ce984f2..3778a71 100644
--- a/playwright.config.ts
+++ b/playwright.config.ts
@@ -15,4 +15,5 @@ export default defineConfig({
     timeout: 30000,
   },
   reporter: [["html", { open: "never" }], ["list"]],
+  workers: 1, // prevent parallel workers from sharing the single dev server
 });