fix(effect): replace hardcoded Date.now() in FiberId.unsafeMake with configurable clock source

[copyleftdev]

Problem

FiberId.unsafeMake() uses Date.now() for startTimeMillis, which feeds into Hash.symbol() and Equal.symbol():

// fiberId.ts:75
[Hash.symbol](): number {
  return Hash.cached(this, Hash.string(`${FiberIdSymbolKey}-${this._tag}-${this.id}-${this.startTimeMillis}`))
}

This means fiber identity hashing and equality are non-deterministic across runs. Two fibers created with the same counter ID but at different wall-clock times produce different hashes and are not equal.

This contributes to scheduler-related issues:

• fix(effect): isolate scheduler runners per fiber #6124 — scheduler runner isolation (fiber-keyed WeakMap behaves inconsistently)
• detectAsyncLeaks false positive: MixedScheduler PROMISE leaks with @effect/vitest #6126 — MixedScheduler PROMISE leaks in @effect/vitest (timing-dependent cache behavior)

It also makes deterministic testing of the fiber runtime impossible without monkey-patching Date.now globally, which breaks timers, logging, and concurrent tests.

Fix

Replace the hardcoded Date.now() call with a globalValue-backed configurable clock source:

const _clockSource = globalValue(
  Symbol.for("effect/Fiber/Id/_clockSource"),
  (): { now: () => number } => ({ now: () => Date.now() })
)

• Default behavior is identical — Date.now() is still called
• setClockSource(fn) / resetClockSource() allow swapping for deterministic testing
• No global mutation of Date.now
• 1 file changed, 22 insertions, 1 deletion

Test plan

• Fiber.test.ts — 16 tests pass
• Effect/concurrency.test.ts — 24 tests pass
• Effect/racing.test.ts — 4 tests pass
• Zero regressions

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 377c9ef

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 36 packages

Name	Type
effect	Patch
@effect/cli	Patch
@effect/cluster	Patch
@effect/experimental	Patch
@effect/opentelemetry	Patch
@effect/platform-browser	Patch
@effect/platform-bun	Patch
@effect/platform-node-shared	Patch
@effect/platform-node	Patch
@effect/platform	Patch
@effect/printer-ansi	Patch
@effect/printer	Patch
@effect/rpc	Patch
@effect/sql-clickhouse	Patch
@effect/sql-d1	Patch
@effect/sql-drizzle	Patch
@effect/sql-kysely	Patch
@effect/sql-libsql	Patch
@effect/sql-mssql	Patch
@effect/sql-mysql2	Patch
@effect/sql-pg	Patch
@effect/sql-sqlite-bun	Patch
@effect/sql-sqlite-do	Patch
@effect/sql-sqlite-node	Patch
@effect/sql-sqlite-react-native	Patch
@effect/sql-sqlite-wasm	Patch
@effect/sql	Patch
@effect/typeclass	Patch
@effect/vitest	Patch
@effect/workflow	Patch
@effect/ai	Patch
@effect/ai-amazon-bedrock	Patch
@effect/ai-anthropic	Patch
@effect/ai-google	Patch
@effect/ai-openai	Patch
@effect/ai-openrouter	Patch

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