[codex] Add timeout option helper

[samlaycock]

Summary

Adds fx.timeoutOption for timeout-as-value boundary workflows without changing existing fx.timeout semantics. The helper delegates to Effect's timeoutOption, returning Option.some(value) when the task completes in time and Option.none() when the timeout wins while preserving original task errors and dependency requirements.

Closes #54.

Changes

• Expose fx.timeoutOption from the public fx API.
• Add runtime tests for slow and fast tasks.
• Add type-level tests for success, error, and dependency inference.
• Document when to use fx.timeoutOption versus fx.timeout and fx.timeoutFail.
• Add a changeset for the new helper.

Validation

• bun fmt
• bun lint:fix
• bun lint
• bun test
• bun typecheck

[greptile-apps]

Greptile Summary

This PR adds fx.timeoutOption, a thin wrapper around Effect's timeoutOption that returns Option.some(value) on success and Option.none() on timeout, preserving original errors and dependencies. It follows the same pattern as timeoutFail and is a clean, additive change.

• src/concurrency.ts: New timeoutOption helper with explicit return type and proper Option import; delegated to Effect.timeoutOption.
• Tests cover both the runtime behavior (slow/fast tasks) and type-level inference (result, error, dependency).
• Docs and changeset are updated consistently with the rest of the module.

Confidence Score: 5/5

Purely additive helper with no changes to existing behavior; safe to merge.

The change is a small, isolated addition that delegates directly to a well-tested Effect primitive. All existing exports are untouched, the return type is explicitly annotated, both runtime and type-level tests are present, and docs plus a changeset are included.

No files require special attention.

Important Files Changed

Filename	Overview
src/concurrency.ts	Adds timeoutOption helper with explicit return type, Option import, and correct delegation to Effect.timeoutOption.
src/index.ts	Exports timeoutOption from the public fx object alongside the other timeout helpers.
test/runtime.test.ts	Adds two runtime tests for the slow (None) and fast (Some) paths of fx.timeoutOption.
test/types.test.ts	Adds type-level tests verifying result, error, and dependency inference for fx.timeoutOption.
docs/retry-timeout.md	Adds documentation for fx.timeoutOption with usage guidance and comparison to fx.timeout/fx.timeoutFail.
docs/api-reference.md	Adds fx.timeoutOption entry to the API reference table.
.changeset/timeout-option-helper.md	Correct minor-version changeset for the new public helper.

_{Reviews (2): Last reviewed commit: "fix: declare timeout option return type" | Re-trigger Greptile}