[FSSDK-12296] Async Hook implementation

[junaed-optimizely]

Summary

• Add useDecideAsync, useDecideForKeysAsync, and useDecideAllAsync hooks — async counterparts to the existing sync decide hooks, required for CMAB, async UPS etc.

Test plan

• Add tests for all 3 new async hooks covering store states, race conditions, re-evaluation triggers, forced decision reactivity, and render optimization

Issues

• FSSDK-12296

[Copilot]

Pull request overview

Adds async counterparts to the existing “decide” React hooks so consumers can evaluate flags via the Optimizely SDK’s async decide APIs (needed for CMAB / async decisioning) while handling loading/error states, cancellation, and forced-decision reactivity.

Changes:

• Introduces useDecideAsync, useDecideForKeysAsync, and useDecideAllAsync and exports them from the public entrypoints.
• Adds shared useAsyncDecision state machine to manage async execution, cancellation of stale promises, and store readiness transitions.
• Adds comprehensive Vitest coverage for the 3 new hooks and extends hook test utilities with async decide method stubs.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/index.ts	Exports the new async hooks from the package entrypoint.
src/hooks/index.ts	Exposes the new async hooks (and related types) from the hooks barrel.
src/hooks/useAsyncDecision.ts	Adds shared async state machine used by all async decide hooks.
src/hooks/useDecideAsync.ts	Implements async single-flag decision hook w/ forced decision subscription.
src/hooks/useDecideForKeysAsync.ts	Implements async multi-key decision hook w/ per-key forced decision subscription.
src/hooks/useDecideAllAsync.ts	Implements async all-flags decision hook w/ global forced decision subscription.
src/hooks/*.spec.tsx	Adds tests covering readiness states, cancellation, re-evaluation triggers, and forced-decision reactivity.
src/hooks/testUtils.tsx	Extends mock user context to support async decide APIs for testing.

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[Copilot]

useAsyncDecision calls setAsyncState({ result: emptyResult, error: null, isLoading: true }) whenever the provider is not ready (!hasConfig || userContext === null). On initial mount (and on any store refresh while still not ready), this will schedule a state update even when the hook is already in the exact same loading state, causing an avoidable extra render. Consider using a functional setAsyncState with a guard (similar to the ready-path guard) so it returns prev when {isLoading:true,error:null,result===emptyResult} is already true.

Suggested change

	setAsyncState({ result: emptyResult, error: null, isLoading: true });
	setAsyncState((prev) => {
	if (prev.isLoading && prev.error === null && prev.result === emptyResult) return prev;
	return { result: emptyResult, error: null, isLoading: true };
	});

[Copilot]

The async hooks rely on as UseDecide*AsyncResult type assertions when returning { result, error, isLoading }, which can mask violations of the intended discriminated union (e.g., accidentally returning isLoading: true with a non-null error after future refactors). Consider making useAsyncDecision return a discriminated union (or a helper that maps its internal state into the union) so TypeScript enforces the invariants and the hooks can return without assertions.