refactor(test): replace setTimeout with deterministic spawn polling

[matthew-petty]

Summary

• Extracted afterSpawnCalled helper from health.test.ts to shared helpers.ts
• Replaced all setTimeout patterns with deterministic spawn polling across test files
• Eliminates flaky test timing issues in CI environments

Changes

File	Replacements
helpers.ts	Added afterSpawnCalled helper function
health.test.ts	Imported helper from shared module
stream.test.ts	16 replacements
generate.test.ts	11 replacements
app.test.ts	8 replacements
sdk.integration.test.ts	6 replacements

How it works

The afterSpawnCalled helper polls every 1ms until mockSpawn has been called, then executes the callback. This eliminates race conditions where setTimeout(50) might fire before or after the actual spawn call depending on CI load.

// Before - timing-dependent and flaky
setTimeout(() => {
  mockProc.emit("close", 0, null);
}, 50);

// After - deterministic
afterSpawnCalled(mockSpawn, () => {
  mockProc.emit("close", 0, null);
});

Closes #29

Test plan

• All 83 tests pass locally
• Pre-commit hooks pass (Biome, TypeScript, secret scanning)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!