fix(once): correct error handling to not cache thrown errors

[Copilot]

The once function was caching error states - when the wrapped function threw on first invocation, subsequent calls returned undefined instead of retrying. This differs from standard once semantics where only successful results are cached.

Changes

• Reordered execution flag assignment - Move called = true after fn.apply() so errors prevent caching
• Updated error handling test - Test now verifies function retries until success rather than returning undefined

Behavior

const initialize = once(() => {
  if (!isReady()) throw new Error('Not ready');
  return setup();
});

// Before: First call throws, second call returns undefined
// After: Retries until isReady() returns true, then caches result
initialize(); // throws
initialize(); // retries (may throw or succeed)
initialize(); // returns cached result if previous call succeeded

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.