[copilot-finds] Bug: Registry._getFunctionName() returns '*' for anonymous generator functions, causing silent registration failure

[github-actions]

Problem

Registry._getFunctionName() in packages/durabletask-js/src/worker/registry.ts has a fallback path that parses function names from fn.toString() when fn.name is empty. This parsing has two bugs:

1. Generator functions (function*() {}): The parser does fnStr.indexOf("function") + "function".length, landing right before the *. It then takes everything up to (, returning "*" as the name. Since "*" is truthy, it passes the if (!name) validation in addNamedOrchestrator, silently registering the orchestrator under name "*".

2. Arrow functions ((x) => x): indexOf("function") returns -1, so start = -1 + 8 = 7. The parser then slices from position 7 to the next (, producing garbage output.

Root Cause

The _getFunctionName fallback parser was written for regular function declarations only. It does not account for:

• The * in generator function syntax
• Arrow functions that lack the function keyword entirely

Proposed Fix

Three guards added to _getFunctionName:

1. Return "" when indexOf("function") returns -1 (arrow functions have no function keyword)
2. Skip past * and whitespace after the function keyword (generator functions)
3. Return "" when indexOf("(", start) returns -1 (malformed input safety)

Impact

Severity: Medium. When addOrchestrator(async function*(ctx) { ... }) is called with a truly anonymous generator (no variable assignment), the orchestrator registers under name "*". No error is thrown — the orchestrator silently never matches any scheduled orchestration. This only affects inline anonymous generators without variable assignment context (since JS engines infer fn.name from variable assignments).