Uncaught 'TypeError: once is not a function' ×5 at every cc startup — chokidar's readdirp stream has .on but not .once, breaking the file watcher #9680

Found during #9673's investigation. Fires 5× on every claude-code startup, uncaught.

Real frame (verified, not a #9521 name-borrow): chokidar's _handleRead does j.on(…).on(…) on the readdirp stream — which works — then j.once(…) throws, because the stream object perry hands back has on but not once.

Consequence: cc's file watcher fails to initialise on every run. That is its own defect, and it may also be why watch-dependent behaviour looks inconsistent under perry.

The likely shape is a stream/EventEmitter surface that implements a subset of the emitter API — once is the classic omission because it is usually implemented in terms of on + self-removal. Check what readdirp returns under perry versus node and diff the method surface (Object.getOwnPropertyNames on the object and its prototype chain), then implement the missing members rather than just once — a partial emitter will keep producing this class of failure.

Verification: fixture creating the same readdirp-style stream and asserting the full node emitter surface (on, once, off, removeListener, emit, prependListener, prependOnceListener, listenerCount, eventNames), byte-compared to node; plus the cc-level check that startup produces zero uncaught TypeErrors and the watcher initialises.