feat(coding-agent): flush registerProvider immediately, add unregisterProvider

[aliou]

Problem

pi.registerProvider() pushed to a pendingProviderRegistrations queue that was only flushed once during bindCore() at startup. Any call after that (e.g. from a command handler following a setup flow) sat dead in the queue until the next /reload.

Changes

model-registry.ts — Added ModelRegistry.unregisterProvider(name): removes the provider from registeredProviders, clears its API key, then calls refresh() so built-in models that were overridden are restored.

extensions/types.ts — Added registerProvider and unregisterProvider fields to ExtensionRuntimeState so the runner can swap them out after bind. Added pi.unregisterProvider() to ExtensionAPI.

extensions/loader.ts — createExtensionRuntime() initialises registerProvider as a queue-push closure and unregisterProvider as a queue-removal closure. createExtensionAPI delegates both to the runtime instead of touching the queue directly.

extensions/runner.ts — In bindCore(), after flushing the pending queue, both functions are replaced with direct ModelRegistry calls. From that point every pi.registerProvider() / pi.unregisterProvider() call takes effect immediately.

docs/extensions.md — Updated pi.registerProvider section to document the immediate-flush behaviour; added pi.unregisterProvider section with example.

CHANGELOG.md — Added Added and Fixed entries under [Unreleased].

[github-actions]

Hi @aliou, thanks for your interest in contributing!

We ask new contributors to open an issue first before submitting a PR. This helps us discuss the approach and avoid wasted effort.

Next steps:

1. Open an issue describing what you want to change and why (keep it concise, write in your human voice, AI slop will be closed)
2. Once a maintainer approves with lgtm, you'll be added to the approved contributors list
3. Then you can submit your PR

This PR will be closed automatically. See https://github.com/badlogic/pi-mono/blob/main/CONTRIBUTING.md for more details.

[aliou]

For more context, i noticed when using two extensions together:

• pi-synthetic defines a provider and its models
• pi-ts-aperture changes the provider's url and api key

Without this, the providers model wouldn't be accessible after the apertures updates it.

[badlogic]

Merged into main with fixes: queue unregister now removes all matching entries (not just first), types/docs aligned, OAuth/API registrations reset on refresh, tests added. Thanks @aliou!

[aliou]

Thanks!