Support AbortSignal-based tool unregistration (Chrome 148)

[kashishhora]

Chrome 148 removes unregisterTool() from navigator.modelContext and replaces it with an AbortSignal passed to registerTool(). This aligns with the addEventListener ownership pattern — you can only unregister a tool if you hold the original AbortController.

What changed

Types (src/types.ts, src/index.ts)

• New RegisterToolOptions interface with optional signal?: AbortSignal
• registerTool accepts optional second arg options?: RegisterToolOptions
• unregisterTool is now optional (?) — won't exist on Chrome 148+
• RegisterToolOptions exported for consumers

Polyfill registry (src/polyfill/registry.ts)

• registerTool accepts signal option
• Pre-aborted signals skip registration entirely
• Abort listener deletes the tool and fires change notification
• Identity check prevents stale abort signals from removing same-name re-registrations
• unregisterTool stays on the polyfill for backward compat

React hook (src/hooks/useMcpTool.ts)

• Creates one AbortController per effect cycle
• Passes { signal } to registerTool
• Cleanup: mc.unregisterTool?.(name) (optional chaining) + controller.abort()
• Works with both old (unregisterTool) and new (signal-only) APIs

Breaking change

navigator.modelContext.unregisterTool is now typed as optional. Downstream TS code calling it directly must add optional chaining (?.). This matches the Chrome 148 runtime behavior.

Testing

• pnpm test — 158/158 pass
• pnpm typecheck — clean
• pnpm lint — clean
• pnpm build — CJS + ESM + types build successfully

New tests:

• Registry: abort removes tool, pre-aborted skip, abort-after-unregister no-op, stale abort safety, notification timing
• Hook: signal-only native API mount/unmount, StrictMode, re-registration on prop change
• Context: native API without unregisterTool reports available