fix(pool): fallback to SDK runner when cursor-agent binary not found on Windows

[rodrigoperaltadev]

Summary

When CURSOR_ACP_AGENT_POOL=1 is enabled on Windows and cursor-agent.cmd is not installed at the expected path (%LOCALAPPDATA%\cursor-agent\cursor-agent.cmd), resolveCursorAgentBinary() returns the bare name without a full path. The pool runner then calls spawn("cursor-agent.cmd", ..., { shell: true }) which fails with an opaque cmd.exe error:

cursor-acp error: ""cursor-agent.cmd"" no se reconoce como un comando interno o externo...

This PR adds:

1. A typed BinaryNotFoundError with a descriptive message (path attempted + CURSOR_AGENT_EXECUTABLE hint)
2. A strict resolver variant (resolveCursorAgentBinaryStrict) used exclusively by the pool — the original resolveCursorAgentBinary is untouched (15 call sites)
3. Graceful fallback to the SDK runner when the binary is missing, with a structured warn log emitted once per pool key
4. Correct EventEmitter-based error propagation for the dual-failure path (binary missing + SDK also fails)

The pool is opt-in (CURSOR_ACP_AGENT_POOL not set = no change). macOS/Linux behavior is unchanged.

Changes

File	Change
src/utils/errors.ts	Add BinaryNotFoundError with attemptedPath field
src/utils/binary.ts	Add resolveCursorAgentBinaryStrict() — throws on win32 when binary missing
src/client/cursor-agent-child.ts	Catch BinaryNotFoundError, log warn once, fall back to SDK runner; fix async throw in error handler
src/plugin.ts	Pass sdkApiKey to pool child for SDK fallback
tests/unit/binary-strict.test.ts	9 tests covering scenarios A–E (win32 throw, found, env override, linux, darwin)
tests/unit/cursor-agent-fallback.test.ts	3 tests: warn-once, SDK factory invoked, dual-failure message
package.json	Add --isolate to test scripts (required for module-mocking isolation); register new test files in CI

Testing

# All new tests (run isolated — module mocks require it)
bun test --isolate tests/unit/binary-strict.test.ts tests/unit/cursor-agent-fallback.test.ts

# Full CI unit suite
bun run test:ci:unit

485/486 pass — the single failure (Plugin entry module ESM resolution) is pre-existing on main.

[Nomadcxx]

This is really helpful man, thank you.

I'm reviewing now, just want to make sure it will not conflict with next slice of changes I have planned for the plugin. At the moment I'm thinking of just biting the bullet and developing a very small hook and rule for cursor-agent so it can steer models better.. at the moment.. converting one set of tooling to another has become a nightmare.. malformed writes here and there (mostly with Composer if not exclusively at this point).