Rust/Windows: pause_execution reports stopReason 'exception' (0x80000003 break-in) instead of 'pause'

[debugmcpdev]

Context

Found during the post-#272/#273/#274 /testdebugger sweep (2026-08-06, Windows, CodeLLDB 1.11.8, GNU-toolchain binaries). Reproduced identically on 4 server variants (local HTTP/SSE/stdio, NPX-tarball HTTP), both on the first pause and after a continue→re-pause cycle.

Problem

On Windows, pause_execution against a running Rust debuggee succeeds, but the resulting stop reports stopReason: 'exception' with description Exception 0x80000003 and the stopped thread parked in the injected break-in frames (DbgUiRemoteBreakin → DbgBreakPoint). Callers that check lastStop.reason === 'pause' (the documented contract for a user-initiated pause) see an exception instead. get_local_variables on the synthetic break-in frame also returns an empty array (the user's threads are listed and inspectable via list_threads/frame selection — this part is inherent to the break-in mechanism).

This is the Windows analog of the SIGSTOP case already handled by RustAdapterPolicy.normalizeStopReason (which maps CodeLLDB's SIGSTOP-delivered pause, reported as 'exception', back to 'pause' on POSIX). Windows delivers the pause via DebugBreakProcess → breakpoint exception 0x80000003, which the current normalizer leaves untouched because the detail text is non-empty and doesn't match /SIGSTOP/i.

Suggested fix

Extend the existing reason === 'exception' branch in packages/shared/src/interfaces/adapter-policy-rust.ts: when context.pausePending is true and the detail matches the Windows break-in signature (0x80000003 / EXCEPTION_BREAKPOINT / DbgBreakPoint), normalize to 'pause'. Keep it gated on pausePending so a genuine __debugbreak()/int3 in user code that fires while no pause is in flight stays an exception stop. Unit cases mirror the SIGSTOP suite in packages/shared/tests/unit/adapter-policy-rust.test.ts:67+.

Evidence

• P3/P8 of the pause workflow on all 4 tested variants: stop body Exception 0x80000003, top frame @DbgBreakPoint, thread DbgUiRemoteBreakin.
• POSIX path already normalizes (SIGSTOP → 'pause'), so this is a Windows-only contract gap.