- Offloaded slow LSP diagnostics to a deferred channel in the `write` tool to prevent blocking agent execution for the full 3-second poll window.
- Abstracted deferred diagnostic logic into a reusable `DeferredDiagnostics` class to standardize tracking and deduplication across tools.
- Updated `WriteTool` to support `beginDeferredDiagnosticsForPath` callbacks, surfacing diagnostics as an aside instead of stalling the tool result.
- Added a regression test validating that `write` completes immediately while diagnostics arrive asynchronously.