Adds an idempotent DELETE /api/traces/:sessionId path that removes only the local trace JSONL file and invalidates trace read cache. The Trace list now exposes a trash action behind a confirmation dialog that states chat history is not deleted.
Tested: bun test src/server/__tests__/trace-capture.test.ts
Tested: cd desktop && bun run test -- src/pages/TraceList.test.tsx --run
Tested: bun run check:server
Tested: bun run check:desktop
Tested: Browser smoke with temporary CLAUDE_CONFIG_DIR verified the Trace list delete button and confirmation dialog on ?traceWindow=1.
Constraint: GitHub issue #868 remains open until a release ships and post-release retest passes.
Confidence: high
Scope-risk: moderate
46f612abd5