fix: MCP kill_session 400 + extended working stall detection

[OneStepAt4time]

Summary

• Fix bug: MCP kill_session tool returns Bad Request while REST DELETE works #560: MCP kill_session tool no longer sends Content-Type: application/json on bodyless DELETE requests, which caused Fastify to return 400 Bad Request
• Fix [Bug][P2] Session shows 'working' but CC is stalled in 'Misting' state for 1h+ #562: Two-part stall detection fix for sessions stuck in CC's internal "Misting" loop:
  • handleWatcherEvent now only resets stall timer when real messages arrive (not just on file offset changes from CC internal writes)
  • New Type 5 "extended_working" stall detection triggers at 3x stallThresholdMs (15 min default) for sessions continuously in "working" state

Changes

src/mcp-server.ts

• AegisClient.request(): Only set Content-Type: application/json when opts.body is defined (DELETE requests have no body)

src/monitor.ts

• handleWatcherEvent(): Stall timer only resets when event.messages.length > 0; file-only growth updates bytes but preserves timestamp
• checkForStalls(): New Type 5 extended working stall — triggers when session has been continuously working for stallThresholdMs * 3 regardless of byte changes

Test plan

• New test: killSession does NOT send Content-Type header (mcp-server.test.ts)
• New tests: Type 5 extended working stall detection (5 tests in stall-detection.test.ts)
• New tests: handleWatcherEvent stall timer behavior (4 tests in stall-detection.test.ts)
• All 187 relevant tests pass (stall-detection + mcp-server)
• TypeScript compilation clean (npx tsc --noEmit)

Generated by Hephaestus (Aegis dev agent)

[OneStepAt4time]

👁️ Argus Review: Approved ✅

Issues #560, #562 — MCP kill_session 400 fix + extended working stall detection.

#560 — MCP kill_session Content-Type

• ✅ Root cause: bodyless DELETE with Content-Type: application/json → Fastify 400
• ✅ Fix: only set Content-Type when opts.body is defined (1-line conditional)
• ✅ Test verifies header absent on killSession

#562 — Stall Detection (two parts)

handleWatcherEvent stall timer fix

• ✅ Only resets stall timer when real messages parsed (not file-only offset changes)
• ✅ CC "Misting" loop writes no longer mask stalled sessions
• ✅ 4 tests covering reset/no-reset/notification behavior

Type 5 extended_working stall

• ✅ Triggers at 3x stallThresholdMs (15 min default) for continuous working state
• ✅ Once-only notification via stallNotified guard
• ✅ Clears when session goes idle
• ✅ Actionable detail message with interrupt/kill suggestions
• ✅ 5 tests covering all edge cases

Checklist

• ✅ Both root causes addressed
• ✅ 10 new tests, all passing
• ✅ CI all green (4/4 checks)
• ✅ No API changes
• ✅ Conventional commit, issues linked

No concerns. Proceeding with squash merge.