Add /compact Command

Adds a /compact session command that compacts conversation history to fight context rot in long-running sessions. Uses the Claude Agent SDK's built-in /compact slash command — no synthetic system prompts.

Session contract: /compact keeps the same logical session alive. The SDK returns a new session ID after compaction (via the init system message), which the agent-runner forwards to the orchestrator as newSessionId. No destructive reset occurs — the agent retains summarized context.

Phase 1: Pre-flight

Check if src/session-commands.ts exists:

test -f src/session-commands.ts && echo "Already applied" || echo "Not applied"

If already applied, skip to Phase 3 (Verify).

Phase 2: Apply Code Changes

Merge the skill branch: