feat(tmux-agent-orchestrate-delete): add --capture-id, --reason, --graceful options

Implements user choice Option A: extend delete instead of adding a 6th 'stop' skill.

Changes:
- skills/lib.sh:
  - capture_conversation_id() — thin wrapper over find_workspace_uuid (race-free)
  - is_already_stopped() — idempotency check
  - _validate(): add 'stopped' to the valid status set (required for the new
    transition; without it atomic_dump_yaml silently rejected the write)
- skills/tmux-agent-orchestrate-delete/scripts/delete_session.sh:
  - --capture-id: records claude_session_id_own / agy_conversation_id_own +
    resumable:true to the row before kill (guarantees tier-1 resume)
  - --reason <reason>: records stop_reason (default manual_stop)
  - --graceful: send-keys exit -> 3s -> kill-session(SIGTERM) -> 5s -> SIGKILL
  - STOP mode (any of the three) transitions running -> stopped (vs terminated)
  - Idempotency: already-stopped session prints message + exit 0
  - No options -> identical legacy behaviour (hard->terminated, soft->archived)
- skills/tmux-agent-orchestrate-delete/SKILL.md: documented options + state machine

5-route surface preserved (no new directory). Other 5 routes unchanged.

Known follow-up (out of scope, monitor edits forbidden this round): monitor
reconcile drift-A treats a tmux-dead 'stopped' row as drift and would re-mark it
'terminated' (skip-set is only terminated/archived). status.sh shows DRIFT=A for
stopped rows. Needs a Phase-2 wiring change to add 'stopped' to the skip-set.

Verified on isolated server -L claude-stop-impl-test (kill-server after):
- syntax PASS; E2E: capture-id, idempotency(exit 0), graceful fallback chain,
  backward-compat(terminated), status renders stopped. Real YAML + main canary untouched.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

skills/lib.sh

@@ -214,7 +214,7 @@ def _validate(d):
     sessions = d.get('tmux_sessions', [])
     if not isinstance(sessions, list):
         raise SystemExit("VALIDATE: tmux_sessions is not a list")
-    valid = {'running', 'terminated', 'archived'}
+    valid = {'running', 'terminated', 'archived', 'stopped'}
     for i, s in enumerate(sessions):
         if not isinstance(s, dict):
             raise SystemExit(f"VALIDATE: tmux_sessions[{i}] not a mapping")
@@ -370,6 +370,46 @@ print('')
 PYEOF
 }
 
+# ---------------------------------------------------------------------------
+# capture_conversation_id <agent> <workdir>
+#
+# Thin wrapper over find_workspace_uuid: resolves THIS workspace's conversation
+# id (claude jsonl sessionId / agy db uuid) and prints it on stdout (empty line
+# if none). find_workspace_uuid is already a workspace-scoped, 3-tier, race-free
+# resolver (per-row own id -> workspace-scoped disk scan -> cwd-matched cache),
+# so recording its result into the row before kill guarantees tier-1 on the next
+# resume. Always exits 0.
+# ---------------------------------------------------------------------------
+capture_conversation_id() {
+  local agent="$1" workdir="$2"
+  find_workspace_uuid "$workdir" "$agent"
+}
+
+# ---------------------------------------------------------------------------
+# is_already_stopped <session_name>
+#
+# Exits 0 if the row's status is 'stopped' (printing "stopped_at=<ts>" on
+# stdout), 1 otherwise (including not-found). Used for idempotency: a second
+# stop on an already-stopped session is a no-op.
+# ---------------------------------------------------------------------------
+is_already_stopped() {
+  local session_name="$1"
+  SESSION_NAME="$session_name" env_python "$AGENT_SESSIONS_YAML" <<'PYEOF'
+import os, yaml
+name = os.environ['SESSION_NAME']
+yaml_path = os.environ['YAML_PATH']
+d = {}
+if os.path.exists(yaml_path):
+    with open(yaml_path) as f:
+        d = yaml.safe_load(f) or {}
+for s in d.get('tmux_sessions', []):
+    if s.get('name') == name and s.get('status') == 'stopped':
+        print(f"stopped_at={s.get('stopped_at', '?')}")
+        raise SystemExit(0)
+raise SystemExit(1)
+PYEOF
+}
+
 # ---------------------------------------------------------------------------
 # tmux-agent-orchestrate-delegate-job integration helpers
 #