fix: placement verification and sidechat policy enforcement

- dm.py: placement-aware verify (verify_placement), checked_uuid logging, placement_mismatch events
- main-chat-watchdog.py: P0 alerts on placement_mismatch
- box-ctl.py: notify routes to sidechat, box policy command
- jobs: ops-audit and pipe-demo use sidechats
- response-harvester.py: chain deduplication

Session: sidechat/ops-restore

bin/followup-sweeper.py

@@ -82,7 +82,9 @@ def append_job_log(entry):
 
 
 def send_dm(sender, recipient, target, text):
-    """Dispatch a DM via dm.py."""
+    """Dispatch a DM via dm.py. The sweeper's delivery target is explicit
+    followup state (or explicit in-code escalation routing), so pass the
+    main-chat opt-in when the target is main (sidechat-first policy)."""
     cmd = [
         sys.executable,
         str(DM_PY),
@@ -90,6 +92,7 @@ def send_dm(sender, recipient, target, text):
         "--agent", sender,
         "--to", recipient,
         "--target", target,
+    ] + (["--allow-main-chat"] if target == "main" else []) + [
         text,
     ]
     try:
@@ -125,6 +128,34 @@ def sweep_cycle(dry_run=False):
         orig_target = rec.get("target", "main")
         thread_uuid = rec.get("thread_uuid")
 
+        # Ghost-followup fail-fast (2026-10-04, operator-main): a null
+        # thread_uuid means the sidechat was never provisioned, so the
+        # harvester can never match a reply. Nudging is pointless -- flag
+        # for manual triage once instead of burning the nudge budget and
+        # escalating a ghost. Main-chat followups are unaffected (the
+        # harvester matches those by target).
+        if thread_uuid is None and orig_target != "main" and not rec.get("needs_review"):
+            rec["needs_review"] = True
+            rec["status"] = "needs_review"
+            rec["review_reason"] = (
+                "ghost: unresolvable, manual triage "
+                f"(thread_uuid null, target={orig_target}; "
+                "reply can never auto-resolve)"
+            )
+            modified = True
+            append_job_log({
+                "ts": utcnow_str(),
+                "type": "followup_ghost_suppressed",
+                "dm_id": dm_id,
+                "recipient": recipient,
+                "target": orig_target,
+                "reason": "ghost: unresolvable, manual triage",
+            })
+            print(f"Sweeper: suppressing ghost followup {dm_id} "
+                  f"(thread_uuid null, target={orig_target}) -> needs_review",
+                  file=sys.stderr)
+            continue
+
         if nudges_sent < nudges_allowed:
             # Deliver next nudge
             nudge_num = nudges_sent + 1
@@ -161,6 +192,44 @@ def sweep_cycle(dry_run=False):
                     })
                 else:
                     print(f"Sweeper WARNING: nudge send failed: {out}", file=sys.stderr)
+                    # Failure-mode fix (2026-10-04): advance state on send
+                    # failure so a failing nudge is never re-fired every
+                    # timer tick. failed_sends is tracked separately from
+                    # nudges_sent so a delivery failure does not consume a
+                    # real nudge. Backoff: 5 min base, doubling per failure.
+                    failed = rec.get("failed_sends", 0) + 1
+                    rec["failed_sends"] = failed
+                    rec["last_failure_at"] = utcnow_str()
+                    backoff_s = 300 * (2 ** min(failed - 1, 4))  # 5m,10m,20m,40m,80m cap
+                    rec["deadline"] = (now + timedelta(seconds=backoff_s)).isoformat()
+                    modified = True
+                    append_job_log({
+                        "ts": utcnow_str(),
+                        "type": "followup_nudge_failed",
+                        "dm_id": dm_id,
+                        "nudge_num": nudge_num,
+                        "recipient": recipient,
+                        "target": delivery_target,
+                        "failed_sends": failed,
+                        "backoff_s": backoff_s,
+                        "error": str(out)[:200],
+                    })
+                    # After 3 consecutive failures, stop retrying blindly and
+                    # flag for manual review (delivery may be uncertain or the
+                    # target may be permanently broken).
+                    if failed >= 3:
+                        rec["needs_review"] = True
+                        rec["review_reason"] = (
+                            f"nudge send failed {failed} times consecutively "
+                            f"(last: {str(out)[:120]})"
+                        )
+                        append_job_log({
+                            "ts": utcnow_str(),
+                            "type": "followup_needs_review",
+                            "dm_id": dm_id,
+                            "recipient": recipient,
+                            "failed_sends": failed,
+                        })
             else:
                 nudges_count += 1