docs(sp38): RUNBOOK entry for orphan-ack housekeeping

Implements task 6 of
docs/superpowers/plans/2026-07-07-cyclone-orphan-ack-housekeeping.md.

Adds 'Known historical drift — the 804 orphan 999s' section under
the existing operator-triage content. Covers:

  - What the orphans are (real production 999s whose source 837s
    predate the current DB snapshot; valid audit history that
    cannot be auto-linked)
  - Why they cannot be auto-linked (source 837s were transmitted
    to HPE and never came back; Cyclone is downstream and does
    not retain copies of outbound 837s)
  - Triage path via the Inbox AckOrphansLane (already working
    as of SP37-followup 893a662)
  - Optional synthetic-batch seeding via 'cyclone ack-orphans
    reconcile' (one-shot, idempotent, --dry-run available)
  - 'cyclone ack-orphans status' for the per-ST02 breakdown

Explicitly calls out what the housekeeping is NOT:
  - Not a backfill (no claims rows are synthesized)
  - Not auto-runnable (operator-invoked only)
  - Not a deletion (orphans are valid audit history)

References the SP38 spec and plan for the design rationale.

docs/RUNBOOK.md

@@ -291,3 +291,77 @@ curl -X PATCH http://127.0.0.1:8000/api/clearhouse \
 ```
 
 To revert, set `stub: true` and `auth: {"method": "keychain", "secret_ref": "sftp.gainwell.password"}`.
+
+## Known historical drift — the 804 orphan 999s
+
+The `acks` table may hold several hundred 999 acks whose source 837
+batch is not present in the `batches` table — the Inbox "Ack orphans"
+lane surfaces them at `GET /api/inbox/ack-orphans`. These are real
+production 999s (e.g. sender_id `COMEDASSISTPROG`) whose source 837s
+were submitted to HPE clearinghouse before the current
+`~/.local/share/cyclone/cyclone.db` snapshot was created. The source
+837s themselves were never re-ingested into the current DB, so the
+`claims` table has no rows that could link against them. SP37's
+canonical submit-batch flow captures ST02 going forward, so the
+orphan count is stable — not a forward-looking bug, just historical
+drift.
+
+**You cannot auto-link these orphans.** The source 837s are not in
+`ingest/`, `backend/var/sftp/staging/`, or any local path — they
+were transmitted to HPE and never came back. Cyclone is downstream
+of the clearinghouse and does not retain copies of outbound 837s
+after SFTP ACK. Do not attempt to re-ingest from SFTP inbound —
+those files are the 999 acks themselves, not the source 837s.
+
+### Triage path
+
+1. **Inspect the Inbox > AckOrphansLane** in the UI. Each row is a
+   999 ack with no resolvable claim. Sort by `parsed_at DESC` to
+   see the most recent first; older orphans are less likely to be
+   actionable.
+2. **Decide per row.** If the operator can identify the source 837
+   outside Cyclone (e.g. a manual record of what was submitted that
+   day), manually create a `claims` row + a `claim_acks` link via
+   `POST /api/parse-837` followed by `POST /api/inbox/candidates/{remit_id}/match`
+   or `POST /api/acks/.../match-claim`. If not, leave the orphan
+   alone — it stays as valid audit history.
+
+### Optional: seed synthetic batch rows (one-shot)
+
+`cyclone ack-orphans reconcile` inserts a synthetic `batches` row
+for every orphan ST02 that doesn't already have one. The synthetic
+row is marked with `input_filename = '<synthetic:orphan-reconcile>'`
+so it's trivially distinguishable in queries. Future 999 acks for
+the same ST02s will resolve against the batch envelope index (so
+the operator can see "this 999 is for a known orphan source") but
+will not link to claims (because no claim rows exist).
+
+```bash
+# Preview the reconcile without writing rows.
+cyclone ack-orphans reconcile --dry-run
+
+# Insert the synthetic batch rows.
+cyclone ack-orphans reconcile
+```
+
+Re-running `cyclone ack-orphans reconcile` after a successful pass
+is a no-op (idempotent). To inspect the per-ST02 breakdown at any
+time:
+
+```bash
+cyclone ack-orphans status
+```
+
+The status command prints a table with ST02, ACK COUNT, and HAS
+BATCH columns, ranked by ack count so the heaviest backlog
+surfaces first.
+
+### What this is NOT
+
+- **Not a backfill.** No `claims` rows are synthesized — the source
+  data is gone.
+- **Not auto-runnable.** The reconcile CLI is operator-invoked only;
+  it does not run on boot, in the SFTP polling scheduler, or via
+  cron.
+- **Not a deletion.** The orphan 999s are valid audit history and
+  must remain queryable.