feat(tickers): record delisting instead of deleting the symbol

Retiring a symbol meant delete_ticker or bootstrap_universe(prune_missing),
both of which cascade through OHLCV, setups and scores. That destroys exactly
the history four research documents already apologise for: today's tracked
universe projected backward is survivorship-biased, and hard-deleting every
delisted name is what causes it. Keeping the rows preserves the option to fix
that — it does not fix it, which needs the replay to model a delisting as an
exit event.

tickers gains delisted_on / delisted_reason (migration 032). NULL means
actively traded.

The filter is opt-in via ticker_service.active_only rather than folded into a
shared getter: the registry and admin views deliberately keep delisted rows so
the delisting is visible, and a silent default would undo that. Applied to the
live path only — scanner, momentum ranking, scoring, breadth, fundamentals
candidates, SEC universe, earnings import, ingestion loops. run_backtest keeps
them on purpose.

Detection runs off OHLCV staleness, not off the SEC fundamentals import: that
importer stalls for days on unrelated Company-Facts gaps and would take
detection down with it. On a stale symbol the scheduler asks SEC for a Form
25/25-NSE/15 and retires it only on a hit, so a halt or a rename (SATS->ECHO)
keeps the existing warning. The probe waits 3 stale days so a market-data
outage cannot turn into one SEC request per symbol per run.

Safe to automate because it is reversible: clear_delisted un-retires a false
positive, where a delete had already taken the history.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/services/sec_client.py

@@ -45,6 +45,13 @@ _CA_VERIFY: str | bool = _CA if _CA and Path(_CA).exists() else True
 
 _FORMS_10 = frozenset({"10-K", "10-Q", "10-K/A", "10-Q/A"})
 
+# Exchange delisting (25 / 25-NSE) and registration termination (15 family).
+# Their presence is SEC confirming a security stopped trading — see
+# ``SecClient.delisting_filing``.
+_DELISTING_FORMS = frozenset({
+    "25", "25-NSE", "15-12B", "15-12G", "15F-12B", "15F-12G",
+})
+
 
 class SecError(ProviderError):
     """SEC request failed (403, exhausted 429/5xx, timeout, transport, parse)."""
@@ -253,6 +260,34 @@ class SecClient:
             "filings": filings,
         }
 
+    async def delisting_filing(self, cik: int | str) -> dict[str, Any] | None:
+        """Newest exchange-delisting / deregistration filing, or ``None``.
+
+        Form 25/25-NSE strikes a security from listing; Form 15 terminates the
+        registration. Either is SEC confirming the security stopped trading —
+        which is what separates a real delisting from a multi-day halt or a
+        ticker rename, neither of which files one. That precision is the reason
+        this can mark a symbol automatically.
+
+        Reads ``filings.recent`` directly: ``submissions()`` keeps only the
+        10-K/10-Q family, so these forms never survive its parser.
+        """
+        base = await self.get_json(f"{_DATA}/submissions/CIK{cik10(cik)}.json")
+        arrays = (base.get("filings") or {}).get("recent") or {}
+        forms = arrays.get("form") or []
+        dates = arrays.get("filingDate") or []
+        best: dict[str, Any] | None = None
+        for i, form in enumerate(forms):
+            if form not in _DELISTING_FORMS or i >= len(dates) or not dates[i]:
+                continue
+            try:
+                filed = date.fromisoformat(dates[i])
+            except ValueError:
+                continue
+            if best is None or filed > best["filing_date"]:
+                best = {"form": form, "filing_date": filed}
+        return best
+
     async def companyfacts(self, cik: int | str) -> dict[str, Any]:
         """Raw companyfacts JSON ({cik, entityName, facts})."""
         return await self.get_json(f"{_DATA}/api/xbrl/companyfacts/CIK{cik10(cik)}.json")