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>

alembic/versions/032_ticker_delisting.py

@@ -0,0 +1,49 @@
+"""Record delisting on tickers instead of deleting them
+
+Revision ID: 032
+Revises: 031
+Create Date: 2026-08-11 00:00:00.000000
+
+Until now the only way to retire a symbol was ``delete_ticker`` (or
+``bootstrap_universe(prune_missing=True)``), 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 later — it does not fix
+it by itself, which needs the replay to model a delisting as an exit event.
+
+``delisted_on`` is the effective date (from SEC Form 25/25-NSE/15 where we can
+confirm it, else the day it was marked); ``delisted_reason`` is a short code
+for how we learned. NULL in both means actively traded — the live signal path
+filters on that, while list and admin views keep showing the row so the
+delisting is visible rather than silently absent.
+
+Nullable and reversible by design: clearing ``delisted_on`` un-retires a
+symbol, which is what makes automatic marking safe where a delete would not be.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = "032"
+down_revision: Union[str, None] = "031"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column("tickers", sa.Column("delisted_on", sa.Date(), nullable=True))
+    op.add_column(
+        "tickers", sa.Column("delisted_reason", sa.String(length=32), nullable=True)
+    )
+    # The live path filters "actively traded" on every universe scan; the index
+    # keeps that predicate cheap as delisted rows accumulate.
+    op.create_index("ix_tickers_delisted_on", "tickers", ["delisted_on"])
+
+
+def downgrade() -> None:
+    op.drop_index("ix_tickers_delisted_on", table_name="tickers")
+    op.drop_column("tickers", "delisted_reason")
+    op.drop_column("tickers", "delisted_on")