feat(universe): separate scanner membership from retained history

bootstrap_universe(prune_missing=True) ran DELETE FROM tickers, cascading OHLCV,
setups, scores and S/R levels away for any symbol that had merely dropped out of
the index. Migration 032's own comment predicted this. The survivorship audit
measured what it costs: 2.09 Sharpe against 1.57 on universe composition alone.

Migration 035 adds untracked_on, the sibling of delisted_on — delisted means the
security stopped trading, untracked means a prune took it out of the scanner.
Nothing is deleted either way.

Migration 036 separates three more things that were still conflated:

  universe_memberships       what the index actually contained, when
  tickers.untracked_on       excluded from scanning by a prune
  tickers.scan_disabled_on   the operator's own "stop scanning this"
  tickers.tracking_source    who owns the row: a bootstrap, or an operator

The operator flag is its own column because with one column serving both
writers, a prune -> re-entry cycle would clear an explicit "off" — re-entry
cannot tell who set it. Re-entry clears untracked_on and never touches
scan_disabled_on.

untracked_on is NOT current index membership. The scheduled sync runs
prune_missing=False, so a symbol can have left the index and still be scanned;
the two legitimately differ and nothing asserts they agree.

Tracking ownership is sticky towards manual: prune touches index-owned rows
only, and a bootstrap never converts manual to index — a hand-added symbol that
joins the index would otherwise lose its protection the moment it left again,
which is exactly when it is needed. An explicit add of an index-owned symbol
claims it as manual without touching either off-switch.

Membership is observed, never asserted. first_seen_on is the first live
sighting; absent_since is the first observation that found the symbol GONE, so
the interval is [first_seen_on, absent_since) — named for what it stores rather
than "last_seen_on", which would have claimed the opposite. Intervals are
append-only, so a symbol that leaves and returns has two and a point-in-time
query for the gap correctly answers "not a member". members_on() implements the
boundary rule once. A date before the first live sync returns empty: that means
"we were not looking", not "the index was empty".

A failed fetch drives nothing. The cache and seed fallbacks mean the live fetch
failed, and the seed lists are ~44 symbols against a ~500-symbol universe — a
regression test caught a seed fallback untracking 2 of 3 tickers. Recording,
pruning and clearing prune flags all require a live source; only adding still
runs, so a cold start can still bootstrap from seeds.

Migration decisions: existing rows become manual (fail-safe — a wrong guess
costs an un-pruned symbol, not one swept out of the scanner), and existing
untracked_on values are copied into scan_disabled_on, since the original writer
is ambiguous and re-entry clears the prune column.

Backtest eligibility is unchanged. _load_backtest_symbols deliberately does not
use active_only, so today's scanner state cannot erase yesterday's candidates,
and untracking a symbol still cannot silence a coverage gap in the report.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HAH7vVtn7qbcn1EVheecHQ

alembic/versions/035_ticker_untracked.py

@@ -0,0 +1,56 @@
+"""Separate scanner membership from retained history
+
+Revision ID: 035
+Revises: 034
+Create Date: 2026-09-07 00:00:00.000000
+
+Migration 032 stopped ``delete_ticker`` and the delisting path from destroying
+history, but left the other half of the problem open — its own comment said so:
+"Pruning a symbol that is merely no longer an index constituent still destroys
+history; that needs a tracked/membership state separate from delisting."
+
+``bootstrap_universe(prune_missing=True)`` still ran ``DELETE FROM tickers``,
+cascading OHLCV, setups and scores away for any symbol that had merely dropped
+out of the index. The survivorship audit measured what that costs: restoring 85
+removed constituents moved the same window from 2.09 Sharpe / 51.6% CAGR to
+1.57 / 38.1%. A prune that deletes is how a universe silently becomes the
+survivors.
+
+``untracked_on`` is the sibling of ``delisted_on``, and the distinction is the
+point:
+
+  delisted_on   the security stopped trading
+  untracked_on  it still trades; we stopped scanning it
+
+Both retain every row. NULL in both means "in the live path" — ``active_only``
+filters on both, so scanning, ranking, scoring, breadth and ingestion skip an
+untracked name, while the backtest's universe query deliberately does not, so
+today's membership cannot erase yesterday's candidates.
+
+Nullable and reversible: a symbol that returns to the index has ``untracked_on``
+cleared by the next bootstrap and rejoins the live path with its history intact.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = "035"
+down_revision: Union[str, None] = "034"
+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("untracked_on", sa.Date(), nullable=True))
+    # Same reasoning as ix_tickers_delisted_on: the live path tests this
+    # predicate on every universe scan, and untracked rows accumulate.
+    op.create_index("ix_tickers_untracked_on", "tickers", ["untracked_on"])
+
+
+def downgrade() -> None:
+    # Dropping the column re-admits every untracked symbol to the live path.
+    # The rows and their history survive either way; that is the whole point.
+    op.drop_index("ix_tickers_untracked_on", table_name="tickers")
+    op.drop_column("tickers", "untracked_on")