feat(replay): R0 snapshot recorder — archive per-cycle decisions into signals

The signals and markets tables existed since Phase 2/5 but never had a
writer; the replay engine (phase plan line 2.1) needs a per-(market, cycle)
archive of what the strategy saw and decided. This wires them up:

- signals: one row per evaluated market per cycle, now carrying INPUTS
  (news_sentiment, feat_*_lo, volume_24h, days_to_resolution) plus the
  existing outputs (probs, edges, gates, skip_reason). skip_reason is
  granular: unsupported/no_signals/prior_extreme/family/edge_net/
  confidence/reentry_guard. news_budget_skipped distinguishes "GNews not
  asked" (5-query budget) from "no news".
- ext_snapshots: one row per cycle with the ExternalSignals snapshot;
  signals rows join on cycle_ts.
- markets: metadata upserted each cycle (replay rebuilds Market from it).
- Retention: prune > SIGNALS_RETENTION_DAYS (default 90) once a day.
- SIGNAL_RECORDER_ENABLED (default true) gates all DB writes; every write
  is try/except — the recorder can never break trading.

Strategy changes are purely additive (record accumulation at each exit
path of evaluate()); no weights, thresholds, gates or sizing touched,
per the freeze in the current phase plan.

Tests: 10 new deterministic tests (85 total passing). Schema migration
dry-run validated against prod postgres inside a rolled-back transaction.

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

bot/data/schema.sql

@@ -318,3 +318,55 @@ CREATE TABLE IF NOT EXISTS manifold_eval_cooldown (
 );
 
 CREATE INDEX IF NOT EXISTS idx_mfld_cooldown_retry ON manifold_eval_cooldown(retry_after);
+
+-- ─────────────────────────────────────────────────────────────────────────────
+-- Replay R0: snapshot recorder — the archive the replay engine reads from
+--
+-- The signals table (Phase 2/5 schema) never had a writer; R0 makes it the
+-- per-(market, cycle) decision archive.  One row per evaluated market per
+-- cycle, carrying both the INPUTS the strategy saw (external signals, news
+-- sentiment, per-feature log-odds) and the OUTPUTS it produced (probs, edges,
+-- gates, skip_reason).  A replay run rebuilds Market/ExternalSignals from
+-- these rows plus ext_snapshots and re-executes evaluate() deterministically.
+--
+-- cycle_ts groups all rows of one trading cycle and joins them to their
+-- ext_snapshots row (same timestamp; no FK to keep writes independent).
+-- days_to_resolution is persisted so replay does not depend on wall-clock.
+-- news_budget_skipped distinguishes "GNews had nothing" from "GNews was not
+-- asked this cycle" (5-query budget) — without it politics replay would treat
+-- budget starvation as absence of news.
+-- Retention: rows older than SIGNALS_RETENTION_DAYS (default 90) are pruned.
+-- ─────────────────────────────────────────────────────────────────────────────
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS cycle_ts            TIMESTAMPTZ;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS category            TEXT;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS prior_prob          DOUBLE PRECISION;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS raw_final_prob      DOUBLE PRECISION;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS days_to_resolution  INTEGER;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS volume_24h          DOUBLE PRECISION;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS news_sentiment      DOUBLE PRECISION;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS news_budget_skipped BOOLEAN;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS guardrail_applied   BOOLEAN;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS guardrail_changed_decision BOOLEAN;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS feat_fg_lo          DOUBLE PRECISION;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS feat_mom_lo         DOUBLE PRECISION;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS feat_news_lo        DOUBLE PRECISION;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS feat_mfld_lo        DOUBLE PRECISION;
+ALTER TABLE signals ADD COLUMN IF NOT EXISTS feat_btc_dom_lo     DOUBLE PRECISION;
+
+CREATE INDEX IF NOT EXISTS idx_signals_cycle ON signals(cycle_ts);
+
+-- One row per trading cycle: the ExternalSignals snapshot every market in
+-- that cycle was evaluated against.  Written once per cycle before the
+-- evaluation loop; signals rows join on cycle_ts.
+CREATE TABLE IF NOT EXISTS ext_snapshots (
+    cycle_ts                TIMESTAMPTZ PRIMARY KEY,
+    btc_price               DOUBLE PRECISION,
+    btc_change_24h          DOUBLE PRECISION,
+    eth_price               DOUBLE PRECISION,
+    eth_change_24h          DOUBLE PRECISION,
+    btc_dominance           DOUBLE PRECISION,
+    fear_greed_index        INTEGER,
+    fear_greed_label        TEXT,
+    total_market_cap_change DOUBLE PRECISION,
+    valid                   BOOLEAN
+);