Initial commit: Add project files

db/migrations/0010_signal_engine.sql

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+create table if not exists signal_engine.evidence_snapshot (
+    evidence_id text primary key,
+    as_of timestamptz not null,
+    published_at_cutoff timestamptz not null,
+    dataset_id text not null,
+    data_hash text not null,
+    model_version text not null,
+    config_version text not null,
+    payload jsonb not null,
+    content_hash text not null unique,
+    created_at timestamptz not null default now()
+);
+
+create table if not exists signal_engine.signal_decision (
+    decision_id uuid primary key,
+    lot_id uuid not null,
+    cycle_id uuid not null,
+    evidence_id text not null references signal_engine.evidence_snapshot(evidence_id),
+    action text not null,
+    sell_fraction numeric(9,6) not null check (sell_fraction between 0 and 1),
+    policy_id text not null,
+    priority integer not null,
+    reason_code text not null,
+    reentry_eligible boolean not null,
+    created_at timestamptz not null,
+    decision_hash text not null unique
+);
+
+create table if not exists signal_engine.reentry_watch (
+    watch_id uuid primary key,
+    sell_decision_id uuid not null unique references signal_engine.signal_decision(decision_id),
+    prior_cycle_id uuid not null,
+    state text not null,
+    minimum_wait_sessions integer not null check (minimum_wait_sessions >= 0),
+    minimum_spacing_sessions integer not null check (minimum_spacing_sessions >= 0),
+    expires_after_sessions integer not null check (expires_after_sessions > 0),
+    created_at timestamptz not null
+);
+
+create table if not exists signal_engine.reentry_stage (
+    watch_id uuid not null references signal_engine.reentry_watch(watch_id),
+    stage_no integer not null,
+    target_fraction numeric(9,6) not null check (target_fraction > 0 and target_fraction <= 1),
+    status text not null,
+    eligible_at timestamptz null,
+    executed_cycle_id uuid null,
+    primary key (watch_id, stage_no)
+);
+
+create or replace function signal_engine.prevent_immutable_change()
+returns trigger language plpgsql as $$
+begin
+  raise exception 'immutable evidence/decision rows cannot be updated or deleted';
+end;
+$$;
+
+drop trigger if exists evidence_snapshot_immutable on signal_engine.evidence_snapshot;
+create trigger evidence_snapshot_immutable
+before update or delete on signal_engine.evidence_snapshot
+for each row execute function signal_engine.prevent_immutable_change();