feat(agent): persist snapshot provenance counterfactuals and replay

migrations/0017_decision_snapshots.sql

@@ -0,0 +1,17 @@
+-- #281: link each agent action back to the context snapshot that drove it
+ALTER TABLE agent_actions ADD COLUMN decision_snapshot_id TEXT;
+
+-- #282: provenance fields on context snapshots so decisions are replayable
+ALTER TABLE agent_context_snapshots ADD COLUMN actor_login TEXT;
+ALTER TABLE agent_context_snapshots ADD COLUMN decision_pack_generated_at TEXT;
+ALTER TABLE agent_context_snapshots ADD COLUMN confidence_level TEXT;
+ALTER TABLE agent_context_snapshots ADD COLUMN freshness_at_decision TEXT;
+ALTER TABLE agent_context_snapshots ADD COLUMN upstream_ruleset_id TEXT;
+
+-- #284: counterfactual reasoning attached to each action
+ALTER TABLE agent_actions ADD COLUMN alternatives_considered_json TEXT NOT NULL DEFAULT '[]';
+ALTER TABLE agent_actions ADD COLUMN counterfactual_reasons_json TEXT NOT NULL DEFAULT '[]';
+
+-- Indexes for snapshot replay lookup (#285)
+CREATE INDEX agent_actions_snapshot_idx ON agent_actions (decision_snapshot_id, created_at);
+CREATE INDEX agent_context_snapshots_actor_idx ON agent_context_snapshots (actor_login, created_at);