[claude] Context injection — pass conversation history to work model (#39) (#78)

lib/db/migrations/0008_session_messages.sql

@@ -0,0 +1,13 @@
+-- Migration: Session conversation history (#38/#39)
+-- Stores user/assistant message pairs for context injection into the work model.
+
+CREATE TABLE IF NOT EXISTS session_messages (
+  id          SERIAL PRIMARY KEY,
+  session_id  TEXT NOT NULL REFERENCES sessions(id),
+  role        TEXT NOT NULL,
+  content     TEXT NOT NULL,
+  token_count INTEGER,
+  created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_session_messages_session_id ON session_messages(session_id);