feat: meanwhile scene schema + state (T63)

chat/db/migrations/0011_meanwhile_scenes.sql

@@ -0,0 +1,27 @@
+-- T63: Meanwhile scene support — extend scenes with a present-set discriminator
+-- and a parent link (you-scene -> meanwhile child), plus a pending-digest queue.
+--
+-- Existing scenes table (0007) has columns:
+--   id, chat_id, container_id, started_at, ended_at, significance,
+--   participants_json
+-- It has no `status` / `closed_at` columns. We treat `ended_at IS NULL` as
+-- "active" and `ended_at IS NOT NULL` as "closed" — consistent with the
+-- existing scene_opened/scene_closed handlers.
+
+ALTER TABLE scenes ADD COLUMN present_set_kind TEXT NOT NULL DEFAULT 'you_host';
+ALTER TABLE scenes ADD COLUMN parent_scene_id INTEGER;
+
+CREATE INDEX scenes_present_set_idx
+    ON scenes(chat_id, present_set_kind, ended_at);
+
+CREATE TABLE meanwhile_digest_pending (
+    id INTEGER PRIMARY KEY,
+    scene_id INTEGER NOT NULL,
+    chat_id TEXT NOT NULL,
+    summary TEXT NOT NULL,
+    created_at TEXT NOT NULL DEFAULT (datetime('now')),
+    consumed_at TEXT
+);
+
+CREATE INDEX meanwhile_digest_chat_idx
+    ON meanwhile_digest_pending(chat_id) WHERE consumed_at IS NULL;