feat(agent): 支持持久化 /btw 旁路提问

db/schema.sql

@@ -1069,3 +1069,42 @@ CREATE TABLE IF NOT EXISTS server_logs (
     text       TEXT NOT NULL DEFAULT ''
 );
 CREATE INDEX IF NOT EXISTS idx_server_logs_id ON server_logs(id DESC);
+
+-- Independent /btw history and the latest provider-ready main checkpoint.
+CREATE TABLE IF NOT EXISTS side_question_sessions (
+    session_key TEXT PRIMARY KEY,
+    conversation_id BIGINT REFERENCES conversations(id) ON DELETE CASCADE,
+    task_id BIGINT REFERENCES tasks(id) ON DELETE CASCADE,
+    exploration_id BIGINT REFERENCES explorations(id) ON DELETE CASCADE,
+    intent_id BIGINT REFERENCES exploration_nodes(id) ON DELETE CASCADE,
+    run_id BIGINT NOT NULL,
+    version BIGINT NOT NULL,
+    snapshot JSONB NOT NULL,
+    generation BIGINT NOT NULL DEFAULT 0,
+    CHECK ((conversation_id IS NOT NULL AND task_id IS NULL AND exploration_id IS NULL AND intent_id IS NULL)
+        OR (conversation_id IS NULL AND task_id IS NOT NULL AND exploration_id IS NOT NULL))
+);
+CREATE INDEX IF NOT EXISTS idx_side_sessions_conv ON side_question_sessions(conversation_id);
+CREATE INDEX IF NOT EXISTS idx_side_sessions_task ON side_question_sessions(task_id);
+CREATE INDEX IF NOT EXISTS idx_side_sessions_exp ON side_question_sessions(exploration_id);
+CREATE INDEX IF NOT EXISTS idx_side_sessions_intent ON side_question_sessions(intent_id);
+
+CREATE TABLE IF NOT EXISTS side_question_requests (
+    id TEXT PRIMARY KEY,
+    ordinal BIGSERIAL UNIQUE,
+    session_key TEXT NOT NULL REFERENCES side_question_sessions(session_key) ON DELETE CASCADE,
+    generation BIGINT NOT NULL,
+    client_id TEXT NOT NULL,
+    question TEXT NOT NULL,
+    answer TEXT NOT NULL DEFAULT '',
+    status TEXT NOT NULL CHECK(status IN ('running','completed','failed','cancelled','interrupted')),
+    error TEXT NOT NULL DEFAULT '',
+    model JSONB NOT NULL,
+    snapshot_at TIMESTAMPTZ NOT NULL,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    sequence BIGINT NOT NULL DEFAULT 0,
+    usage JSONB NOT NULL DEFAULT '{}',
+    UNIQUE(session_key,generation,client_id)
+);
+CREATE UNIQUE INDEX IF NOT EXISTS idx_side_request_running ON side_question_requests(session_key) WHERE status='running';
+CREATE INDEX IF NOT EXISTS idx_side_requests_history ON side_question_requests(session_key,ordinal DESC);