fix(gateway): hold the agent lock when deleting a session

Makefile

@@ -372,7 +372,7 @@ $(HTTP_O): src/gateway/http.c src/gateway/http.h src/gateway/http_lws.h src/gate
 $(HTTP_LWS_O): src/gateway/http_lws.c src/gateway/http_lws.h src/gateway/asap_http_body.h src/gateway/routes.h src/gateway/auth.h src/gateway/static.h src/gateway/ws.h
 	$(CC) $(CFLAGS) $(INC) $(GATEWAY_CFLAGS) -pthread -c -o $@ src/gateway/http_lws.c
 
-$(ROUTES_O): src/gateway/routes.c src/gateway/routes.h src/gateway/routes_hardware.h src/gateway/http.h src/gateway/http_lws.h src/gateway/auth.h src/gateway/rate_limit.h src/tools/context.h src/asap/manifest.h src/asap/envelope.h src/asap/server.h src/asap/log.h src/core/bootstrap.h src/core/agent.h src/core/config.h src/core/config_patch.h src/core/reload.h src/core/memory.h src/core/skill.h src/providers/provider.h src/channels/channel.h src/tools/cron.h src/tools/tool.h
+$(ROUTES_O): src/gateway/routes.c src/gateway/routes.h src/gateway/routes_hardware.h src/gateway/http.h src/gateway/http_lws.h src/gateway/auth.h src/gateway/rate_limit.h src/tools/context.h src/asap/manifest.h src/asap/envelope.h src/asap/server.h src/asap/log.h src/core/bootstrap.h src/core/agent.h src/core/config.h src/core/config_patch.h src/core/dispatch.h src/core/reload.h src/core/memory.h src/core/skill.h src/providers/provider.h src/channels/channel.h src/tools/cron.h src/tools/tool.h
 	$(CC) $(CFLAGS) $(INC) $(GATEWAY_CFLAGS) -pthread -c -o $@ src/gateway/routes.c
 
 $(ROUTES_HARDWARE_O): src/gateway/routes_hardware.c src/gateway/routes_hardware.h src/gateway/routes.h src/gateway/http_lws.h src/gateway/uri_match.h src/hardware/hardware.h src/hardware/hardware_gpio_snapshot.h src/hardware/hardware_tegrastats.h src/hardware/board_detect.h src/core/config.h

src/core/agent.h

@@ -54,6 +54,7 @@ int agent_run(const config_t *cfg, const char *session_id, const char *user_mess
  * Every agent_run() caller (main-loop handle_message, inbound ASAP HTTP,
  * WebSocket dispatcher) must hold this mutex for the duration of agent_run().
  * /reset in handle_message must also hold it around session_delete().
+ * Dashboard DELETE /api/sessions/:id must use dispatch_delete_session().
  * After a successful cron ch->send, handle_message re-takes it around
  * cron_ack_delivery() (SQLite amalgamation is SQLITE_THREADSAFE=0).
  * Inbound mcp.tool_call must hold it around tool execute (see #60).

src/core/dispatch.c

@@ -43,6 +43,18 @@ static int send_then_maybe_ack_cron(const channel_t *ch, const channel_incoming_
 	return maybe_ack_cron(ch, msg);
 }
 
+int dispatch_delete_session(const char *session_id)
+{
+	int rc;
+	if (!session_id || session_id[0] == '\0')
+		return -1;
+	/* Serialize with agent_run so session_save cannot recreate the row. */
+	agent_lock();
+	rc = session_delete(session_id);
+	agent_unlock();
+	return rc;
+}
+
 int handle_message(const channel_t *ch, const channel_incoming_msg_t *msg)
 {
 	const char *text = msg->text ? msg->text : "";

src/core/dispatch.h

@@ -18,6 +18,20 @@ extern "C" {
  */
 int handle_message(const channel_t *ch, const channel_incoming_msg_t *msg);
 
+/**
+ * Delete one session while holding the agent mutex.
+ *
+ * Dashboard `DELETE /api/sessions/:id` runs on the gateway thread. agent_run()
+ * loads history, talks to the model, then session_save()s. Without this lock
+ * the delete lands in that window and the save puts the old transcript back.
+ *
+ * Example: `if (dispatch_delete_session(id) != 0) respond 404;`
+ *
+ * @param session_id Session row id. Empty or NULL is rejected.
+ * @return 0 when a row was removed, non-zero otherwise.
+ */
+int dispatch_delete_session(const char *session_id);
+
 #ifdef __cplusplus
 }
 #endif

src/gateway/routes.c

@@ -17,6 +17,7 @@
 #include "asap/log.h"
 #include "core/agent.h"
 #include "core/bootstrap.h"
+#include "core/dispatch.h"
 #include "core/config.h"
 #include "core/config_patch.h"
 #include "core/memory.h"
@@ -500,7 +501,7 @@ static void handle_sessions_list(char *buf, size_t size, int *status)
 
 static void handle_session_delete(const char *id, char *buf, size_t size, int *status)
 {
-	if (session_delete(id) != 0) {
+	if (dispatch_delete_session(id) != 0) {
 		json_error(buf, size, status, 404, "Session not found");
 		return;
 	}

tests/test_dispatch.c

@@ -468,8 +468,32 @@ static int test_handle_message_holds_agent_mutex(void)
 	return 0;
 }
 
+static int test_api_session_delete_holds_agent_mutex(void)
+{
+	const char *db_path = "build/test_dispatch_api_delete.db";
+	char history[128];
+
+	memory_cleanup();
+	remove(db_path);
+	ASSERT(memory_init(db_path) == 0);
+	ASSERT(session_save("webchat:9", "[{\"role\":\"user\",\"content\":\"secret\"}]") == 0);
+	g_agent_mutex_held_during_reset = 0;
+	session_delete_set_hook_for_test(reset_lock_probe);
+	ASSERT(dispatch_delete_session("webchat:9") == 0);
+	session_delete_set_hook_for_test(NULL);
+	ASSERT(g_agent_mutex_held_during_reset == 1);
+	ASSERT(agent_mutex_is_locked_for_test() == 0);
+	ASSERT(session_load("webchat:9", history, sizeof(history)) != 0);
+	ASSERT(dispatch_delete_session("") != 0);
+	ASSERT(dispatch_delete_session(NULL) != 0);
+	memory_cleanup();
+	remove(db_path);
+	return 0;
+}
+
 int main(void)
 {
+	RUN(test_api_session_delete_holds_agent_mutex());
 	RUN(test_reset_clears_session());
 	RUN(test_status_returns_version());
 	RUN(test_agent_failure_fallback_message());