fix(stream): end a replay cleanly when terminal metadata has no terminal event

Terminal metadata is the authoritative end-of-run signal — the happy path
writes it atomically with the terminal event, and a run whose terminal
event could not be buffered records the status on its own. The reader
required both, so the degraded case threw and turned a replay that was
merely incomplete into a broken one.

Metadata without a matching event means the buffer degraded, not that the
run is still going. Log it and close the stream: the reader has already
received every event that was buffered, and the durable record is
unaffected either way.

Author: waleedlatif1

apps/sim/app/api/workflows/[id]/executions/[executionId]/stream/route.test.ts

@@ -90,7 +90,7 @@ describe('execution stream reconnect route', () => {
     expect(mockReadExecutionEventsState).toHaveBeenNthCalledWith(2, 'exec-1', 3)
   })
 
-  it('errors when terminal metadata has no terminal event to replay', async () => {
+  it('ends the stream cleanly when terminal metadata has no terminal event to replay', async () => {
     mockReadExecutionMetaState
       .mockResolvedValueOnce({
         status: 'found',
@@ -115,9 +115,7 @@ describe('execution stream reconnect route', () => {
     })
 
     expect(response.status).toBe(200)
-    await expect(response.text()).rejects.toThrow(
-      'Execution reached terminal metadata without a terminal event'
-    )
+    await expect(response.text()).resolves.toContain('data: [DONE]')
   })
 
   it('allows replay event id gaps from reserved but unused writer ids', async () => {

apps/sim/app/api/workflows/[id]/executions/[executionId]/stream/route.ts

@@ -142,9 +142,20 @@ export const GET = withRouteHandler(
             if (!closed) controller.close()
           }
 
+          /**
+           * Terminal metadata is the authoritative end-of-run signal. The
+           * happy path writes it atomically with the terminal event, and a run
+           * whose terminal event could not be buffered records the status on
+           * its own — so metadata without a matching event means the buffer
+           * degraded, not that the run is still going. End the stream cleanly:
+           * the reader has already received every event that was buffered, and
+           * failing here would turn a degraded replay into a broken one.
+           */
           const closeAfterTerminalEvent = (events: ExecutionEventEntry[]) => {
             if (!enqueueEvents(events)) {
-              throw new Error('Execution reached terminal metadata without a terminal event')
+              logger.warn('Execution reached terminal metadata without a terminal event', {
+                executionId,
+              })
             }
             closeWithDone()
           }