fix(mothership): explain a Chat turn the worker ends without a reason

When the worker rebuilds an ended run from its log (a resume or reattach
that reaches a run that already ended, for example at its deadline), it
sends an error terminal with no error event. Sim then fell back to the
generic "An unexpected error occurred while processing the response."
The turn now says the run had already ended and can be continued by
sending a message. A reason the worker reports, a replay refusal, and a
Stop all still take precedence.

Also:
- Log the Go stream's error text under errorMessage/detail so it no longer
  overwrites the log line's own message (stream.ts, buffer.ts).
- Rename STREAM_TIMEOUT_MS to CHAT_RUN_DEADLINE_MS and document it as the
  worker's default run deadline, now only the base of USAGE_SETTLE_MS.
- Update the byte-budget doc: a reader behind the ring trim is re-synced
  from the worker log; replay_gap is only the fallback.

Author: waleedlatif1

apps/sim/lib/billing/core/usage-analytics.ts

@@ -8,7 +8,7 @@ import {
 } from '@/lib/billing/core/reporting-period'
 import type { BillingEntity } from '@/lib/billing/core/usage-log'
 import { zonedWallClockToUtc } from '@/lib/core/utils/timezone'
-import { STREAM_TIMEOUT_MS } from '@/lib/mothership/constants'
+import { CHAT_RUN_DEADLINE_MS } from '@/lib/mothership/constants'
 
 /**
  * Pure half of organization usage analytics: window resolution, the ledger scope
@@ -510,15 +510,15 @@ export function usageBucketTimestamps(
  * How long after a stretch of time ends before its ledger rows are final.
  *
  * Rows are stamped when inserted, but a cumulative model charge tops up its row's
- * cost in place for as long as its stream runs — which {@link STREAM_TIMEOUT_MS}
- * caps — plus the retry flushes that follow it. Past the cap and this margin a day or
- * hour can no longer change and is treated as settled.
+ * cost in place for as long as its run lasts — which the worker's run deadline
+ * ({@link CHAT_RUN_DEADLINE_MS}) caps — plus the retry flushes that follow it. Past
+ * the cap and this margin a day or hour can no longer change and is treated as settled.
  *
  * Without a run deadline a Chat turn can top up its row for longer than that, so a
  * settled hour's cached aggregate can under-report that turn's later spend. This is
  * display only: invoices, threshold billing, and the usage gate read live ledger sums.
  */
-export const USAGE_SETTLE_MS = STREAM_TIMEOUT_MS + 2 * 60 * 60 * 1000
+export const USAGE_SETTLE_MS = CHAT_RUN_DEADLINE_MS + 2 * 60 * 60 * 1000
 
 const HOUR_MS = 60 * 60 * 1000
 

apps/sim/lib/core/redis/byte-budget.server.ts

@@ -12,7 +12,8 @@ import type { Logger } from '@sim/logger'
  * execution's event history is read from a cursor, so the write that would breach
  * the ceiling is refused and the buffer stops growing. The copilot replay ring trims
  * its oldest events by bytes below its ceiling instead, refunding what it drops, so a
- * long run slides rather than refuses; a reader behind the trim gets a replay gap.
+ * long run slides rather than refuses; a reader behind the trim is re-synced from the
+ * worker's run log, and ends with a replay gap only when that log cannot serve it.
  * A live-update feed is bounded differently — see `lib/realtime/event-log.ts`, whose
  * readers already handle a prune by refetching, so it drops oldest-first instead.
  *

apps/sim/lib/mothership/constants.ts

@@ -45,8 +45,13 @@ export const CLIENT_TOOL_RESULT_TIMEOUT_MS = 60 * 60 * 1000
 /** Extra slack the resume gate allows past the slowest pending tool's watchdog. */
 export const TOOL_WATCHDOG_RESUME_GRACE_MS = 30_000
 
-/** Timeout for the client-side streaming response handler (60 min). */
-export const STREAM_TIMEOUT_MS = 3_600_000
+/**
+ * The worker's default deadline for one Chat run (60 min).
+ *
+ * Sim does not enforce it: stream legs have no wall clock. It is the base of
+ * `USAGE_SETTLE_MS`, since it bounds how long a run tops up its model charge.
+ */
+export const CHAT_RUN_DEADLINE_MS = 3_600_000
 
 /**
  * How long a workflow tool call waits for a browser to pick it up before the

apps/sim/lib/mothership/request/go/stream.ts

@@ -413,7 +413,7 @@ export async function runStreamLoop(
           context.errors.push(failureMessage)
           logger.error('Received invalid stream event on shared path', {
             reason: parsedEvent.reason,
-            message: parsedEvent.message,
+            detail: parsedEvent.message,
             errors: parsedEvent.errors,
           })
           throw new FatalSseEventError(failureMessage)
@@ -458,7 +458,7 @@ export async function runStreamLoop(
             agentId: streamEvent.scope?.agentId,
             code: errorPayload.code,
             provider: errorPayload.provider,
-            message: errorPayload.message,
+            errorMessage: errorPayload.message,
             error: errorPayload.error,
             displayMessage: errorPayload.displayMessage,
             data: errorPayload.data,

apps/sim/lib/mothership/request/lifecycle/run.test.ts

@@ -3326,9 +3326,82 @@ describe('runCopilotLifecycle', () => {
     )
 
     expect(result.success).toBe(false)
+    expect(result.error).toBeUndefined()
     expect(result.errors).toEqual(['The provider is overloaded'])
   })
 
+  it('explains an error terminal that arrives without a reason as an already-ended run', async () => {
+    const executionContext: ExecutionContext = {
+      userId: 'user-1',
+      workflowId: '',
+      workspaceId: 'ws-1',
+      chatId: 'chat-1',
+    }
+
+    mockRunStreamLoop.mockImplementationOnce(
+      async (
+        _fetchUrl: string,
+        _fetchOptions: RequestInit,
+        context: StreamingContext
+      ): Promise<void> => {
+        context.completionStatus = MothershipStreamV1CompletionStatus.error
+      }
+    )
+
+    const result = await runCopilotLifecycle(
+      { message: 'hello', messageId: 'stream-1' },
+      {
+        userId: 'user-1',
+        workspaceId: 'ws-1',
+        chatId: 'chat-1',
+        executionId: 'exec-1',
+        runId: 'run-1',
+        executionContext,
+      }
+    )
+
+    expect(result.success).toBe(false)
+    expect(result.cancelled).toBe(false)
+    expect(result.error).toEqual(expect.stringContaining('already ended'))
+  })
+
+  it('keeps a Stop a cancellation when the error terminal carries no reason', async () => {
+    const executionContext: ExecutionContext = {
+      userId: 'user-1',
+      workflowId: '',
+      workspaceId: 'ws-1',
+      chatId: 'chat-1',
+    }
+    const abortController = new AbortController()
+
+    mockRunStreamLoop.mockImplementationOnce(
+      async (
+        _fetchUrl: string,
+        _fetchOptions: RequestInit,
+        context: StreamingContext
+      ): Promise<void> => {
+        context.completionStatus = MothershipStreamV1CompletionStatus.error
+        abortController.abort()
+      }
+    )
+
+    const result = await runCopilotLifecycle(
+      { message: 'hello', messageId: 'stream-1' },
+      {
+        userId: 'user-1',
+        workspaceId: 'ws-1',
+        chatId: 'chat-1',
+        executionId: 'exec-1',
+        runId: 'run-1',
+        executionContext,
+        abortSignal: abortController.signal,
+      }
+    )
+
+    expect(result.cancelled).toBe(true)
+    expect(result.error).toBeUndefined()
+  })
+
   it('force-fails a hung tool promise and resumes with an error result instead of wedging', async () => {
     vi.useFakeTimers()
     try {

apps/sim/lib/mothership/request/lifecycle/run.ts

@@ -90,6 +90,10 @@ const logger = createLogger('CopilotLifecycle')
 
 const COPILOT_MODEL_CONTENT_PROJECTION_ERROR = 'Copilot model input could not be safely projected'
 
+/** Shown when the worker ends a turn with an error terminal but gives no reason. */
+const ENDED_RUN_MESSAGE =
+  'This run had already ended before it could continue. Send a message to pick up where it left off.'
+
 class CopilotModelContentProjectionError extends Error {
   constructor() {
     super(COPILOT_MODEL_CONTENT_PROJECTION_ERROR)
@@ -573,6 +577,14 @@ export async function runCopilotLifecycle(
         !refusal &&
         !turnWasAborted &&
         (backendFinishedTurn || (!context.completionStatus && context.errors.length === 0))
+      // The worker sends an error terminal with no `error` event only when it rebuilds an
+      // ended run from its log, which drops the stored reason: a resume or reattach that
+      // reaches a run that already ended, for example at its deadline. Say so rather than
+      // leave the turn to a generic failure; a reported reason always wins.
+      const endedWithoutReason =
+        !turnWasAborted &&
+        context.completionStatus === MothershipStreamV1CompletionStatus.error &&
+        context.errors.length === 0
 
       const result: OrchestratorResult = {
         success: succeeded,
@@ -591,6 +603,7 @@ export async function runCopilotLifecycle(
         toolCalls: buildToolCallSummaries(context),
         chatId: context.chatId,
         requestId: context.requestId,
+        ...(endedWithoutReason ? { error: ENDED_RUN_MESSAGE } : {}),
         ...(refusal ? { error: refusal.userMessage, errorCode: refusal.code } : {}),
         errors: !succeeded && context.errors.length ? context.errors : undefined,
         usage: context.usage,

apps/sim/lib/mothership/request/session/buffer.ts

@@ -487,7 +487,7 @@ export async function readEvents(
       logger.warn('Skipping corrupt outbox entry', {
         streamId,
         reason: parsed.reason,
-        message: parsed.message,
+        detail: parsed.message,
         errors: parsed.errors,
       })
       continue