fix(agent-loop): balance inbox invariant on continuation-reason steer

The FIFO-conservation invariant fired on the loop-authored continuation
reason path: a continue-with-reason decision entered the steering FIFO
without an agent/inbox/enqueue, so its later dequeue/discard had no
matching enqueue. Emit the enqueue for that steer too, add a regression
test that mounts the invariant over a continue-with-reason turn and a
cancel, and hoist the duplicated inboxInfo helper into inbox.ts.

Found by fresh-eye review.

packages/core/agent-loop/src/agent.ts

@@ -9,12 +9,12 @@
 import type { Context } from 'cordis'
 import { agentEvents } from '@deepseek-ai/dsh-agent'
 import { Agent } from '@deepseek-ai/dsh-agent'
-import type { AgentCancelCause, AgentOptions, AgentStatus, CancelOptions, HookContext, InboxItemInfo, SendOptions } from '@deepseek-ai/dsh-agent'
+import type { AgentCancelCause, AgentOptions, AgentStatus, CancelOptions, HookContext, SendOptions } from '@deepseek-ai/dsh-agent'
 import { deepFreeze, errorChain } from '@deepseek-ai/dsh-llm'
 import type { ContentBlock, MessageSource } from '@deepseek-ai/dsh-llm'
 import { snapshotJsonValue, type Session, type SessionId } from '@deepseek-ai/dsh-session'
 import { DISPOSED_INTERRUPT_REASON, TurnCancellation } from './cancellation.ts'
-import { Inbox, type InboxMessage } from './inbox.ts'
+import { Inbox, inboxInfo, type InboxMessage } from './inbox.ts'
 import { isTurnOpen, lastTurnNumber, runLoop } from './loop.ts'
 
 /** Sessions already claimed by a concrete driver construction. */
@@ -205,11 +205,6 @@ export class ReactLoopAgent extends Agent {
     return deepFreeze(accepted)
   }
 
-  /** Build the `agent/inbox/*` payload for one accepted item. */
-  private inboxInfo(message: InboxMessage, steering: boolean): InboxItemInfo {
-    return { content: message.content, source: message.source, contexts: message.contexts, steering, wakeup: message.wakeup }
-  }
-
   /** Detach one context before it can outlive its caller in the active-batch FIFO. */
   private acceptContext(context: HookContext): HookContext {
     const accepted = snapshotJsonValue(context)
@@ -240,7 +235,7 @@ export class ReactLoopAgent extends Agent {
     } else {
       this.#inbox.enqueue(accepted, wakeup)
     }
-    agentEvents(this.loopCtx, this).emit('agent/inbox/enqueue', this.inboxInfo(accepted, steering))
+    agentEvents(this.loopCtx, this).emit('agent/inbox/enqueue', inboxInfo(accepted, steering))
   }
 
   /** The `next-step`/no-wakeup injection path: durable context, no FIFO, no run. */
@@ -351,7 +346,7 @@ export class ReactLoopAgent extends Agent {
       // Clear work already present before abort observers run.
       this.#inbox.clear()
       if (discarded.length > 0) {
-        const items = discarded.map(({ message, steering }) => this.inboxInfo(message, steering))
+        const items = discarded.map(({ message, steering }) => inboxInfo(message, steering))
         agentEvents(this.loopCtx, this).emit('agent/inbox/discard', items)
       }
     }

packages/core/agent-loop/src/inbox.ts

@@ -7,7 +7,7 @@
  */
 
 import type { ContentBlock, MessageSource } from '@deepseek-ai/dsh-llm'
-import type { HookContext } from '@deepseek-ai/dsh-agent'
+import type { HookContext, InboxItemInfo } from '@deepseek-ai/dsh-agent'
 
 /** One message waiting in an agent's inbox. */
 export interface InboxMessage {
@@ -18,6 +18,16 @@ export interface InboxMessage {
   wakeup: boolean
 }
 
+/**
+ * Build the `agent/inbox/*` event payload for one inbox item.
+ * @param message - the accepted inbox record.
+ * @param steering - whether the item is in the steering FIFO (`next-step`).
+ * @returns the live-event facts for enqueue/dequeue/discard.
+ */
+export function inboxInfo(message: InboxMessage, steering: boolean): InboxItemInfo {
+  return { content: message.content, source: message.source, contexts: message.contexts, steering, wakeup: message.wakeup }
+}
+
 /**
  * Per-agent inbox: a queued FIFO (dequeued once per turn start) and a steering FIFO
  * (drained between steps of a running turn). Purely an in-memory mechanism of

packages/core/agent-loop/src/loop.ts

@@ -10,7 +10,7 @@ import type { ContentBlock, FinishReason, GenerateOptions, LlmCallConfig, LlmFai
 import { isDeepStrictEqual } from 'node:util'
 import { BlockAssembler, HarnessError, LlmError, assertNever, deepFreeze, errorChain, llmFailureOf, markAgentLoopRequest } from '@deepseek-ai/dsh-llm'
 import { agentEvents, agentInterruptReasonOf, assembleContextFor } from '@deepseek-ai/dsh-agent'
-import type { AgentEventDispatch, ContinuationDecision, HookContext, InboxItemInfo, PromptDecision, RequestError, RequestErrorDecision } from '@deepseek-ai/dsh-agent'
+import type { AgentEventDispatch, ContinuationDecision, HookContext, PromptDecision, RequestError, RequestErrorDecision } from '@deepseek-ai/dsh-agent'
 import { canonicalHeader } from '@deepseek-ai/dsh-session'
 import type { PromptMessageData, Session, TurnEndReason, TurnTrigger } from '@deepseek-ai/dsh-session'
 import { createTransmissionLog, recordRequestHeader } from './request-log.ts'
@@ -19,14 +19,9 @@ import { renderPrompt } from '@deepseek-ai/dsh-system-prompt'
 import type { PromptAssembly } from '@deepseek-ai/dsh-system-prompt'
 import type {} from '@deepseek-ai/dsh-tools'
 import { executeToolCalls } from './tool-calls.ts'
-import type { Inbox, InboxMessage } from './inbox.ts'
+import { inboxInfo, type Inbox, type InboxMessage } from './inbox.ts'
 import type { TurnCancellation } from './cancellation.ts'
 
-/** Build the `agent/inbox/dequeue` payload for one claimed inbox item. */
-function inboxInfo(message: InboxMessage, steering: boolean): InboxItemInfo {
-  return { content: message.content, source: message.source, contexts: message.contexts, steering, wakeup: message.wakeup }
-}
-
 /** Normalize thrown values while preserving an existing error code. */
 function toError(error: unknown): RequestError {
   return error instanceof Error ? error : new HarnessError(String(error), 'UNKNOWN', { cause: error })
@@ -543,9 +538,13 @@ async function runTurn(
         break
       }
 
-      // A continuation reason becomes next-step steering.
+      // A continuation reason becomes next-step steering. Publish the same
+      // enqueue event a public steer would, so the inbox ledger stays balanced
+      // (every FIFO entry has a matching enqueue before its dequeue/discard).
       if (decision.action === 'continue' && decision.reason) {
-        handle.inbox.steer({ content: decision.reason.content, source: decision.reason.source, contexts: [], wakeup: true })
+        const item: InboxMessage = { content: decision.reason.content, source: decision.reason.source, contexts: [], wakeup: true }
+        handle.inbox.steer(item)
+        events.emit('agent/inbox/enqueue', inboxInfo(item, true))
       }
       let shouldContinue = decision.action === 'continue'