fix(prompt-gate): harden internal prompt dispatch

src/plugin/event.model-fallback.test.ts

@@ -6,6 +6,10 @@ import { createChatMessageHandler } from "./chat-message"
 import { _resetForTesting, setMainSession } from "../features/claude-code-session-state"
 import { createModelFallbackHook, clearPendingModelFallback } from "../hooks/model-fallback/hook"
 import * as connectedProvidersCache from "../shared/connected-providers-cache"
+import {
+  releaseAllPromptAsyncReservationsForTesting,
+  releasePromptAsyncReservation,
+} from "../hooks/shared/prompt-async-gate"
 import { unsafeTestValue } from "../../test-support/unsafe-test-value"
 
 type EventInput = { event: { type: string; properties?: unknown } }
@@ -95,6 +99,7 @@ describe("createEventHandler - model fallback", () => {
     readConnectedProvidersCacheSpy = undefined
     readProviderModelsCacheSpy = undefined
     _resetForTesting()
+    releaseAllPromptAsyncReservationsForTesting()
   })
 
   test("triggers retry prompt for assistant message.updated APIError payloads (headless resume)", async () => {
@@ -139,6 +144,56 @@ describe("createEventHandler - model fallback", () => {
     expect(promptCalls).toEqual([sessionID])
   })
 
+  test("#given model-fallback promptAsync may have been accepted before EOF #when the same assistant error repeats after the gate hold #then fallback continue is not duplicated", async () => {
+    //#given
+    const sessionID = "ses_message_updated_fallback_eof"
+    const modelFallback = createModelFallbackHook()
+    const { handler, abortCalls, promptAsyncCalls } = createHandler({
+      hooks: { modelFallback },
+      promptAsync: async () => {
+        throw new Error("JSON Parse error: Unexpected EOF")
+      },
+    })
+    const input: EventInput = {
+      event: {
+        type: "message.updated",
+        properties: {
+          info: {
+            id: "msg_err_eof",
+            sessionID,
+            role: "assistant",
+            time: { created: 1, completed: 2 },
+            error: {
+              name: "APIError",
+              data: {
+                message:
+                  "Bad Gateway: {\"error\":{\"message\":\"unknown provider for model claude-opus-4-7-thinking\"}}",
+                isRetryable: true,
+              },
+            },
+            parentID: "msg_user_eof",
+            modelID: "claude-opus-4-7-thinking",
+            providerID: "anthropic",
+            agent: "Sisyphus - Ultraworker",
+            path: { cwd: "/tmp", root: "/tmp" },
+          },
+        },
+      },
+    }
+
+    //#when
+    await handler(input)
+    const released = releasePromptAsyncReservation(sessionID, "test:simulate-expired-hold", {
+      reservedBy: "model-fallback:message.updated",
+    })
+    await handler(input)
+
+    //#then
+    expect(released).toBe(true)
+    expect(abortCalls).toEqual([sessionID])
+    expect(promptAsyncCalls).toEqual([sessionID])
+  })
+
   test("triggers retry prompt for nested model error payloads", async () => {
     //#given
     const sessionID = "ses_main_fallback_nested"

src/plugin/event.ts

@@ -42,7 +42,11 @@ import { buildTeamIdleWakeHintClient } from "./build-team-idle-wake-hint-client"
 import { createTeamLeadOrphanHandler } from "../hooks/team-session-events/team-lead-orphan-handler";
 import { createTeamMemberErrorHandler } from "../hooks/team-session-events/team-member-error-handler";
 import { createTeamMemberStatusHandler } from "../hooks/team-session-events/team-member-status-handler";
-import { dispatchInternalPrompt, releasePromptAsyncReservation } from "../hooks/shared/prompt-async-gate";
+import {
+  dispatchInternalPrompt,
+  isInternalPromptDispatchAccepted,
+  releasePromptAsyncReservation,
+} from "../hooks/shared/prompt-async-gate";
 
 import type { CreatedHooks } from "../create-hooks";
 import type { Managers } from "../create-managers";
@@ -519,7 +523,7 @@ export function createEventHandler(args: {
           source: `model-fallback:${source}`,
           input: promptBody,
         });
-        if (promptResult.status === "dispatched") {
+        if (isInternalPromptDispatchAccepted(promptResult)) {
           dispatched = true;
         } else if (promptResult.status === "failed") {
           const error = promptResult.error;
@@ -537,7 +541,7 @@ export function createEventHandler(args: {
         source: `model-fallback:${source}:sync`,
         input: promptBody,
       });
-      if (promptResult.status === "dispatched") {
+      if (isInternalPromptDispatchAccepted(promptResult)) {
         dispatched = true;
       } else if (promptResult.status === "failed") {
         log("[event] model-fallback prompt failed", { sessionID, source, error: promptResult.error });
@@ -959,7 +963,7 @@ export function createEventHandler(args: {
             });
             if (promptResult.status === "failed") {
               log("[event] recovery continue prompt failed", { sessionID, error: promptResult.error });
-            } else if (promptResult.status !== "dispatched") {
+            } else if (!isInternalPromptDispatchAccepted(promptResult)) {
               log("[event] recovery continue prompt skipped by gate", { sessionID, status: promptResult.status });
             }
           }

src/plugin/unstable-agent-babysitter.ts

@@ -25,7 +25,6 @@ export function createUnstableAgentBabysitter(args: {
             return []
           },
           status: async () => ctx.client.session.status(),
-          prompt: async (promptArgs) => ctx.client.session.prompt(promptArgs),
           promptAsync: async (promptArgs) => ctx.client.session.promptAsync(promptArgs),
         },
       },