Merge pull request #4030 from code-yeongyu/fix/promptasync-concurrency-20260515

fix(fallback): dedupe overlapping fallback continuations

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

@@ -1,5 +1,5 @@
-declare const require: (name: string) => any
+/// <reference types="bun-types" />
-const { afterEach, describe, expect, spyOn, test } = require("bun:test")
+import { afterEach, describe, expect, spyOn, test } from "bun:test"
 
 import { createEventHandler } from "./event"
 import { createChatMessageHandler } from "./chat-message"
@@ -8,6 +8,17 @@ import { createModelFallbackHook, clearPendingModelFallback } from "../hooks/mod
 import * as connectedProvidersCache from "../shared/connected-providers-cache"
 import { unsafeTestValue } from "../../test-support/unsafe-test-value"
 
+type EventInput = { event: { type: string; properties?: unknown } }
+type EventHandlerInput = Parameters<ReturnType<typeof createEventHandler>>[0]
+type ChatMessageOutput = {
+  message: Record<string, unknown>
+  parts: Array<{ type: string; text?: string }>
+}
+
+function asEventHandlerInput(input: EventInput): EventHandlerInput {
+  return unsafeTestValue<EventHandlerInput>(input)
+}
+
 let readConnectedProvidersCacheSpy: { mockRestore: () => void } | undefined
 let readProviderModelsCacheSpy: { mockRestore: () => void } | undefined
 
@@ -17,25 +28,40 @@ function setupConnectedProviderCacheMocks(): void {
 }
 
 describe("createEventHandler - model fallback", () => {
-  const createHandler = (args?: { hooks?: any; pluginConfig?: any }) => {
+  const createHandler = (args?: {
+    hooks?: any
+    pluginConfig?: any
+    promptAsync?: (input: { path: { id: string } }) => Promise<unknown>
+  }) => {
     setupConnectedProviderCacheMocks()
     const abortCalls: string[] = []
     const promptCalls: string[] = []
+    const promptAsyncCalls: string[] = []
 
-    const handler = createEventHandler({
+    const sessionClient = {
+      abort: async ({ path }: { path: { id: string } }) => {
+        abortCalls.push(path.id)
+        return {}
+      },
+      prompt: async ({ path }: { path: { id: string } }) => {
+        promptCalls.push(path.id)
+        return {}
+      },
+      ...(args?.promptAsync
+        ? {
+            promptAsync: async (input: { path: { id: string } }) => {
+              promptAsyncCalls.push(input.path.id)
+              return args.promptAsync?.(input)
+            },
+          }
+        : {}),
+    }
+
+    const eventHandler = createEventHandler({
       ctx: unsafeTestValue({
         directory: "/tmp",
         client: {
-          session: {
+          session: sessionClient,
-            abort: async ({ path }: { path: { id: string } }) => {
-              abortCalls.push(path.id)
-              return {}
-            },
-            prompt: async ({ path }: { path: { id: string } }) => {
-              promptCalls.push(path.id)
-              return {}
-            },
-          },
         },
       }),
       pluginConfig: unsafeTestValue((args?.pluginConfig ?? {})),
@@ -54,8 +80,9 @@ describe("createEventHandler - model fallback", () => {
       }),
       hooks: args?.hooks ?? (unsafeTestValue({})),
     })
+    const handler = (input: EventInput): Promise<void> => eventHandler(asEventHandlerInput(input))
 
-    return { handler, abortCalls, promptCalls }
+    return { handler, abortCalls, promptCalls, promptAsyncCalls }
   }
 
   afterEach(() => {
@@ -139,6 +166,207 @@ describe("createEventHandler - model fallback", () => {
     expect(promptCalls).toEqual([sessionID])
   })
 
+  test("does not dispatch duplicate fallback continuations when error events overlap", async () => {
+    //#given
+    const sessionID = "ses_model_fallback_concurrent_events"
+    setMainSession(sessionID)
+    let releasePromptAsync: (() => void) | undefined
+    const promptAsyncBlocked = new Promise<void>((resolve) => {
+      releasePromptAsync = resolve
+    })
+    let firstPromptAsyncStartedResolve: (() => void) | undefined
+    const firstPromptAsyncStarted = new Promise<void>((resolve) => {
+      firstPromptAsyncStartedResolve = resolve
+    })
+    let pendingFallbackArms = 0
+    const modelFallback = unsafeTestValue({
+      setSessionFallbackChain: () => {},
+      setPendingModelFallback: () => {
+        pendingFallbackArms += 1
+        return true
+      },
+    })
+    const { handler, abortCalls, promptAsyncCalls } = createHandler({
+      hooks: { modelFallback },
+      promptAsync: async () => {
+        if (promptAsyncCalls.length === 1) {
+          firstPromptAsyncStartedResolve?.()
+        }
+        await promptAsyncBlocked
+        return {}
+      },
+    })
+
+    const assistantError = {
+      name: "APIError",
+      data: {
+        message:
+          "Bad Gateway: {\"error\":{\"message\":\"unknown provider for model claude-opus-4-7-thinking\"}}",
+        isRetryable: true,
+      },
+    }
+
+    //#when
+    const messageUpdated = handler({
+      event: {
+        type: "message.updated",
+        properties: {
+          info: {
+            id: "msg_err_concurrent_1",
+            sessionID,
+            role: "assistant",
+            error: assistantError,
+            modelID: "claude-opus-4-7-thinking",
+            providerID: "anthropic",
+            agent: "Sisyphus - Ultraworker",
+          },
+        },
+      },
+    })
+    await firstPromptAsyncStarted
+    const sessionError = handler({
+      event: {
+        type: "session.error",
+        properties: {
+          sessionID,
+          providerID: "anthropic",
+          modelID: "claude-opus-4-7-thinking",
+          error: assistantError,
+        },
+      },
+    })
+
+    releasePromptAsync?.()
+    await Promise.all([messageUpdated, sessionError])
+
+    //#then
+    expect(pendingFallbackArms).toBe(1)
+    expect(promptAsyncCalls).toEqual([sessionID])
+    expect(abortCalls).toEqual([sessionID])
+  })
+
+  test("does not dispatch duplicate fallback continuations when session.error omits provider after dispatch", async () => {
+    //#given
+    const sessionID = "ses_model_fallback_providerless_duplicate"
+    setMainSession(sessionID)
+    let pendingFallbackArms = 0
+    const modelFallback = unsafeTestValue({
+      setSessionFallbackChain: () => {},
+      setPendingModelFallback: () => {
+        pendingFallbackArms += 1
+        return true
+      },
+    })
+    const { handler, abortCalls, promptAsyncCalls } = createHandler({
+      hooks: { modelFallback },
+      promptAsync: async () => ({}),
+    })
+
+    const assistantError = {
+      name: "APIError",
+      data: {
+        message:
+          "Bad Gateway: {\"error\":{\"message\":\"unknown provider for model claude-opus-4-7-thinking\"}}",
+        isRetryable: true,
+      },
+    }
+
+    await handler({
+      event: {
+        type: "message.updated",
+        properties: {
+          info: {
+            id: "msg_err_providerless_duplicate_1",
+            sessionID,
+            role: "assistant",
+            error: assistantError,
+            modelID: "claude-opus-4-7-thinking",
+            providerID: "anthropic",
+            agent: "Sisyphus - Ultraworker",
+          },
+        },
+      },
+    })
+
+    //#when - same failed model arrives without provider metadata after first dispatch resolved
+    await handler({
+      event: {
+        type: "session.error",
+        properties: {
+          sessionID,
+          error: assistantError,
+        },
+      },
+    })
+
+    //#then
+    expect(pendingFallbackArms).toBe(1)
+    expect(promptAsyncCalls).toEqual([sessionID])
+    expect(abortCalls).toEqual([sessionID])
+  })
+
+  test("does not collapse fallback continuations for different providers with the same model id", async () => {
+    //#given
+    const sessionID = "ses_model_fallback_same_model_different_provider"
+    setMainSession(sessionID)
+    let pendingFallbackArms = 0
+    const modelFallback = unsafeTestValue({
+      setSessionFallbackChain: () => {},
+      setPendingModelFallback: () => {
+        pendingFallbackArms += 1
+        return true
+      },
+    })
+    const { handler, abortCalls, promptAsyncCalls } = createHandler({
+      hooks: { modelFallback },
+      promptAsync: async () => ({}),
+    })
+
+    const assistantError = {
+      name: "APIError",
+      data: {
+        message:
+          "Bad Gateway: {\"error\":{\"message\":\"unknown provider for model claude-opus-4-7-thinking\"}}",
+        isRetryable: true,
+      },
+    }
+
+    await handler({
+      event: {
+        type: "message.updated",
+        properties: {
+          info: {
+            id: "msg_err_same_model_provider_1",
+            sessionID,
+            role: "assistant",
+            error: assistantError,
+            modelID: "claude-opus-4-7-thinking",
+            providerID: "anthropic",
+            agent: "Sisyphus - Ultraworker",
+          },
+        },
+      },
+    })
+
+    //#when - a distinct provider reports the same normalized model id before idle cleanup
+    await handler({
+      event: {
+        type: "session.error",
+        properties: {
+          sessionID,
+          providerID: "quotio",
+          modelID: "claude-opus-4-7-thinking",
+          error: assistantError,
+        },
+      },
+    })
+
+    //#then
+    expect(pendingFallbackArms).toBe(2)
+    expect(promptAsyncCalls).toEqual([sessionID, sessionID])
+    expect(abortCalls).toEqual([sessionID, sessionID])
+  })
+
   test("triggers retry prompt on session.status retry events and applies fallback", async () => {
     //#given
     const sessionID = "ses_status_retry_fallback"
@@ -208,7 +436,7 @@ describe("createEventHandler - model fallback", () => {
       },
     })
 
-    const output = { message: {}, parts: [] as Array<{ type: string; text?: string }> }
+    const output: ChatMessageOutput = { message: {}, parts: [] }
     await chatMessageHandler(
       {
         sessionID,
@@ -289,7 +517,7 @@ describe("createEventHandler - model fallback", () => {
     expect(promptCalls).toEqual([sessionID])
   })
 
-  test("does not re-arm fallback when a duplicate error reports the same failed model after fallback was applied", async () => {
+  test("does not leave stale pending fallback when a providerless duplicate arrives after fallback was applied", async () => {
     //#given
     const sessionID = "ses_model_fallback_duplicate_surface"
     setMainSession(sessionID)
@@ -344,7 +572,7 @@ describe("createEventHandler - model fallback", () => {
       },
     })
 
-    const output = { message: {}, parts: [] as Array<{ type: string; text?: string }> }
+    const output: ChatMessageOutput = { message: {}, parts: [] }
     await chatMessageHandler(
       {
         sessionID,
@@ -354,14 +582,12 @@ describe("createEventHandler - model fallback", () => {
       output,
     )
 
-    //#when - same failed model arrives again through another OpenCode event surface
+    //#when - same failed model arrives again without provider metadata after fallback was applied
     await handler({
       event: {
         type: "session.error",
         properties: {
           sessionID,
-          providerID: "anthropic",
-          modelID: "claude-opus-4-7-thinking",
           error: {
             name: "UnknownError",
             data: {
@@ -375,9 +601,21 @@ describe("createEventHandler - model fallback", () => {
       },
     })
 
+    const staleOutput: ChatMessageOutput = { message: {}, parts: [] }
+    await chatMessageHandler(
+      {
+        sessionID,
+        agent: "sisyphus",
+        model: { providerID: "opencode-go", modelID: "kimi-k2.6" },
+      },
+      staleOutput,
+    )
+
     //#then
     expect(abortCalls).toEqual([sessionID])
     expect(promptCalls).toEqual([sessionID])
+    expect(modelFallback.hasPendingModelFallback(sessionID)).toBe(false)
+    expect(staleOutput.message["model"]).toBeUndefined()
   })
 
   test("does not trigger model-fallback from session.status when runtime_fallback is enabled", async () => {
@@ -509,7 +747,7 @@ describe("createEventHandler - model fallback", () => {
       },
     })
 
-    const output = { message: {}, parts: [] as Array<{ type: string; text?: string }> }
+    const output: ChatMessageOutput = { message: {}, parts: [] }
     await chatMessageHandler(
       {
         sessionID,
@@ -603,7 +841,7 @@ describe("createEventHandler - model fallback", () => {
     })
 
     const triggerRetryCycle = async (providerID: string, modelID: string) => {
-      await eventHandler({
+      await eventHandler(asEventHandlerInput({
         event: {
           type: "session.error",
           properties: {
@@ -621,9 +859,9 @@ describe("createEventHandler - model fallback", () => {
             },
           },
         },
-      })
+      }))
 
-      const output = { message: {}, parts: [] as Array<{ type: string; text?: string }> }
+      const output: ChatMessageOutput = { message: {}, parts: [] }
       await chatMessageHandler(
         {
           sessionID,

src/plugin/event.ts

@@ -54,6 +54,24 @@ type FirstMessageVariantGate = {
   clear: (sessionID: string) => void;
 };
 
+type FallbackContinuationDedupeKeys = {
+  modelKey?: string;
+  providerModelKey?: string;
+};
+
+type FallbackContinuationDedupeState = {
+  modelKeys: Set<string>;
+  providerModelKeys: Set<string>;
+  providerlessModelKeys: Set<string>;
+};
+
+type FallbackContinuationContext = {
+  agentName?: string;
+  providerID?: string;
+  dedupeProviderID?: string;
+  modelID?: string;
+};
+
 function isRecord(value: unknown): value is Record<string, unknown> {
   return typeof value === "object" && value !== null;
 }
@@ -219,6 +237,8 @@ export function createEventHandler(args: {
   const lastHandledModelErrorMessageID = new Map<string, string>();
   const lastHandledRetryStatusKey = new Map<string, string>();
   const lastKnownModelBySession = new Map<string, { providerID: string; modelID: string }>();
+  const modelFallbackContinuationsInFlight = new Set<string>();
+  const lastDispatchedModelFallbackContinuationKeys = new Map<string, FallbackContinuationDedupeState>();
 
   const resolveFallbackProviderID = (sessionID: string, providerHint?: string): string => {
     const normalizedProviderHint = providerHint?.trim();
@@ -359,55 +379,147 @@ export function createEventHandler(args: {
     return true;
   };
 
+  const getFallbackContinuationKeys = (fallbackContext?: FallbackContinuationContext): FallbackContinuationDedupeKeys => {
+    const agentKey = fallbackContext?.agentName
+      ? getAgentConfigKey(fallbackContext.agentName).trim().toLowerCase()
+      : "";
+    const providerID = fallbackContext?.dedupeProviderID?.trim().toLowerCase() ?? "";
+    const modelID = fallbackContext?.modelID?.trim().toLowerCase() ?? "";
+
+    if (!agentKey || !modelID) {
+      return {};
+    }
+
+    return {
+      modelKey: `${agentKey}:${modelID}`,
+      ...(providerID ? { providerModelKey: `${agentKey}:${providerID}:${modelID}` } : {}),
+    };
+  };
+
+  const getFallbackContinuationDedupeState = (sessionID: string): FallbackContinuationDedupeState => {
+    const existingState = lastDispatchedModelFallbackContinuationKeys.get(sessionID);
+    if (existingState) {
+      return existingState;
+    }
+
+    const state = {
+      modelKeys: new Set<string>(),
+      providerModelKeys: new Set<string>(),
+      providerlessModelKeys: new Set<string>(),
+    };
+    lastDispatchedModelFallbackContinuationKeys.set(sessionID, state);
+    return state;
+  };
+
+  const wasFallbackContinuationAlreadyDispatched = (
+    state: FallbackContinuationDedupeState | undefined,
+    keys: FallbackContinuationDedupeKeys,
+  ): boolean => {
+    if (!state || !keys.modelKey) {
+      return false;
+    }
+
+    if (!keys.providerModelKey) {
+      return state.modelKeys.has(keys.modelKey);
+    }
+
+    return state.providerModelKeys.has(keys.providerModelKey) || state.providerlessModelKeys.has(keys.modelKey);
+  };
+
+  const shouldSkipFallbackContinuation = (
+    sessionID: string,
+    source: string,
+    fallbackContext?: FallbackContinuationContext,
+  ): boolean => {
+    const fallbackKeys = getFallbackContinuationKeys(fallbackContext);
+
+    if (modelFallbackContinuationsInFlight.has(sessionID)) {
+      log("[event] model-fallback continuation skipped because one is already in flight", { sessionID, source });
+      return true;
+    }
+
+    const lastDispatchedKeys = lastDispatchedModelFallbackContinuationKeys.get(sessionID);
+    if (wasFallbackContinuationAlreadyDispatched(lastDispatchedKeys, fallbackKeys)) {
+      log("[event] model-fallback continuation skipped because matching fallback was already dispatched", {
+        sessionID,
+        source,
+      });
+      return true;
+    }
+
+    return false;
+  };
+
   const autoContinueAfterFallback = async (
     sessionID: string,
     source: string,
-    fallbackContext?: {
+    fallbackContext?: FallbackContinuationContext,
-      agentName?: string;
-      providerID?: string;
-      modelID?: string;
-    },
   ): Promise<void> => {
-    await pluginContext.client.session.abort({ path: { id: sessionID } }).catch((error) => {
+    const fallbackKeys = getFallbackContinuationKeys(fallbackContext);
-      log("[event] model-fallback abort failed", { sessionID, source, error });
-    });
 
-    const launchAgent = fallbackContext?.agentName
+    if (shouldSkipFallbackContinuation(sessionID, source, fallbackContext)) {
-      ? resolveRegisteredAgentName(fallbackContext.agentName)
-      : undefined;
-    const launchModel = fallbackContext?.providerID && fallbackContext?.modelID
-      ? { providerID: fallbackContext.providerID, modelID: fallbackContext.modelID }
-      : undefined;
-
-    const agentConfigKey = fallbackContext?.agentName
-      ? getAgentConfigKey(fallbackContext.agentName)
-      : undefined;
-    const agentSettings = agentConfigKey
-      ? pluginConfig.agents?.[agentConfigKey as keyof NonNullable<typeof pluginConfig.agents>]
-      : undefined;
-    const launchVariant = (agentSettings as { variant?: string } | undefined)?.variant;
-
-    const promptBody = {
-      path: { id: sessionID },
-      body: {
-        ...(launchAgent ? { agent: launchAgent } : {}),
-        ...(launchModel ? { model: launchModel } : {}),
-        ...(launchVariant ? { variant: launchVariant } : {}),
-        parts: [createInternalAgentContinuationTextPart("continue")],
-      },
-      query: { directory: pluginContext.directory },
-    };
-
-    if (typeof pluginContext.client.session.promptAsync === "function") {
-      await pluginContext.client.session.promptAsync(promptBody).catch((error) => {
-        log("[event] model-fallback promptAsync failed", { sessionID, source, error });
-      });
       return;
     }
 
-    await pluginContext.client.session.prompt(promptBody).catch((error) => {
+    modelFallbackContinuationsInFlight.add(sessionID);
-      log("[event] model-fallback prompt failed", { sessionID, source, error });
+    let dispatched = false;
-    });
+    try {
+      await pluginContext.client.session.abort({ path: { id: sessionID } }).catch((error) => {
+        log("[event] model-fallback abort failed", { sessionID, source, error });
+      });
+
+      const launchAgent = fallbackContext?.agentName
+        ? resolveRegisteredAgentName(fallbackContext.agentName)
+        : undefined;
+      const launchModel = fallbackContext?.providerID && fallbackContext?.modelID
+        ? { providerID: fallbackContext.providerID, modelID: fallbackContext.modelID }
+        : undefined;
+
+      const agentConfigKey = fallbackContext?.agentName
+        ? getAgentConfigKey(fallbackContext.agentName)
+        : undefined;
+      const agentSettings = agentConfigKey
+        ? pluginConfig.agents?.[agentConfigKey as keyof NonNullable<typeof pluginConfig.agents>]
+        : undefined;
+      const launchVariant = (agentSettings as { variant?: string } | undefined)?.variant;
+
+      const promptBody = {
+        path: { id: sessionID },
+        body: {
+          ...(launchAgent ? { agent: launchAgent } : {}),
+          ...(launchModel ? { model: launchModel } : {}),
+          ...(launchVariant ? { variant: launchVariant } : {}),
+          parts: [createInternalAgentContinuationTextPart("continue")],
+        },
+        query: { directory: pluginContext.directory },
+      };
+
+      if (typeof pluginContext.client.session.promptAsync === "function") {
+        await pluginContext.client.session.promptAsync(promptBody).then(() => {
+          dispatched = true;
+        }).catch((error) => {
+          log("[event] model-fallback promptAsync failed", { sessionID, source, error });
+        });
+        return;
+      }
+
+      await pluginContext.client.session.prompt(promptBody).then(() => {
+        dispatched = true;
+      }).catch((error) => {
+        log("[event] model-fallback prompt failed", { sessionID, source, error });
+      });
+    } finally {
+      if (dispatched && fallbackKeys.modelKey) {
+        const dispatchedKeys = getFallbackContinuationDedupeState(sessionID);
+        dispatchedKeys.modelKeys.add(fallbackKeys.modelKey);
+        if (fallbackKeys.providerModelKey) {
+          dispatchedKeys.providerModelKeys.add(fallbackKeys.providerModelKey);
+        } else {
+          dispatchedKeys.providerlessModelKeys.add(fallbackKeys.modelKey);
+        }
+      }
+      modelFallbackContinuationsInFlight.delete(sessionID);
+    }
   };
 
   return async (input): Promise<void> => {
@@ -526,6 +638,8 @@ export function createEventHandler(args: {
         lastHandledModelErrorMessageID.delete(sessionID);
         lastHandledRetryStatusKey.delete(sessionID);
         lastKnownModelBySession.delete(sessionID);
+        modelFallbackContinuationsInFlight.delete(sessionID);
+        lastDispatchedModelFallbackContinuationKeys.delete(sessionID);
         if (modelFallback) {
           clearPendingModelFallback(modelFallback, sessionID);
           clearSessionFallbackChain(modelFallback, sessionID);
@@ -643,29 +757,30 @@ export function createEventHandler(args: {
               }
 
               if (agentName) {
-                const currentProvider = resolveFallbackProviderID(
+                const providerHint = info?.providerID as string | undefined;
-                  sessionID,
+                const currentProvider = resolveFallbackProviderID(sessionID, providerHint);
-                  info?.providerID as string | undefined,
-                );
                 const rawModel = (info?.modelID as string | undefined) ?? "claude-opus-4-7";
                 const currentModel = normalizeFallbackModelID(rawModel);
-                applyUserConfiguredFallbackChain(modelFallback, sessionID, agentName, currentProvider, args.pluginConfig);
+                const fallbackContext = {
+                  agentName,
+                  providerID: currentProvider,
+                  dedupeProviderID: providerHint,
+                  modelID: currentModel,
+                };
+                const shouldAutoContinue = shouldAutoRetrySession(sessionID) &&
+                  !hooks.stopContinuationGuard?.isStopped(sessionID);
 
-                const setFallback = modelFallback
+                if (!shouldAutoContinue || !shouldSkipFallbackContinuation(sessionID, "message.updated", fallbackContext)) {
-                  ? setPendingModelFallback(modelFallback, sessionID, agentName, currentProvider, currentModel)
+                  applyUserConfiguredFallbackChain(modelFallback, sessionID, agentName, currentProvider, args.pluginConfig);
-                  : false;
 
-                if (
+                  const setFallback = modelFallback
-                  setFallback &&
+                    ? setPendingModelFallback(modelFallback, sessionID, agentName, currentProvider, currentModel)
-                  shouldAutoRetrySession(sessionID) &&
+                    : false;
-                  !hooks.stopContinuationGuard?.isStopped(sessionID)
+
-                ) {
+                  if (setFallback && shouldAutoContinue) {
-                  lastHandledModelErrorMessageID.set(sessionID, assistantMessageID);
+                    lastHandledModelErrorMessageID.set(sessionID, assistantMessageID);
-                  await autoContinueAfterFallback(sessionID, "message.updated", {
+                    await autoContinueAfterFallback(sessionID, "message.updated", fallbackContext);
-                    agentName,
+                  }
-                    providerID: currentProvider,
-                    modelID: currentModel,
-                  });
                 }
               }
             }
@@ -684,6 +799,7 @@ export function createEventHandler(args: {
       // (non-retry idle) so future failures with the same key can trigger fallback again.
       if (sessionID && status?.type === "idle") {
         lastHandledRetryStatusKey.delete(sessionID);
+        lastDispatchedModelFallbackContinuationKeys.delete(sessionID);
       }
 
       if (sessionID && status?.type === "retry" && isModelFallbackEnabled && !isRuntimeFallbackEnabled) {
@@ -718,22 +834,25 @@ export function createEventHandler(args: {
               const currentProvider = resolveFallbackProviderID(sessionID, parsed.providerID);
               let currentModel = parsed.modelID ?? lastKnown?.modelID ?? "claude-opus-4-7";
               currentModel = normalizeFallbackModelID(currentModel);
-              applyUserConfiguredFallbackChain(modelFallback, sessionID, agentName, currentProvider, args.pluginConfig);
+              const fallbackContext = {
+                agentName,
+                providerID: currentProvider,
+                dedupeProviderID: parsed.providerID,
+                modelID: currentModel,
+              };
+              const shouldAutoContinue = shouldAutoRetrySession(sessionID) &&
+                !hooks.stopContinuationGuard?.isStopped(sessionID);
 
-              const setFallback = modelFallback
+              if (!shouldAutoContinue || !shouldSkipFallbackContinuation(sessionID, "session.status", fallbackContext)) {
-                ? setPendingModelFallback(modelFallback, sessionID, agentName, currentProvider, currentModel)
+                applyUserConfiguredFallbackChain(modelFallback, sessionID, agentName, currentProvider, args.pluginConfig);
-                : false;
 
-              if (
+                const setFallback = modelFallback
-                setFallback &&
+                  ? setPendingModelFallback(modelFallback, sessionID, agentName, currentProvider, currentModel)
-                shouldAutoRetrySession(sessionID) &&
+                  : false;
-                !hooks.stopContinuationGuard?.isStopped(sessionID)
+
-              ) {
+                if (setFallback && shouldAutoContinue) {
-                await autoContinueAfterFallback(sessionID, "session.status", {
+                  await autoContinueAfterFallback(sessionID, "session.status", fallbackContext);
-                  agentName,
+                }
-                  providerID: currentProvider,
-                  modelID: currentModel,
-                });
               }
             }
           }
@@ -804,28 +923,29 @@ export function createEventHandler(args: {
 
           if (agentName) {
             const parsed = extractProviderModelFromErrorMessage(errorMessage);
-            const currentProvider = resolveFallbackProviderID(
+            const providerHint = (props?.providerID as string | undefined) || parsed.providerID;
-              sessionID,
+            const currentProvider = resolveFallbackProviderID(sessionID, providerHint);
-              (props?.providerID as string | undefined) || parsed.providerID,
-            );
             let currentModel = (props?.modelID as string) || parsed.modelID || "claude-opus-4-7";
             currentModel = normalizeFallbackModelID(currentModel);
-            applyUserConfiguredFallbackChain(modelFallback, sessionID, agentName, currentProvider, args.pluginConfig);
+            const fallbackContext = {
+              agentName,
+              providerID: currentProvider,
+              dedupeProviderID: providerHint,
+              modelID: currentModel,
+            };
+            const shouldAutoContinue = shouldAutoRetrySession(sessionID) &&
+              !hooks.stopContinuationGuard?.isStopped(sessionID);
 
-            const setFallback = modelFallback
+            if (!shouldAutoContinue || !shouldSkipFallbackContinuation(sessionID, "session.error", fallbackContext)) {
-              ? setPendingModelFallback(modelFallback, sessionID, agentName, currentProvider, currentModel)
+              applyUserConfiguredFallbackChain(modelFallback, sessionID, agentName, currentProvider, args.pluginConfig);
-              : false;
 
-            if (
+              const setFallback = modelFallback
-              setFallback &&
+                ? setPendingModelFallback(modelFallback, sessionID, agentName, currentProvider, currentModel)
-              shouldAutoRetrySession(sessionID) &&
+                : false;
-              !hooks.stopContinuationGuard?.isStopped(sessionID)
+
-            ) {
+              if (setFallback && shouldAutoContinue) {
-              await autoContinueAfterFallback(sessionID, "session.error", {
+                await autoContinueAfterFallback(sessionID, "session.error", fallbackContext);
-                agentName,
+              }
-                providerID: currentProvider,
-                modelID: currentModel,
-              });
             }
           }
         }