Merge pull request #3169 from code-yeongyu/fix/sisyphus-junior-model

fix(model-fallback): respect user model override for sisyphus-junior category sessions (#2941)

src/hooks/model-fallback/hook.test.ts

@@ -332,6 +332,25 @@ describe("model fallback hook", () => {
     clearPendingModelFallback(sessionID)
   })
 
+  test("does not fall back to hardcoded agent chain when session explicitly stores no fallback chain [regression #2941]", () => {
+    //#given
+    const sessionID = "ses_model_fallback_explicit_none"
+    clearPendingModelFallback(sessionID)
+    setSessionFallbackChain(sessionID, undefined)
+
+    //#when
+    const set = setPendingModelFallback(
+      sessionID,
+      "Sisyphus - Junior",
+      "anthropic",
+      "claude-sonnet-4-6",
+    )
+
+    //#then
+    expect(set).toBe(false)
+    clearPendingModelFallback(sessionID)
+  })
+
   test("shows toast when fallback is applied", async () => {
     //#given
     const toastCalls: Array<{ title: string; message: string }> = []

src/hooks/model-fallback/hook.ts

@@ -42,8 +42,12 @@ const sessionFallbackChains = new Map<string, FallbackEntry[]>()
 
 export function setSessionFallbackChain(sessionID: string, fallbackChain: FallbackEntry[] | undefined): void {
   if (!sessionID) return
-  if (!fallbackChain || fallbackChain.length === 0) {
+  if (!fallbackChain) {
-    sessionFallbackChains.delete(sessionID)
+    sessionFallbackChains.set(sessionID, [])
+    return
+  }
+  if (fallbackChain.length === 0) {
+    sessionFallbackChains.set(sessionID, [])
     return
   }
   sessionFallbackChains.set(sessionID, fallbackChain)
@@ -65,8 +69,9 @@ export function setPendingModelFallback(
 ): boolean {
   const agentKey = getAgentConfigKey(agentName)
   const requirements = AGENT_MODEL_REQUIREMENTS[agentKey]
+  const hasSessionFallback = sessionFallbackChains.has(sessionID)
   const sessionFallback = sessionFallbackChains.get(sessionID)
-  const fallbackChain = sessionFallback && sessionFallback.length > 0
+  const fallbackChain = hasSessionFallback
     ? sessionFallback
     : requirements?.fallbackChain
 

src/plugin/event.model-fallback-2941.test.ts

@@ -0,0 +1,165 @@
+declare const require: (name: string) => any
+const { afterEach, describe, expect, spyOn, test } = require("bun:test")
+
+import { createEventHandler } from "./event"
+import { createChatMessageHandler } from "./chat-message"
+import { _resetForTesting, setSessionAgent } from "../features/claude-code-session-state"
+import { clearPendingModelFallback, createModelFallbackHook, setSessionFallbackChain } from "../hooks/model-fallback/hook"
+import * as connectedProvidersCache from "../shared/connected-providers-cache"
+
+type EventInput = { event: { type: string; properties?: unknown } }
+type EventHandlerArgs = Parameters<typeof createEventHandler>[0]
+type EventHandlerInput = Parameters<ReturnType<typeof createEventHandler>>[0]
+type ChatMessageHandlerArgs = Parameters<typeof createChatMessageHandler>[0]
+
+function asEventHandlerInput(input: EventInput): EventHandlerInput {
+	return input as unknown as EventHandlerInput
+}
+
+function asEventHandlerContext(ctx: unknown): EventHandlerArgs["ctx"] {
+	return ctx as unknown as EventHandlerArgs["ctx"]
+}
+
+function asPluginConfig(config: unknown): EventHandlerArgs["pluginConfig"] {
+	return config as unknown as EventHandlerArgs["pluginConfig"]
+}
+
+function asChatMessageHandlerContext(ctx: unknown): ChatMessageHandlerArgs["ctx"] {
+	return ctx as unknown as ChatMessageHandlerArgs["ctx"]
+}
+
+function asChatPluginConfig(config: unknown): ChatMessageHandlerArgs["pluginConfig"] {
+	return config as unknown as ChatMessageHandlerArgs["pluginConfig"]
+}
+
+function createEventHandlerManagers(): EventHandlerArgs["managers"] {
+	return {
+		tmuxSessionManager: {
+			onSessionCreated: async () => {},
+			onSessionDeleted: async () => {},
+		},
+		skillMcpManager: {
+			disconnectSession: async () => {},
+		},
+	} as unknown as EventHandlerArgs["managers"]
+}
+
+function createEventHandlerHooks(modelFallback: ReturnType<typeof createModelFallbackHook>): EventHandlerArgs["hooks"] {
+	return {
+		modelFallback,
+	} as unknown as EventHandlerArgs["hooks"]
+}
+
+function createChatMessageHandlerHooks(modelFallback: ReturnType<typeof createModelFallbackHook>): ChatMessageHandlerArgs["hooks"] {
+	return {
+		modelFallback,
+		stopContinuationGuard: null,
+		keywordDetector: null,
+		claudeCodeHooks: null,
+		autoSlashCommand: null,
+		startWork: null,
+		ralphLoop: null,
+	} as unknown as ChatMessageHandlerArgs["hooks"]
+}
+
+let readConnectedProvidersCacheSpy: { mockRestore: () => void } | undefined
+let readProviderModelsCacheSpy: { mockRestore: () => void } | undefined
+
+afterEach(() => {
+	readConnectedProvidersCacheSpy?.mockRestore()
+	readProviderModelsCacheSpy?.mockRestore()
+	readConnectedProvidersCacheSpy = undefined
+	readProviderModelsCacheSpy = undefined
+	_resetForTesting()
+})
+
+describe("createEventHandler - category runtime fallback suppression", () => {
+	test("does not arm retry fallback when category session explicitly stores no fallback chain [regression #2941]", async () => {
+		//#given
+		const sessionID = "ses_category_override_no_fallback"
+		const abortCalls: string[] = []
+		const promptCalls: string[] = []
+
+		readConnectedProvidersCacheSpy = spyOn(connectedProvidersCache, "readConnectedProvidersCache").mockReturnValue(null)
+		readProviderModelsCacheSpy = spyOn(connectedProvidersCache, "readProviderModelsCache").mockReturnValue(null)
+
+		clearPendingModelFallback(sessionID)
+		setSessionAgent(sessionID, "sisyphus-junior")
+		setSessionFallbackChain(sessionID, undefined)
+
+		const modelFallback = createModelFallbackHook()
+		const eventHandler = createEventHandler({
+			ctx: asEventHandlerContext({
+				directory: "/tmp",
+				client: {
+					session: {
+						abort: async ({ path }: { path: { id: string } }) => {
+							abortCalls.push(path.id)
+							return {}
+						},
+						prompt: async ({ path }: { path: { id: string } }) => {
+							promptCalls.push(path.id)
+							return {}
+						},
+					},
+				},
+			}),
+			pluginConfig: asPluginConfig({}),
+			firstMessageVariantGate: {
+				markSessionCreated: () => {},
+				clear: () => {},
+			},
+			managers: createEventHandlerManagers(),
+			hooks: createEventHandlerHooks(modelFallback),
+		})
+
+		const chatMessageHandler = createChatMessageHandler({
+			ctx: asChatMessageHandlerContext({
+				client: {
+					tui: {
+						showToast: async () => ({}),
+					},
+				},
+			}),
+			pluginConfig: asChatPluginConfig({}),
+			firstMessageVariantGate: {
+				shouldOverride: () => false,
+				markApplied: () => {},
+			},
+			hooks: createChatMessageHandlerHooks(modelFallback),
+		})
+
+		//#when
+		await eventHandler(asEventHandlerInput({
+			event: {
+				type: "session.error",
+				properties: {
+					sessionID,
+					error: {
+						name: "APIError",
+						data: {
+							message:
+								"Bad Gateway: {\"error\":{\"message\":\"unknown provider for model claude-sonnet-4-6\"}}",
+							isRetryable: true,
+						},
+					},
+				},
+			},
+		}))
+
+		const output = { message: {}, parts: [] as Array<{ type: string; text?: string }> }
+		await chatMessageHandler(
+			{
+				sessionID,
+				agent: "sisyphus-junior",
+				model: { providerID: "anthropic", modelID: "claude-sonnet-4-6" },
+			},
+			output,
+		)
+
+		//#then
+		expect(abortCalls).toEqual([])
+		expect(promptCalls).toEqual([])
+		expect(output.message["model"]).toBeUndefined()
+	})
+})

src/tools/delegate-task/category-resolver.test.ts

@@ -484,4 +484,32 @@ describe("resolveCategoryExecution", () => {
 		})
 		expect(result.fallbackChain).toBeUndefined()
 	})
+
+	test("does not inherit hardcoded fallbackChain when sisyphus-junior model override is set [regression #2941]", async () => {
+		//#given
+		const args = {
+			category: "quick",
+			prompt: "test prompt",
+			description: "Test task",
+			run_in_background: false,
+			load_skills: [],
+			blockedBy: undefined,
+			enableSkillTools: false,
+		}
+		const executorCtx = createMockExecutorContext()
+		executorCtx.sisyphusJuniorModel = "anthropic/claude-sonnet-4-6"
+
+		//#when
+		const result = await resolveCategoryExecution(args, executorCtx, undefined, "anthropic/claude-sonnet-4-6")
+
+		//#then
+		expect(result.error).toBeUndefined()
+		expect(result.actualModel).toBe("anthropic/claude-sonnet-4-6")
+		expect(result.categoryModel).toEqual({
+			providerID: "anthropic",
+			modelID: "claude-sonnet-4-6",
+			variant: undefined,
+		})
+		expect(result.fallbackChain).toBeUndefined()
+	})
 })

src/tools/delegate-task/category-resolver.ts

@@ -275,6 +275,6 @@ Available categories: ${categoryNames.join(", ")}`,
     actualModel,
     isUnstableAgent,
     // Don't use hardcoded fallback chain when resolution was skipped (cold cache)
-    fallbackChain: configuredFallbackChain ?? ((isModelResolutionSkipped || explicitCategoryModel) ? undefined : requirement?.fallbackChain),
+    fallbackChain: configuredFallbackChain ?? ((isModelResolutionSkipped || explicitCategoryModel || overrideModel) ? undefined : requirement?.fallbackChain),
   }
 }

src/tools/delegate-task/tools.test.ts

@@ -2963,6 +2963,7 @@ describe("sisyphus-task", () => {
       // then - sisyphus-junior override model should be used, not category default
       expect(launchInput.model.providerID).toBe("anthropic")
       expect(launchInput.model.modelID).toBe("claude-sonnet-4-6")
+      expect(launchInput.fallbackChain).toBeUndefined()
     })
 
     test("sisyphus-junior model override works with user-defined category (#1295)", async () => {