Fix cooldown fallback switching across model/runtime fallback hooks

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

@@ -140,6 +140,121 @@ describe("model fallback hook", () => {
     expect(secondOutput.message["variant"]).toBeUndefined()
   })
 
+  test("does not re-arm fallback when one is already pending", () => {
+    //#given
+    const sessionID = "ses_model_fallback_pending_guard"
+    clearPendingModelFallback(sessionID)
+
+    //#when
+    const firstSet = setPendingModelFallback(
+      sessionID,
+      "Sisyphus (Ultraworker)",
+      "anthropic",
+      "claude-opus-4-6-thinking",
+    )
+    const secondSet = setPendingModelFallback(
+      sessionID,
+      "Sisyphus (Ultraworker)",
+      "anthropic",
+      "claude-opus-4-6-thinking",
+    )
+
+    //#then
+    expect(firstSet).toBe(true)
+    expect(secondSet).toBe(false)
+    clearPendingModelFallback(sessionID)
+  })
+
+  test("skips no-op fallback entries that resolve to same provider/model", async () => {
+    //#given
+    const sessionID = "ses_model_fallback_noop_skip"
+    clearPendingModelFallback(sessionID)
+
+    const hook = createModelFallbackHook() as unknown as {
+      "chat.message"?: (
+        input: { sessionID: string },
+        output: { message: Record<string, unknown>; parts: Array<{ type: string; text?: string }> },
+      ) => Promise<void>
+    }
+
+    setSessionFallbackChain(sessionID, [
+      { providers: ["anthropic"], model: "claude-opus-4-6" },
+      { providers: ["opencode"], model: "kimi-k2.5-free" },
+    ])
+
+    expect(
+      setPendingModelFallback(
+        sessionID,
+        "Sisyphus (Ultraworker)",
+        "anthropic",
+        "claude-opus-4-6",
+      ),
+    ).toBe(true)
+
+    const output = {
+      message: {
+        model: { providerID: "anthropic", modelID: "claude-opus-4-6" },
+      },
+      parts: [{ type: "text", text: "continue" }],
+    }
+
+    //#when
+    await hook["chat.message"]?.({ sessionID }, output)
+
+    //#then
+    expect(output.message["model"]).toEqual({
+      providerID: "opencode",
+      modelID: "kimi-k2.5-free",
+    })
+    clearPendingModelFallback(sessionID)
+  })
+
+  test("skips no-op fallback entries even when variant differs", async () => {
+    //#given
+    const sessionID = "ses_model_fallback_noop_variant_skip"
+    clearPendingModelFallback(sessionID)
+
+    const hook = createModelFallbackHook() as unknown as {
+      "chat.message"?: (
+        input: { sessionID: string },
+        output: { message: Record<string, unknown>; parts: Array<{ type: string; text?: string }> },
+      ) => Promise<void>
+    }
+
+    setSessionFallbackChain(sessionID, [
+      { providers: ["quotio"], model: "claude-opus-4-6", variant: "max" },
+      { providers: ["quotio"], model: "gpt-5.2" },
+    ])
+
+    expect(
+      setPendingModelFallback(
+        sessionID,
+        "Sisyphus (Ultraworker)",
+        "quotio",
+        "claude-opus-4-6",
+      ),
+    ).toBe(true)
+
+    const output = {
+      message: {
+        model: { providerID: "quotio", modelID: "claude-opus-4-6" },
+        variant: "max",
+      },
+      parts: [{ type: "text", text: "continue" }],
+    }
+
+    //#when
+    await hook["chat.message"]?.({ sessionID }, output)
+
+    //#then
+    expect(output.message["model"]).toEqual({
+      providerID: "quotio",
+      modelID: "gpt-5.2",
+    })
+    expect(output.message["variant"]).toBeUndefined()
+    clearPendingModelFallback(sessionID)
+  })
+
   test("shows toast when fallback is applied", async () => {
     //#given
     const toastCalls: Array<{ title: string; message: string }> = []
@@ -199,7 +314,7 @@ describe("model fallback hook", () => {
       sessionID,
       "Atlas (Plan Executor)",
       "github-copilot",
-      "claude-sonnet-4-6",
+      "claude-sonnet-4-5",
     )
     expect(set).toBe(true)
 

src/hooks/model-fallback/hook.ts

@@ -39,6 +39,12 @@ const pendingModelFallbacks = new Map<string, ModelFallbackState>()
 const lastToastKey = new Map<string, string>()
 const sessionFallbackChains = new Map<string, FallbackEntry[]>()
 
+function canonicalizeModelID(modelID: string): string {
+  return modelID
+    .toLowerCase()
+    .replace(/\./g, "-")
+}
+
 export function setSessionFallbackChain(sessionID: string, fallbackChain: FallbackEntry[] | undefined): void {
   if (!sessionID) return
   if (!fallbackChain || fallbackChain.length === 0) {
@@ -77,6 +83,11 @@ export function setPendingModelFallback(
   const existing = pendingModelFallbacks.get(sessionID)
 
   if (existing) {
+    if (existing.pending) {
+      log("[model-fallback] Pending fallback already armed for session: " + sessionID)
+      return false
+    }
+
     // Preserve progression across repeated session.error retries in same session.
     // We only mark the next turn as pending fallback application.
     existing.providerID = currentProviderID
@@ -140,13 +151,24 @@ export function getNextFallback(
     }
 
     const providerID = selectFallbackProvider(fallback.providers, state.providerID)
+    const modelID = transformModelForProvider(providerID, fallback.model)
+
+    const isNoOpFallback =
+      providerID.toLowerCase() === state.providerID.toLowerCase() &&
+      canonicalizeModelID(modelID) === canonicalizeModelID(state.modelID)
+
+    if (isNoOpFallback) {
+      log("[model-fallback] Skipping no-op fallback for session: " + sessionID + ", attempt: " + attemptCount + ", model: " + fallback.model)
+      continue
+    }
+
     state.pending = false
 
     log("[model-fallback] Using fallback for session: " + sessionID + ", attempt: " + attemptCount + ", model: " + fallback.model)
 
     return {
       providerID,
-      modelID: transformModelForProvider(providerID, fallback.model),
+      modelID,
       variant: fallback.variant,
     }
   }