diff --git a/src/agents/utils.test.ts b/src/agents/utils.test.ts
index 2feb71216..fdee0a606 100644
--- a/src/agents/utils.test.ts
+++ b/src/agents/utils.test.ts
@@ -589,20 +589,22 @@ describe("createBuiltinAgents with requiresProvider gating (hephaestus)", () =>
     }
   })
 
-  test("hephaestus is created when github-copilot provider is connected", async () => {
-    // #given - github-copilot provider has models available
+  test("hephaestus is NOT created when only github-copilot is connected (gpt-5.3-codex unavailable via github-copilot)", async () => {
+    // #given - github-copilot provider has models available, but no cache
     const fetchSpy = spyOn(shared, "fetchAvailableModels").mockResolvedValue(
       new Set(["github-copilot/gpt-5.3-codex"])
     )
+    const cacheSpy = spyOn(connectedProvidersCache, "readConnectedProvidersCache").mockReturnValue(null)
 
     try {
       // #when
       const agents = await createBuiltinAgents([], {}, undefined, TEST_DEFAULT_MODEL, undefined, undefined, [], {})
 
-      // #then
-      expect(agents.hephaestus).toBeDefined()
+      // #then - hephaestus requires openai/opencode, github-copilot alone is insufficient
+      expect(agents.hephaestus).toBeUndefined()
     } finally {
       fetchSpy.mockRestore()
+      cacheSpy.mockRestore()
     }
   })
 
diff --git a/src/plugin/ultrawork-model-override.test.ts b/src/plugin/ultrawork-model-override.test.ts
index 4f167e963..cee2dd59b 100644
--- a/src/plugin/ultrawork-model-override.test.ts
+++ b/src/plugin/ultrawork-model-override.test.ts
@@ -308,7 +308,10 @@ describe("applyUltraworkModelOverrideOnMessage", () => {
     //#then
     expect(output.message.model).toEqual({ providerID: "anthropic", modelID: "claude-opus-4-6" })
     expect(output.message["variant"]).toBe("max")
-    expect(output.message["thinking"]).toBe("max")
+    expect(output.message["thinking"]).toEqual({
+      type: "enabled",
+      budgetTokens: 16000,
+    })
     expect(dbOverrideSpy).not.toHaveBeenCalled()
   })
 
@@ -324,7 +327,10 @@ describe("applyUltraworkModelOverrideOnMessage", () => {
     //#then
     expect(output.message.model).toBeUndefined()
     expect(output.message["variant"]).toBe("high")
-    expect(output.message["thinking"]).toBe("high")
+    expect(output.message["thinking"]).toEqual({
+      type: "enabled",
+      budgetTokens: 16000,
+    })
     expect(dbOverrideSpy).not.toHaveBeenCalled()
   })
 
diff --git a/src/plugin/ultrawork-model-override.ts b/src/plugin/ultrawork-model-override.ts
index f6aa87bd2..7700f8274 100644
--- a/src/plugin/ultrawork-model-override.ts
+++ b/src/plugin/ultrawork-model-override.ts
@@ -8,6 +8,7 @@ import { scheduleDeferredModelOverride } from "./ultrawork-db-model-override"
 const CODE_BLOCK = /```[\s\S]*?```/g
 const INLINE_CODE = /`[^`]+`/g
 const ULTRAWORK_PATTERN = /\b(ultrawork|ulw)\b/i
+const ULTRAWORK_THINKING_CONFIG = { type: "enabled", budgetTokens: 16000 } as const
 
 export function detectUltrawork(text: string): boolean {
   const clean = text.replace(CODE_BLOCK, "").replace(INLINE_CODE, "")
@@ -117,7 +118,7 @@ export function applyUltraworkModelOverrideOnMessage(
   if (!override.providerID || !override.modelID) {
     if (override.variant) {
       output.message["variant"] = override.variant
-      output.message["thinking"] = override.variant
+      output.message["thinking"] = { ...ULTRAWORK_THINKING_CONFIG }
     }
     return
   }
@@ -134,7 +135,7 @@ export function applyUltraworkModelOverrideOnMessage(
     output.message.model = targetModel
     if (override.variant) {
       output.message["variant"] = override.variant
-      output.message["thinking"] = override.variant
+      output.message["thinking"] = { ...ULTRAWORK_THINKING_CONFIG }
     }
     return
   }