fix(prompt): default size probe survives the gpt row

openai/gpt-4.1 now resolves to the gpt family, so the default column
measured the narrate-before-tools nudge. Probe an unrecognized provider
instead — default family regardless of shipped rows — and assert the
default column carries neither the claude block nor the gpt nudge.

Author: TheGreatAxios

src/agent/prompt-sizes.test.ts

@@ -345,10 +345,11 @@ describe("grok tool-budget residual (CL-8297)", () => {
   test("default-family and orchestrator prompts carry no tool budget", () => {
     const defaultPrompt = assembleDirectorPrompt("builder", "default");
     expect(defaultPrompt).not.toContain("Tool budget:");
-    // The default probe (openai/gpt-4.1) resolves to the default family, so
-    // the default column carries no family residual at all — not the claude
-    // task_guidance block either.
+    // The default probe resolves to the default family, so the default
+    // column carries no family residual — neither the claude task_guidance
+    // block nor the gpt narrate-before-tools nudge.
     expect(defaultPrompt).not.toContain("<task_guidance>");
+    expect(defaultPrompt).not.toContain("Narrate before tools (GPT worker):");
     expect(assembleDirectorPrompt("skywalker", "grok")).not.toContain(
       "Tool budget:",
     );

src/agent/prompt-sizes.ts

@@ -57,11 +57,12 @@ export const CANONICAL_PROMPT_ENV: EnvironmentInfo = {
 };
 
 const GROK_PROVIDER = { providerName: "xai/default", model: "grok-4.6" };
-// Default-family probe: openai/gpt-4.1 resolves to the default family (the
-// gpt row lands later in CL-8310), so the default column carries no residual.
+// Default-family probe: an unrecognized provider stays on the default
+// family no matter how many family rows land (claude/gpt already ship),
+// so the default column carries no residual.
 const DEFAULT_PROVIDER = {
-  providerName: "openai",
-  model: "gpt-4.1",
+  providerName: "unknown-provider",
+  model: "unknown-model",
 };
 
 /** Families in the size table: default assembly vs Grok (+finish-bias note). */