fix(confidence-engine): sanitize reasoning error responses

tests/app/api/cases-start-route.test.js

@@ -169,7 +169,7 @@ describe("app/api/cases/start route", () => {
     expect(JSON.stringify(body)).not.toMatch(/ollama|generate|timed out/i);
   });
 
-  it("returns provider/internal failures as 5xx without stack traces", async () => {
+  it("sanitizes provider/internal failures at the browser boundary", async () => {
     const rawResponse = `{"reconstruction":{"observedStates":[{"id":"obs-1"${"x".repeat(2500)}}]}}`;
     mockStartCase.mockResolvedValue({
       success: false,
@@ -207,26 +207,8 @@ describe("app/api/cases/start route", () => {
 
     expect(response.status).toBe(502);
     const body = await response.json();
-    expect(body).toHaveProperty("rawResponse");
-    expect(body.rawResponse).toBe(rawResponse);
-    expect(body.rawResponse.length).toBeGreaterThan(2000);
-    expect(body.analysisErrors).toEqual(["reconstruction: Required"]);
-    expect(body.validationIssues).toEqual([
-      expect.objectContaining({
-        path: ["reconstruction", "observedStates", 2, "description"],
-        code: "invalid_type",
-        message: "Required",
-        expected: "string",
-        received: "undefined",
-      }),
-    ]);
-    expect(body.providerApiPath).toBe("/api/generate");
-    expect(body.providerExecution).toEqual({
-      chatCapabilityDetected: false,
-      chatRequestAttempted: false,
-      chatRequestSucceeded: false,
-      generateRequestAttempted: true,
-    });
+    expect(body).toEqual({ success: false, error: "Reasoning request could not be completed." });
+    expect(JSON.stringify(body)).not.toMatch(/provider unavailable|generate|llama3|rawResponse/i);
     expect(errorSpy).toHaveBeenCalledTimes(1);
     expect(errorSpy).toHaveBeenCalledWith(
       "[api/cases/start] error response",