fix(rectification): stop forcing named tool_choice on thinking models

Homepage opening failed immediately because thinking-mode providers reject a required first-tool choice.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/lib/rectification-agentic/v9/agent-run.ts

@@ -134,6 +134,9 @@ function safeErrorCode(error: unknown): string {
   if (message.includes("agentic_rectification_case_terminal")) return "case_terminal";
   if (message.includes("agentic_rectification_case_not_found")) return "case_not_found";
   if (message.includes("agentic_rectification_case_session_mismatch")) return "case_session_mismatch";
+  if (message.includes("Thinking mode does not support this tool_choice")) {
+    return "thinking_tool_choice_unsupported";
+  }
   return "run_failed";
 }
 
@@ -276,6 +279,10 @@ export async function runV9AgentTurn(options: V9AgentRunOptions): Promise<V9Agen
       outcome = await streamAttempt(attemptNumber, attemptId);
     } catch (error) {
       const errorCode = safeErrorCode(error);
+      const reason = error instanceof Error ? error.message.slice(0, 180) : "UnknownError";
+      console.error(
+        `[rectification-v10] attempt failed case=${caseId} turn=${turnId} attempt=${attemptId} code=${errorCode} reason=${reason}`,
+      );
       outcome = {
         ok: false,
         status: isRetryableError(errorCode) ? "retryable" : "failed",
@@ -486,7 +493,7 @@ export async function runV9AgentTurn(options: V9AgentRunOptions): Promise<V9Agen
             abortSignal: AbortSignal;
             prepareStep: (input: { stepNumber: number }) => {
               activeTools: string[];
-              toolChoice: { type: "tool"; toolName: string };
+              toolChoice: "auto";
             } | undefined;
           },
         ): Promise<{
@@ -500,10 +507,13 @@ export async function runV9AgentTurn(options: V9AgentRunOptions): Promise<V9Agen
       }).stream(messages, {
         maxSteps,
         abortSignal: abortController.signal,
+        // Thinking-mode providers reject named/required tool_choice. Restrict
+        // the first step to read-case and keep tool_choice auto; the runner
+        // still refuses any other public tool before case.loaded.
         prepareStep: ({ stepNumber }) => stepNumber === 0
           ? {
               activeTools: ["rectification-read-case"],
-              toolChoice: { type: "tool", toolName: "rectification-read-case" },
+              toolChoice: "auto",
             }
           : undefined,
       });