fix(consult): 第 0 步改回 auto，供应商 error 块不再被吞掉

BUG-937 撤回 thinking 模式下的 required toolChoice，只留 activeTools。BUG-938 让咨询流识别 Mastra error 块，公开码 calculation_failed，内部码进日志且不触发合同 retry。

frontend/src/lib/agent-observability.ts

@@ -185,6 +185,8 @@ const knownErrorCodes = new Set([
   "timeout",
   "cancelled",
   "settlement_failed",
+  "thinking_tool_choice_unsupported",
+  "provider_error",
 ]);
 
 export function toAgentObservabilityErrorCode(error: unknown): string {

frontend/src/lib/stream-agent-response.ts

@@ -20,7 +20,7 @@ import {
   type PublicThinkingSection,
 } from "./consultation-thinking-plan.ts";
 
-type Chunk = { type?: string; payload?: Record<string, unknown>; data?: unknown };
+type Chunk = { type?: string; payload?: Record<string, unknown>; data?: unknown; error?: unknown };
 type ChunkStream = AsyncIterable<unknown> | ReadableStream<unknown>;
 
 async function* readChunks(stream: ChunkStream): AsyncIterable<Chunk> {
@@ -90,11 +90,33 @@ function isTimeoutOrAbort(error: unknown) {
 }
 
 type RunFailedCode = "runtime_contract_incomplete" | "empty_answer" | "answer_truncated" | "calculation_failed";
+type ProviderStreamErrorCode = "thinking_tool_choice_unsupported" | "provider_error";
+
+function providerErrorMessage(error: unknown): string {
+  return error instanceof Error ? error.message : String(error);
+}
+
+function classifyProviderStreamError(error: unknown): ProviderStreamErrorCode {
+  return providerErrorMessage(error).includes("Thinking mode does not support this tool_choice")
+    ? "thinking_tool_choice_unsupported"
+    : "provider_error";
+}
+
+function chunkProviderError(chunk: Chunk): unknown {
+  if (chunk.error !== undefined) return chunk.error;
+  return chunk.payload?.error;
+}
 
 function runFailedCode(error: unknown, emitted: boolean): RunFailedCode {
   if (error instanceof Error && error.message === "runtime_contract_incomplete") return "runtime_contract_incomplete";
   if (error instanceof Error && error.message === "empty_answer") return "empty_answer";
   if (error instanceof Error && error.message === "answer_truncated") return "answer_truncated";
+  if (
+    error instanceof Error
+    && (error.message === "thinking_tool_choice_unsupported" || error.message === "provider_error")
+  ) {
+    return "calculation_failed";
+  }
   if (emitted && isTimeoutOrAbort(error)) return "answer_truncated";
   return "calculation_failed";
 }
@@ -383,6 +405,21 @@ export function streamAgentResponse(options: StreamAgentResponseOptions) {
     const stepCountBeforeAttempt = options.state.modelStepCount;
     try {
       for await (const chunk of readChunks(stream)) {
+        if (chunk.type === "error") {
+          const raw = chunkProviderError(chunk);
+          const code = classifyProviderStreamError(raw);
+          appendConsultationRuntimeStep(options.state, {
+            kind: "validation",
+            name: "model-stream-error",
+            status: "failed",
+          });
+          console.error("[consult-provider-error]", {
+            requestId: options.requestId,
+            code,
+            messageHead: providerErrorMessage(raw).slice(0, 200),
+          });
+          throw new Error(code);
+        }
         for (const event of mapChunk(chunk, options, startedAt, toolErrors)) send(controller, event);
         flushThinkingPlan(controller);
         if (chunk.type === "step-finish") options.state.modelStepCount += 1;