diff --git a/apps/x/packages/core/src/turns/bridges/real-model-registry.test.ts b/apps/x/packages/core/src/turns/bridges/real-model-registry.test.ts
index 0f3ef353..26de134c 100644
--- a/apps/x/packages/core/src/turns/bridges/real-model-registry.test.ts
+++ b/apps/x/packages/core/src/turns/bridges/real-model-registry.test.ts
@@ -243,6 +243,70 @@ describe("RealModelRegistry", () => {
         ]);
     });
 
+    it("attaches finish-step metadata as message-level providerOptions (OpenRouter signed reasoning)", async () => {
+        // OpenRouter streams per-delta reasoning_details FRAGMENTS on
+        // reasoning events, but puts the fully accumulated, signed array on
+        // the finish event's providerMetadata — and its read-back gives
+        // message-level reasoning_details precedence over per-part ones.
+        // The message-level attachment is what round-trips thinking
+        // signatures through tool loops (Bedrock rejects unsigned blocks).
+        const signedDetails = [
+            {
+                type: "reasoning.text",
+                text: "full thought",
+                format: "anthropic-claude-v1",
+                index: 0,
+                signature: "sig-full",
+            },
+        ];
+        const registry = makeRegistry(
+            [
+                { type: "reasoning-start" },
+                {
+                    type: "reasoning-delta",
+                    text: "full ",
+                    providerMetadata: { openrouter: { reasoning_details: [{ type: "reasoning.text", text: "full " }] } },
+                },
+                {
+                    type: "reasoning-delta",
+                    text: "thought",
+                    providerMetadata: { openrouter: { reasoning_details: [{ type: "reasoning.text", text: "thought" }] } },
+                },
+                { type: "reasoning-end" },
+                { type: "tool-call", toolCallId: "tc1", toolName: "echo", input: {} },
+                {
+                    type: "finish-step",
+                    finishReason: "tool-calls",
+                    usage: {},
+                    providerMetadata: { openrouter: { reasoning_details: signedDetails, usage: { cost: 1 } } },
+                },
+            ],
+            [],
+        );
+        const events = await collect(registry, request());
+        const completed = events[events.length - 1];
+        expect(
+            completed.type === "completed" ? completed.message.providerOptions : undefined,
+        ).toEqual({
+            openrouter: { reasoning_details: signedDetails, usage: { cost: 1 } },
+        });
+    });
+
+    it("echoes message-level providerOptions through encodeMessages", async () => {
+        const registry = makeRegistry([], []);
+        const model = await registry.resolve({ provider: "openai", model: "gpt-test" });
+        const encoded = model.encodeMessages([
+            {
+                role: "assistant",
+                content: [{ type: "text", text: "done" }],
+                providerOptions: { openrouter: { reasoning_details: [{ type: "reasoning.text", text: "t", signature: "s" }] } },
+            },
+        ] as never) as Array<{ role: string; providerOptions?: unknown }>;
+        expect(encoded[0].providerOptions).toEqual({
+            openrouter: { reasoning_details: [{ type: "reasoning.text", text: "t", signature: "s" }] },
+        });
+    });
+
     it("drops empty blocks that carry no metadata", async () => {
         const registry = makeRegistry(
             [
diff --git a/apps/x/packages/core/src/turns/bridges/real-model-registry.ts b/apps/x/packages/core/src/turns/bridges/real-model-registry.ts
index c7fa5348..11897908 100644
--- a/apps/x/packages/core/src/turns/bridges/real-model-registry.ts
+++ b/apps/x/packages/core/src/turns/bridges/real-model-registry.ts
@@ -184,6 +184,12 @@ export class RealModelRegistry implements IModelRegistry {
         let finishReason = "unknown";
         let usage: z.infer<typeof TurnUsage> = {};
         let providerMetadata: JsonValue | undefined;
+        // finish-step metadata also rides the assistant message as
+        // message-level providerOptions: providers put whole-response
+        // round-trip state there (OpenRouter's accumulated reasoning_details
+        // with thinking signatures — message-level wins over per-part
+        // fragments on read-back), and convertFromMessages echoes it.
+        let messageProviderOptions: PartProviderOptions | undefined;
 
         const tagPart = (
             part: TextContentPart | ReasoningContentPart,
@@ -302,6 +308,10 @@ export class RealModelRegistry implements IModelRegistry {
                     finishReason = event.finishReason ?? "unknown";
                     usage = mapUsage(event.usage);
                     providerMetadata = toJsonValue(event.providerMetadata);
+                    messageProviderOptions = mergeProviderOptions(
+                        messageProviderOptions,
+                        event.providerMetadata,
+                    );
                     yield {
                         type: "step_event",
                         event: {
@@ -339,6 +349,9 @@ export class RealModelRegistry implements IModelRegistry {
             message: {
                 role: "assistant",
                 content: content.length > 0 ? content : "",
+                ...(messageProviderOptions === undefined
+                    ? {}
+                    : { providerOptions: messageProviderOptions }),
             },
             finishReason,
             usage,
diff --git a/apps/x/packages/core/src/turns/runtime.ts b/apps/x/packages/core/src/turns/runtime.ts
index 08d9120e..d027e385 100644
--- a/apps/x/packages/core/src/turns/runtime.ts
+++ b/apps/x/packages/core/src/turns/runtime.ts
@@ -1299,7 +1299,22 @@ function parseToolAdditions(
 }
 
 function errorMessage(error: unknown): string {
-    return error instanceof Error ? error.message : String(error);
+    const message = error instanceof Error ? error.message : String(error);
+    // Provider API errors carry the actual upstream failure in responseBody
+    // (AI SDK APICallError; RetryError wraps the last one as lastError).
+    // "Failed after 3 attempts" alone is undebuggable — persist the payload,
+    // bounded so request events stay reference-sized.
+    const source = (error as { lastError?: unknown }).lastError ?? error;
+    const statusCode = (source as { statusCode?: unknown }).statusCode;
+    const responseBody = (source as { responseBody?: unknown }).responseBody;
+    const details: string[] = [];
+    if (typeof statusCode === "number") {
+        details.push(`status ${statusCode}`);
+    }
+    if (typeof responseBody === "string" && responseBody.trim().length > 0) {
+        details.push(responseBody.slice(0, 2000));
+    }
+    return details.length > 0 ? `${message} [${details.join(" — ")}]` : message;
 }
 
 function outcomeFromTerminal(state: TurnState): TurnOutcome {