diff --git a/packages/cloud-agents/src/__tests__/opencode-identity-plugin.test.ts b/packages/cloud-agents/src/__tests__/opencode-identity-plugin.test.ts
index 4708cebab7..13dfe9f42f 100644
--- a/packages/cloud-agents/src/__tests__/opencode-identity-plugin.test.ts
+++ b/packages/cloud-agents/src/__tests__/opencode-identity-plugin.test.ts
@@ -10,8 +10,26 @@ type SystemTransformHook = (
   output: { system: string[] },
 ) => Promise<void>;
 
+type MessageTransformHook = (
+  input: unknown,
+  output: {
+    messages: Array<{
+      info: { role: string; providerID?: string; modelID?: string };
+      parts: Array<Record<string, unknown>>;
+    }>;
+  },
+) => Promise<void>;
+
 describe('OPENCODE_IDENTITY_PLUGIN_SCRIPT', () => {
   async function loadSystemTransformHook(): Promise<SystemTransformHook> {
+    const hooks = await loadHooks();
+    return hooks['experimental.chat.system.transform'];
+  }
+
+  async function loadHooks(): Promise<{
+    'experimental.chat.system.transform': SystemTransformHook;
+    'experimental.chat.messages.transform': MessageTransformHook;
+  }> {
     const tempDir = fs.mkdtempSync(
       path.join(os.tmpdir(), 'roomote-opencode-identity-plugin-'),
     );
@@ -24,10 +42,10 @@ describe('OPENCODE_IDENTITY_PLUGIN_SCRIPT', () => {
       )) as {
         RoomoteOpenCodeIdentity: () => Promise<{
           'experimental.chat.system.transform': SystemTransformHook;
+          'experimental.chat.messages.transform': MessageTransformHook;
         }>;
       };
-      const hooks = await plugin.RoomoteOpenCodeIdentity();
-      return hooks['experimental.chat.system.transform'];
+      return await plugin.RoomoteOpenCodeIdentity();
     } finally {
       fs.rmSync(tempDir, { recursive: true, force: true });
     }
@@ -93,4 +111,125 @@ describe('OPENCODE_IDENTITY_PLUGIN_SCRIPT', () => {
 
     expect(output.system).toEqual(original);
   });
+
+  it('preserves and consolidates OpenRouter Gemini reasoning details for tool-call replay', async () => {
+    const hooks = await loadHooks();
+    const encrypted = {
+      type: 'reasoning.encrypted',
+      data: 'opaque-provider-data',
+      id: 'tool_read_1',
+      format: 'google-gemini-v1',
+      index: 0,
+    };
+    const text = {
+      type: 'reasoning.text',
+      text: 'summary',
+      format: 'google-gemini-v1',
+      index: 0,
+    };
+    const output = {
+      messages: [
+        {
+          info: {
+            role: 'assistant',
+            providerID: 'openrouter',
+            modelID: 'google/gemini-3.8-flash',
+          },
+          parts: [
+            {
+              type: 'reasoning',
+              text: 'summary',
+              metadata: { openrouter: { reasoning_details: [text] } },
+            },
+            {
+              type: 'tool',
+              callID: 'tool_read_1',
+              metadata: {
+                openrouter: { reasoning_details: [text, encrypted] },
+              },
+            },
+          ],
+        },
+      ],
+    };
+
+    await hooks['experimental.chat.messages.transform']({}, output);
+
+    expect(output.messages[0]?.parts[0]?.metadata).toEqual({
+      openrouter: { reasoning_details: [text, encrypted] },
+    });
+    expect(output.messages[0]?.parts[1]?.metadata).toEqual({
+      openrouter: { reasoning_details: [text, encrypted] },
+    });
+  });
+
+  it('adds the Gemini validator bypass only when encrypted reasoning is unavailable', async () => {
+    const hooks = await loadHooks();
+    const output = {
+      messages: [
+        {
+          info: {
+            role: 'assistant',
+            providerID: 'openrouter',
+            modelID: 'google/gemini-3.8-flash',
+          },
+          parts: [
+            {
+              type: 'tool',
+              callID: 'tool_read_1',
+              metadata: { existing: 'metadata' },
+            },
+          ],
+        },
+      ],
+    };
+
+    const transform = hooks['experimental.chat.messages.transform'];
+    await transform({}, output);
+    await transform({}, output);
+
+    expect(output.messages[0]?.parts[0]?.metadata).toEqual({
+      existing: 'metadata',
+      openrouter: {
+        reasoning_details: [
+          {
+            type: 'reasoning.encrypted',
+            data: 'skip_thought_signature_validator',
+            id: 'tool_read_1',
+            format: 'google-gemini-v1',
+            index: 0,
+          },
+        ],
+      },
+    });
+  });
+
+  it('leaves non-OpenRouter and pre-Gemini-3 histories unchanged', async () => {
+    const hooks = await loadHooks();
+    const output = {
+      messages: [
+        {
+          info: {
+            role: 'assistant',
+            providerID: 'google',
+            modelID: 'gemini-3.8-flash',
+          },
+          parts: [{ type: 'tool', callID: 'google-tool' }],
+        },
+        {
+          info: {
+            role: 'assistant',
+            providerID: 'openrouter',
+            modelID: 'google/gemini-2.5-pro',
+          },
+          parts: [{ type: 'tool', callID: 'old-gemini-tool' }],
+        },
+      ],
+    };
+    const original = structuredClone(output);
+
+    await hooks['experimental.chat.messages.transform']({}, output);
+
+    expect(output).toEqual(original);
+  });
 });
diff --git a/packages/cloud-agents/src/opencode-identity-plugin.ts b/packages/cloud-agents/src/opencode-identity-plugin.ts
index a57332203f..fb3526625b 100644
--- a/packages/cloud-agents/src/opencode-identity-plugin.ts
+++ b/packages/cloud-agents/src/opencode-identity-plugin.ts
@@ -13,5 +13,65 @@ export const OPENCODE_IDENTITY_PLUGIN_SCRIPT = `export const RoomoteOpenCodeIden
         .replace(/^You are OpenCode,\\s*/iu, '');
     }
   },
+  'experimental.chat.messages.transform': async (_input, output) => {
+    // OpenRouter replays only the first reasoning_details array it finds. Keep
+    // split metadata together, and make legacy unsigned Gemini 3 tool calls
+    // explicitly use Google's documented validator-bypass sentinel.
+    for (const message of output.messages ?? []) {
+      if (
+        message.info?.role !== 'assistant' ||
+        message.info.providerID !== 'openrouter' ||
+        !/(^|\\/)gemini-3(?:[.-]|$)/iu.test(message.info.modelID ?? '')
+      ) {
+        continue;
+      }
+
+      const tool = message.parts?.find(
+        (part) => part?.type === 'tool' && typeof part.callID === 'string',
+      );
+      if (!tool) continue;
+
+      const details = [];
+      const seen = new Set();
+      for (const part of message.parts ?? []) {
+        const partDetails = part?.metadata?.openrouter?.reasoning_details;
+        if (!Array.isArray(partDetails)) continue;
+
+        for (const detail of partDetails) {
+          const key = JSON.stringify(detail);
+          if (seen.has(key)) continue;
+          seen.add(key);
+          details.push(detail);
+        }
+      }
+
+      if (
+        !details.some(
+          (detail) =>
+            detail?.type === 'reasoning.encrypted' &&
+            typeof detail.data === 'string' &&
+            detail.data.length > 0,
+        )
+      ) {
+        details.push({
+          type: 'reasoning.encrypted',
+          data: 'skip_thought_signature_validator',
+          id: tool.callID,
+          format: 'google-gemini-v1',
+          index: 0,
+        });
+      }
+
+      const target =
+        message.parts.find((part) => part?.type === 'reasoning') ?? tool;
+      target.metadata = {
+        ...target.metadata,
+        openrouter: {
+          ...target.metadata?.openrouter,
+          reasoning_details: details,
+        },
+      };
+    }
+  },
 });
 `;