diff --git a/extensions/opencode-go/index.test.ts b/extensions/opencode-go/index.test.ts
new file mode 100644
index 00000000000..b0d998c61f6
--- /dev/null
+++ b/extensions/opencode-go/index.test.ts
@@ -0,0 +1,48 @@
+import { describe, expect, it } from "vitest";
+import { registerSingleProviderPlugin } from "../../test/helpers/plugins/plugin-registration.js";
+import plugin from "./index.js";
+
+describe("opencode-go provider plugin", () => {
+  it("owns passthrough-gemini replay policy for Gemini-backed models", async () => {
+    const provider = await registerSingleProviderPlugin(plugin);
+
+    expect(
+      provider.buildReplayPolicy?.({
+        provider: "opencode-go",
+        modelApi: "openai-completions",
+        modelId: "gemini-2.5-pro",
+      } as never),
+    ).toMatchObject({
+      applyAssistantFirstOrderingFix: false,
+      validateGeminiTurns: false,
+      validateAnthropicTurns: false,
+      sanitizeThoughtSignatures: {
+        allowBase64Only: true,
+        includeCamelCase: true,
+      },
+    });
+  });
+
+  it("keeps non-Gemini replay policy minimal on passthrough routes", async () => {
+    const provider = await registerSingleProviderPlugin(plugin);
+
+    expect(
+      provider.buildReplayPolicy?.({
+        provider: "opencode-go",
+        modelApi: "openai-completions",
+        modelId: "qwen3-coder",
+      } as never),
+    ).toMatchObject({
+      applyAssistantFirstOrderingFix: false,
+      validateGeminiTurns: false,
+      validateAnthropicTurns: false,
+    });
+    expect(
+      provider.buildReplayPolicy?.({
+        provider: "opencode-go",
+        modelApi: "openai-completions",
+        modelId: "qwen3-coder",
+      } as never),
+    ).not.toHaveProperty("sanitizeThoughtSignatures");
+  });
+});
diff --git a/extensions/opencode/index.test.ts b/extensions/opencode/index.test.ts
new file mode 100644
index 00000000000..4e12b4e24e2
--- /dev/null
+++ b/extensions/opencode/index.test.ts
@@ -0,0 +1,48 @@
+import { describe, expect, it } from "vitest";
+import { registerSingleProviderPlugin } from "../../test/helpers/plugins/plugin-registration.js";
+import plugin from "./index.js";
+
+describe("opencode provider plugin", () => {
+  it("owns passthrough-gemini replay policy for Gemini-backed models", async () => {
+    const provider = await registerSingleProviderPlugin(plugin);
+
+    expect(
+      provider.buildReplayPolicy?.({
+        provider: "opencode",
+        modelApi: "openai-completions",
+        modelId: "gemini-2.5-pro",
+      } as never),
+    ).toMatchObject({
+      applyAssistantFirstOrderingFix: false,
+      validateGeminiTurns: false,
+      validateAnthropicTurns: false,
+      sanitizeThoughtSignatures: {
+        allowBase64Only: true,
+        includeCamelCase: true,
+      },
+    });
+  });
+
+  it("keeps non-Gemini replay policy minimal on passthrough routes", async () => {
+    const provider = await registerSingleProviderPlugin(plugin);
+
+    expect(
+      provider.buildReplayPolicy?.({
+        provider: "opencode",
+        modelApi: "openai-completions",
+        modelId: "claude-opus-4.6",
+      } as never),
+    ).toMatchObject({
+      applyAssistantFirstOrderingFix: false,
+      validateGeminiTurns: false,
+      validateAnthropicTurns: false,
+    });
+    expect(
+      provider.buildReplayPolicy?.({
+        provider: "opencode",
+        modelApi: "openai-completions",
+        modelId: "claude-opus-4.6",
+      } as never),
+    ).not.toHaveProperty("sanitizeThoughtSignatures");
+  });
+});