diff --git a/packages/server/src/server/agent/providers/opencode-server-manager.test.ts b/packages/server/src/server/agent/providers/opencode-server-manager.test.ts
index 027ef949c..e4ad07d14 100644
--- a/packages/server/src/server/agent/providers/opencode-server-manager.test.ts
+++ b/packages/server/src/server/agent/providers/opencode-server-manager.test.ts
@@ -1,10 +1,12 @@
 import type { ChildProcess } from "node:child_process";
 import { EventEmitter } from "node:events";
 import { mkdtempSync, rmSync } from "node:fs";
+import net from "node:net";
 import os from "node:os";
 import path from "node:path";
 import { afterEach, describe, expect, test, vi } from "vitest";
 
+import { findExecutable } from "../../../executable-resolution/executable-resolution.js";
 import { createTestLogger } from "../../../test-utils/test-logger.js";
 import type {
   ManagedProcessRecord,
@@ -236,6 +238,58 @@ describe("OpenCodeServerManager managed process ledger", () => {
   });
 });
 
+describe.runIf(process.platform === "win32")(
+  "OpenCodeServerManager Windows OpenCode npm install",
+  () => {
+    test("starts the helper server from opencode.exe instead of the npm opencode.cmd shim", async () => {
+      const detectedOpenCode = await findExecutable("opencode");
+      expect(detectedOpenCode, "Windows CI must install opencode-ai before server tests").not.toBe(
+        null,
+      );
+      expect(path.extname(detectedOpenCode!).toLowerCase()).toBe(".cmd");
+
+      const tempDir = mkdtempSync(path.join(os.tmpdir(), "opencode-real-windows-"));
+      const opencodeHomeDir = path.join(tempDir, "opencode-home");
+      const managedProcesses = new FakeManagedProcesses();
+      const manager = new OpenCodeServerManager({
+        logger: createTestLogger(),
+        managedProcesses,
+        resolveHomeDir: () => opencodeHomeDir,
+      });
+      let acquiredPort: number | null = null;
+
+      try {
+        const acquisition = await manager.acquireDedicated({
+          OPENCODE_AUTH_CONTENT: "{}",
+          OPENCODE_DISABLE_AUTOUPDATE: "1",
+          OPENCODE_DISABLE_AUTOCOMPACT: "1",
+          OPENCODE_DISABLE_MODELS_FETCH: "1",
+          OPENCODE_DISABLE_PROJECT_CONFIG: "1",
+          OPENCODE_PURE: "1",
+          OPENCODE_TEST_HOME: path.join(tempDir, "test-home"),
+        });
+        acquiredPort = acquisition.server.port;
+
+        const records = await managedProcesses.list();
+        expect(records).toHaveLength(1);
+        const record = records[0]!;
+        expect(path.extname(record.command).toLowerCase()).toBe(".exe");
+        expect(path.normalize(record.command).toLowerCase()).toContain(
+          path.normalize("node_modules/opencode-ai/bin/opencode.exe").toLowerCase(),
+        );
+        expect(record.command.toLowerCase()).not.toBe(detectedOpenCode!.toLowerCase());
+        expect(record.args).toEqual(["serve", "--port", String(acquiredPort)]);
+      } finally {
+        await manager.shutdown().catch(() => undefined);
+        if (acquiredPort !== null) {
+          await waitForClosedPort(acquiredPort, 5_000);
+        }
+        rmSync(tempDir, { recursive: true, force: true, maxRetries: 5, retryDelay: 100 });
+      }
+    }, 60_000);
+  },
+);
+
 function createTestManager(
   ports: number[],
   options: { autoAnnounce?: boolean; opencodeHomeDir?: string } = {},
@@ -413,3 +467,37 @@ class FakeManagedProcesses implements ManagedProcessRegistry {
     };
   }
 }
+
+async function waitForClosedPort(port: number, timeoutMs: number): Promise<void> {
+  const deadline = Date.now() + timeoutMs;
+  while (Date.now() < deadline) {
+    if (!(await canConnectToPort(port))) {
+      return;
+    }
+    await sleep(100);
+  }
+  throw new Error(`OpenCode helper server still accepts connections on port ${port}`);
+}
+
+function canConnectToPort(port: number): Promise<boolean> {
+  return new Promise((resolve) => {
+    const socket = net.createConnection({ host: "127.0.0.1", port });
+    let settled = false;
+    const settle = (connected: boolean) => {
+      if (settled) {
+        return;
+      }
+      settled = true;
+      socket.destroy();
+      resolve(connected);
+    };
+
+    socket.once("connect", () => settle(true));
+    socket.once("error", () => settle(false));
+    socket.setTimeout(500, () => settle(false));
+  });
+}
+
+function sleep(ms: number): Promise<void> {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}
diff --git a/packages/server/src/server/agent/providers/opencode/server-manager.ts b/packages/server/src/server/agent/providers/opencode/server-manager.ts
index 634cc55c6..566151f73 100644
--- a/packages/server/src/server/agent/providers/opencode/server-manager.ts
+++ b/packages/server/src/server/agent/providers/opencode/server-manager.ts
@@ -1,6 +1,8 @@
 import type { ChildProcess } from "node:child_process";
 import { mkdirSync } from "node:fs";
+import { stat } from "node:fs/promises";
 import net from "node:net";
+import path from "node:path";
 import type { Logger } from "pino";
 
 import { findExecutable } from "../../../../executable-resolution/executable-resolution.js";
@@ -495,12 +497,50 @@ export class OpenCodeServerManager implements OpenCodeServerManagerLike {
 
 async function resolveOpenCodeBinary(): Promise<string> {
   const found = await findExecutable("opencode");
-  if (found) {
-    return found;
+  if (!found) {
+    throw new Error(
+      "OpenCode binary not found. Install OpenCode (https://github.com/opencode-ai/opencode) and ensure it is available in your shell PATH.",
+    );
+  }
+
+  if (process.platform === "win32" && path.extname(found).toLowerCase() === ".cmd") {
+    // Global npm: <prefix>/opencode.cmd → <prefix>/node_modules/opencode-ai/bin/opencode.exe
+    const globalCandidate = path.join(
+      path.dirname(found),
+      "node_modules",
+      "opencode-ai",
+      "bin",
+      "opencode.exe",
+    );
+    if (await pathExists(globalCandidate)) return globalCandidate;
+
+    // Local/pnpm: <project>/node_modules/.bin/opencode.cmd → <project>/node_modules/opencode-ai/bin/opencode.exe
+    const localCandidate = path.join(
+      path.dirname(found),
+      "..",
+      "opencode-ai",
+      "bin",
+      "opencode.exe",
+    );
+    if (await pathExists(localCandidate)) return localCandidate;
+
+    console.warn(
+      "[opencode-server] Found opencode.cmd but could not resolve the real opencode.exe. " +
+        "The process may not be properly terminated on exit. Path: %s",
+      found,
+    );
+  }
+
+  return found;
+}
+
+async function pathExists(filePath: string): Promise<boolean> {
+  try {
+    await stat(filePath);
+    return true;
+  } catch {
+    return false;
   }
-  throw new Error(
-    "OpenCode binary not found. Install OpenCode (https://github.com/opencode-ai/opencode) and ensure it is available in your shell PATH.",
-  );
 }
 
 function findAvailablePort(): Promise<number> {