diff --git a/plugins/opencode/scripts/lib/opencode-server.mjs b/plugins/opencode/scripts/lib/opencode-server.mjs
index f4192a8..15f6867 100644
--- a/plugins/opencode/scripts/lib/opencode-server.mjs
+++ b/plugins/opencode/scripts/lib/opencode-server.mjs
@@ -4,6 +4,7 @@
 
 import { spawn } from "node:child_process";
 
+const IS_WINDOWS = process.platform === "win32";
 const DEFAULT_PORT = 4096;
 const DEFAULT_HOST = "127.0.0.1";
 const SERVER_START_TIMEOUT = 30_000;
@@ -43,10 +44,12 @@ export async function ensureServer(opts = {}) {
   }
 
   // Start the server
+  // Windows npm shims are .cmd/.ps1; spawn() only resolves those via a shell.
   const proc = spawn("opencode", ["serve", "--port", String(port)], {
     stdio: ["ignore", "pipe", "pipe"],
     detached: true,
     cwd: opts.cwd,
+    shell: IS_WINDOWS,
   });
   proc.unref();
 
diff --git a/plugins/opencode/scripts/lib/process.mjs b/plugins/opencode/scripts/lib/process.mjs
index a199e78..0806d8d 100644
--- a/plugins/opencode/scripts/lib/process.mjs
+++ b/plugins/opencode/scripts/lib/process.mjs
@@ -2,16 +2,22 @@
 
 import { spawn } from "node:child_process";
 
+const IS_WINDOWS = process.platform === "win32";
+
 /**
  * Resolve the full path to the `opencode` binary.
  * @returns {Promise<string|null>}
  */
 export async function resolveOpencodeBinary() {
   return new Promise((resolve) => {
-    const proc = spawn("which", ["opencode"], { stdio: ["ignore", "pipe", "ignore"] });
+    // `which` isn't a native Windows binary; `where` is the equivalent.
+    const proc = spawn(IS_WINDOWS ? "where" : "which", ["opencode"], {
+      stdio: ["ignore", "pipe", "ignore"],
+    });
     let out = "";
     proc.stdout.on("data", (d) => (out += d));
-    proc.on("close", (code) => resolve(code === 0 ? out.trim() : null));
+    proc.on("close", (code) => resolve(code === 0 ? out.trim().split(/\r?\n/)[0] : null));
+    proc.on("error", () => resolve(null));
   });
 }
 
@@ -30,12 +36,15 @@ export async function isOpencodeInstalled() {
  */
 export async function getOpencodeVersion() {
   return new Promise((resolve) => {
+    // Windows npm shims are .cmd/.ps1; spawn() only resolves those via a shell.
     const proc = spawn("opencode", ["--version"], {
       stdio: ["ignore", "pipe", "ignore"],
+      shell: IS_WINDOWS,
     });
     let out = "";
     proc.stdout.on("data", (d) => (out += d));
     proc.on("close", (code) => resolve(code === 0 ? out.trim() : null));
+    proc.on("error", () => resolve(null));
   });
 }
 
@@ -52,12 +61,14 @@ export function runCommand(cmd, args, opts = {}) {
       stdio: ["ignore", "pipe", "pipe"],
       cwd: opts.cwd,
       env: { ...process.env, ...opts.env },
+      shell: IS_WINDOWS,
     });
     let stdout = "";
     let stderr = "";
     proc.stdout.on("data", (d) => (stdout += d));
     proc.stderr.on("data", (d) => (stderr += d));
     proc.on("close", (exitCode) => resolve({ stdout, stderr, exitCode: exitCode ?? 1 }));
+    proc.on("error", (err) => resolve({ stdout: "", stderr: String(err), exitCode: 1 }));
   });
 }
 
@@ -74,6 +85,7 @@ export function spawnDetached(cmd, args, opts = {}) {
     detached: true,
     cwd: opts.cwd,
     env: { ...process.env, ...opts.env },
+    shell: IS_WINDOWS,
   });
   child.unref();
   return child;