fix: opencode is not on PATH on Windows

apps/server/src/provider/opencodeRuntime.test.ts

@@ -7,6 +7,9 @@ const childProcessMock = vi.hoisted(() => ({
     if (command === "which" && args[0] === "opencode") {
       return "/opt/homebrew/bin/opencode\n";
     }
+    if (command === "where.exe" && args[0] === "opencode") {
+      return "C:\\Users\\testuser\\.bun\\bin\\opencode.exe\r\n";
+    }
     return "";
   }),
   spawn: vi.fn(),
@@ -25,6 +28,22 @@ describe("resolveOpenCodeBinaryPath", () => {
   it("resolves command names through PATH", async () => {
     const { resolveOpenCodeBinaryPath } = await import("./opencodeRuntime.ts");
 
+    if (process.platform === "win32") {
+      assert.equal(
+        resolveOpenCodeBinaryPath("opencode"),
+        "C:\\Users\\testuser\\.bun\\bin\\opencode.exe",
+      );
+      assert.deepEqual(childProcessMock.execFileSync.mock.calls[0], [
+        "where.exe",
+        ["opencode"],
+        {
+          encoding: "utf8",
+          timeout: 3_000,
+        },
+      ]);
+      return;
+    }
+
     assert.equal(resolveOpenCodeBinaryPath("opencode"), "/opt/homebrew/bin/opencode");
     assert.deepEqual(childProcessMock.execFileSync.mock.calls[0], [
       "which",

apps/server/src/provider/opencodeRuntime.ts

@@ -304,6 +304,17 @@ export function resolveOpenCodeBinaryPath(binaryPath: string): string {
   if (Path.isAbsolute(binaryPath)) {
     return binaryPath;
   }
+  if (process.platform === "win32") {
+    return (
+      execFileSync("where.exe", [binaryPath], {
+        encoding: "utf8",
+        timeout: 3_000,
+      })
+        .split(/\r?\n/)
+        .map((s) => s.trim())
+        .find((s) => s.length > 0) ?? ""
+    );
+  }
   return execFileSync("which", [binaryPath], {
     encoding: "utf8",
     timeout: 3_000,
@@ -361,6 +372,8 @@ export async function startOpenCodeServerProcess(input: {
   const args = ["serve", `--hostname=${hostname}`, `--port=${port}`];
   const child = spawn(input.binaryPath, args, {
     stdio: ["ignore", "pipe", "pipe"],
+    // Windows needs shell mode to resolve opencode.cmd shim
+    shell: process.platform === "win32",
     env: {
       ...process.env,
       OPENCODE_CONFIG_CONTENT: JSON.stringify({}),