diff --git a/.changeset/fix-windows-unc-watch.md b/.changeset/fix-windows-unc-watch.md
new file mode 100644
index 0000000000..50f5e882e1
--- /dev/null
+++ b/.changeset/fix-windows-unc-watch.md
@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+Fix startup on Windows network shares by normalizing UNC paths before opening native filesystem watchers.
diff --git a/packages/agent-core-v2/src/os/backends/node-local/hostFsWatchService.ts b/packages/agent-core-v2/src/os/backends/node-local/hostFsWatchService.ts
index 333f631498..43396ca8b7 100644
--- a/packages/agent-core-v2/src/os/backends/node-local/hostFsWatchService.ts
+++ b/packages/agent-core-v2/src/os/backends/node-local/hostFsWatchService.ts
@@ -6,7 +6,7 @@
  */
 
 import { watch as fsWatch } from 'node:fs';
-import { basename, isAbsolute, join, relative } from 'node:path';
+import { basename, isAbsolute, join, relative, win32 } from 'node:path';
 
 import { FSWatcher } from 'chokidar';
 
@@ -159,13 +159,16 @@ class SignalWatchHandle implements IHostFsWatchHandle {
   private startNativeLeg(): void {
     if (this.disposed) return;
     try {
-      const watcher = this.runtime.watchNative(this.root, (_eventType, filename) => {
-        if (this.disposed) return;
-        this.retryAttempts = 0;
-        const absPath = resolveNativeSignalPath(this.root, filename);
-        if (absPath !== this.root && this.ignored(absPath)) return;
-        this.fireInvalidation();
-      });
+      const watcher = this.runtime.watchNative(
+        toNativeWatchRoot(this.root, this.runtime.platform),
+        (_eventType, filename) => {
+          if (this.disposed) return;
+          this.retryAttempts = 0;
+          const absPath = resolveNativeSignalPath(this.root, filename);
+          if (absPath !== this.root && this.ignored(absPath)) return;
+          this.fireInvalidation();
+        },
+      );
       watcher.on('error', (error: NodeJS.ErrnoException) => {
         this.onNativeError(watcher, error);
       });
@@ -255,6 +258,10 @@ function useNativeRecursive(
   );
 }
 
+function toNativeWatchRoot(root: string, platform: NodeJS.Platform): string {
+  return platform === 'win32' ? win32.normalize(root) : root;
+}
+
 function resolveNativeSignalPath(root: string, filename: string | null): string {
   if (filename === null || filename === '' || filename === basename(root)) return root;
   return clampToRoot(root, isAbsolute(filename) ? filename : join(root, filename));
diff --git a/packages/agent-core-v2/test/os/backends/node-local/hostFsWatchService.test.ts b/packages/agent-core-v2/test/os/backends/node-local/hostFsWatchService.test.ts
index 95e9bb9d45..25f8d697d0 100644
--- a/packages/agent-core-v2/test/os/backends/node-local/hostFsWatchService.test.ts
+++ b/packages/agent-core-v2/test/os/backends/node-local/hostFsWatchService.test.ts
@@ -48,6 +48,7 @@ class TestNativeWatcher {
 }
 
 interface TestNativeAttempt {
+  readonly root: string;
   readonly watcher: TestNativeWatcher;
   emit(filename: string | null): void;
 }
@@ -58,7 +59,10 @@ interface TestRetry {
   run(): void;
 }
 
-function signalRig(options?: { readonly synchronousFailures?: number }): {
+function signalRig(options?: {
+  readonly platform?: NodeJS.Platform;
+  readonly synchronousFailures?: number;
+}): {
   readonly service: IHostFsWatchService;
   readonly attempts: TestNativeAttempt[];
   readonly retries: TestRetry[];
@@ -69,14 +73,15 @@ function signalRig(options?: { readonly synchronousFailures?: number }): {
   const retries: TestRetry[] = [];
   let synchronousFailures = options?.synchronousFailures ?? 0;
   const runtime: HostFsWatchRuntime = {
-    platform: 'darwin',
-    watchNative: (_root, listener) => {
+    platform: options?.platform ?? 'darwin',
+    watchNative: (root, listener) => {
       if (synchronousFailures > 0) {
         synchronousFailures -= 1;
         throw Object.assign(new Error('native watch creation failed'), { code: 'EIO' });
       }
       const watcher = new TestNativeWatcher();
       attempts.push({
+        root,
         watcher,
         emit: (filename) => {
           listener('rename', filename);
@@ -164,6 +169,13 @@ describe('host filesystem change notifications', () => {
     expect(events).toEqual([{ path: '/repo', action: 'modified', kind: 'directory' }]);
   });
 
+  it('passes Windows UNC roots to the native watcher with native separators', () => {
+    const rig = signalRig({ platform: 'win32' });
+    handle = rig.service.watch('//server/share/repo', { signal: true });
+
+    expect(rig.attempt(0).root).toBe('\\\\server\\share\\repo');
+  });
+
   it('does not invalidate when a native signal path is ignored', () => {
     const rig = signalRig();
     const events: HostFsChange[] = [];