fix: preserve config symlink writes

.changeset/preserve-config-symlinks.md

@@ -0,0 +1,6 @@
+---
+"@moonshot-ai/agent-core": patch
+"@moonshot-ai/kimi-code": patch
+---
+
+Preserve symlinked config files when saving configuration updates.

packages/agent-core/src/config/toml.ts

@@ -1,6 +1,6 @@
 import { existsSync, readFileSync } from 'node:fs';
-import { mkdir, open } from 'node:fs/promises';
-import { dirname } from 'pathe';
+import { lstat, mkdir, open, readlink } from 'node:fs/promises';
+import { dirname, resolve } from 'pathe';
 
 import { ErrorCodes, KimiError } from '#/errors';
 import { applyEnvModelConfig, stripEnvModelConfig } from './env-model';
@@ -450,7 +450,26 @@ export async function writeConfigFile(filePath: string, config: KimiConfig): Pro
   // stripEnvModelConfig / the getConfig -> setConfig round-trip).
   const validated = validateConfig(stripEnvModelConfig(config));
   await mkdir(dirname(filePath), { recursive: true, mode: 0o700 });
-  await atomicWrite(filePath, `${stringifyToml(configToTomlData(validated))}\n`);
+  await atomicWrite(
+    await configWriteTarget(filePath),
+    `${stringifyToml(configToTomlData(validated))}\n`,
+  );
+}
+
+async function configWriteTarget(filePath: string): Promise<string> {
+  let stat: Awaited<ReturnType<typeof lstat>>;
+  try {
+    stat = await lstat(filePath);
+  } catch (error) {
+    const code = (error as NodeJS.ErrnoException).code;
+    if (code === 'ENOENT') return filePath;
+    throw error;
+  }
+  if (!stat.isSymbolicLink()) return filePath;
+  // Preserve user-created config sync links while still atomically replacing
+  // the real target file.
+  const target = await readlink(filePath);
+  return resolve(dirname(filePath), target);
 }
 
 export function configToTomlData(config: KimiConfig): Record<string, unknown> {

packages/agent-core/test/config/configs.test.ts

@@ -1,5 +1,5 @@
 import { mkdtempSync } from 'node:fs';
-import { readFile, rm, writeFile } from 'node:fs/promises';
+import { lstat, readFile, rm, symlink, writeFile } from 'node:fs/promises';
 import { tmpdir } from 'node:os';
 import { join } from 'pathe';
 
@@ -389,6 +389,21 @@ removed_flag = true
     expect(text).not.toContain('default_permission_mode');
   });
 
+  it('preserves config.toml symlinks when rewriting config files', async () => {
+    const dir = makeTempDir();
+    const syncDir = makeTempDir();
+    const configPath = join(dir, 'config.toml');
+    const targetPath = join(syncDir, 'config.toml');
+    await writeFile(targetPath, 'default_thinking = false\n', 'utf-8');
+    await symlink(targetPath, configPath);
+
+    const config = parseConfigString('default_thinking = true\n', configPath);
+    await writeConfigFile(configPath, config);
+
+    expect((await lstat(configPath)).isSymbolicLink()).toBe(true);
+    await expect(readFile(targetPath, 'utf-8')).resolves.toContain('default_thinking = true');
+  });
+
   it('rejects invalid TOML and invalid schema with KimiError(config.invalid)', () => {
     expectKimiErrorCode(
       () => parseConfigString('[[[', 'broken.toml'),