diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index e8d163ec2..f7ceb283d 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -12,6 +12,7 @@
 
 ### Fixed
 
+- Fixed writes to `auth.json` and `models-store.json` overriding administrator-managed file permissions and ACLs ([#7779](https://github.com/earendil-works/pi/issues/7779)).
 - Fixed UTF-8 BOM markers preventing frontmatter and user configuration files from loading ([#8337](https://github.com/earendil-works/pi/issues/8337)).
 - Fixed invalid settings files being easy to miss during interactive startup by rendering warnings with the file path inside the TUI ([#7829](https://github.com/earendil-works/pi/issues/7829)).
 - Fixed the subagent example repeatedly prompting before running project-local agents in trusted repositories ([#8261](https://github.com/earendil-works/pi/issues/8261)).
diff --git a/packages/coding-agent/src/core/auth-storage.ts b/packages/coding-agent/src/core/auth-storage.ts
index 71be9d022..9d6495919 100644
--- a/packages/coding-agent/src/core/auth-storage.ts
+++ b/packages/coding-agent/src/core/auth-storage.ts
@@ -4,7 +4,7 @@
  */
 
 import type { AuthOperationOptions, Credential, CredentialInfo, CredentialStore } from "@earendil-works/pi-ai";
-import { chmodSync, existsSync, mkdirSync, readFileSync, writeFileSync } from "fs";
+import { existsSync, mkdirSync, readFileSync, writeFileSync } from "fs";
 import { dirname, join } from "path";
 import lockfile from "proper-lockfile";
 import { setTimeout as sleep } from "timers/promises";
@@ -21,6 +21,7 @@ type LockResult<T> = {
 	next?: string;
 };
 
+// The mode applies only on creation so administrator-managed modes and ACLs remain intact.
 const AUTH_FILE_WRITE_OPTIONS = { encoding: "utf-8", mode: 0o600 } as const;
 
 type AuthFileReload = {
@@ -62,7 +63,6 @@ export class FileAuthStorageBackend implements AuthStorageBackend {
 	private ensureFileExists(): void {
 		if (!existsSync(this.authPath)) {
 			writeFileSync(this.authPath, "{}", AUTH_FILE_WRITE_OPTIONS);
-			chmodSync(this.authPath, 0o600);
 		}
 	}
 
@@ -104,7 +104,6 @@ export class FileAuthStorageBackend implements AuthStorageBackend {
 			const { result, next } = fn(current);
 			if (next !== undefined) {
 				writeFileSync(this.authPath, next, AUTH_FILE_WRITE_OPTIONS);
-				chmodSync(this.authPath, 0o600);
 			}
 			return result;
 		} finally {
@@ -186,7 +185,6 @@ export class FileAuthStorageBackend implements AuthStorageBackend {
 			options?.signal?.throwIfAborted();
 			if (next !== undefined) {
 				writeFileSync(this.authPath, next, AUTH_FILE_WRITE_OPTIONS);
-				chmodSync(this.authPath, 0o600);
 			}
 			throwIfCompromised();
 			return result;
diff --git a/packages/coding-agent/test/auth-storage.test.ts b/packages/coding-agent/test/auth-storage.test.ts
index 801697ee2..61cdbefba 100644
--- a/packages/coding-agent/test/auth-storage.test.ts
+++ b/packages/coding-agent/test/auth-storage.test.ts
@@ -1,4 +1,4 @@
-import { existsSync, mkdirSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import { chmodSync, existsSync, mkdirSync, readFileSync, rmSync, statSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { type CredentialStore, createModels, type Provider } from "@earendil-works/pi-ai";
@@ -139,6 +139,22 @@ describe("AuthStorage", () => {
 		expect(release).toHaveBeenCalledTimes(1);
 	});
 
+	test.skipIf(process.platform === "win32")("creates new auth files with owner-only permissions", () => {
+		AuthStorage.create(authJsonPath);
+
+		expect(statSync(authJsonPath).mode & 0o777).toBe(0o600);
+	});
+
+	test.skipIf(process.platform === "win32")("preserves the mode of an existing auth file", async () => {
+		writeAuthJson({ anthropic: { type: "api_key", key: "old" } });
+		chmodSync(authJsonPath, 0o660);
+		const storage = AuthStorage.create(authJsonPath);
+
+		await storage.modify("anthropic", async () => ({ type: "api_key", key: "new" }));
+
+		expect(statSync(authJsonPath).mode & 0o777).toBe(0o660);
+	});
+
 	test("modify persists a credential while preserving unrelated external edits", async () => {
 		writeAuthJson({ anthropic: { type: "api_key", key: "old" } });
 		const storage = AuthStorage.create(authJsonPath);
diff --git a/packages/coding-agent/test/models-store.test.ts b/packages/coding-agent/test/models-store.test.ts
index 30e592f7c..bf645042c 100644
--- a/packages/coding-agent/test/models-store.test.ts
+++ b/packages/coding-agent/test/models-store.test.ts
@@ -1,4 +1,4 @@
-import { existsSync, mkdirSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import { chmodSync, existsSync, mkdirSync, readFileSync, rmSync, statSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import type { Model } from "@earendil-works/pi-ai";
@@ -53,6 +53,17 @@ describe("FileModelsStore", () => {
 		expect((await reloaded.read("two"))?.models.map((entry) => entry.id)).toEqual(["m2"]);
 	});
 
+	it.skipIf(process.platform === "win32")("preserves the mode of an existing models file", async () => {
+		const managedModelsPath = join(sharedTempDir, "managed-mode.json");
+		writeFileSync(managedModelsPath, "{}");
+		chmodSync(managedModelsPath, 0o660);
+		const store = new FileModelsStore(managedModelsPath);
+
+		await store.write("one", { models: [model("one", "m1")], checkedAt: 100 });
+
+		expect(statSync(managedModelsPath).mode & 0o777).toBe(0o660);
+	});
+
 	it("coalesces file reloads across concurrent readers and interleaved storage instances", async () => {
 		writeFileSync(
 			sharedModelsPath,