feat(ext/sw): GitHost.writeFileCreateOnly() refuses to overwrite

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

extension/src/service-worker/__tests__/git-host-extensions.test.ts

@@ -59,3 +59,53 @@ describe('lastCommit (GitHub)', () => {
     expect(await host.lastCommit('manifest.enc')).toBeNull();
   });
 });
+
+describe('writeFileCreateOnly (Gitea)', () => {
+  let fetchSpy: ReturnType<typeof vi.spyOn>;
+  beforeEach(() => { fetchSpy = vi.spyOn(globalThis, 'fetch'); });
+
+  it('creates when file does not exist', async () => {
+    fetchSpy
+      .mockResolvedValueOnce(new Response('', { status: 404 }))     // pre-check
+      .mockResolvedValueOnce(new Response('{}', { status: 201 })); // POST
+    const host = new GiteaHost('https://git.example.com', 'user/vault', 'tok');
+    await host.writeFileCreateOnly('manifest.enc', new Uint8Array([1, 2, 3]), 'init');
+    expect(fetchSpy).toHaveBeenCalledTimes(2);
+    expect((fetchSpy.mock.calls[1][1] as RequestInit).method).toBe('POST');
+  });
+
+  it('throws when file already exists', async () => {
+    fetchSpy.mockResolvedValueOnce(new Response(
+      JSON.stringify({ sha: 'abc' }), { status: 200 },
+    ));
+    const host = new GiteaHost('https://git.example.com', 'user/vault', 'tok');
+    await expect(
+      host.writeFileCreateOnly('manifest.enc', new Uint8Array([1]), 'init'),
+    ).rejects.toThrow(/already exists/);
+    expect(fetchSpy).toHaveBeenCalledTimes(1);  // pre-check only, no write
+  });
+});
+
+describe('writeFileCreateOnly (GitHub)', () => {
+  let fetchSpy: ReturnType<typeof vi.spyOn>;
+  beforeEach(() => { fetchSpy = vi.spyOn(globalThis, 'fetch'); });
+
+  it('throws when file already exists', async () => {
+    fetchSpy.mockResolvedValueOnce(new Response(
+      JSON.stringify({ sha: 'abc' }), { status: 200 },
+    ));
+    const host = new GitHubHost('user/vault', 'tok');
+    await expect(
+      host.writeFileCreateOnly('manifest.enc', new Uint8Array([1]), 'init'),
+    ).rejects.toThrow(/already exists/);
+  });
+
+  it('creates when file does not exist', async () => {
+    fetchSpy
+      .mockResolvedValueOnce(new Response('', { status: 404 }))
+      .mockResolvedValueOnce(new Response('{}', { status: 201 }));
+    const host = new GitHubHost('user/vault', 'tok');
+    await host.writeFileCreateOnly('manifest.enc', new Uint8Array([1]), 'init');
+    expect(fetchSpy).toHaveBeenCalledTimes(2);
+  });
+});

extension/src/service-worker/git-host.ts

@@ -11,6 +11,11 @@ export interface GitHost {
   /// Create or update a file in the repo with a commit message.
   writeFile(path: string, content: Uint8Array, message: string): Promise<void>;
 
+  /// Like writeFile, but throws if the file already exists. Used by setup
+  /// wizard to refuse to clobber existing vault state. Implementation must
+  /// pre-check existence and only POST/PUT-create — never include a sha.
+  writeFileCreateOnly(path: string, content: Uint8Array, message: string): Promise<void>;
+
   /// Delete a file from the repo with a commit message.
   deleteFile(path: string, message: string): Promise<void>;
 

extension/src/service-worker/gitea.ts

@@ -82,6 +82,23 @@ export class GiteaHost implements GitHost {
     }
   }
 
+  async writeFileCreateOnly(path: string, content: Uint8Array, message: string): Promise<void> {
+    const existing = await fetch(`${this.baseUrl}/${path}`, { headers: this.headers });
+    if (existing.ok) {
+      throw new Error(`writeFileCreateOnly: ${path} already exists`);
+    }
+    const b64 = uint8ArrayToBase64(content);
+    const resp = await fetch(`${this.baseUrl}/${path}`, {
+      method: 'POST',
+      headers: this.headers,
+      body: JSON.stringify({ content: b64, message }),
+    });
+    if (!resp.ok) {
+      const text = await resp.text();
+      throw new Error(`Gitea writeFileCreateOnly ${path}: ${resp.status} ${text}`);
+    }
+  }
+
   async deleteFile(path: string, message: string): Promise<void> {
     // Need the current SHA to delete.
     const existing = await fetch(`${this.baseUrl}/${path}`, {

extension/src/service-worker/github.ts

@@ -76,6 +76,23 @@ export class GitHubHost implements GitHost {
     }
   }
 
+  async writeFileCreateOnly(path: string, content: Uint8Array, message: string): Promise<void> {
+    const existing = await fetch(`${this.baseUrl}/${path}`, { headers: this.headers });
+    if (existing.ok) {
+      throw new Error(`writeFileCreateOnly: ${path} already exists`);
+    }
+    const b64 = uint8ArrayToBase64(content);
+    const resp = await fetch(`${this.baseUrl}/${path}`, {
+      method: 'PUT',
+      headers: this.headers,
+      body: JSON.stringify({ content: b64, message }),  // no sha → create-only
+    });
+    if (!resp.ok) {
+      const text = await resp.text();
+      throw new Error(`GitHub writeFileCreateOnly ${path}: ${resp.status} ${text}`);
+    }
+  }
+
   async deleteFile(path: string, message: string): Promise<void> {
     const existing = await fetch(`${this.baseUrl}/${path}`, {
       headers: this.headers,