[keyman] phase 2: guard the directories nothing creates

encrypt read ~/.ssh and the tmp directory, and decrypt read <vault>/keys,
with no existsSync between them. main.ts created vaultRoot and tmpDir but
never keysDir, so decrypt on a fresh vault threw ENOENT instead of
printing the "no encrypted keys" message it already had — the message was
unreachable until something else created the directory.

Both functions now fall through to their warning. main.ts creates all
three directories, 0700: the vault holds the age identity and tmp holds
plaintext private keys.

age spawns go through runTool, which separates "not installed" (ENOENT,
whose message is `spawn age ENOENT`) from "age refused" (whose reason is
on stderr and nowhere in the thrown message). Tested against real
processes, not a mocked execa — the shape of the failure is the point.

list.ts kept statSync rather than switching to withFileTypes as planned:
withFileTypes reports a symlinked key directory as a link and would have
silently dropped it. `throwIfNoEntry: false` fixes the dangling-symlink
throw and keeps following the good ones. Both cases now have a test.

Also deletes the three debug logs (encrypt.ts printed both key arrays,
decrypt.ts printed every candidate path from inside a filter).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

packages/keyman/tests/decrypt.test.ts

@@ -69,6 +69,23 @@ describe('decryptKeys', () => {
     expect(prompt).not.toHaveBeenCalled();
   });
 
+  it('warns instead of throwing when the vault has no keys directory', async () => {
+    fs.rmSync(keyDir, { recursive: true });
+
+    await expect(decryptKeys(sshDir, vaultDir, AGE_KEY)).resolves.toBeUndefined();
+    expect(messages(logSpy)).toContain('No encrypted keys found.');
+  });
+
+  it('reports a missing age binary rather than an ENOENT', async () => {
+    vaultKey('prod');
+    prompt.mockResolvedValue({ selectedKeys: ['prod'], decryptMode: LOCAL });
+    execa.mockRejectedValue(Object.assign(new Error('spawn age ENOENT'), { code: 'ENOENT' }));
+
+    await expect(decryptKeys(sshDir, vaultDir, AGE_KEY)).rejects.toThrow(
+      '`age` was not found on PATH'
+    );
+  });
+
   it('offers only directories that actually contain an encrypted key', async () => {
     vaultKey('prod');
     fs.mkdirSync(path.join(keyDir, 'empty'), { recursive: true });