[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/main.test.ts

@@ -106,6 +106,17 @@ describe('keyman', () => {
     expect(output()).toContain(paths.keyPath);
     expect(fs.existsSync(paths.vaultRoot)).toBe(true);
     expect(fs.existsSync(paths.tmpDir)).toBe(true);
+    // keysDir too: decrypt reads it, and nothing created it before the first
+    // encrypt, so a fresh vault could not be decrypted from.
+    expect(fs.existsSync(paths.keysDir)).toBe(true);
+  });
+
+  it('creates the vault directories private to the owner', async () => {
+    await keyman();
+
+    for (const dir of [paths.vaultRoot, paths.keysDir, paths.tmpDir]) {
+      expect(fs.statSync(dir).mode & 0o777, dir).toBe(0o700);
+    }
   });
 
   it('quits without running any operation', async () => {