[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/utils.test.ts

@@ -9,7 +9,7 @@ import fs from 'node:fs';
 import os from 'node:os';
 import path from 'node:path';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
-import { extractAgePublicKey } from '../src/keyman.utils.js';
+import { extractAgePublicKey, runTool } from '../src/keyman.utils.js';
 
 describe('extractAgePublicKey', () => {
   let tmpDir: string;
@@ -77,3 +77,42 @@ describe('extractAgePublicKey', () => {
     expect(errorSpy.mock.calls[0][0]).toContain('Failed to read key file');
   });
 });
+
+/**
+ * These spawn real processes rather than mocking execa. The whole point of
+ * runTool is the shape of an execa failure, and a mock would only assert what
+ * this test already assumes.
+ */
+describe('runTool', () => {
+  it('returns the result on success', async () => {
+    const result = await runTool('node', ['-e', 'process.stdout.write("hi")']);
+
+    expect(result.stdout).toBe('hi');
+  });
+
+  it('passes options through', async () => {
+    const result = await runTool('node', ['-e', 'process.stdout.write(process.env.PROBE ?? "")'], {
+      env: { PROBE: 'from-options' },
+    });
+
+    expect(result.stdout).toBe('from-options');
+  });
+
+  it('reports a missing binary as an instruction rather than an ENOENT', async () => {
+    await expect(runTool('keyman-no-such-binary', [])).rejects.toThrow(
+      '`keyman-no-such-binary` was not found on PATH. Install it and try again.'
+    );
+  });
+
+  it('surfaces what the binary wrote to stderr', async () => {
+    await expect(
+      runTool('node', ['-e', 'process.stderr.write("no recipient\\n"); process.exit(1)'])
+    ).rejects.toThrow('`node` failed: no recipient');
+  });
+
+  it('falls back to the command summary when stderr is empty', async () => {
+    await expect(runTool('node', ['-e', 'process.exit(3)'])).rejects.toThrow(
+      /`node` failed: .*exit code 3/
+    );
+  });
+});