security: fix 5 findings from issue #42 — env leak, ant gate, depth DoS, URL parse, CA cert

Finding 1 [CRITICAL] — sessionRunner leaks full process.env to child
Extract buildChildEnv() with an explicit allowlist of safe OS/runtime vars.
Child process no longer inherits ANTHROPIC_API_KEY, OPENAI_API_KEY, DB
credentials, or any other secret present in the parent shell environment.
Only CLAUDE_CODE_* bridge vars, PATH, HOME, and standard OS env are passed.

Finding 2 [HIGH] — USER_TYPE=ant activatable by external users
Add isAntEmployee() -> false constant in src/utils/buildConfig.ts.
Replace all three direct process.env.USER_TYPE === 'ant' checks in
setup.ts and onChangeAppState.ts so no external user can activate
Anthropic-internal code paths (commit attribution, system prompt clearing,
dangerously-skip-permissions bypass) by setting USER_TYPE in their shell.

Finding 3 [HIGH] — memoryScan.ts unlimited directory walk
Add MAX_DEPTH=3 guard on readdir({ recursive: true }) results.
Deep or symlink-looped memory directories no longer cause an unbounded
blocking walk before the MAX_MEMORY_FILES cap takes effect.

Finding 5 [HIGH] — buildSdkUrl uses string.includes for protocol detection
Replace apiBaseUrl.includes('localhost') with new URL(apiBaseUrl).hostname
comparison so a remote URL containing 'localhost' in its path no longer
incorrectly gets ws:// (unencrypted) instead of wss://.

Finding 6 [HIGH] — upstream proxy writes unvalidated CA cert to disk
Add isValidPemContent() validation before writeFile in the CA cert download
path. A compromised proxy sending non-PEM data (HTML, JSON, scripts) is now
rejected before it can be appended to the system CA bundle.

Each fix is covered by new unit tests (25 tests across 5 new test files).
All 52 tests pass. Build verified clean on v0.1.7.

Fixes #42

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

src/bridge/workSecret.ts

@@ -39,8 +39,8 @@ export function decodeWorkSecret(secret: string): WorkSecret {
  * and /v1/ for production (Envoy rewrites /v1/ → /v2/).
  */
 export function buildSdkUrl(apiBaseUrl: string, sessionId: string): string {
-  const isLocalhost =
-    apiBaseUrl.includes('localhost') || apiBaseUrl.includes('127.0.0.1')
+  const hostname = new URL(apiBaseUrl).hostname
+  const isLocalhost = hostname === 'localhost' || hostname === '127.0.0.1'
   const protocol = isLocalhost ? 'ws' : 'wss'
   const version = isLocalhost ? 'v2' : 'v1'
   const host = apiBaseUrl.replace(/^https?:\/\//, '').replace(/\/+$/, '')