fix(mosaic): close dup-proxy race + verify listener identity (re-review #2, #790)

Addresses the three items from PR #793 re-review #2, all TDD red-first on this
branch:

F1 (BLOCKER, dup-proxy race) — ensureProxyRunning no longer falls back to nohup
after `systemctl start` is ACCEPTED. An accepted-but-not-yet-healthy systemd
unit may bind late or be restarted; spawning nohup then would create a second
proxy contending for :18765. Once systemd accepts the job we poll to the startup
deadline and, on a miss, report a managed-service startup failure. nohup is now
reachable only when systemd never accepted the job. New test: "does NOT fall back
to nohup after systemd accepts but never binds".

F2 (BLOCKER, CWE-345) — a 2xx on /healthz is liveness, not identity. Added
verifyListenerIdentity(): an OS-level check (via `ss` + /proc) that the process
owning :18765 is the current uid running the expected proxy executable, failing
CLOSED (`unknown`) when identity can't be established — needs no upstream
shared-secret/unix-socket support. ensureProxyRunning now gates EVERY trust point
on it: an already-present responder that fails identity returns `untrusted`
without starting anything; a started proxy is trusted only once it is both live
AND identity-verified. probeLiveness doc-comment updated to record the residual
CWE-345 risk and point at the identity check (multi-user warning deferred).

F3 (SHOULD-FIX) — parseAuthStatus no longer treats a signal-terminated check
(status null) with an auth-looking line as valid; a clean exit 0 is required.
Regression test: { status: null, stdout: 'Authenticated' } → unknown.

Gates green: typecheck, lint, format:check; full mosaic suite 1110 passing;
claudex-proxy.ts coverage 92.3% stmts/lines, 88.13% branch (>= 85%).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/mosaic/src/commands/claudex-proxy.spec.ts

@@ -21,11 +21,13 @@ import {
   systemdUnitPath,
   installSystemdUnit,
   startNohupProxy,
+  verifyListenerIdentity,
   runProxyPreflight,
   ensureProxyRunning,
   type AuthStatus,
   type ProxyRunResult,
   type SpawnedChild,
+  type ListenerIdentity,
 } from './claudex-proxy.js';
 
 /**
@@ -94,6 +96,14 @@ describe('parseAuthStatus', () => {
     expect(s.state).toBe('unknown');
   });
 
+  it('does NOT trust a signal-terminated check (status null) even with an auth-looking line', () => {
+    // status: null means the process was killed by a signal — an INCOMPLETE
+    // check. An auth-looking line that happened to be flushed must not be read
+    // as valid, or preflight passes on a check that never finished.
+    const s = parseAuthStatus({ status: null, stdout: 'Authenticated', stderr: '' });
+    expect(s.state).toBe('unknown');
+  });
+
   it('extracts a best-effort expiry in days when present', () => {
     const s = parseAuthStatus({
       status: 0,
@@ -521,15 +531,93 @@ describe('startNohupProxy (finding #1 — async spawn error must not crash)', ()
   });
 });
 
+describe('verifyListenerIdentity (finding #2 — OS-level listener identity, CWE-345)', () => {
+  const me: ListenerIdentity = {
+    pid: 4242,
+    uid: 1000,
+    exePath: '/home/me/.local/bin/claude-code-proxy',
+  };
+
+  it('accepts a listener owned by the current uid whose exe is the expected proxy path', () => {
+    const verdict = verifyListenerIdentity({
+      identify: () => me,
+      currentUid: () => 1000,
+      expectedExe: () => '/home/me/.local/bin/claude-code-proxy',
+    });
+    expect(verdict).toBe('ok');
+  });
+
+  it('accepts by basename when the expected path is unknown but the exe is claude-code-proxy', () => {
+    const verdict = verifyListenerIdentity({
+      identify: () => me,
+      currentUid: () => 1000,
+      expectedExe: () => null,
+    });
+    expect(verdict).toBe('ok');
+  });
+
+  it('rejects a listener owned by a DIFFERENT uid (foreign-user) — fail closed', () => {
+    const verdict = verifyListenerIdentity({
+      identify: () => ({ ...me, uid: 0 }),
+      currentUid: () => 1000,
+      expectedExe: () => '/home/me/.local/bin/claude-code-proxy',
+    });
+    expect(verdict).toBe('foreign-user');
+  });
+
+  it('rejects a same-user listener whose exe is NOT the proxy (wrong-exe)', () => {
+    const verdict = verifyListenerIdentity({
+      identify: () => ({ ...me, exePath: '/usr/bin/nc' }),
+      currentUid: () => 1000,
+      expectedExe: () => '/home/me/.local/bin/claude-code-proxy',
+    });
+    expect(verdict).toBe('wrong-exe');
+  });
+
+  it('returns unknown (fail closed) when the listener cannot be identified', () => {
+    const verdict = verifyListenerIdentity({
+      identify: () => null,
+      currentUid: () => 1000,
+      expectedExe: () => '/home/me/.local/bin/claude-code-proxy',
+    });
+    expect(verdict).toBe('unknown');
+  });
+
+  it('returns unknown when the current uid is unavailable (non-posix)', () => {
+    const verdict = verifyListenerIdentity({
+      identify: () => me,
+      currentUid: () => -1,
+      expectedExe: () => '/home/me/.local/bin/claude-code-proxy',
+    });
+    expect(verdict).toBe('unknown');
+  });
+
+  it('returns unknown when the listener exe path cannot be read', () => {
+    const verdict = verifyListenerIdentity({
+      identify: () => ({ ...me, exePath: null }),
+      currentUid: () => 1000,
+      expectedExe: () => '/home/me/.local/bin/claude-code-proxy',
+    });
+    expect(verdict).toBe('unknown');
+  });
+
+  it('runs with real defaults without throwing (identity may be unresolved → verdict)', () => {
+    const verdict = verifyListenerIdentity();
+    expect(['ok', 'foreign-user', 'wrong-exe', 'unknown']).toContain(verdict);
+  });
+});
+
 describe('ensureProxyRunning', () => {
   const ok: ProxyRunResult = { status: 0, stdout: '', stderr: '' };
   const nohupOk = async (): Promise<ProxyRunResult> => ok;
+  const trusted = () => 'ok' as const;
 
-  it('is a no-op when the proxy is already live', async () => {
+  it('is a no-op when the proxy is already live AND identity-verified', async () => {
     const startSystemd = vi.fn(() => ok);
     const startNohup = vi.fn(nohupOk);
     const r = await ensureProxyRunning({
       probe: async () => true,
+      verifyListener: trusted,
       startSystemd,
       startNohup,
       waitMs: async () => {},
@@ -540,10 +628,30 @@ describe('ensureProxyRunning', () => {
     expect(startNohup).not.toHaveBeenCalled();
   });
 
-  it('starts via systemd when available and then becomes live', async () => {
+  it('fails closed as untrusted when a responder holds :18765 but identity is NOT ours', async () => {
+    // A foreign process answers /healthz but the listener is not our proxy
+    // (foreign uid / wrong exe / unidentifiable). We must NOT trust it and must
+    // NOT start a second proxy (the port is already taken) — fail closed.
+    const startSystemd = vi.fn(() => ok);
+    const startNohup = vi.fn(nohupOk);
+    const r = await ensureProxyRunning({
+      probe: async () => true,
+      verifyListener: () => 'foreign-user',
+      startSystemd,
+      startNohup,
+      waitMs: async () => {},
+    });
+    expect(r.method).toBe('untrusted');
+    expect(r.live).toBe(false);
+    expect(startSystemd).not.toHaveBeenCalled();
+    expect(startNohup).not.toHaveBeenCalled();
+  });
+
+  it('starts via systemd when available and then becomes trusted-live', async () => {
     let calls = 0;
     const r = await ensureProxyRunning({
       probe: async () => calls++ > 0, // dead first, live after start
+      verifyListener: trusted,
       startSystemd: () => ok,
       startNohup: async () => {
         throw new Error('should not fall back');
@@ -554,7 +662,7 @@ describe('ensureProxyRunning', () => {
     expect(r.live).toBe(true);
   });
 
-  it('waits past a slow systemd bind before falling back (finding #2 — no duplicate proxy)', async () => {
+  it('waits past a slow systemd bind before giving up (finding #2 — no duplicate proxy)', async () => {
     // systemd `start` returns 0 (job accepted) but the socket only binds on the
     // 4th probe — still well within the startup deadline. nohup must NOT run,
     // or two proxies would contend for :18765.
@@ -562,6 +670,7 @@ describe('ensureProxyRunning', () => {
     const startNohup = vi.fn(nohupOk);
     const r = await ensureProxyRunning({
       probe: async () => probes++ >= 3,
+      verifyListener: trusted,
       startSystemd: () => ok,
       startNohup,
       waitMs: async () => {},
@@ -573,28 +682,54 @@ describe('ensureProxyRunning', () => {
     expect(startNohup).not.toHaveBeenCalled();
   });
 
-  it('falls back to nohup when systemd is accepted but never binds in the deadline', async () => {
+  it('does NOT fall back to nohup after systemd accepts but never binds (finding #1 — dup-proxy race)', async () => {
+    // systemctl start exit 0 means the job was ACCEPTED, not bound. If it binds
+    // just after our deadline (or systemd restarts it), a nohup fallback would
+    // create a SECOND proxy contending for :18765. Once systemd has accepted the
+    // job we never spawn nohup — we report a managed-service startup failure.
     const startNohup = vi.fn(nohupOk);
     const r = await ensureProxyRunning({
-      // Dead until nohup has actually run; systemd's whole poll window stays dead.
+      probe: async () => false, // never becomes live within the deadline
-      probe: async () => startNohup.mock.calls.length > 0,
+      verifyListener: trusted,
       startSystemd: () => ok,
       startNohup,
       waitMs: async () => {},
       settleMs: 10,
       startupDeadlineMs: 30,
     });
-    expect(startNohup).toHaveBeenCalledTimes(1);
+    expect(startNohup).not.toHaveBeenCalled();
-    expect(r.method).toBe('nohup');
+    expect(r.method).toBe('failed');
-    expect(r.live).toBe(true);
+    expect(r.live).toBe(false);
   });
 
-  it('falls back to nohup when systemd start fails outright', async () => {
+  it('does NOT trust a systemd-started responder whose identity cannot be verified', async () => {
+    // Dead at first (so we reach the systemd start), then the socket binds — but
+    // identity never verifies (e.g. a squatter beat systemd to the port). A live
+    // responder that fails identity must never be reported as a successful start.
+    let calls = 0;
+    const startNohup = vi.fn(nohupOk);
+    const r = await ensureProxyRunning({
+      probe: async () => calls++ > 0,
+      verifyListener: () => 'wrong-exe',
+      startSystemd: () => ok,
+      startNohup,
+      waitMs: async () => {},
+      settleMs: 10,
+      startupDeadlineMs: 30,
+    });
+    expect(startNohup).not.toHaveBeenCalled();
+    expect(r.method).toBe('failed');
+    expect(r.live).toBe(false);
+  });
+
+  it('falls back to nohup only when systemd start FAILS outright (not accepted)', async () => {
     let calls = 0;
     const r = await ensureProxyRunning({
       // A failed systemd start skips its post-start poll, so probes are:
-      // #0 initial (dead), #1 after nohup (live).
+      // #0 initial (dead), #1 after nohup (live). nohup fallback is reachable
+      // ONLY because systemd never accepted the job (status 1).
       probe: async () => calls++ > 0,
+      verifyListener: trusted,
       startSystemd: () => ({ status: 1, stdout: '', stderr: 'no systemd' }),
       startNohup: nohupOk,
       waitMs: async () => {},
@@ -605,9 +740,25 @@ describe('ensureProxyRunning', () => {
     expect(r.live).toBe(true);
   });
 
+  it('does NOT trust a nohup-started responder whose identity cannot be verified', async () => {
+    let calls = 0;
+    const r = await ensureProxyRunning({
+      probe: async () => calls++ > 0,
+      verifyListener: () => 'unknown',
+      startSystemd: () => ({ status: 1, stdout: '', stderr: 'no systemd' }),
+      startNohup: nohupOk,
+      waitMs: async () => {},
+      settleMs: 10,
+      startupDeadlineMs: 30,
+    });
+    expect(r.method).toBe('failed');
+    expect(r.live).toBe(false);
+  });
+
   it('reports failed when nothing brings the proxy up', async () => {
     const r = await ensureProxyRunning({
       probe: async () => false,
+      verifyListener: trusted,
       startSystemd: () => ({ status: 1, stdout: '', stderr: '' }),
       startNohup: async () => ({ status: 1, stdout: '', stderr: '' }),
       waitMs: async () => {},

packages/mosaic/src/commands/claudex-proxy.ts

@@ -17,9 +17,9 @@
  */
 
 import { execFileSync, spawn, spawnSync } from 'node:child_process';
-import { mkdirSync, writeFileSync } from 'node:fs';
+import { mkdirSync, readFileSync, readlinkSync, writeFileSync } from 'node:fs';
 import { homedir } from 'node:os';
-import { dirname, join } from 'node:path';
+import { basename, dirname, join } from 'node:path';
 
 // ─── Endpoint / command constants (spec table) ──────────────────────────────
 
@@ -126,7 +126,10 @@ export function parseAuthStatus(result: ProxyRunResult): AuthStatus {
     state = 'expired';
   } else if (unauth) {
     state = 'unauthenticated';
-  } else if (authed && (result.status === 0 || result.status === null)) {
+  } else if (authed && result.status === 0) {
+    // A `null` status means the check was killed by a signal — an INCOMPLETE
+    // run. We require a clean exit 0 for `valid`; a partially-flushed auth line
+    // from a signal-terminated check must never be trusted (finding #3).
     state = 'valid';
   } else if (result.status === 0) {
     state = 'valid';
@@ -181,16 +184,21 @@ export function runDeviceReauth(spawnImpl: InheritSpawn = defaultInheritSpawn):
  * Probe the proxy for liveness by hitting its dedicated `GET /healthz` endpoint
  * and requiring a 2xx response.
  *
- * This deliberately does NOT trust an arbitrary HTTP response on the port. The
+ * This is a LIVENESS check only — it answers "is a healthy proxy responding?",
- * proxy binds loopback with no client authentication, so on a shared host any
+ * not "is that responder actually ours?". Requiring a 2xx on the proxy's own
- * local process could occupy :18765; trusting "any response = alive" (as an
+ * `/healthz` contract (rather than "any HTTP response = alive") resolves spec
- * earlier revision did) would let such a squatter be mistaken for the proxy and
+ * gotcha #1: the root path returns non-2xx, but `/healthz` returns 2xx when
- * intercept Claude traffic (CWE-345). Requiring a 2xx on the proxy's own
+ * healthy, so a live proxy is never mistaken for dead and no duplicate proxy is
- * `/healthz` contract is the strongest identity signal available without an
+ * spawned.
- * upstream shared-secret/unix-socket handshake (which `claude-code-proxy` does
+ *
- * not provide). It also resolves spec gotcha #1: the root path returns non-2xx,
+ * Residual risk (CWE-345): the proxy binds loopback with NO client
- * but `/healthz` returns 2xx when healthy, so a live proxy is never mistaken for
+ * authentication, so on a shared host a local process could occupy :18765 and
- * dead and no duplicate is spawned.
+ * serve a 2xx here. A 2xx therefore does NOT by itself establish that the
+ * listener is our proxy. Identity is verified SEPARATELY and at every trust
+ * point by {@link verifyListenerIdentity} (OS-level uid + executable check),
+ * which fails closed when identity can't be established. See
+ * {@link ensureProxyRunning}. (Broader multi-user hardening — a persistent
+ * warning when a foreign listener is seen — is tracked for a later phase.)
  */
 export async function probeLiveness(
   url: string = CLAUDEX_HEALTH_URL,
@@ -222,6 +230,92 @@ export async function probeLiveness(
   }
 }
 
+// ─── Listener identity (OS-level, CWE-345 mitigation) ─────────────────────────
+
+/**
+ * The result of verifying who actually owns the :18765 listener.
+ *  - `ok`           — same-user process running the expected proxy binary.
+ *  - `foreign-user` — a process owned by a DIFFERENT uid holds the port.
+ *  - `wrong-exe`    — same-user, but the executable is not the proxy.
+ *  - `unknown`      — identity could not be established (fail closed).
+ */
+export type ListenerVerdict = 'ok' | 'foreign-user' | 'wrong-exe' | 'unknown';
+
+/** OS-level identity of the process bound to the proxy port. */
+export interface ListenerIdentity {
+  pid: number;
+  uid: number;
+  /** Absolute path of the process executable, or null if unreadable. */
+  exePath: string | null;
+}
+
+export interface VerifyListenerDeps {
+  /** Resolve the process bound to the proxy port (null → unidentifiable). */
+  identify?: () => ListenerIdentity | null;
+  /** The current process uid (-1 when unavailable, e.g. non-posix). */
+  currentUid?: () => number;
+  /** The expected proxy executable path (null when it can't be resolved). */
+  expectedExe?: () => string | null;
+}
+
+/**
+ * Identify the process listening on the proxy port via `ss` + `/proc`. Every
+ * failure path returns null so the caller fails closed. Reads no credential
+ * material — only pid/uid/exe path of the listener.
+ */
+function defaultIdentifyListener(port: number = CLAUDEX_PROXY_PORT): ListenerIdentity | null {
+  try {
+    const out = execFileSync('ss', ['-H', '-ltnp', `sport = :${port}`], { encoding: 'utf8' });
+    const pidMatch = /pid=(\d+)/.exec(out);
+    if (!pidMatch) return null;
+    const pid = Number(pidMatch[1]);
+    if (!Number.isInteger(pid) || pid <= 0) return null;
+
+    const status = readFileSync(`/proc/${pid}/status`, 'utf8');
+    const uidLine = /^Uid:\s*(\d+)/m.exec(status);
+    if (!uidLine) return null;
+    const uid = Number(uidLine[1]);
+
+    let exePath: string | null = null;
+    try {
+      exePath = readlinkSync(`/proc/${pid}/exe`);
+    } catch {
+      exePath = null;
+    }
+    return { pid, uid, exePath };
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Verify that the process owning :18765 is genuinely OUR proxy before trusting
+ * it. The proxy binds loopback with NO client authentication, so on a shared
+ * host any local process could squat the port and a liveness 2xx alone does not
+ * prove identity (CWE-345). We check the OS-level identity of the listener — it
+ * must be owned by the current uid and be the expected proxy executable — and
+ * FAIL CLOSED (`unknown`) whenever identity cannot be established. This needs no
+ * upstream shared-secret/unix-socket support from `claude-code-proxy`.
+ */
+export function verifyListenerIdentity(deps: VerifyListenerDeps = {}): ListenerVerdict {
+  const identify = deps.identify ?? (() => defaultIdentifyListener());
+  const currentUid =
+    deps.currentUid ?? (() => (typeof process.getuid === 'function' ? process.getuid() : -1));
+  const expectedExe = deps.expectedExe ?? (() => checkProxyBinary().path);
+
+  const id = identify();
+  if (!id) return 'unknown'; // can't see the listener → don't trust it
+  const uid = currentUid();
+  if (uid < 0) return 'unknown'; // can't establish our own identity → fail closed
+  if (id.uid !== uid) return 'foreign-user'; // someone else's process holds the port
+  if (!id.exePath) return 'unknown'; // can't confirm the executable → fail closed
+
+  const expected = expectedExe();
+  if (expected && id.exePath === expected) return 'ok';
+  if (basename(id.exePath) === CLAUDEX_PROXY_BINARY) return 'ok';
+  return 'wrong-exe';
+}
+
 // ─── systemd user unit ───────────────────────────────────────────────────────
 
 export function systemdUnitPath(home: string = homedir()): string {
@@ -383,7 +477,7 @@ export async function runProxyPreflight(deps: PreflightDeps = {}): Promise<Prefl
 
 // ─── Lifecycle: ensure the proxy is running ──────────────────────────────────
 
-export type ProxyStartMethod = 'already' | 'systemd' | 'nohup' | 'failed';
+export type ProxyStartMethod = 'already' | 'systemd' | 'nohup' | 'untrusted' | 'failed';
 
 export interface EnsureProxyResult {
   live: boolean;
@@ -458,6 +552,8 @@ export function startNohupProxy(deps: StartNohupDeps = {}): Promise<ProxyRunResu
 
 export interface EnsureProxyDeps {
   probe?: () => Promise<boolean>;
+  /** OS-level identity check for the process holding the proxy port. */
+  verifyListener?: () => ListenerVerdict;
   startSystemd?: () => ProxyRunResult;
   startNohup?: () => Promise<ProxyRunResult>;
   waitMs?: (ms: number) => Promise<void>;
@@ -476,12 +572,15 @@ function defaultStartSystemd(): ProxyRunResult {
 }
 
 /**
- * Poll liveness up to a bounded startup deadline. A start command returning 0
+ * Poll for a TRUSTED-live proxy up to a bounded startup deadline. A start command
- * only means the job was ACCEPTED, not that the socket is bound — so we keep
+ * returning 0 only means the job was ACCEPTED, not that the socket is bound — so
- * probing at `intervalMs` until either a probe succeeds or the deadline elapses.
+ * we keep probing at `intervalMs` until either the deadline elapses or the port
+ * both responds AND passes the OS-level identity check. Liveness alone is not
+ * enough: a responder that fails identity (a squatter) must never be trusted.
  */
-async function waitForLive(
+async function waitForTrusted(
   probe: () => Promise<boolean>,
+  verifyListener: () => ListenerVerdict,
   waitMs: (ms: number) => Promise<void>,
   intervalMs: number,
   deadlineMs: number,
@@ -490,7 +589,7 @@ async function waitForLive(
   while (elapsed < deadlineMs) {
     await waitMs(intervalMs);
     elapsed += intervalMs;
-    if (await probe()) {
+    if ((await probe()) && verifyListener() === 'ok') {
       return true;
     }
   }
@@ -501,16 +600,29 @@ async function waitForLive(
  * Ensure a proxy is listening. No-op when already live. Otherwise prefer the
  * systemd user unit, then fall back to a detached background process.
  *
- * After a start command is accepted we poll liveness to a bounded startup
+ * Every trust point is gated on OS-level listener identity, not just liveness:
- * deadline BEFORE considering the next method: `systemctl start` exit 0 means
+ * the proxy has no client authentication, so on a shared host a local process
- * the job was accepted, not that the socket bound within one probe interval. If
+ * could squat :18765 and a 2xx `/healthz` alone would not prove it is our proxy
- * we fell back on the first miss we could launch a second proxy that then
+ * (CWE-345, finding #2). We only trust a responder whose owning process is the
- * contends with the (slower) systemd one for :18765 — the very duplicate-proxy
+ * current uid running the expected proxy binary; otherwise we fail closed.
- * outcome this function exists to prevent. Liveness itself is the proxy-specific
+ *
- * `/healthz` check (see {@link probeLiveness}).
+ * If a responder is already present but its identity does NOT verify, we return
+ * `untrusted` WITHOUT starting anything — the port is taken, so spawning would
+ * only create contention, and we must never route Claude traffic through an
+ * unverified listener.
+ *
+ * After a start command is accepted we poll to a bounded startup deadline before
+ * giving up: `systemctl start` exit 0 means the job was accepted, not that the
+ * socket bound within one probe interval. Critically, once systemd ACCEPTS the
+ * job we do NOT fall back to nohup even if it never becomes trusted-live in the
+ * deadline (finding #1): the accepted unit may bind late or be restarted by
+ * systemd, and a second proxy would then contend for :18765 — the very
+ * duplicate-proxy outcome this function exists to prevent. nohup is reachable
+ * only when systemd never accepted the job at all.
  */
 export async function ensureProxyRunning(deps: EnsureProxyDeps = {}): Promise<EnsureProxyResult> {
   const probe = deps.probe ?? (() => probeLiveness());
+  const verifyListener = deps.verifyListener ?? (() => verifyListenerIdentity());
   const startSystemd = deps.startSystemd ?? defaultStartSystemd;
   const startNohup = deps.startNohup ?? (() => startNohupProxy());
   const waitMs = deps.waitMs ?? defaultWait;
@@ -518,19 +630,25 @@ export async function ensureProxyRunning(deps: EnsureProxyDeps = {}): Promise<En
   const startupDeadlineMs = deps.startupDeadlineMs ?? 5000;
 
   if (await probe()) {
-    return { live: true, method: 'already' };
+    // Something answers on :18765 — trust it ONLY if it is provably our proxy.
+    return verifyListener() === 'ok'
+      ? { live: true, method: 'already' }
+      : { live: false, method: 'untrusted' };
   }
 
   const systemd = startSystemd();
   if (systemd.status === 0) {
-    if (await waitForLive(probe, waitMs, settleMs, startupDeadlineMs)) {
+    // systemd accepted the job. Wait for a trusted-live bind, but never fall
+    // back to nohup afterward — that would risk a duplicate proxy (finding #1).
+    if (await waitForTrusted(probe, verifyListener, waitMs, settleMs, startupDeadlineMs)) {
       return { live: true, method: 'systemd' };
     }
+    return { live: false, method: 'failed' };
   }
 
   const nohup = await startNohup();
   if (nohup.status === 0) {
-    if (await waitForLive(probe, waitMs, settleMs, startupDeadlineMs)) {
+    if (await waitForTrusted(probe, verifyListener, waitMs, settleMs, startupDeadlineMs)) {
       return { live: true, method: 'nohup' };
     }
   }