diff --git a/test/helpers/hermetic-env.test.ts b/test/helpers/hermetic-env.test.ts
index 74901ff83..6d18f7faf 100644
--- a/test/helpers/hermetic-env.test.ts
+++ b/test/helpers/hermetic-env.test.ts
@@ -3,7 +3,8 @@
  *
  * Pins three contracts:
  * 1. Allowlist semantics: contamination vars dropped, basics/auth/network
- *    kept, overrides merge last, EVALS_HERMETIC=0 is byte-identical legacy.
+ *    kept, overrides merge last, EVALS_HERMETIC=0 is the legacy env plus the
+ *    DISABLE_AUTOUPDATER pin.
  * 2. Seed-config shape: 20-char key suffix, trusted dirs, undefined-key safe.
  * 3. Dir lifecycle: /.claude suffix (extractPlanFilePath contract —
  *    claude-pty-runner.ts:191), sync singleton reuse, pid-aware GC.
@@ -167,7 +168,7 @@ describe('buildHermeticEnv allowlist', () => {
 });
 
 describe('EVALS_HERMETIC=0 escape hatch', () => {
-  test('returns byte-identical legacy env, overrides still last', () => {
+  test('returns the legacy env plus the updater pin, overrides still last', () => {
     const base = { ...CONTAMINATED, EVALS_HERMETIC: '0' } as NodeJS.ProcessEnv;
     const e = buildHermeticEnv(base, HERMETIC_VARS, { GSTACK_HEADLESS: '1' });
     // Legacy spread: every base var survives, hermeticVars NOT applied.
@@ -175,7 +176,7 @@ describe('EVALS_HERMETIC=0 escape hatch', () => {
     expect(e.CLAUDE_CONFIG_DIR).toBe('/Users/op/.claude');
     expect(e.GSTACK_HOME).toBe('/Users/op/.gstack');
     expect(e.GSTACK_HEADLESS).toBe('1');
-    expect(e).toEqual({ ...(base as Record<string, string>), GSTACK_HEADLESS: '1' });
+    expect(e).toEqual({ ...(base as Record<string, string>), DISABLE_AUTOUPDATER: '1', GSTACK_HEADLESS: '1' });
   });
 
   test('isHermeticEnabled reads at call time (ESM-hoist safety)', () => {
diff --git a/test/helpers/hermetic-env.ts b/test/helpers/hermetic-env.ts
index 2867fb1e7..cb6c8c1c2 100644
--- a/test/helpers/hermetic-env.ts
+++ b/test/helpers/hermetic-env.ts
@@ -21,11 +21,15 @@
  *   └─────────────────────────────┘
  *      + per-runner extraAllow (codex: OpenAI vars; gemini: Google vars)
  *      + CLAUDE_CONFIG_DIR=<runRoot>/.claude  GSTACK_HOME=<runRoot>/gstack-home
+ *      + DISABLE_AUTOUPDATER=1 (pinned in both branches; the scrub drops the
+ *        workflow's copy and every PTY screen otherwise shows the updater's
+ *        "no write permission to npm prefix" failure)
  *      + per-test overrides spread LAST
  *
  * Escape hatch: EVALS_HERMETIC=0 restores the legacy contaminated env
- * byte-identically (runners must also gate --strict-mcp-config on
- * isHermeticEnabled() so the escape hatch restores args too).
+ * plus only the DISABLE_AUTOUPDATER pin (runners must also gate
+ * --strict-mcp-config on isHermeticEnabled() so the escape hatch restores
+ * args too).
  *
  * isHermeticEnabled() is evaluated at CALL time, never at module load —
  * ESM hoists imports above any in-file `process.env.EVALS_HERMETIC = '0'`
@@ -100,9 +104,10 @@ export function buildHermeticEnv(
   opts?: HermeticEnvOpts,
 ): Record<string, string> {
   if (!isHermeticEnabled(base)) {
-    // Escape hatch: byte-identical to the legacy spread.
+    // Escape hatch: the legacy spread plus the updater pin.
     const legacy: Record<string, string> = {};
     for (const [k, v] of Object.entries(base)) if (v !== undefined) legacy[k] = v;
+    legacy.DISABLE_AUTOUPDATER = '1';
     for (const [k, v] of Object.entries(overrides ?? {})) if (v !== undefined) legacy[k] = v;
     return legacy;
   }
@@ -127,6 +132,7 @@ export function buildHermeticEnv(
     if (allowed) out[k] = v;
   }
   if (!out.TERM) out.TERM = 'xterm-256color';
+  out.DISABLE_AUTOUPDATER = '1';
   Object.assign(out, hermeticVars);
   for (const [k, v] of Object.entries(overrides ?? {})) if (v !== undefined) out[k] = v;
   return out;
diff --git a/test/hermetic-wiring.test.ts b/test/hermetic-wiring.test.ts
index 78fa96679..f47fa738a 100644
--- a/test/hermetic-wiring.test.ts
+++ b/test/hermetic-wiring.test.ts
@@ -17,7 +17,7 @@ import { describe, test, expect } from 'bun:test';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as os from 'os';
-import { getHermeticDirs, hermeticSkillsConfigDir } from './helpers/hermetic-env';
+import { buildHermeticEnv, getHermeticDirs, hermeticSkillsConfigDir } from './helpers/hermetic-env';
 
 const ROOT = path.resolve(import.meta.path, '..', '..');
 
@@ -87,6 +87,17 @@ describe('hermetic wiring tripwire', () => {
     }
   });
 
+  test('both EVALS_HERMETIC branches pin DISABLE_AUTOUPDATER=1 over the workflow env', () => {
+    // The allowlist scrubs the workflow's own copy; without this pin every PTY
+    // screen carries "Auto-update failed: no write permission to npm prefix".
+    for (const EVALS_HERMETIC of ['1', '0']) {
+      const base = { PATH: '/usr/bin', EVALS_HERMETIC, DISABLE_AUTOUPDATER: '0' };
+      expect(buildHermeticEnv(base, {}).DISABLE_AUTOUPDATER, `EVALS_HERMETIC=${EVALS_HERMETIC}`).toBe('1');
+      expect(buildHermeticEnv(base, {}, { DISABLE_AUTOUPDATER: '0' }).DISABLE_AUTOUPDATER, 'per-test override stays last').toBe('0');
+    }
+    expect(read('test/helpers/hermetic-env.ts')).toContain('DISABLE_AUTOUPDATER=1 (pinned in both branches');
+  });
+
   test('claude runners gate --strict-mcp-config on isHermeticEnabled()', () => {
     // Zero MCP servers for hermetic children; EVALS_HERMETIC=0 must restore
     // operator MCP along with the operator env (the flag may not be
diff --git a/test/test-free-shards.test.ts b/test/test-free-shards.test.ts
index e15c37de5..57a01dd6b 100644
--- a/test/test-free-shards.test.ts
+++ b/test/test-free-shards.test.ts
@@ -1,4 +1,4 @@
-import { describe, test, expect } from 'bun:test';
+import { describe, test, expect, spyOn } from 'bun:test';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as os from 'os';
@@ -1284,16 +1284,23 @@ describe('test-free-shards: duration-aware packing (full-suite LPT)', () => {
     fs.writeFileSync(seedPath, '{ definitely not json');
     const prev = process.env.GSTACK_FREE_TEST_DURATIONS;
     process.env.GSTACK_FREE_TEST_DURATIONS = seedPath;
+    // The corrupt seed's warning is the expected output; keep it off the console.
+    const warn = spyOn(console, 'error').mockImplementation(() => {});
     try {
       expect(loadFreeTestDurations()).toBeNull();
+      expect(warn.mock.calls.map(call => String(call[0]))).toEqual([
+        expect.stringContaining(`[test:free] WARNING: corrupt durations seed ${seedPath}`),
+      ]);
       // Missing file: silent null (fresh checkouts are normal).
       process.env.GSTACK_FREE_TEST_DURATIONS = path.join(dir, 'missing.json');
       expect(loadFreeTestDurations()).toBeNull();
+      expect(warn).toHaveBeenCalledTimes(1);
       // Valid seed round-trips, non-numeric entries dropped.
       fs.writeFileSync(seedPath, JSON.stringify({ version: 1, durations: { 'test/a.test.ts': 42, bad: 'nope' } }));
       process.env.GSTACK_FREE_TEST_DURATIONS = seedPath;
       expect(loadFreeTestDurations()).toEqual({ 'test/a.test.ts': 42 });
     } finally {
+      warn.mockRestore();
       if (prev === undefined) delete process.env.GSTACK_FREE_TEST_DURATIONS;
       else process.env.GSTACK_FREE_TEST_DURATIONS = prev;
       fs.rmSync(dir, { recursive: true, force: true });