diff --git a/browse/test/windows-spawn-hide.test.ts b/browse/test/windows-spawn-hide.test.ts
index 512279446..10d538aae 100644
--- a/browse/test/windows-spawn-hide.test.ts
+++ b/browse/test/windows-spawn-hide.test.ts
@@ -70,6 +70,7 @@ describe('windowsHide on Windows-reachable spawns (#1835)', () => {
     const EXEMPT: Array<{ file: string; needle: string; reason: string }> = [
       {
         file: 'domain-skill-commands.ts',
+        // tripwire-exempt: grep NEEDLE string for this census, not a call
         needle: 'spawnSync(editor',
         reason: "interactive $EDITOR with stdio:'inherit' — windowsHide would detach a console editor into an invisible console",
       },
diff --git a/test/gbrain-exec-invariant.test.ts b/test/gbrain-exec-invariant.test.ts
index a0d962b4a..ae747b65f 100644
--- a/test/gbrain-exec-invariant.test.ts
+++ b/test/gbrain-exec-invariant.test.ts
@@ -35,9 +35,11 @@ const GUARDED_FILES = [
 // Patterns that would bypass lib/gbrain-exec.ts. Match the literal `"gbrain"`
 // as the first argument since these helpers are the failure mode.
 const BANNED_PATTERNS: Array<{ name: string; regex: RegExp }> = [
+  // tripwire-exempt: grep-needle STRING for this invariant, not a process spawn
   { name: 'spawnSync("gbrain", ...)', regex: /spawnSync\s*\(\s*["']gbrain["']/g },
   { name: 'spawn("gbrain", ...)', regex: /\bspawn\s*\(\s*["']gbrain["']/g },
   { name: 'execFileSync("gbrain", ...)', regex: /execFileSync\s*\(\s*["']gbrain["']/g },
+  // tripwire-exempt: grep-needle STRING for this invariant, not a process spawn
   { name: 'execSync("...gbrain...")', regex: /execSync\s*\(\s*["'`][^"'`]*\bgbrain\b/g },
 ];
 
diff --git a/test/skill-e2e-triage.test.ts b/test/skill-e2e-triage.test.ts
index e971c5e23..89f75db18 100644
--- a/test/skill-e2e-triage.test.ts
+++ b/test/skill-e2e-triage.test.ts
@@ -101,6 +101,7 @@ const path = require('path');
 let failures = 0;
 for (const f of ['math.test.js', 'string.test.js']) {
   try {
+    // tripwire-exempt: line below is CONTENT of the generated run.js fixture (child-executed), not a test-process call
     execSync('node ' + path.join(__dirname, f), { stdio: 'inherit' });
   } catch (e) {
     failures++;
diff --git a/test/spawnsync-timeout-tripwire.test.ts b/test/spawnsync-timeout-tripwire.test.ts
new file mode 100644
index 000000000..acde0099d
--- /dev/null
+++ b/test/spawnsync-timeout-tripwire.test.ts
@@ -0,0 +1,132 @@
+/**
+ * Synchronous-spawn timeout tripwire — the enforcement for the shard-wedge
+ * class that reached main.
+ *
+ * Mechanism: spawnSync / execSync / Bun.spawnSync BLOCK the main thread, so
+ * bun's in-process per-test timeout can never fire while one waits. A child
+ * that hangs (stdin read, network probe, dead daemon) wedges the whole shard
+ * until the runner's external wall-clock SIGKILL — observed live on main:
+ * test/gstack-memory-ingest.test.ts (normally 2.3s) held shard 2 at the
+ * 360s wall on free-tests run 33262077256 while its five siblings finished
+ * in ~65s. The 2026-08 sweep added a `timeout` to ~400 call sites across
+ * ~130 test files; this tripwire keeps the class extinct.
+ *
+ * Rule: every sync-spawn call site in the test trees must carry a `timeout`
+ * within its options window (WINDOW_LINES below), or the line above / the
+ * call line must carry an explicit exemption marker with a reason:
+ *
+ *   // tripwire-exempt: <why this call may legitimately block unbounded>
+ *
+ * Exemptions are counted and ratcheted (EXEMPT_CEILING can only go down).
+ */
+import { describe, expect, test } from 'bun:test';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+
+const ROOT = path.resolve(import.meta.dir, '..');
+
+// Mirrors the free runner's TEST_ROOTS plus test/helpers (helpers spawn on
+// behalf of tests and wedge shards just the same).
+const SCAN_ROOTS = [
+  'test',
+  'browse/test',
+  'design/test',
+  'make-pdf/test',
+  'ios-qa/daemon/test',
+  'ios-qa/scripts',
+  'browser-skills',
+];
+
+const SYNC_SPAWN = /\b(?:spawnSync|execSync|Bun\.spawnSync)\s*\(/;
+/** Generous on purpose: multi-line arg arrays push the options object far
+ *  below the call line (observed: +13 lines in codex-model-probe). A wide
+ *  window trades a sliver of false-negative risk for zero rename churn. */
+const WINDOW_LINES = 30;
+const EXEMPT_MARKER = /tripwire-exempt:/;
+/** Comment lines legitimately NAME the calls (doc headers, grep-needle
+ *  tables in sibling tripwires) without being call sites. */
+const COMMENT_LINE = /^\s*(?:\/\/|\*|\/\*)/;
+
+/** Shrink-only: lower it when exemptions burn down; never raise it. */
+const EXEMPT_CEILING = 6;
+
+const SELF = path.join('test', 'spawnsync-timeout-tripwire.test.ts');
+
+function walk(dir: string, out: string[] = []): string[] {
+  for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+    const full = path.join(dir, entry.name);
+    if (entry.isDirectory()) walk(full, out);
+    else if (/\.(?:[cm]?[jt]s|tsx)$/.test(entry.name)) out.push(full);
+  }
+  return out;
+}
+
+interface Violation { file: string; line: number; text: string }
+
+function scan(): { violations: Violation[]; exempt: Violation[] } {
+  const violations: Violation[] = [];
+  const exempt: Violation[] = [];
+  for (const root of SCAN_ROOTS) {
+    const abs = path.join(ROOT, root);
+    if (!fs.existsSync(abs)) continue;
+    for (const file of walk(abs)) {
+      const rel = path.relative(ROOT, file);
+      if (rel === SELF) continue;
+      const lines = fs.readFileSync(file, 'utf-8').split('\n');
+      for (let i = 0; i < lines.length; i += 1) {
+        if (!SYNC_SPAWN.test(lines[i])) continue;
+        if (COMMENT_LINE.test(lines[i])) continue;
+        const record = { file: rel, line: i + 1, text: lines[i].trim().slice(0, 120) };
+        if (EXEMPT_MARKER.test(lines[i]) || (i > 0 && EXEMPT_MARKER.test(lines[i - 1]))) {
+          exempt.push(record);
+          continue;
+        }
+        const window = lines.slice(i, i + WINDOW_LINES).join('\n');
+        if (!/\btimeout\b/.test(window)) violations.push(record);
+      }
+    }
+  }
+  return { violations, exempt };
+}
+
+describe('sync-spawn timeout tripwire', () => {
+  const { violations, exempt } = scan();
+
+  test('every sync spawn in the test trees carries a timeout (or a reasoned exemption)', () => {
+    const detail = violations
+      .map((v) => `  ${v.file}:${v.line}  ${v.text}`)
+      .join('\n');
+    expect(
+      violations,
+      `sync-spawn call site(s) without a timeout — each one can wedge a whole shard to its wall-clock kill (bun's per-test timeout cannot interrupt a blocking spawn):\n${detail}\n`
+      + 'Fix: add `timeout: 30_000` (120_000 for genuinely slow ops) to the options, or fix the wrapping helper once. '
+      + 'A call that must legitimately block unbounded gets `// tripwire-exempt: <reason>` on or above the line.',
+    ).toEqual([]);
+  });
+
+  test('exemptions only shrink', () => {
+    expect(
+      exempt.length,
+      `tripwire-exempt count ${exempt.length} exceeds the ceiling ${EXEMPT_CEILING}. `
+      + 'New unbounded sync spawns are not allowed — add a timeout instead. If an exemption was '
+      + `removed, lower EXEMPT_CEILING in ${SELF} in the same commit:\n`
+      + exempt.map((v) => `  ${v.file}:${v.line}`).join('\n'),
+    ).toBeLessThanOrEqual(EXEMPT_CEILING);
+  });
+
+  test('scan sanity: the pattern still matches real code (must not rot to vacuous green)', () => {
+    // The test trees legitimately contain hundreds of sync spawns WITH
+    // timeouts; if the scanner suddenly sees none at all, the regex or the
+    // roots rotted and the tripwire is scanning nothing.
+    let total = 0;
+    for (const root of SCAN_ROOTS) {
+      const abs = path.join(ROOT, root);
+      if (!fs.existsSync(abs)) continue;
+      for (const file of walk(abs)) {
+        const src = fs.readFileSync(file, 'utf-8');
+        for (const line of src.split('\n')) if (SYNC_SPAWN.test(line)) total += 1;
+      }
+    }
+    expect(total).toBeGreaterThan(100);
+  });
+});
diff --git a/test/test-free-shards.test.ts b/test/test-free-shards.test.ts
index 0e7daa157..c807c9b0e 100644
--- a/test/test-free-shards.test.ts
+++ b/test/test-free-shards.test.ts
@@ -83,6 +83,7 @@ describe('test-free-shards: Windows curation', () => {
   });
 
   test('detects spawn("sh", ...)', () => {
+    // tripwire-exempt: string fixture fed to detectWindowsFragility, not a call
     withTempFile(`spawnSync('sh', ['-c', 'command -v claude']);`, (f) => {
       expect(detectWindowsFragility(f)?.reason).toBe('spawn("sh", ...)');
     });
@@ -95,6 +96,7 @@ describe('test-free-shards: Windows curation', () => {
   });
 
   test('detects which claude shell command', () => {
+    // tripwire-exempt: string fixture fed to detectWindowsFragility, not a call
     withTempFile(`execSync('which claude').trim();`, (f) => {
       expect(detectWindowsFragility(f)?.reason).toBe('which claude (use Bun.which)');
     });