diff --git a/test/adapters/claude-session-swap.test.ts b/test/adapters/claude-session-swap.test.ts
index 2768edb..bedf229 100644
--- a/test/adapters/claude-session-swap.test.ts
+++ b/test/adapters/claude-session-swap.test.ts
@@ -7,7 +7,7 @@
 // the command that caused it.
 import test from 'node:test'
 import assert from 'node:assert/strict'
-import { mkdtempSync, mkdirSync, readFileSync, statSync, writeFileSync } from 'node:fs'
+import { chmodSync, mkdirSync, mkdtempSync, readFileSync, statSync, writeFileSync } from 'node:fs'
 import { tmpdir } from 'node:os'
 import { join } from 'node:path'
 import { readRawCredential, swapCredential } from '../../src/adapters/claude-session/swap.ts'
@@ -169,20 +169,29 @@ test('a source with no login is refused, and nothing is written', async () => {
 })
 
 test('an unwritable target is refused, and says nothing changed', async () => {
+  // A read-only PARENT, so the target cannot be created inside it. Not
+  // `/proc/nonexistent/...`: that path throws ENOENT on macOS but makes
+  // `mkdirSync(recursive)` HANG on Linux, which wedged the whole suite in CI
+  // the first time this branch met a Linux runner.
   const from = fresh()
   const fake = fakeSecurity({ [keychainService(from, env)]: BLOB })
-  // A path whose parent cannot be created.
-  const result = swapCredential(from, '/proc/nonexistent/swisscode-target', {
-    env,
-    platform: 'darwin',
-    exec: fake.exec,
-  })
-  assert.equal(result.ok, false)
-  assert.equal(
-    fake.calls.filter((c) => c.args[0] === 'delete-generic-password').length,
-    0,
-    'a failed write must never drop the target\'s existing login',
-  )
+  const parent = fresh()
+  chmodSync(parent, 0o500)
+  try {
+    const result = swapCredential(from, join(parent, 'target'), {
+      env,
+      platform: 'darwin',
+      exec: fake.exec,
+    })
+    assert.equal(result.ok, false)
+    assert.equal(
+      fake.calls.filter((c) => c.args[0] === 'delete-generic-password').length,
+      0,
+      "a failed write must never drop the target's existing login",
+    )
+  } finally {
+    chmodSync(parent, 0o700)
+  }
 })
 
 test('the identity block is COPIED, or the swap is only half done', async () => {
diff --git a/test/adapters/fs-usage-store.test.ts b/test/adapters/fs-usage-store.test.ts
index 8cee4e8..220ff52 100644
--- a/test/adapters/fs-usage-store.test.ts
+++ b/test/adapters/fs-usage-store.test.ts
@@ -5,7 +5,7 @@
 // fail the command that triggered it.
 import test from 'node:test'
 import assert from 'node:assert/strict'
-import { mkdtempSync, readFileSync, statSync, writeFileSync } from 'node:fs'
+import { chmodSync, mkdirSync, mkdtempSync, readFileSync, statSync, writeFileSync } from 'node:fs'
 import { tmpdir } from 'node:os'
 import { join } from 'node:path'
 import { SNAPSHOT_TTL_MS, createFsUsageStore } from '../../src/adapters/store/fs-usage-store.ts'
@@ -87,9 +87,25 @@ test('a snapshot with nothing usable left in it reads as absent', () => {
 })
 
 test('an unwritable directory does not throw — the measurement already happened', () => {
-  const store = createFsUsageStore({ dir: '/proc/nonexistent/swisscode' })
-  assert.doesNotThrow(() => store.write({ remaining: { a: 1 }, checkedAt: Date.now() }))
-  assert.equal(store.read(), null)
+  // A REAL read-only directory, matching fs-cursor-store.test.ts.
+  //
+  // The first version of this used `/proc/nonexistent/...` as a path that
+  // "obviously cannot be written". On macOS there is no /proc, so it failed
+  // fast with ENOENT and the test passed. ON LINUX `mkdirSync(recursive)`
+  // AGAINST THAT PATH HANGS — not throws, hangs, with no output and no exit —
+  // which wedged the whole suite in CI. Portable fixtures only.
+  const parent = fresh()
+  const dir = join(parent, 'state')
+  mkdirSync(dir)
+  chmodSync(dir, 0o500)
+  const store = createFsUsageStore({ dir })
+  try {
+    assert.doesNotThrow(() => store.write({ remaining: { a: 1 }, checkedAt: Date.now() }))
+    assert.equal(store.read(), null)
+  } finally {
+    // Restored so the temp tree can be cleaned up by whoever cleans /tmp.
+    chmodSync(dir, 0o700)
+  }
 })
 
 test('the file holds no credential — only account names and figures', () => {