fix(test): a real home is never "the test HOME" to the deletion guards

safeRmHomeTree and isUnderTestHome answered "is this path under process.env.HOME?".
With test/setup.ts skipped (a bare vitest) HOME is the developer's real home, so every
real file passed, which is how the real linked-cases registry was deleted on 2026-10-10.

They now also require HOME to be the throwaway codeman-vitest-* directory setup.ts
creates, and the shared route harness throws when it is not, so every route test refuses
to start against a real ~/.codeman rather than just the one file that checked.

test/mocks/index.ts

@@ -7,5 +7,13 @@
 
 export { MockSession, createMockSession, terminalOutputs } from './mock-session.js';
 export { MockStateStore } from './mock-state-store.js';
-export { waitForEvent, createDeferred, safeRmHomeTree, isUnderTestHome } from './test-helpers.js';
+export {
+  waitForEvent,
+  createDeferred,
+  safeRmHomeTree,
+  isUnderTestHome,
+  isSandboxedHome,
+  assertSandboxedHome,
+  TEST_HOME_PREFIX,
+} from './test-helpers.js';
 export { createMockRouteContext, type MockRouteContext } from './mock-route-context.js';

test/mocks/test-helpers.ts

@@ -3,7 +3,7 @@
  */
 
 import { rmSync } from 'node:fs';
-import { resolve } from 'node:path';
+import { basename, resolve } from 'node:path';
 
 /** Wait for an EventEmitter to emit a specific event, with timeout */
 export function waitForEvent(
@@ -39,37 +39,68 @@ export function createDeferred<T = void>(): {
 }
 
 /**
- * Delete a directory tree, but ONLY when it lives inside the test HOME.
- *
- * SAFETY (2026-08-29): `test/setup.ts` redirects `process.env.HOME` to a
- * throwaway dir and `os.homedir()` follows it, so a `rmSync(CASES_DIR,
- * recursive)` normally lands inside the fixture. This gate is defense in depth
- * for the day that stops being true (a test that runs outside setup.ts, an
- * env override that anchors a path elsewhere): it refuses to delete anything
- * not under the redirected `process.env.HOME`, so the failure mode is a
- * leftover temp dir rather than a deleted PRODUCTION `~/codeman-cases`.
- * Lexical `resolve()` is used because the leaf often does not exist and
- * `realpathSync` would throw.
+ * Prefix of the throwaway HOME `test/setup.ts` creates (`mkdtempSync(join(tmpdir(), 'codeman-vitest-'))`).
+ * Pinned by test/test-env-isolation.test.ts, so renaming one without the other fails there.
  */
-export function safeRmHomeTree(path: string): void {
+export const TEST_HOME_PREFIX = 'codeman-vitest-';
+
+/**
+ * True only when `process.env.HOME` is the throwaway directory `test/setup.ts` made.
+ *
+ * ⚠️ This is what the helpers below hang on, and it exists because "is the path under HOME"
+ * is a vacuous question when setup never ran: a bare `vitest` invocation has no setupFiles,
+ * HOME is the developer's REAL home, and every real file is then "under the test HOME". That is
+ * how a bare run on 2026-10-10 deleted the real linked-cases registry through a guard that was
+ * written to prevent exactly that. The temp directory's name is the only thing a real home
+ * cannot have.
+ */
+export function isSandboxedHome(): boolean {
   const home = process.env.HOME;
-  if (!home) return;
-  const target = resolve(path);
-  const root = resolve(home);
-  if (target === root || target.startsWith(root + '/')) {
-    rmSync(target, { recursive: true, force: true });
+  return !!home && basename(resolve(home)).startsWith(TEST_HOME_PREFIX);
+}
+
+/**
+ * Throw unless the suite is running under `test/setup.ts`'s temp HOME. The shared route harness
+ * calls this, so every route test refuses to start against a real `~/.codeman`.
+ */
+export function assertSandboxedHome(what = 'this test'): void {
+  if (!isSandboxedHome()) {
+    throw new Error(
+      `${what} reads and writes Codeman's data files and must run under test/setup.ts's temp HOME ` +
+        `(HOME=${process.env.HOME ?? '(unset)'}). Run it with \`npm test\` or ` +
+        `\`npx vitest run --config config/vitest.ci.config.ts <file>\`, never with a bare vitest.`
+    );
   }
 }
 
 /**
- * True when `path` resolves strictly inside `process.env.HOME` (or to it).
- * Same rationale as `safeRmHomeTree`; use for guarded non-recursive deletes
- * (single files like `linked-cases.json`) so they can never touch prod state.
+ * Delete a directory tree, but ONLY when it lives inside the test HOME.
+ *
+ * SAFETY (2026-08-29, tightened 2026-10-12): `test/setup.ts` redirects `process.env.HOME` to a
+ * throwaway dir and `os.homedir()` follows it, so a `rmSync(CASES_DIR, recursive)` normally
+ * lands inside the fixture. This gate is defense in depth for the day that stops being true
+ * (a test that runs outside setup.ts, an env override that anchors a path elsewhere): it
+ * refuses to delete anything unless HOME IS the throwaway dir ({@link isSandboxedHome}) and the
+ * target is under it, so the failure mode is a leftover temp dir rather than a deleted
+ * PRODUCTION `~/codeman-cases`. The first version only checked "under HOME", which a run
+ * without setup.ts satisfied for the user's real home.
+ * Lexical `resolve()` is used because the leaf often does not exist and
+ * `realpathSync` would throw.
+ */
+export function safeRmHomeTree(path: string): void {
+  if (!isUnderTestHome(path)) return;
+  rmSync(resolve(path), { recursive: true, force: true });
+}
+
+/**
+ * True when `path` resolves strictly inside the throwaway test HOME (or to it), and false
+ * whenever HOME is anything else. Same rationale as `safeRmHomeTree`; use for guarded
+ * non-recursive deletes (single files like `linked-cases.json`) so they can never touch
+ * prod state.
  */
 export function isUnderTestHome(path: string): boolean {
-  const home = process.env.HOME;
-  if (!home) return false;
+  if (!isSandboxedHome()) return false;
+  const root = resolve(process.env.HOME as string);
   const target = resolve(path);
-  const root = resolve(home);
   return target === root || target.startsWith(root + '/');
 }