test: consent-gate E2E suite + functional fs-capability probes

Five hermetic gate-tier E2E cases (tpa-present / absent-linux / broken /
absent-darwin / apple-ban) drive the real contract section through
claude -p with PATH shims for aside and uname; the absent cases filter
any REAL aside binary out of the child PATH and assert absence with
Bun.which before spawning, so dev machines cannot leak into detection.
Registered per-case in E2E_TOUCHFILES/E2E_TIERS with template-level
deps (ship/SKILL.md.tmpl, gen-skill-docs.ts) and added to the evals.yml
matrix with tier: gate. eval:bg:periodic's detach timeout rises to
36000s for the grown periodic shard census (floor-enforced by
test/eval-detach-timeout-floor.test.ts); CLAUDE.md doc updated to match.

test/helpers/fs-caps.ts adds canRevokeWrites/canRevokeReads functional
probes; 13 chmod-based tests swap their uid-0-only guards for the
probes so suites skip honestly on CAP_DAC_OVERRIDE containers (this
sandbox: uid 1000 with full caps) instead of asserting revocations the
kernel ignores. path-validation's symlink test targets /etc/passwd
(exists everywhere; /etc/crontab is absent on Amazon Linux).

browse/test/session-persist.test.ts

@@ -16,6 +16,7 @@
  */
 
 import { describe, test, expect, afterAll } from 'bun:test';
+import { canRevokeWrites } from '../../test/helpers/fs-caps';
 import * as fs from 'fs';
 import * as os from 'os';
 import * as path from 'path';
@@ -128,7 +129,7 @@ describe('session-persist units', () => {
 
   test('a failed snapshot write preserves the previous good snapshot', async () => {
     // chmod-based read-only dirs don't bind on Windows or when running as root.
-    if (process.platform === 'win32' || process.getuid?.() === 0) return;
+    if (!canRevokeWrites()) return; // chmod is advisory here (win32, root, DAC-override containers)
     const dir = path.join(tmpRoot, 'ro');
     fs.mkdirSync(dir);
     const file = path.join(dir, 'session-state.json');