feat: provider-cache bypass knob; reject non-final comparator chain steps

- check() gains cacheProviderResults (per-check option + policy default): the
  provider cache is a STORE-RETRIEVAL cache (wall-clock), independent of the
  caller's decision { now }; callers who pin time or want fresh retrieval can
  opt out per-check or globally.
- The generator now rejects a comparator evidence referenced at a NON-final
  chain position (a comparator compares values at (src, candidate) but
  provides no candidate set, so it cannot enumerate intermediate nodes).
  Final-position comparators still lower to condition steps.

Tests: cache bypass (per-check + policy), comparator final OK / intermediate
error.

tests/DSLRuntimeCache.test.js

@@ -173,4 +173,31 @@ describe('DSLRuntime provider-result caching', () => {
     await rt.check('u:1', 'can_spend', 'doc:9');
     assert.equal(calls, 2, 're-invoked past the DSL-declared 1h TTL');
   });
+
+  it('cacheProviderResults:false bypasses the cache per check', async () => {
+    const rt = makeRuntime();
+    rt.addNode('u:1', 'Employee', {});
+    rt.addNode('doc:9', 'Doc', {});
+    let calls = 0;
+    rt.registerFact('owns', async () => { calls++; return 0.9; });
+    await rt.check('u:1', 'can_read', 'doc:9');
+    assert.equal(calls, 1);
+    // Bypass forces a fresh retrieval without clearing the cache.
+    await rt.check('u:1', 'can_read', 'doc:9', { cacheProviderResults: false });
+    assert.equal(calls, 2);
+    // Cache still intact for the next default check.
+    await rt.check('u:1', 'can_read', 'doc:9');
+    assert.equal(calls, 2);
+  });
+
+  it('policy.cacheProviderResults:false disables caching globally', async () => {
+    const rt = makeRuntime({ policy: { cacheProviderResults: false } });
+    rt.addNode('u:1', 'Employee', {});
+    rt.addNode('doc:9', 'Doc', {});
+    let calls = 0;
+    rt.registerFact('owns', async () => { calls++; return 0.9; });
+    await rt.check('u:1', 'can_read', 'doc:9');
+    await rt.check('u:1', 'can_read', 'doc:9');
+    assert.equal(calls, 2, 'no caching when disabled globally');
+  });
 });