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.

src/generator/RuleGenerator.js

@@ -1111,6 +1111,15 @@ export class RuleGenerator {
             out.push(...this._expandChainSteps(resolved.steps, refStack));
             continue;
           }
+          if (resolved.type === 'relational_comparator' && idx !== steps.length - 1) {
+            // A comparator compares values at (src, candidate) but provides no
+            // candidate set — it cannot enumerate intermediate nodes, so only
+            // a FINAL comparator step (verified at the known object) lowers.
+            this.errors.push(`Chain step '${stepName}' references a comparator evidence at a non-final position. ` +
+              'Comparators can only be the final chain step (the object is known); intermediate positions are not enumerable.');
+            out.push(step);
+            continue;
+          }
           // Condition step: inline the evidence's config as a rule step. As the
           // FINAL step the engine verifies it at (intermediate, object); as an
           // INTERMEDIATE step the engine EXPANDS it from the current node

src/runtime/DSLRuntime.js

@@ -60,6 +60,12 @@ export class DSLRuntime {
     this.clock = typeof options.clock === 'function' ? options.clock : (() => Date.now());
     // Default provider-result TTL in ms (0 disables caching).
     this.defaultProviderCacheTTL = options.policy?.providerCacheTTL ?? options.providerCacheTTL ?? 30_000;
+    // Provider caching is a STORE-RETRIEVAL cache (wall-clock), deliberately
+    // independent of the caller's decision `{ now }` — a provider returns the
+    // store's current data, not a time-travel snapshot. Callers who pin time
+    // or otherwise want fresh retrieval can disable it per-check
+    // (options.cacheProviderResults: false) or globally (policy).
+    this.cacheProviderResults = options.policy?.cacheProviderResults ?? options.cacheProviderResults ?? true;
     // Per-fact overrides (ms). DSL-declared ttl behaviors are indexed here too.
     this.factTTLs = new Map(Object.entries(options.factTTLs || {}));
   }
@@ -593,8 +599,11 @@ export class DSLRuntime {
         // provider overrides are one-off observations — they bypass the cache
         // entirely (no read, no write) so a fresh override is never masked by
         // a cached registered-provider result, nor does it pollute the cache.
+        // options.cacheProviderResults:false (or the policy default) disables
+        // the cache for this check.
+        const cachingEnabled = options.cacheProviderResults ?? this.cacheProviderResults;
         const isPerCheckOverride = !!(options.factProviders && fact in options.factProviders);
-        const cacheHit = isPerCheckOverride ? null : this._providerCacheGet(fact, user, object);
+        const cacheHit = (cachingEnabled && !isPerCheckOverride) ? this._providerCacheGet(fact, user, object) : null;
         let edges = null;
         let fromCache = false;
         if (cacheHit) {
@@ -626,7 +635,7 @@ export class DSLRuntime {
             continue;
           }
           edges = this._normalizeProviderEdges(result, factMeta, user, object);
-          if (!isPerCheckOverride) this._providerCacheSet(fact, user, object, edges);
+          if (cachingEnabled && !isPerCheckOverride) this._providerCacheSet(fact, user, object, edges);
         } else {
           missingFacts.push({ relation: fact, reason: 'no_provider' });
           satisfied.add(fact);