feat: intermediate chain condition steps, graph-version cache invalidation, rolling-hash chain keys; fix vacuous rigor invariants

Chain intermediates (rule-based reachability):
- ChainRule: a condition step ({ rule, conditionStep }) at an INTERMEDIATE
  position is now EXPANDED from the current node — the rule's base edges'
  destinations, filtered by its defeaters/requirements — and traversal
  continues from each discovered node. Adds _expandRuleFromSrc / direct /
  logical(union/intersection) / defeasible / nested-chain expansion.
- RuleEvaluator: _subjectIsObject flag for unary predicate calls whose subject
  entity IS the object parameter (trusted(other) inside peer_trusted(user,
  other)); previously only subject-var unary calls (_subjectAsObject) were
  handled, so object-var unary defeaters never fired.

Graph-version cache invalidation:
- Arbiter gains a monotonic _graphVersion, incremented on every relation
  mutation. ChainRule result cache, RuleEvaluator rule-result cache, and
  DecisionCache rule cache now stamp entries with the graph version and treat
  any mismatch as a miss — graph mutations can no longer serve stale
  chain/authorization results.

Rolling-hash cache keys:
- UnifiedKeyManager.createChainKey now builds a 53-bit rolling hash (dual
  FNV-1a lanes, exact for ints/floats/strings/nested configs) instead of
  JSON.stringify — no string allocation or serialization on the chain-cache
  hot path. Composite keys stay structured strings because the direct-check
  cache pattern-invalidates by relation ID.

Rigor invariant migration (correctness):
- All 43 rigor test files' throw-based invariants ({ error, errorMessage } =>
  !error && !errorMessage) never saw fn throws — vacuous. Migrated to
  ({ actual }) => actual !== undefined, which fails on any thrown violation
  while passing legitimate null-skips. The migration immediately surfaced
  two latent bugs, now fixed:
    * node-manager/graph-indices skip paths returned bare undefined (falsy
      sentinel) — return { skipped: true }.
    * complex-graph-values-crucible expiry section rewrote values equal to the
      mutation loop's last write; the engine (by design) keeps the old
      timestamp on same-value rewrites so the pre-expiry grant never
      materialized. Now writes guaranteed-different values.

tests/rigor/zanzibar-semantics.test.js

@@ -310,7 +310,7 @@ describe('Zanzibar rewrite-rule semantics (rigor)', () => {
         ))
       ],
       rigor.crucible([
-        rigor.invariant('union-max', ({ error, errorMessage }) => !error && !errorMessage)
+        rigor.invariant('union-max', ({ actual }) => actual !== undefined)
       ])
     ).run({ effort: 400, seed: 'zanzibar-union' , artifacts: { dir: '', persist: 'never' }});
 
@@ -354,7 +354,7 @@ describe('Zanzibar rewrite-rule semantics (rigor)', () => {
         ))
       ],
       rigor.crucible([
-        rigor.invariant('intersection-min', ({ error, errorMessage }) => !error && !errorMessage)
+        rigor.invariant('intersection-min', ({ actual }) => actual !== undefined)
       ])
     ).run({ effort: 400, seed: 'zanzibar-intersection' , artifacts: { dir: '', persist: 'never' }});
 
@@ -397,7 +397,7 @@ describe('Zanzibar rewrite-rule semantics (rigor)', () => {
         ))
       ],
       rigor.crucible([
-        rigor.invariant('exclusion-blocks', ({ error, errorMessage }) => !error && !errorMessage)
+        rigor.invariant('exclusion-blocks', ({ actual }) => actual !== undefined)
       ])
     ).run({ effort: 400, seed: 'zanzibar-exclusion' , artifacts: { dir: '', persist: 'never' }});
 
@@ -432,7 +432,7 @@ describe('Zanzibar rewrite-rule semantics (rigor)', () => {
         ))
       ],
       rigor.crucible([
-        rigor.invariant('expand-parity', ({ error, errorMessage }) => !error && !errorMessage)
+        rigor.invariant('expand-parity', ({ actual }) => actual !== undefined)
       ])
     ).run({ effort: 800, seed: 'zanzibar-expand-parity' , artifacts: { dir: '', persist: 'never' }});
 
@@ -488,7 +488,7 @@ describe('Zanzibar rewrite-rule semantics (rigor)', () => {
         ))
       ],
       rigor.crucible([
-        rigor.invariant('nested-weakest-link', ({ error, errorMessage }) => !error && !errorMessage)
+        rigor.invariant('nested-weakest-link', ({ actual }) => actual !== undefined)
       ])
     ).run({ effort: 500, seed: 'zanzibar-nested-chain' , artifacts: { dir: '', persist: 'never' }});
 
@@ -544,7 +544,7 @@ describe('Zanzibar rewrite-rule semantics (rigor)', () => {
         ))
       ],
       rigor.crucible([
-        rigor.invariant('cycle-safe', ({ error, errorMessage }) => !error && !errorMessage)
+        rigor.invariant('cycle-safe', ({ actual }) => actual !== undefined)
       ])
     ).run({ effort: 400, seed: 'zanzibar-cycle-safety' , artifacts: { dir: '', persist: 'never' }});