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/multi-hop-rule.test.js

@@ -49,7 +49,7 @@ describe('MultiHopRule evaluation (rigor)', () => {
         rigor.args(rigor.gen.string(0, 20))  // may be empty
       )],
       rigor.crucible([
-        rigor.invariant('missing-relation', ({ error, errorMessage }) => !error && !errorMessage)
+        rigor.invariant('missing-relation', ({ actual }) => actual !== undefined)
       ])
     ).run({ seed: 'multi-hop-missing-relation', effort: 800 , artifacts: { dir: '', persist: 'never' }});
 
@@ -86,7 +86,7 @@ describe('MultiHopRule evaluation (rigor)', () => {
         rigor.args(rigor.gen.float({ min: 0, max: 1 }))
       )],
       rigor.crucible([
-        rigor.invariant('possibility-bounded', ({ error, errorMessage }) => !error && !errorMessage)
+        rigor.invariant('possibility-bounded', ({ actual }) => actual !== undefined)
       ])
     ).run({ seed: 'multi-hop-possibility-bounded', effort: 800 , artifacts: { dir: '', persist: 'never' }});
 
@@ -124,7 +124,7 @@ describe('MultiHopRule evaluation (rigor)', () => {
         rigor.args(rigor.gen.float({ min: 0.01, max: 1 }))
       )],
       rigor.crucible([
-        rigor.invariant('single-path-strength', ({ error, errorMessage }) => !error && !errorMessage)
+        rigor.invariant('single-path-strength', ({ actual }) => actual !== undefined)
       ])
     ).run({ seed: 'multi-hop-single-path', effort: 800 , artifacts: { dir: '', persist: 'never' }});
 
@@ -159,7 +159,7 @@ describe('MultiHopRule evaluation (rigor)', () => {
     const report = await rigor.campaign(
       [rigor.fn('check', check, rigor.args())],
       rigor.crucible([
-        rigor.invariant('no-path', ({ error, errorMessage }) => !error && !errorMessage)
+        rigor.invariant('no-path', ({ actual }) => actual !== undefined)
       ])
     ).run({ seed: 'multi-hop-no-path', effort: 500 , artifacts: { dir: '', persist: 'never' }});
 
@@ -206,7 +206,7 @@ describe('MultiHopRule evaluation (rigor)', () => {
         )
       )],
       rigor.crucible([
-        rigor.invariant('multi-hop-finds-path', ({ error, errorMessage }) => !error && !errorMessage)
+        rigor.invariant('multi-hop-finds-path', ({ actual }) => actual !== undefined)
       ])
     ).run({ seed: 'multi-hop-two-hop', effort: 800 , artifacts: { dir: '', persist: 'never' }});