acl: hardening suite (+25) — diamonds, cycles, validation, audit save/restore

New adversarial/cross-phase coverage: diamond resource+group hierarchies
(deny wins per path), chain inheritance + leaf deny, cycle termination,
multi-peer delegation, fact validation, audit snapshot/restore round-trip.
Adds acl-validate-facts/acl-facts-valid? (schema) and acl-audit-snapshot/
restore!/copy (audit). Fixed acl-audit-restore! rebuilding the live log via
map (append! silently no-ops on map-derived lists).

Suite is prover-free: a substrate JIT bug loops the recursive proof
reconstructor on deep chains in warm processes (documented in Blockers);
acl-permit? is unaffected. 145/145.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plans/acl-on-sx.md

@@ -15,7 +15,7 @@ and federation extension. Reuses `lib/datalog/` evaluator and term model where p
 
 ## Status (rolling)
 
-`bash lib/acl/conformance.sh` → **120/120** (all four phases complete)
+`bash lib/acl/conformance.sh` → **145/145** (all four phases + hardening)
 
 ## Ground rules
 
@@ -224,6 +224,58 @@ One engine rule carries federation:
     forms. `sx_write_file`, `sx_validate`, `sx_find_all`, `sx_summarise`,
     `sx_eval` all work; used full-file rewrites instead of path edits throughout.
 
+## Hardening (post-roadmap)
+
+- **`lib/acl/tests/harden.sx` (+25).** Adversarial / cross-phase coverage beyond
+  the per-phase suites. **Prover-free by design** (see JIT blocker below): only
+  `acl-permit?` (compiled Datalog, safe at any depth) + pure data ops, never
+  `acl-explain`/`acl-prove-d`.
+  - Diamond hierarchies (resource and group): grant on one path + deny on
+    another → deny wins; both-grant → permit; deny does not leak to siblings.
+  - Chain inheritance (literal 4-link): top-group grant reaches leaf member and
+    intermediates; leaf-member deny overrides the top grant; deny on the leaf
+    doesn't block a higher level.
+  - Cycle termination: self-membership, self-child, and 2-node membership cycles
+    all reach a fixpoint and decide correctly.
+  - Federation conflicts: federated group-grant with a locally-denied member →
+    deny; multi-peer delegation (one trusted, or both trusted) → permit.
+  - Degenerate inputs: empty db permits nothing.
+  - Fact validation: `acl-validate-facts` surfaces wrong-arity + unknown
+    predicates; `acl-facts-valid?` on clean/empty sets.
+  - Audit save/restore: snapshot → clear → restore round-trips entries + seq;
+    seq continues without collision after restore; snapshot is an immutable copy.
+  - Proof reconstruction itself is covered by tests/explain.sx + tests/fed.sx
+    (both stay under the warm-process JIT depth threshold); the depth-cap safety
+    net is verified manually in a warm REPL image but excluded from conformance.
+- **New API:** `acl-validate-facts`/`acl-facts-valid?` (schema.sx, opt-in — build
+  stays lenient); `acl-audit-snapshot`/`acl-audit-restore!`/`acl-audit-copy`
+  (audit.sx).
+- **Substrate gotcha (recorded):** `append!` extends a list built with `(list)`
+  but **silently no-ops on a `map`/`rest`-derived list** in this runtime. Bit the
+  first cut of `acl-audit-restore!` (rebuilt the live log via `map`, so later
+  records didn't append). Fix: always rebuild mutable lists via `(list)` +
+  `append!` (`acl-audit-copy`). Worth flagging to kernel owners; out of acl scope.
+
 ## Blockers
 
-(loop fills this in)
+- **JIT loops on deep proof reconstruction (substrate, not acl).** Once the
+  kernel JIT-compiles the mutually-recursive prover (`acl-prove-d`/
+  `acl-prove-rules`/`acl-prove-build` in `explain.sx`) — which happens after a
+  process has run enough explains to cross the compile threshold — the compiled
+  version **loops indefinitely** on a `member_of`/`child_of` chain deeper than
+  ~3. Symptoms: `acl-explain` over a 4+-deep chain returns instantly in a cold /
+  warm-REPL image but **hangs** in a long-lived process. The per-phase explain
+  and fed suites pass only because their proofs stay ≤3 deep; a 5th suite that
+  explained deeper chains hung the whole conformance run (no per-suite timeout
+  in dict mode). Matches `[[project_jit_bytecode_bug]]` (ACTIVE).
+  - *Impact beyond tests:* `acl-explain` is unsafe for deep hierarchies in a
+    warm production OCaml server. `acl-permit?` is unaffected (it reduces to
+    compiled Datalog, no SX-side recursion) — only the SX proof reconstructor is.
+  - *Workaround in acl:* harden suite is prover-free; explain is exercised only
+    at shallow depth. *Real fix is in the kernel JIT* (out of acl scope) — e.g.
+    the `_jit_compiling` guard / disabling JIT for the recursive prover, or
+    fixing the bytecode loop. Recommend the kernel owners reproduce with:
+    `acl-explain` over a 6-deep `member_of` chain after ~70 prior explains.
+  - *Minimal repro recorded.* Until fixed, callers needing explanations for
+    deep hierarchies should flatten or cap depth, or run explain in a cold
+    worker.