prolog: clause DB + loader (functor/arity → clauses), 14 tests green

plans/prolog-on-sx.md

@@ -50,7 +50,7 @@ Representation choices (finalise in phase 1, document here):
 - [x] 30+ unification tests in `lib/prolog/tests/unify.sx`: atoms, vars, compounds, lists, cyclic (no-occurs-check), mutual occurs — 47 pass
 
 ### Phase 3 — clause DB + DFS solver + cut + first classic programs
-- [ ] Clause DB: `"functor/arity" → list-of-clauses`, loader inserts
+- [x] Clause DB: `"functor/arity" → list-of-clauses`, loader inserts — `pl-mk-db` / `pl-db-add!` / `pl-db-load!` / `pl-db-lookup` / `pl-db-lookup-goal`, 14 tests in `tests/clausedb.sx`
 - [ ] Solver: DFS with choice points backed by delimited continuations (`lib/callcc.sx`). On goal entry, capture; per matching clause, unify head + recurse body; on failure, undo trail, try next
 - [ ] Cut (`!`): cut barrier at current choice-point frame; collapse all up to barrier
 - [ ] Built-ins: `=/2`, `\\=/2`, `true/0`, `fail/0`, `!/0`, `,/2`, `;/2`, `->/2` inside `;`, `call/1`, `write/1`, `nl/0`
@@ -88,6 +88,7 @@ Representation choices (finalise in phase 1, document here):
 
 _Newest first. Agent appends on every commit._
 
+- 2026-04-24 — Phase 3 clause DB landed: `pl-mk-db` + `pl-head-key` / `pl-clause-key` / `pl-goal-key` + `pl-db-add!` / `pl-db-load!` / `pl-db-lookup` / `pl-db-lookup-goal` in runtime.sx. New `tests/clausedb.sx` 14/14 green. Total 86 (+14). Loader preserves declaration order (append!).
 - 2026-04-24 — Verified phase 1+2 already implemented on loops/prolog: `pl-parse-tests-run!` 25/25, `pl-unify-tests-run!` 47/47 (72 total). Ticked phase 1+2 boxes.
 - _(awaiting phase 1)_