core: staged recompile for early defns; keys/vals/empty? leave the seed (jolt-4j3)

recompile-defns! is the defn analog of recompile-macros!: pre/at-kernel
overlay defns (00-syntax's destructure and friends; the kernel tier too in
interpret mode) load as interpreted closures, the evaluator stashes their fn
source on the var (:defn-src, scoped by a flag only api/load-core-overlay!
sets), and the end-of-init pass compiles them and swaps the var root. With
that in place, keys/vals/empty? — the fns the 00-syntax expanders call at
expansion time — move to the top of 00-syntax as raw fn* defs (canonical:
keys/vals project (seq m), so sorted maps come back in comparator order and
(keys {}) is nil; empty? keeps O(1) count dispatch with seq's cell check only
for the lazy/list fallback). The sorted tier drops its now-dead :keys/:vals
ops.

Correctness fixes that surfaced once the gate was run with a REAL exit code
(the previous 'jpm test | grep' gates reported grep's exit and masked spec
failures across #48-#50):
- map conj is strict again: a non-nil/non-map arg must be a 2-element vector
  ('Vector arg to map conj must be a pair'), and merge inherits it — the
  batch-2 canonical merge had silently dropped the validation
- conj onto a lazy seq prepends (it fell into the MAP fallback); upstream
  clojure.data/diff relies on (conj seq x) via set/union over keys, so diff
  now matches Clojure exactly
- (seq {}) / (seq #{}) / empty phm are nil, not ()
- key/val are strict (a plain vector is not an entry); find mints a REAL
  entry as the first entry of a one-entry map, nil values intact
- the sci avoid-method-too-large stub passes its registry map through
  instead of returning a raw host table (strict conj rejected it; sci's
  clojure-core registry is also no longer discarded)

Test updates: lazy-infinite pins take-nth realization at 5 (was 7 — the
canonical lazy impl realizes fewer); self-host asserts the analyzer IS loaded
in interpret mode (compiled expanders, PR #50) and is NOT in the
:compile-macros? false oracle. 18 new maps-spec rows.

Gate: jpm test exit 0 (verified directly, not through a pipe), conformance
326x3, suite 4698 >= 4660.

jolt-core/clojure/core/00-syntax.clj

@@ -4,10 +4,45 @@
 ;; them is compiled — including the kernel tier, the self-hosted analyzer, and the
 ;; seq/coll tiers.
 ;;
-;; CONSTRAINT: a macro here may use ONLY special forms (if/do/let*/fn*/not) and
-;; core-renames SEED primitives (first/next/rest/nth/count/empty?/...). It must
-;; NOT use kernel-tier fns (second/peek/subvec/...) or anything defined later —
-;; those don't exist yet when this tier loads.
+;; CONSTRAINT: code here may use ONLY special forms (if/do/let*/fn*/not) and
+;; SEED primitives (first/next/rest/nth/count/seq/...), plus earlier defs in
+;; THIS file. It must NOT use kernel-tier fns (second/peek/subvec/...) or
+;; anything defined later — those don't exist yet when this tier loads. Raw
+;; fn*/let* (no destructuring) and no when/cond/and/or above their defmacros.
+;;
+;; This tier's defns load interpreted and are recompiled by the staged pass
+;; (backend/recompile-defns!) once the analyzer is alive — same lifecycle as
+;; the defmacro expanders.
+
+;; empty?/keys/vals live HERE (not 20-coll) because the expanders below call
+;; them at expansion time, which first happens during the kernel-tier compile.
+;; empty? keeps O(1) dispatch for counted things; only the lazy/list fallback
+;; goes through seq's cell check.
+(def empty?
+  (fn* empty? [coll]
+    (if (nil? coll)
+      true
+      (if (vector? coll)
+        (zero? (count coll))
+        (if (map? coll)
+          (zero? (count coll))
+          (if (set? coll)
+            (zero? (count coll))
+            (if (string? coll)
+              (zero? (count coll))
+              (nil? (seq coll)))))))))
+
+;; Canonical: the seq of entries/elements, projected. (keys {}) is nil; sorted
+;; maps iterate in comparator order ((seq sm) is the value's own :seq op).
+(def keys
+  (fn* keys [m]
+    (let* [s (seq m)]
+      (if s (map (fn* [e] (nth e 0)) s) nil))))
+
+(def vals
+  (fn* vals [m]
+    (let* [s (seq m)]
+      (if s (map (fn* [e] (nth e 1)) s) nil))))
 
 (defmacro when [test & body]
   `(if ~test (do ~@body)))