scheme: Phase 7 — eval/interaction-environment/null-env + 13 tests [shapes-reflective]

runtime.sx binds R7RS reflective primitives:
- eval EXPR ENV
- interaction-environment        — returns env captured by closure
- null-environment VERSION       — fresh empty env (ignores version)
- scheme-report-environment N    — fresh full standard env
- environment? V

interaction-environment closes over the standard env being built;
each invocation of scheme-standard-env produces a distinct
interaction env that returns ITSELF when queried — so user-side
(define name expr) inside (eval ... (interaction-environment))
persists for subsequent (eval 'name ...) lookups.

13 tests cover:
- eval over quoted forms (literal + constructed via list)
- define-then-lookup through interaction-environment
- eqv? identity of interaction-environment across calls
- sandbox semantics: eval in null-environment errors on +
- scheme-report-environment is fresh and distinct from interaction

**Second consumer for lib/guest/reflective/evaluator.sx unlocked.**
Scheme's eval/interaction-environment/null-environment triple is
the same protocol Kernel exposes via eval-applicative /
get-current-environment / make-environment. Extraction now
satisfies the two-consumer rule — same playbook as env.sx and
class-chain.sx, awaits a follow-up commit to actually extract
the kit.

270 total Scheme tests (62 + 23 + 49 + 78 + 25 + 20 + 13).

lib/scheme/tests/reflection.sx

@@ -0,0 +1,100 @@
+;; lib/scheme/tests/reflection.sx — Phase 7 reflective primitives.
+
+(define scm-ref-pass 0)
+(define scm-ref-fail 0)
+(define scm-ref-fails (list))
+
+(define
+  scm-ref-test
+  (fn
+    (name actual expected)
+    (if
+      (= actual expected)
+      (set! scm-ref-pass (+ scm-ref-pass 1))
+      (begin
+        (set! scm-ref-fail (+ scm-ref-fail 1))
+        (append! scm-ref-fails {:name name :actual actual :expected expected})))))
+
+(define
+  scm-ref
+  (fn (src) (scheme-eval (scheme-parse src) (scheme-standard-env))))
+
+(define
+  scm-ref-all
+  (fn
+    (src)
+    (scheme-eval-program (scheme-parse-all src) (scheme-standard-env))))
+
+;; ── eval ─────────────────────────────────────────────────────────
+
+(scm-ref-test
+  "eval: arithmetic"
+  (scm-ref "(eval '(+ 1 2 3) (interaction-environment))")
+  6)
+(scm-ref-test
+  "eval: nested"
+  (scm-ref "(eval '(* (+ 1 2) (- 5 1)) (interaction-environment))")
+  12)
+(scm-ref-test
+  "eval: constructed form"
+  (scm-ref "(eval (list '+ 10 20) (interaction-environment))")
+  30)
+(scm-ref-test
+  "eval: variable reference"
+  (scm-ref-all "(define x 42) (eval 'x (interaction-environment))")
+  42)
+
+;; ── interaction-environment ─────────────────────────────────────
+
+(scm-ref-test
+  "interaction-environment: is an env"
+  (scm-ref "(environment? (interaction-environment))")
+  true)
+(scm-ref-test
+  "interaction-environment: define persists"
+  (scm-ref-all
+    "(define ie (interaction-environment))\n     (eval '(define stashed 99) ie)\n     (eval 'stashed ie)")
+  99)
+(scm-ref-test
+  "interaction-environment: same env across calls"
+  (scm-ref-all
+    "(define a (interaction-environment))\n     (define b (interaction-environment))\n     (eqv? a b)")
+  true)
+
+;; ── null-environment ────────────────────────────────────────────
+
+(scm-ref-test
+  "null-environment: is an env"
+  (scm-ref "(environment? (null-environment 7))")
+  true)
+(scm-ref-test
+  "null-environment: has no + binding"
+  (scm-ref-all
+    "(define ne (null-environment 7))\n     (guard (e (else 'unbound)) (eval '+ ne))")
+  "unbound")
+
+;; ── scheme-report-environment ───────────────────────────────────
+
+(scm-ref-test
+  "scheme-report-environment: is an env"
+  (scm-ref "(environment? (scheme-report-environment 7))")
+  true)
+(scm-ref-test
+  "scheme-report-environment: has +"
+  (scm-ref "(eval '(+ 1 2) (scheme-report-environment 7))")
+  3)
+(scm-ref-test
+  "scheme-report-environment: distinct from interaction"
+  (scm-ref-all
+    "(define ie (interaction-environment))\n     (define re (scheme-report-environment 7))\n     (eval '(define only-in-ie 1) ie)\n     (guard (e (else 'unbound)) (eval 'only-in-ie re))")
+  "unbound")
+
+;; ── eval with explicit env for sandboxing ──────────────────────
+
+(scm-ref-test
+  "eval: sandbox with null-environment"
+  (scm-ref-all
+    "(define sandbox (null-environment 7))\n     (guard (e (else 'unbound))\n       (eval '(+ 1 1) sandbox))")
+  "unbound")
+
+(define scm-ref-tests-run! (fn () {:total (+ scm-ref-pass scm-ref-fail) :passed scm-ref-pass :failed scm-ref-fail :fails scm-ref-fails}))