kernel: Phase 4 standard env + factorial + 49 tests [shapes-reflective]

kernel-standard-env extends kernel-base-env with $if/$define!/$sequence/
$quote, reflection (eval/make-environment/get-current-environment),
binary arithmetic, comparison, list/pair, boolean primitives. Headline
test is recursive factorial (5! = 120, 10! = 3628800). Recursive sum,
length, map-add1, closures, curried arithmetic, and a $vau-using-$define!
demo also covered.

plans/kernel-on-sx.md

@@ -75,8 +75,8 @@ The whole interesting thing: there are no special forms hardcoded in the evaluat
 - [x] Tests: define a custom operative, define a custom applicative on top of it.
 
 ### Phase 4 — Standard environment
-- [ ] Standard env construction: bind `$if`, `$define!`, `$lambda`, `$vau`, `wrap`, `unwrap`, `eval`, `make-environment`, `get-current-environment`, plus arithmetic and list primitives.
-- [ ] Tests: classic Kernel programs (factorial, list operations, environment manipulation).
+- [x] Standard env construction: bind `$if`, `$define!`, `$lambda`, `$vau`, `wrap`, `unwrap`, `eval`, `make-environment`, `get-current-environment`, plus arithmetic and list primitives.
+- [x] Tests: classic Kernel programs (factorial, list operations, environment manipulation).
 
 ### Phase 5 — Encapsulations
 - [ ] `make-encapsulation-type` returns three operatives: encapsulator, predicate, decapsulator. Standard Kernel idiom for opaque types.
@@ -100,6 +100,12 @@ The whole interesting thing: there are no special forms hardcoded in the evaluat
 
 **May propose:** `lib/guest/reflective/` sub-layer — environment manipulation, evaluator-as-value, applicative/operative dispatch protocols.
 
+**Proposed `lib/guest/reflective/evaluator.sx` API** (from Phase 4 chiselling — pending second consumer):
+- `(refl-eval EXPR ENV)` — the primary entry. Used to be implicit; exposing it as a function lets guests call into their own evaluator.
+- `(refl-make-environment [PARENT])` — fresh evaluation context, optionally a child of an existing one.
+- `(refl-current-env-operative)` — a Kernel-shaped operative that returns the dyn-env when called. Other reflective languages will need the same mechanism (an operative-equivalent that exposes "the env at this point").
+- Driving insight: the eval/make-env/current-env triple IS the reflective evaluator interface. Every reflective Lisp eventually exposes these three. Even more so when you start needing macro-expansion-time vs run-time vs call-time envs (the Kernel hygienic operatives work in Phase 6 will reveal whether more `refl-env-at-foo-time` accessors should join the kit).
+
 **Proposed `lib/guest/reflective/combiner.sx` API** (from Phase 3 chiselling — pending second consumer):
 - `(refl-make-primitive-operative IMPL)` — IMPL receives `(args dyn-env)`, args unevaluated.
 - `(refl-make-user-operative PARAMS EPARAM BODY STATIC-ENV)` — for $vau-like constructors. The EPARAM sentinel for "ignore dyn-env" is a fixed keyword (`:refl-ignore` in the proposal).
@@ -128,6 +134,7 @@ The motivation is that SX's host `make-env` family is registered only in HTTP/si
 
 ## Progress log
 
+- 2026-05-11 — Phase 4 standard env landed. `kernel-standard-env` extends `kernel-base-env` with: control (`$if`, `$define!`, `$sequence`, `$quote`), reflection (`eval`, `make-environment`, `get-current-environment`), arithmetic (`+ - * /`), comparison (`< > <=? >=? =? eq? equal?`), list/pair (`cons car cdr list length null? pair?`), boolean (`not`). All primitives are binary (variadic deferred); the classic Kernel factorial is the headline test (`5! = 120`, `10! = 3628800`). 49 tests in `tests/standard.sx`, covering $if branching, $define! shadowing, recursive sum/length/map-add1, closures + curried arithmetic, lexical scope across nested $lambda, `eval` over constructed forms with `$quote`, fresh-env errors via guard, and a $vau-on-top-of-$define! example. chisel: shapes-reflective. Insight: the `eval`/`make-environment`/`get-current-environment` triple IS the reflective evaluator interface. Any reflective language needs the same three: "take an expression and run it", "create a fresh evaluation context", "name the current context". That goes in the proposed `lib/guest/reflective/evaluator.sx` candidate. Second chisel — `$define!` was a one-liner because env-bind! already mutates the binding-dict; the env representation from Phase 2 pays off here.
 - 2026-05-11 — Phase 3 operatives landed. `lib/kernel/runtime.sx` adds `$vau` (primitive operative that returns a user operative), `$lambda` (sugar for `wrap ∘ $vau`), `wrap` and `unwrap` (Kernel-level applicatives), plus `operative?` and `applicative?` predicates. `kernel-base-env` wires them all into a fresh env. `kernel-eval.sx` now dispatches in `kernel-call-operative` between primitive ops (carry `:impl`) and user ops (carry `:params :env-param :body :static-env`). Parameter binding is a flat list — destructuring/`&rest` deferred. Env-param sentinel: spell `_` or `#ignore` → `:knl-ignore`, which skips the dyn-env bind. 34 tests in `tests/vau.sx`, including the headline custom-operative + custom-applicative composition. chisel: shapes-reflective. Two further reflective-API candidates surfaced: (a) the operative/applicative tag protocol — `make-primitive-operative`, `make-user-operative`, `wrap`, `unwrap` are general for any Lisp-of-fexprs; (b) the call-dispatch fork (primitive vs user) is a *single decision* that every reflective evaluator hits. Both shape go into the proposed `lib/guest/reflective/combiner.sx` candidate.
 - 2026-05-10 — Phase 2 evaluator landed. `lib/kernel/eval.sx` is `lookup-and-combine`: zero hardcoded special forms. `kernel-eval EXPR ENV` dispatches on shape — literals self-evaluate, Kernel strings unwrap, symbols lookup, lists evaluate head and combine. `kernel-combine` distinguishes operatives (impl receives un-evaluated args + dynamic env) from applicatives (eval args, recurse into underlying op). `kernel-wrap`/`kernel-unwrap` round-trip cleanly. 36 tests verify literal evaluation, symbol lookup with parent-chain shadowing, tagged-value predicates, and the operative-vs-applicative contract (notably `$if` only evaluates the chosen branch, `$quote` returns its arg unevaluated). chisel: shapes-reflective. Substrate gap surfaced: SX's `make-env` / `env-bind!` family is only registered in HTTP/site mode (`http_setup_platform_constructors`), not in CLI epoch mode used for tests. So Kernel envs are modelled in pure SX as `{:knl-tag :env :bindings DICT :parent P}` — a binding-dict + parent-pointer + recursive lookup walk. This is exactly the `lib/guest/reflective/env.sx` candidate API: any reflective language needs first-class env values that can be extended, queried, and walked. Recording the shape (constructor, extend, bind!, has?, lookup) here for the eventual Phase 7 extraction.
 - 2026-05-10 — Phase 1 parser landed. `lib/kernel/parser.sx` reads R-1RK lexical syntax: numbers (int/float/exp), strings (with escapes), symbols (permissive — anything non-delimiting), booleans `#t`/`#f`, the empty list `()`, nested lists, and `;` line comments. Reader macros (`'` `,` `,@`) deferred per plan. AST: numbers/booleans/lists pass through; strings are wrapped as `{:knl-string …}` to distinguish from symbols which are bare SX strings. 54 tests in `lib/kernel/tests/parse.sx` pass via `sx_server.exe` epoch protocol. chisel: consumes-lex (uses `lex-digit?` and `lex-whitespace?` from `lib/guest/lex.sx` — pratt deliberately not consumed because Kernel is plain s-expressions, no precedence climbing).