apl: named function definitions f ← {…} (+7 tests, 467/467)

Parser: apl-collect-fn-bindings pre-scans stmt-groups for
`name ← { ... }` patterns and populates apl-known-fn-names.
is-fn-tok? consults this list; collect-segments-loop emits
(:fn-name nm) for known names so they parse as functions.

Resolver: apl-resolve-{monadic,dyadic} handle :fn-name by
looking up env, asserting the binding is a dfn, returning
a closure that dispatches to apl-call-dfn{-m,}.

Recursion still works: `fact ← {0=⍵:1 ⋄ ⍵×∇⍵-1} ⋄ fact 5` → 120.

plans/apl-on-sx.md

@@ -148,7 +148,7 @@ programs run from source, and starts pushing on performance.
     a single `:name "⎕←"` token (don't split on the assign glyph);
   - string values in `apl-eval-ast` — handle `:str` (parser already produces
     them) by wrapping into a vector of character codes (or rank-0 string).
-- [ ] **Named function definitions** — `f ← {⍺+⍵} ⋄ 1 f 2` and `2 f 3`.
+- [x] **Named function definitions** — `f ← {⍺+⍵} ⋄ 1 f 2` and `2 f 3`.
   - parser: when `:assign`'s RHS is a `:dfn`, mark it as a function binding;
   - eval-ast: `:assign` of a dfn stores the dfn in env;
   - parser: a name in fn-position whose env value is a dfn dispatches as a fn;
@@ -186,6 +186,7 @@ data; format for string templating.
 
 _Newest first._
 
+- 2026-05-07: Phase 8 step 2 — named function defs end-to-end via parser pre-scan; apl-known-fn-names + apl-collect-fn-bindings detect `name ← {...}` patterns; collect-segments-loop emits :fn-name for known names; resolver looks up env for :fn-name; supports recursion (∇ in named dfn); +7 tests including fact via ∇; 467/467
 - 2026-05-07: Phase 8 step 1 — quick-wins bundle: decimal literals (3.7, ¯2.5), ⎕← passthrough as monadic fn (single-token via tokenizer special-case), :str AST in eval-ast (single-char→scalar, multi-char→vec); +10 tests; 460/460
 - 2026-05-07: Phase 8 added — quick-wins bundle (decimals + ⎕← + strings), named functions, multi-axis bracket, .apl-files-as-tests, trains, perf
 - 2026-05-07: Phase 7 step 6 — :Trap exception machinery via R7RS guard; apl-throw raises tagged error, apl-trap-matches? checks codes (0=catch-all), :trap clause in apl-tradfn-eval-stmt wraps try-block with guard; :throw AST for testing; **Phase 7 complete, all unchecked plan items done**; +5 tests; 450/450