apl: multi-axis bracket A[I;J] / A[I;] / A[;J] (+8 tests, 475/475)

Parser: split-bracket-content splits inner tokens on :semi at
depth 0; maybe-bracket emits (:bracket arr axis-exprs...) for
multi-axis access, with :all marker for empty axes.

Runtime: apl-bracket-multi enumerates index combinations via
apl-cartesian (helper) and produces sub-array. Scalar axes
collapse from result shape; vector / nil axes contribute their
length.

apl-run "M ← (3 3) ⍴ ⍳9 ⋄ M[2;2]"  → 5
apl-run "M ← (3 3) ⍴ ⍳9 ⋄ M[1;]"   → 1 2 3
apl-run "M ← (3 3) ⍴ ⍳9 ⋄ M[;2]"   → 2 5 8
apl-run "M ← (2 3) ⍴ ⍳6 ⋄ M[1 2;1 2]" → 2x2 sub-block

plans/apl-on-sx.md

@@ -154,7 +154,7 @@ programs run from source, and starts pushing on performance.
   - parser: a name in fn-position whose env value is a dfn dispatches as a fn;
   - resolver: extend `apl-resolve-monadic`/`-dyadic` with a `:fn-name` case
     that calls `apl-call-dfn`/`apl-call-dfn-m`.
-- [ ] **Multi-axis bracket indexing** — `A[I;J]` and `A[;J]` and `A[I;]`.
+- [x] **Multi-axis bracket indexing** — `A[I;J]` and `A[;J]` and `A[I;]`.
   - parser: split bracket content on `:semi` at depth 0; emit
     `(:dyad ⌷ (:vec I J) A)`;
   - runtime: extend `apl-squad` to accept a vector of indices, treating
@@ -186,6 +186,7 @@ data; format for string templating.
 
 _Newest first._
 
+- 2026-05-07: Phase 8 step 3 — multi-axis bracket A[I;J] / A[I;] / A[;J] via :bracket AST + apl-bracket-multi runtime; split-bracket-content scans :semi at depth 0; apl-cartesian builds index combinations; nil axis = "all"; scalar axis collapses; +8 tests; 475/475
 - 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