js-on-sx: object + array destructuring

Parser: jp-parse-vardecl handles {a, b} obj pattern and [a, , c]
arr pattern (with hole support) in addition to plain idents.
Emits (js-vardecl-obj names rhs) and (js-vardecl-arr names rhs).

Transpile: js-vardecl-forms dispatches on tag. Destructures emit
(define __destruct__ rhs) then (define name (js-get-prop __destruct__
key-or-index)) for each pattern element. Array holes (nil) are skipped.

418/420 unit (+4), 148/148 slice unchanged.

plans/js-on-sx.md

@@ -193,6 +193,8 @@ Append-only record of completed iterations. Loop writes one line per iteration:
 
 - 2026-04-23 — **String.replace/search/match + Array.from; js-num-to-int coerces strings; spread operator `...`.** Strings: `replace(regex|str, repl)`, `search(regex|str)`, `match(regex|str)` all handle both regex and plain-string args. Regex path walks via `js-string-index-of` with case-adjusted hay/needle. Array.from(iterable, mapFn?) via `js-iterable-to-list`. `js-num-to-int` now routes through `js-to-number` so `'abcd'.charAt('2')` and `.slice('1','3')` coerce properly. **Spread `...` in array literals and call args.** Parser: `jp-array-loop` and `jp-call-args-loop` detect `punct "..."` and emit `(js-spread inner)` entries. Transpile: if any element has a spread, the array/args list is built via `(js-array-spread-build (list "js-value" v) (list "js-spread" xs) ...)`. Runtime `js-array-spread-build` walks items, appending values directly and splicing spread via `js-iterable-to-list`. Works in call args (including variadic `Math.max(...arr)`) and in array literals (prefix, middle, and string-spread `[...'abc']`). Gotcha: early pass used `(js-sym ":js-spread")` thinking it'd make a keyword — `js-sym` makes a SYMBOL which becomes an env lookup (and fails as undefined). Use plain STRING `"js-spread"` as the discriminator. 10 new tests (replace/search/match both arg types, Array.from, coercion, 5 spread variants), **414/416** (399→+15). Conformance unchanged.
 
+- 2026-04-23 — **Object + array destructuring in var/let/const decls.** Parser: `jp-parse-vardecl` now handles three shapes — plain `ident`, `{a, b, c}` object pattern, `[a, , c]` array pattern with hole support. `jp-parse-obj-pattern` / `jp-parse-arr-pattern` / their loops collect the names. AST: `(js-vardecl-obj (names...) rhs)` and `(js-vardecl-arr (names-with-holes-as-nil...) rhs)`. Transpile: `js-vardecl-forms` dispatches on the three tags. Destructures emit `(define __destruct__ rhs)` then `(define name (js-get-prop __destruct__ key-or-index))` for each pattern element (skips nil holes in array patterns). 4 new unit tests. 418/420 (414→+4). Conformance unchanged. Gotcha: running destructuring tests sequentially — if epoch N defines `a, b` globally and epoch N+1 uses the same names as different types, "Not callable: N" results. Top-level `var` transpiles to `(define name value)`; re-defining a name that's held a value in a prior call to eval carries over. The proper fix would be to use `let` block-scoping; workaround for tests is unique names.
+
 ## Phase 3-5 gotchas
 
 Worth remembering for later phases: