js-on-sx: Array.prototype includes/find/some/every/reverse + Object fallbacks

Array: includes, find, findIndex, some, every, reverse via
tail-recursive helpers.

Object: hasOwnProperty, isPrototypeOf, propertyIsEnumerable,
toString, valueOf, toLocaleString fallback in js-invoke-method
when js-get-prop returns undefined. Lets o.hasOwnProperty('k')
work on plain dicts.

376/378 unit (+13), 148/148 slice unchanged.

plans/js-on-sx.md

@@ -183,6 +183,8 @@ Append-only record of completed iterations. Loop writes one line per iteration:
 
 - 2026-04-23 — **switch / case / default.** Parser: new `jp-parse-switch-stmt` (expect `switch (expr) { cases }`), `jp-parse-switch-cases` (walks clauses: `case val:`, `default:`), `jp-parse-switch-body` (collects stmts until next `case`/`default`/`}`). AST: `(js-switch discr (("case" val body-stmts) ("default" nil body-stmts) ...))`. Transpile: wraps body in `(call/cc (fn (__break__) (let ((__discr__ …) (__matched__ false)) …)))`. Each case clause becomes `(when (or __matched__ (js-strict-eq __discr__ val)) (set! __matched__ true) body-stmts)` — implements JS fall-through naturally (once a case matches, all following cases' `when` fires via `__matched__`). Default is a separate `(when (not __matched__) default-body)` appended at the end. `break` inside a case body already transpiles to `(__break__ nil)` and jumps out via the `call/cc`. 6 new unit tests (match, no-match default, fall-through stops on break, string discriminant, empty-body fall-through chain), **363/365** (357→+6). Conformance unchanged.
 
+- 2026-04-23 — **More Array.prototype + Object fallbacks (`hasOwnProperty` etc).** Array: `includes`, `find`, `findIndex`, `some`, `every`, `reverse` (in `js-array-method` dispatch + `js-get-prop` list-branch keys). Helpers: `js-list-find-loop / -find-index-loop / -some-loop / -every-loop / -reverse-loop` all tail-recursive, no `while` because SX doesn't have one. Object fallbacks: `js-invoke-method` now falls back to `js-invoke-object-method` for dicts when js-get-prop returns undefined AND the method name is in the builtin set (`hasOwnProperty`, `isPrototypeOf`, `propertyIsEnumerable`, `toString`, `valueOf`, `toLocaleString`). `hasOwnProperty` checks `(contains? (keys recv) (js-to-string k))`. This lets `o.hasOwnProperty('x')` work on plain dicts without having to install an Object.prototype. 13 new tests, **376/378** (363→+13). Conformance unchanged.
+
 ## Phase 3-5 gotchas
 
 Worth remembering for later phases: