JavaScript: parser for ES5 scripts, with cargo xtask test262

New crate vectorcraft-js reads ECMAScript 5.1 source into a syntax tree
with source positions: a UTF-16 lexer (line and column tracking, automatic
semicolon insertion, the regexp and division goals), preprocessor lines
read as directive tokens, a recursive-descent parser to an arena tree, and
the ES5 early errors, strict mode included. Nesting deeper than
Options::max_depth (200 by default) gives a SyntaxError with its line and
column rather than overflowing the stack. Nothing runs scripts yet.

cargo xtask test262 downloads test262 at a pinned commit, checks its
SHA-256, unpacks it into the gitignored corpus/ folder and runs the ES5
syntax tests. A differential test in the engine compares the lexer with
scriptcheck on line counts, directives and unterminated literals.

docs/target-app-parity.md

@@ -653,6 +653,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   - MCP protocol: five prompts (`prompts/list` / `prompts/get`: poster, icon set, recolour, trace-and-style, export set), `completion/complete` for prompt arguments and template variables read from the live catalogues (formats, effect ids, command ids, trace presets, swatch and object ids), four resource templates (`vectorcraft://object/{id}`, `//command/{id}`, `//effect/{id}`, `//swatch/{name}`) so an agent reads one thing instead of the whole document, and `logging/setLevel` with `notifications/message`. `window.panel` ids are case-insensitive (display labels work too), `vectorcraft://object/{id}` reads through `document.node {summary: true}` (the same reply bytes from one lookup instead of summarizing the whole document: a leaf read on a 2,000-object document drops from ~20 ms to ~0.06 ms), large containers slice with `document.node {depth?, childLimit?}` (truncated levels report `childCount`), `document.inspect` and the `inspect_document` tool slice the same way so a depth-0 read is the layer skeleton (~9.7 KB instead of ~2 MB on a 2,000-object document), `document.find` locates nodes by name/kind/text with ancestor paths, and the CLI sweeps the protocol surface over stdio against the compiled binary. `docs/mcp.md` has a Protocol section covering the capability table and what is deliberately absent (subscriptions, progress, cancellation, sampling, elicitation, Streamable HTTP — all of which need the transport to interleave reads).
   - Headless CLI (`vectorcraft-cli run`, `convert`, `info`, `bench`, `perf`, `mcp`). A `run` step, like a `command_batch` step over MCP, can use an earlier step's result (`"$1.id"`, #785); `run --commands FILE` (or `-` for standard input) reads the steps from a JSON array or JSON Lines, past the Windows command-line limit (#3147, `apps/vectorcraft-cli/tests/it/cli.rs` `run_reads_*`, `run_refuses_malformed_commands_naming_the_step`).
   - File › Scripts › Check Script… reads a script written for Illustrator (`.jsx`, `.jsxinc` or a compiled `.jsxbin`) without running any of it and reports what it needs (the document model, files, dialogs, menu commands, features only Illustrator has), what it would do outside the document, the menu commands and document-model members it uses, its directives and included files, and the problems that would stop it loading (`script.check`, which also reads `.js` files); File › Open and drag-and-drop show the report for `.jsx`, `.jsxinc` and `.jsxbin` files.
+  - `vectorcraft-js` parses JavaScript as ECMAScript 5.1 defines it, with the legacy octal forms, block functions and lenient regular expressions of Annex B, into a syntax tree with source spans; it reads the `#target`, `#include` and other preprocessor lines as directives without running them, and a script that breaks the grammar or an early-error rule gives a `SyntaxError` with its line and column. Nesting past the parser's depth limit (`Options::max_depth`, 200 by default) gives a `SyntaxError` instead of exhausting the stack. `cargo xtask test262` fetches the conformance suite at a pinned commit and parses its ES5 tests: 5,411 of 5,418 runs pass (the 7 others use `let` and `const`). Nothing runs scripts yet. Tests: `crates/js/src/tests.rs`, `crates/engine/tests/it/js_lexer_vs_scriptcheck.rs`.
 - **UI:** Illustrator 2026 layout restyled to measured values:
   - Medium Dark theme, categorized and Advanced toolbars (a tool group's flyout opens on a right press, a long press or a press on its corner triangle), 35 pt document tabs, 33 pt panel tabs.
   - Hint bar, contextual task bar, 19 dock panels with ≡ menus.