fix(shortcuts): Alt is called Option on a Mac

[PathGao]

The shortcuts panel told macOS users to press a key their keyboard does not have. Apple keyboards print ⌥ option; the word "Alt" appears on no modern Mac keyboard.

Rendered as Opt, not Option, because the panel already abbreviates every modifier it can — Cmd not Command, Ctrl not Control. Spelling this one out would have been the odd row.

formatChord's docblock stated the assumption outright:

Only Mod is substituted. Everything else — Ctrl, Alt, F5, Shift — is already the literal the key carries.

True for Ctrl and Shift, false for Alt. Caught during hand-testing, when a proposed Cmd+Alt+T binding sent someone looking for a key that isn't labelled that.

Three rows were affected, not two — the new test found the third:

id	before (macOS)	after
nav-back	Alt+Left	Opt+Left
nav-forward	Alt+Right	Opt+Right
view-preview-width	Cmd+Alt+[ / ]	Cmd+Opt+[ / ]

Windows and Linux output is byte-identical, verified by rendering both.

Where the substitution went

A per-platform word table inside formatChord, keyed by the Mod word:

const PLATFORM_KEY_WORDS = {
	Cmd:  { Mod: 'Cmd',  Alt: 'Opt' },
	Ctrl: { Mod: 'Ctrl', Alt: 'Alt' },
} as const;

I asked for the signature to take a platform instead, on the theory that formatChord could not know which platform it was rendering for and so any second modifier would have to be a special case. That premise is wrong in a useful way: modifierFor is the only producer of 'Cmd' | 'Ctrl', and it returns 'Cmd' iff osType === 'macos'. The argument is already a total encoding of the platform distinction — it only had to be read as a platform tag rather than as one output word. The table is therefore the general fix, not a second special case beside the first.

The signature change was traced before being rejected: a platform argument propagates through shortcutLabel, EditorToolbarTool.shortcut's public function type, EditorToolbar's modifier prop and ~25 call sites in TitleBar, Tab, TabList and MarkdownViewer — and would leave modifierFor with no callers outside shortcuts.ts, breaking assertions in singleImplementationConvention.test.ts (an entry whose whole rationale is the four sites that failed to adopt modifierFor) and platformSource.spec.ts. Six source files and four test files to move one word.

The guardrail is the point

This is the shape the codebase has been closing all session: a translation mechanism existed and one member never joined. A one-line rename leaves the next modifier free to repeat it.

The new test enumerates modifier tokens across SHORTCUTS — every +-separated part except the last, sequence-aware for Mod+K T — requires each to appear in a table carrying both platform names, then requires the panel to render them positionally on both platforms.

The part that stops the repeat: an unlisted token fails outright rather than defaulting to "same word everywhere" — that default is exactly the assumption that produced this defect. A row added later with Meta+X cannot pass until someone states what macOS calls that key.

✖ every modifier the panel prints is what that platform calls the key
  AssertionError: view-preview-width: the panel shows "Cmd+Alt+[" on macos,
  but macos calls that key "Opt", not "Alt"

Scope checks

No i18n string hard-codes a key name. The locale table was grepped for Alt+, quoted 'Alt', Option+ and ⌥; every hit is a Spanish/Portuguese/Italian/Turkish word (Alternar, Altrimenti, Altı). Every displayed chord routes through formatChord, so those three rows were the entire user-visible surface.

The machine side cannot desync. toMonacoLabel and keymapHarness parse raw registry chords (Alt+Left), never formatChord output, and MarkdownViewer's altKey branches read the DOM event. Display and binding stay independent.

Not done deliberately: the ⌘⌥⇧⌃ symbol set. That is a separate question about matching macOS convention wholesale; the panel uses word form throughout, and mixing one symbol into words would be worse than either choice.

npm test 900 → 901 · vitest 356 · check 0 errors.

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