fix: normalize dead-key grave input in composer

[StiensWout]

Summary

• Normalize dead-key grave look-alike composition input in the web composer before it reaches stored prompt text.
• Reuse the existing selected-text backtick surround behavior and insert ASCII backticks for collapsed selections.

Root cause

Some keyboard layouts emit grave-like Unicode characters (ˋ, ‵, ｀) through insertCompositionText after a dead-key press. The composer accepted those literal characters, so Markdown inline-code delimiters were not recognized.

Impact

Dead-key grave input now produces ASCII backticks only at the input boundary. Pasted text and non-dead-key Unicode content are left unchanged.

Validation

• vp check
• vp run typecheck
• cd apps/web && vp test run --project browser src/components/ChatView.browser.tsx -t "supports dead-key composition"
• Temporary browser assertion for Dead + U+02CB -> ASCII backtick passed locally and was removed.

Closes #3142

Note

Normalize dead-key grave input to backtick in ComposerSurroundSelectionPlugin

• Dead-key grave sequences (e.g. on macOS) can produce lookalike characters (U+02CB, U+2035, U+FF40) instead of a backtick, breaking backtick-based surround insertion in the composer.
• Tracks plain dead-key keydown events via recentDeadKeyDownRef with a 1,000 ms recency window; when a grave-lookalike character arrives via insertCompositionText within that window, it is treated as a backtick.
• Applies surround insertion if a selection is pending, or inserts a literal backtick otherwise, suppressing the original lookalike character.
• Adds hasCommandModifier helper to centralize meta/ctrl modifier checks across key event handlers.

^{Macroscope summarized 8c94e32.}

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Note

Low Risk
Scoped to composer keyboard/composition handling for a specific dead-key pattern; no auth, persistence, or broad input-path changes.

Overview
Fixes composer markdown inline-code behavior when some layouts emit grave lookalike Unicode (ˋ, ‵, ｀) via insertCompositionText after a Dead key instead of ASCII `.

ComposerSurroundSelectionPlugin now records a plain Dead keydown (1s window, cleared on most other keys but not plain Space) and, on matching composition input, runs the existing backtick surround path or inserts a literal backtick, then suppresses the lookalike character. Modifier checks use a shared hasCommandModifier helper. Pasted text and unrelated Unicode are unchanged.

^{Reviewed by Cursor Bugbot for commit 8c94e32. Bugbot is set up for automated code reviews on this repo. Configure here.}

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[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

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[macroscopeapp]

Approvability

Verdict: Approved

Straightforward bug fix that normalizes international keyboard dead-key grave characters to standard backticks in the composer. Changes are self-contained within input handling logic with clear intent and limited scope.

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