fix: surrogate pair (emoji) handling for a, r, s, ~, ga commands

[k1832]

What this PR does / why we need it:

When the cursor is on a character encoded as a UTF-16 surrogate pair — emojis (😄), rare CJK characters (𩸽), mathematical symbols (𝒟, 𝔸), musical symbols (𝄞), etc. — several character-level commands break.

position.getRight() increments by 1 UTF-16 code unit, but these characters are 2 code units. Moving by 1 lands between the pair, and VSCode's validatePosition clamps it back to the start — so the cursor effectively goes backward.

Command	Broken behavior
a (Append)	Cursor lands before the character instead of after
r (Replace)	Only replaces half the character, corrupting the text
s (Change char)	Only deletes half the character before entering Insert mode
~ (Toggle case)	Corrupts the character into a lone surrogate
ga (Unicode info)	Shows the half-surrogate value instead of the full codepoint

Previous fixes addressed insert mode (PR #7977 / #6046) and motions (l/h) and operators (x/X/y), but these 5 commands were missed. This PR completes the surrogate pair handling for character-level commands and adds 12 regression tests to prevent future breakage.

Adds getSurrogateAwareRight()/getSurrogateAwareLeft() helpers on the Position prototype that skip past surrogate pairs, following the same pattern already used by MoveRight (l) / MoveLeft (h). Uses these helpers in the 5 affected commands. Also switches ga from charCodeAt() to codePointAt() to report the full Unicode codepoint.

Which issue(s) this PR fixes

Fixes #9931
Partially addresses #8321 — this PR fixes r and other character-level commands reported there. Remaining issues not addressed: easymotion uses raw character arithmetic for match positioning and marker decorations; xp (transpose) on surrogate pairs is also still broken (TODO added in put.ts).

Special notes for your reviewer:

• 19/19 surrogate pair tests passing (7 existing + 12 new)
• Full test suite passes (3157 passing, 0 regressions)
• Tests cover emojis, rare CJK (𩸽), and mathematical symbols (𝒟, 𝔸) from U+1D400 block
• Tests require fix: add missing @types/minimatch devDependency #9928 to build when re-resolving dependencies

[k1832]

Forgot to re-request a review...

[NanoUser3000]

note about p: p working depends one additional factor
when using j to move cursor over 2-wide / surrogate pair symbol, we can go from two columns (assuming they are normal characters). the cursor over emoji may be in 1 of 2 states: "in column more to the left" or "more to the right".

Screen capture showing the difference of going from space versus t (I x the a, then do jjpukljp…). Despite using p with cursor showing over the same character, the results are different)
Screencast from 2026-05-22 18-45-15.webm

Same thing is happening for a yanked word: the word is pasted before or after the emoji under cursor depending on this internal state.

shift+p / P seems to be working fine

[Copilot]

Pull request overview

This PR addresses incorrect handling of UTF-16 surrogate pairs (e.g., emoji and other non-BMP codepoints) in several character-level VSCodeVim commands by ensuring cursor movement and ranges don’t land between surrogate halves, which can corrupt text or misplace the cursor.

Changes:

• Added Position.getSurrogateAwareRight() / Position.getSurrogateAwareLeft() helpers to skip over surrogate pairs safely.
• Updated a, r, ~, and ga to use surrogate-aware movement; updated ChangeOperator to correct surrogate boundaries for s/change flows.
• Added regression tests covering append/replace/toggle/change/delete behaviors with surrogate-pair characters.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/operator/surrogate.test.ts	Adds regression tests for surrogate-pair behavior across several commands.
src/common/motion/position.ts	Introduces surrogate-aware left/right helpers on Position.
src/actions/operator.ts	Adjusts ChangeOperator deletion range to avoid splitting surrogate pairs.
src/actions/motion.ts	Adds TODO notes about possibly adopting the new surrogate-aware helpers.
src/actions/commands/replace.ts	Uses surrogate-aware right movement to compute replacement range for r.
src/actions/commands/put.ts	Adds a TODO noting xp transpose is still broken for surrogate pairs.
src/actions/commands/insert.ts	Updates a (Append) to move right surrogate-safely before entering Insert mode.
src/actions/commands/actions.ts	Updates ~ to advance surrogate-safely and ga to use codePointAt() with surrogate-safe range.

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[k1832]

Thanks for the detailed report and the screen recording, @NanoUser3000! That p behavior is a separate issue from this PR's scope — this PR only covers the character-level commands a, r, s, ~, and ga. The paste positioning you're seeing (text landing before/after the emoji depending on the cursor's internal column state) shares the same surrogate-pair root cause but lives in different code paths (put.ts / cursor column tracking). I'd rather not expand this PR's surface, so I'll open a follow-up issue to track p/xp on surrogate pairs so it doesn't get lost here.