[devin-ai-integration]

What and why

internal/frontend/mcp/toolkit carried its own utf16Len(r rune) uint32 (2 for a rune at or above U+10000, otherwise 1), which is unicode/utf16.RuneLen — the function internal/syntax/semtok/encode.go already uses for the same count. Position.ToProtocol and FromProtocol now call utf16.RuneLen directly and the local helper is gone.

Behaviour is identical. Both callers range over the runes of a Go string, which decodes invalid bytes to U+FFFD and never yields a surrogate, so RuneLen is always 1 or 2 here and never its −1 sentinel. The two uint32(...) conversions carry a #nosec G115 line for that reason, as lineNumber in the same file already does.

How it was verified

TestPositionRoundTripsThroughUTF16 and TestColumnsCountCharactersNotBytes in internal/frontend/mcp/toolkit/toolkit_test.go pin the emoji (two-unit) case and the round trip through both functions; they pass unchanged.

go build ./...          ok
go vet ./...            ok
gofmt -l .              (nothing)
staticcheck ./internal/frontend/mcp/toolkit/...   ok
gosec ./internal/frontend/mcp/toolkit/...         0 issues
python3 scripts/changelog.py check                ok
go test ./...           all packages ok except cmd/sysml and tests/codegen, which hit Go's
                        10 m per-package default under full-suite load (goroutine dump,
                        no assertion failure); rerun alone:
go test -count=1 -timeout 40m ./cmd/sysml ./tests/codegen
ok  github.com/Open-MBEE/OpenSysML/cmd/sysml      348.887s
ok  github.com/Open-MBEE/OpenSysML/tests/codegen  373.585s

Checklist

• make test and make lint pass locally (see above; lint run on the touched package)
• Tests added or updated for the change — existing toolkit tests already pin the preserved behaviour
• Documentation extended where it already covers the surface (nothing documents the helper)
• Changelog entry added as changes/unreleased/toolkit-utf16-runelen.changed.md, not as an edit to CHANGELOG.md
• baselines regenerated and make docs-counts run if a gate count moved (none moved)
• No internal work-item labels (waves, slices, F4, K5) in the body, docs, or changelog

Link to Devin session: https://nasa-jpl-demo.devinenterprise.com/sessions/dd67c09df22146688969e4a7459a5eed
Open in Devin Desktop: https://nasa-jpl-demo.devinenterprise.com/desktop/session/dd67c09df22146688969e4a7459a5eed?variant=devin
Requested by: @HuiJun

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.