Greptile Summary

This PR fixes invisible word-level highlights in Pierre split-view by introducing a wordDiffHighlightBg helper that checks whether the theme's existing addedContentBg/removedContentBg has enough contrast against the row background, and if not, blends incrementally toward the sign color until a minimum Manhattan distance of 28 is reached. It also consolidates the blendHex utility (previously local to renderRows.tsx) into a new shared src/ui/lib/color.ts module alongside the new hexColorDistance helper.

Confidence Score: 5/5

• This PR is safe to merge — the logic is correct, the type narrowing is sound, and both model-level and render-level tests are in place.
• No P0 or P1 findings. The strengthening loop correctly returns the first blend that meets the threshold, the StackLineCell["kind"] subset is compatible with the SplitLineCell["kind"]-typed cache, and the module-level cache is bounded to the small fixed set of themes. All remaining observations are P2 style notes.
• No files require special attention.

Important Files Changed

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["wordDiffHighlightBg(kind, theme)"] --> B{Cache hit\nfor theme.id?}
    B -- Yes --> C["Return cached[kind]"]
    B -- No --> D["Check hexColorDistance(\naddedContentBg, addedBg\n) ≥ 28?"]
    D -- Yes --> E["addition = addedContentBg"]
    D -- No --> F["strengthenWordDiffBg(\naddedBg, addedSignColor\n)"]
    F --> G["Loop: blend ratio 0.005→0.2\nstep 0.005"]
    G --> H{distance from\nlineBg ≥ 28?}
    H -- Yes --> I["Return candidate\n(early exit)"]
    H -- No, more steps --> G
    H -- No, loop done --> J["Return max-blend\ncandidate (0.2)"]
    E --> K["Build cache record\naddition / deletion / context / empty"]
    F --> K
    J --> K
    I --> K
    K --> L["wordDiffBackgroundCache\n.set(theme.id, cached)"]
    L --> C

_{Reviews (1): Last reviewed commit: "fix(diff): rebalance split-view word hig..." | Re-trigger Greptile}

@copilot resolve the merge conflicts in this pull request