[jsgrrchg]

Summary

Keep the active file header visible while scrolling through long diffs in the Changes panel.

The sticky header preserves the existing file path, binary status, addition/deletion counts, chevron, hover state, and collapse/expand interaction. When the next file header reaches the top boundary, it pushes the current sticky header away.

What changed

• Added a pure StickyFileHeader resolver based on the flattened diff row ranges.
• Reused the existing file-header composition for both regular and sticky presentations.
• Added distinct GPUI element IDs for regular and sticky headers.
• Added a clipped, relative container around the virtualized diff list.
• Rendered at most one additional sticky header overlay.
• Calculated the push-off position from measured GPUI list and viewport bounds.
• Preserved the regular header's translucent wash with a small backdrop blur on glass themes, plus an opaque fallback elsewhere.
• Added a subtle bottom border and shadow to separate the overlay from the diff.
• Allowed wheel and trackpad scrolling to pass through the sticky header.
• Kept fold/collapse behavior shared between regular and sticky headers.
• Added coverage for empty ranges, header boundaries, collapsed files, invalid indices, and push-off offsets.

Performance

• The diff remains line-virtualized.
• Active-file lookup uses partition_point over row_ranges (O(log n)).
• No persistent scroll state, timers, debouncing, or manual height accumulation were introduced.
• Only one additional 36 px overlay is rendered when needed.
• The 16 px backdrop blur is restricted to that single header strip and only runs on glass themes.
• Missing measurements for the next header safely fall back to top: 0.

Scope

Covered through the shared Changes renderer:

• Working tree
• Branch changes
• Latest turn
• Commit

Out of scope:

• History diffs
• Inline tool-call diffs inside the transcript
• Hunk-level sticky headers
• Parser, engine, RPC, protocol, or data-model changes

Validation

• cargo fmt --all -- --check
• cargo test -p zeron-ui changes
• cargo test -p zeron-ui — 425 tests passed
• git diff --check

cargo clippy -p zeron-ui --all-targets -- -D warnings is currently blocked by pre-existing unrelated lints in the workspace and other UI modules.

Manual QA checklist

• Long single-file diff keeps its header visible while scrolling.
• Multiple files transition through the push-off behavior in both directions.
• Collapse/expand works from both the regular and sticky header.
• Collapse all / expand all preserves a valid scroll position.
• Wheel and trackpad scrolling work while the pointer is over the sticky header.
• Added, deleted, renamed, binary, and truncated paths render correctly.
• Working tree refreshes and scope changes do not leave stale sticky headers.
• Summary strip, scrollbar, titlebar controls, and hover hit-testing remain unaffected.

[jsgrrchg]

fixed an issue with light mode, forgot to test it in light mode

[jsgrrchg]

Updated the sticky diff headers to properly follow the active theme in both light and dark modes. Frosted themes now use a theme-aware content background tint, hover state, and border, while opaque themes preserve their expected appearance. Added tests covering both appearance modes and theme variants.

[wingleeio]

No blocking findings.

Safety review: this stays within GPUI presentation/list-state code in crates/ui/src/changes.rs; it adds no dependency, network, filesystem, process, protocol, or unsafe-code surface. The sticky-header resolver bounds-checks stale indices, and the overlay preserves scroll pass-through and the existing collapse callback.

Validation:

• git diff --check origin/main...c4a14a8
• rustfmt --check --edition 2024 crates/ui/src/changes.rs
• cargo test -p zeron-ui changes — 33 passed
• cargo test -p zeron-ui — 556 passed
• cargo build -p zeron
• Live QA in an isolated synthetic repository: unified/split layouts, push-off transition, sticky-header collapse, wheel pass-through, long-path truncation, and themed presentation

The repository-wide clippy command still reports 22 unrelated pre-existing warnings outside changes.rs; this patch introduces none of them.

Unified push-off transition:

Split-view sticky header:

Scroll pass-through and long-path truncation:

[wingleeio]

One visual change requested: please remove .shadow_sm() from the sticky diff header. It reads like a raised Material-style card and separates the header too heavily from the diff content. The existing 1px bottom border plus the themed surface tint/blur is enough to establish stickiness without introducing elevation.

[jsgrrchg]

Fixed, good catch, looks much better now

[wingleeio]

Re-reviewed commit faff962 against main 2ebe6ed. No blocking findings; the requested shadow removal is present. The prospective merge is conflict-free, formatting and diff checks pass, all 575 zeron-ui tests pass, and cargo build -p zeron succeeds.