Module sticky_context 

TC.3b — the sticky-context layer both renderers paint from.

StickyContext is the resolved answer to “which source lines are pinned above this pane’s text, and what do they look like”. It is built by cells_worker in the same pass that builds the pane’s DisplayMatrix and IndentGuides, from the same snapshot and stamped with the same MatrixVersion — so the three cannot disagree and this layer needs no staleness axis of its own.

Why the rows are built here rather than copied by the renderer

A context header is, by construction, a line that has scrolled ABOVE the viewport. The CellMatrix is chunked above 4 × viewport_height lines, so a header three thousand lines up is routinely not resident in any built chunk. A renderer copying from the published matrix would find nothing and have to fall back to unhighlighted text — a visible colour flicker on scroll, which the UX contract vetoes.

The worker holds the rope, the syntax snapshot and the cell builder, so it can build a row for any line whether or not a chunk covers it. That is also what makes the highlighting identical to the document’s rather than merely similar: there is one derivation, not two.

Why it is keyed by pane and not by buffer

Every other per-pane layer is keyed by BufferId, which means two panes showing one buffer share it. IndentGuides gets away with that by publishing block extents and letting each renderer pick the active one from its own cursor. Context cannot: the ROWS differ per pane, not just which one is emphasised. One buffer open in two splits with cursors in different scopes must show different context.

Design: docs/dev/architecture/treesitter-context.md.

Structs

StickyContext

The pane’s pinned context strip, outermost scope first.

StickyContextRow

One pinned context row: the source line it mirrors, and its cells.