Module modes 

Major modes for buffer kinds owned by the TUI layer.

Three majors corresponding to the existing BufferKind variants beyond Document:

• help-mode – :describe-* / :apropos / :keymap views. Read-only; markdown-mode-style content with link navigation (<CR> follows a link).
• file-tree-mode – the file-tree navigation buffer. Tree expansion / collapse, open-on-<CR>.
• oil-mode – editable directory listing (oil.nvim-style). Writable; :w diffs the rope and applies filesystem ops.

Pure declarations in M.3.0. The actual behavior currently lives in scattered call sites in app.rs / render.rs / input.rs; M.3.1 routes those through the mode-id queries and M.4 unifies rendering through ResolvedOptions.

Per mode-architecture.md §4.1 the TUI also hosts command-line-mode and search-line-mode for the rich minibuffer (DESIGN.md §5.9.10), but the rich minibuffer refactor isn’t landed yet – those modes are deferred to the slice that ships them.

Structs

CenterContentWidth

DB.4: the content block width (widest line, in cells) for a buffer that should be horizontally centred by widening its gutter. Set by the dashboard; the renderer computes left_pad = (viewport_width - width) / 2 and adds it to the gutter, so content + cursor shift right (centred) with no text mutation — markdown / links stay intact. Absent = not centred.

DocumentFolds

Per-document fold list. Empty means “not yet computed for this buffer.” First-activation seeds from the active foldmethod; subsequent re-activations restore the user’s open / closed state. Universal across language majors – the foundational text-mode owns the data shape; per-language fold queries are a presentation-layer concern read through the syntax local.

DocumentLastParsedTextVersion

Document version (the rope’s monotonic edit counter) of the most recent successful parse. The renderer’s syntax walk short-circuits when text_version == last_parsed_text_version; the reparse seam treats inequality as “edits to drain into the worker” and fires an incremental reparse.

DocumentLastSyncedSyntaxVersion

Document version that was the baseline for the last syntax- worker request fired for this buffer. Sent as from_version on each request so the worker can verify edits apply to the expected tree baseline before running the incremental tree.edit(). Independent of last_parsed_text_version because the worker may still be in flight when the next request fires.

DocumentSyntax

Per-document tree-sitter syntax handle. Some once a language has been detected for the buffer and a parse has been requested; None for Lang::Plain documents and for buffers that haven’t been activated yet.

ExtraHighlights

PU.1b-2a: generic per-buffer static highlight spans, merged into the cells-worker DisplayMatrix ON TOP OF (overriding, by first-match precedence) the live grammar spans on their byte ranges. Indexed by source line. Unlike DocumentSyntax (the live grammar handle, dynamic per edit) these are fixed for the buffer’s content — the home for styling the grammar can’t derive because the source text was transformed before parsing (help-link labels, whose [label](target) markup is stripped before the markdown grammar runs, so the grammar never emits a link capture). Property-derived, NOT kind-specific: any buffer carrying this local gets the merge; empty/absent is the universal default and renders byte-identically.

ExtraInlays

DL.3b: generic per-buffer inline virtual text, merged beside the LSP inlay hints when the pane’s cells inputs are built.

ExtraRefinement

DR.3 (2026-08-12): per-buffer intra-line diff refinement — the byte ranges whose BACKGROUND differs from their row’s diff tint.

FileTreeEntries

Flat tree-of-entries backing the file-tree buffer. Each entry carries its depth + expansion state. The rendered rope is derived from this list – App-side toggle handlers mutate the entries through the [crate::toggle_entries_at] helper and re-write this local

FileTreeMode

Major mode for file-tree buffers. Read-only contribution (ReadOnly = true); any buffer whose major is file-tree-mode rejects mutating operators.

FileTreeNerdFonts

Whether the file-tree renders nerd-font icon glyphs inline.

FileTreeRoot

Filesystem path the file-tree buffer is rooted at. Single source of truth (M.3.2.c.5).

HelpAnchors

Help buffer’s named anchors (heading slugs + introspection-recorded anchors).

HelpLinks

Help buffer’s parsed [label](url) markdown links.

HelpMode

help-mode — the minor that makes a (markdown-major) buffer a help buffer: read-only, gutterless, no-file, <Esc> dismisses it, and its motions run through the read-only help invocation runner. Activated by the host on :help / :describe-* / :apropos / :keymap / … views; see the module docs.

HoverMode

hover-mode — marker minor on the hover popup buffer (activated alongside markdown-mode). Wraps long lines and borrows help-mode’s read-only invocation runner; see the module docs.

OilDir

BufferLocal carrying the filesystem path the oil buffer’s listing represents (M.3.2.c.3 mirror of OilBuffer::dir). Renderers / writers read through this rather than poking OilBuffer::dir directly so the canonical “what directory does this oil buffer represent” lookup is uniform with the rest of the mode-owned per-buffer state.

OilMode

Major mode for oil-style directory-listing buffers. Any buffer whose major is oil-mode is an OilBuffer; the renderer dispatches accordingly.

Functions

auto_activated_minors_for_buffer_kind

CSM.K1 (insert-completion.md §12): additional minor modes the App activates alongside the buffer’s major + the kind’s default_minor. Today: completion-mode on writable kinds (Document) so <C-Space> opens the popup; read-only kinds (Help, FileTree, Oil) don’t activate it, so the trigger chord is a silent no-op there.

default_minor_mode_id_for_buffer_kind

M.4 (Option B): minor modes the App activates alongside the major resolved by major_mode_id_for_buffer_kind. Returns the per-kind minor that gives the buffer its full identity. Help buffers get help-mode (read-only + link/anchor follow); other kinds currently get nothing – their majors already carry their full contribution set.

major_mode_id_for_buffer_kind

Resolve the default major-mode id for a BufferKind via the registry’s kind index (H.2).

register_buffer_kind_modes

M.4 follow-up: the per-kind modes (HelpMode, HoverMode, FileTreeMode, OilMode) moved to lattice_mode::modes and register through lattice_mode::modes::register_foundation_modes alongside TextMode. This shim is kept as a no-op so existing register_buffer_kind_modes callers don’t break; the App’s boot path now calls register_foundation_modes directly and drops this helper in a follow-up.

resolve_major_mode

Resolve the major-mode id a buffer should activate based on its kind + (for Document kinds) detected language.