vamp/docs/architecture.md

# Architecture

[README](../README.md)

Contributor-facing module boundaries and implementation contracts. Project terminology and interface conventions live in [CONTEXT.md](../CONTEXT.md); verification is in [development](development.md).

## Module ownership

One editor crate; the workspace also includes its patched Crossterm dependency. Terminal-coordinate types remain outside the editing backend:

- `editor`: owns shared buffer lifecycle/text/saved state/undo history and independent tab/pane layouts, focused views, modes, selections, searches, explorers, and comparisons; session-wide clipboard policy, independent registers and owned-system fragment metadata, semantic native repeat, action metadata, command-palette and file-picker focus/dispatch, key notation, key-sequence/count prefixes and binding resolution, modal paste policy, saving, command ownership, capabilities, and validated edit effects. Its low-level interface returns an `Invocation` when an external command is selected.
- `chrome`: owns validated top/bottom bar anchor groups, segment title templates and padding/edge options, builtin defaults, named-value validation, and typed command/search popup anchors. Both bars accept the same segments and layout options. It has no terminal geometry or render callbacks.
- `battery`: reads native charge off the input thread, sampling immediately and every 30 seconds through an interruptible worker. macOS CoreFoundation references are type-checked and owned Copy/Create values released; Linux reads system battery sysfs and Windows reads native power status. A one-slot atomic mailbox retains the latest sample; absent/invalid readings clear cached presentation instead of inventing a percentage. Session starts collection only while an unoverridden battery segment is configured.
- `files`: owns the gitignore-aware directory/file catalog, authoritative OS paths, compact tree projection, query filtering, browse/search focus, expansion/selection restoration, navigation, and scan/error state shared by floating and docked presentations.
  Virtual file leaves retain their original catalog input index for caller-owned annotations; scanned entries and directories remain unannotated.
- `diff`: owns searchable Before/After selection, category, focus and explorer visibility, request freshness, read-only comparison DTOs, aligned rows with cached grapheme-level change ranges, and shared vertical/independent horizontal offsets. Changed paths form a virtual `files::FilePicker` catalog, reusing the normal tree projection, filtering, and navigation without scanning disk. It has no subprocess or terminal dependencies.
- `repository`: discovers jj/Git repositories and local/advertised remote revisions, builds disk snapshots and changed-file hunks, and owns isolated temporary comparison repositories with bounded, cancellable subprocesses. It never saves editor buffers or modifies active refs/checkouts.
- `clipboard`: owns native plain-text provider selection and bounded subprocess I/O; it never computes selections or editing offsets.
- `syntax`: owns Tree-sitter grammar detection, per-buffer incremental trees, bundled highlight/local/injection queries, and syntax byte spans; it has no terminal color/geometry or editing dependency.
- `markdown`: owns native Markdown link/reference resolution, local destination decoding, and heading fragment lookup through the installed block/inline grammars. It has no editor lifecycle, terminal, LSP, or external-process dependency.
- `plugin`: owns generic document snapshots/events, zero-based grapheme positions, diagnostics, frontend-independent semantic token kinds/modifiers and completion edit/item DTOs, and versioned asynchronous update contracts. Semantic token and completion updates are native-only, not part of the Ruby wire protocol; it has no LSP protocol types.
- `lsp`: owns opt-in native server workers, bounded framed JSON-RPC, synchronization/capability negotiation, settings, UTF-16/file-URI conversion, definition/hover results, completion decoding, and semantic token requests/legend decoding. Its private configuration resolver supplies presets without restricting language IDs.
- `snippet`: owns bounded, frontend-independent template parsing and expansion into plain replacement text and byte-relative tabstops with per-occurrence ancestry. It never edits documents or owns input policy.
- `session`: `EditorSession` owns the editor, native LSP, and Ruby hosts together. It loads configuration once, registers eligible plugins before installing shared bindings, tracks document open/change/save/close events, polls native and plugin results, validates versioned diagnostics/navigation/completion, and retires failed plugin ownership. Each tab with a comparison has a cancellable repository worker; inactive tabs keep their workers and receive tagged results without changing visible focus. Closed or superseded comparisons reject stale results. Focused diff text supports native LSP navigation, hover, and diagnostics; read-only buffers still reject asynchronous editing effects, and selectors/file lists are not document-action targets.
- `tui`: translates terminal events to session input, renders read-only active-buffer state, keeps frontend-owned viewports and syntax caches by stable buffer ID or immutable diff snapshot/file identity, and advertises `text`, `styled_text`, and `diagnostics` capabilities. It maps semantic tokens and diagnostics to terminal styling and has no server/protocol logic or paste acceptance policy.
- `ruby`: evaluates configuration and runs isolated plugin hosts. Protocol, deadlines, and process cleanup stay inside this module.
- The executable selects paths and frontend capabilities, opens an editor session, and launches the TUI.

## Frontend interface

Frontends drive `EditorSession::handle` or `execute`, periodically call `poll()` even without input, and inspect `editor()`; there is no mutable editor getter that could independently alter plugin registration. `poll()` reports whether background activity requires redrawing. Pasted text uses `Input::Paste(String)` through the same input seam as keys. Plugin effects are applied internally so a rejected result also retires its owner; there is no generic frontend effects entry point.
Frontends inspect `selections()` for document-ordered, end-exclusive Visual ranges of grapheme coordinates (empty outside Visual), `carets()` for all active cursors in document order, `cursor()` for the primary, and `selection_count()` for the total target count. `visual_linewise()` is true only for the whole-row shape in `Mode::Visual`; it changes neither binding modes nor Ruby mode names. Linewise ranges expand to complete rows. A range ending at the next row's column 0 includes the previous row's newline; an empty final-row range contains no text. `linewise_rows()` exposes inclusive selected row ranges only in linewise Visual, including an empty final row without changing `selections()` cardinality. The TUI highlights the copied text on those rows and one cell for each copied newline, never unused viewport space or the gutter, and labels their mode VISUAL LINE. Selection normalization, clipboard shape and contents, edit planning, and history remain inside the editor module.
The TUI also observes the editor's logical caret-reveal generation. Core motion/navigation dispatch advances it even when the resulting position is unchanged, so a detached viewport can resume following without duplicating key-binding policy or changing text revisions and LSP freshness.
Frontends inspect `palette()` for the optional read-only query, filtered command entries, selected index, effective bindings, and eligibility. Palette input handling and acceptance stay in the editor; registered command execution stays in the session.
Frontends use cached `selection_navigation_hint()` for command lists and `file_navigation_hint()` for the active file view/context, without reconstructing input policy.
Frontends inspect `count()` for the optional pending numeric prefix; parsing, counted motion dispatch, and counted Normal line actions remain editor-owned.
Frontends inspect `sequence_pending()` for the cached display of a pending key sequence; prefix recognition, cancellation, and dispatch remain editor-owned. Symbolic leader routes and explicit key prefixes share the same binding storage and dispatcher; explicit prefixes do not change when the leader is reconfigured.
Frontends inspect `g_pending()` for the built-in Normal/Visual `gt`/`gb` prefix and Normal-only `gf`. Document-edge motions share multi-target motion dispatch and viewport reveal, retaining Visual anchors and selection shape. Markdown following preflights links and headings before buffer/caret mutation; an unloaded target is validated/prepared once, while loaded targets use their current unsaved text. File identity and activation stay editor-owned.
Frontends inspect `line_operator_pending()` for the optional Normal `d`/`c` prefix. Dedicated `dd`/`cc` actions project counted caret rows through existing linewise selection normalization, clipboard publication, and atomic range editing, without exposing a temporary Visual mode. Clipboard failures restore the original targets before returning. Repeat recipes retain the requested row count rather than the originally clamped range; change recipes share the existing Insert undo group. There is no general operator–motion parser.
Editor-owned jump history is a bounded 100-location `VecDeque` of buffer IDs and grapheme cursors plus a current index, with no copied paths/text. Successful high-level navigation records departure/destination once; traversal uses unrecorded buffer activation and position placement, skips closed/clamped-duplicate locations, and truncates forward entries only on a distinct new jump. Session synchronization permanently invalidates pending LSP position requests after their source buffer/revision/caret/mode is left, so returning through history cannot revive an old definition reply.
Frontends inspect `buffer_id()`, `buffer_count()`, `has_buffer(id)`, and the ascending-ID `buffers()` iterator of borrowed path/dirty/active metadata. Existing text, cursor, selection, search, and mode methods describe only the active buffer.
Frontends inspect `tab_id()` for stable identity, `tab_index()` for display order, `tab_count()`, and `tab_buffer(index)` for borrowed title metadata. `pane_layout()` describes only the active tab; globally unique pane IDs keep inactive tabs' viewports alive. Documents remain unique across all tabs, while independent pane/buffer views are parked and restored without copying text.
Frontends borrow `top_bar_config()` and `bottom_bar_config()` for validated ordered left/center/right segment groups and effective segment styles, and `label(name)` for session-wide custom values. The TUI owns terminal-cell widths, full-row center anchoring, clipping, and accent styling. Label effects carry only a name and plain text; they are global presentation updates, not buffer/revision-bound results or render callbacks.
Frontends borrow `popup_config()` for independently configured command/search anchors. The TUI resolves each anchor against the chrome-free workspace using the existing bounded popup size; startup configuration does not alter buffer text, modal input, or notification positioning.
Frontends borrow `lsp_label()` / `lsp_names()` for the focused buffer's cached ready-server metadata. Initialization-only worker events trigger status redraws independently of diagnostics; session synchronization clears or replaces names when focus changes or a server retires. `notification_visible()` gates persistent operation/diagnostic popups independently of stored message text, so Escape dismissal neither alters text nor collapses carets. Display-only home abbreviation does not change document identity.

Frontends inspect `file_picker()` for query, presentation, view, explorer-local INSERT/filter subfocus, selection, and errors, and iterate borrowed `FileRow` metadata (actual path, display label, directory flag, visible depth, expansion). Dock side is a logical preference. They allocate rectangles, add folder suffixes/colors, and render; hierarchy, filtering, parent/child navigation, focus transitions, and selected-file opening remain backend-owned.
Frontends inspect `diagnostics()` and `diagnostic_at_cursor()` for validated active-buffer annotations. Diagnostics are owned by core LSP or a plugin and buffer revision; text changes clear them. Native server retirement removes only that server's contribution, preserving sibling diagnostics. The TUI underlines annotated text, colors affected gutter numbers by severity, and displays the primary caret's diagnostic message without replacing search/selection backgrounds.
Frontends borrow `semantic_tokens()` for sorted, single-line grapheme spans from the active buffer. Immutable `Arc` slices are shared by native LSP and buffer storage; painting does not copy tokens. Text/path changes discard overlays, and native updates validate the whole applicable annotation batch before mutation. The TUI merges semantic styling into its existing glyph pass above syntax foregrounds but below diagnostic/search/selection/caret styling.
Frontends inspect `hover()` for optional read-only content and logical-line/grapheme scroll offsets. Popup request eligibility, dismissal, and scrolling stay editor/session-owned; the TUI clips the panel inside the full editor area without changing the primary cursor or viewport. Its hover-local syntax cache treats content as Markdown, including named fenced-code injections, and rebuilds only when content changes. The popup shares the document syntax palette and preserves raw Markdown text and logical scroll coordinates.
Frontends borrow `completion()` for the read-only item list and selected index: zero is Original text, and other indices select `items[selected - 1]`. The editor owns the immutable original document/carets, atomic candidate transactions, cycling/dismissal, pending Insert undo, and final-only repeat recording. It changes only the primary completion target and translates secondary carets through all edits. The TUI places a windowed list near the current caret, bounded by the full editor rather than its pane, sanitizes/clips labels and detail by grapheme, and preserves hardware cursor ownership; wheel input over the list is consumed without dispatching edits.
Frontends borrow `snippet_selections()` for the active argument's end-exclusive grapheme ranges, including mirrors and empty tabstops. The editor caches those ranges after previews, argument edits, and navigation; rendering adds no snippet allocation. Template edits stay primary-only, translate other carets, and fold resolved replacement text and caret placement into the pending completion repeat step. Per-occurrence ancestry distinguishes nested arguments from adjacent empty stops, allowing enclosing replacements to retire only overwritten descendants.

## Terminal lifecycle and layout

The terminal adapter owns raw mode, alternate-screen state, bracketed paste, mouse capture, focus reporting, DEC 2031 color-scheme notifications, and its panic hook for one session lifetime. Entry failure, normal return, I/O errors, and unwinding panics restore the caller's hook; active-terminal cleanup runs before caller panic diagnostics. Panics retain their original payload and propagate rather than being swallowed. Terminal state and panic hooks are process-global: run one TUI at a time and do not replace its hook while that session is active.

Redraws stage Ratatui's buffer diff, cursor placement, and DEC synchronized-update commands (mode 2026) in a reusable byte buffer, then write and flush the complete frame to the terminal. Frame computation never suspends terminal presentation; synchronization covers transmitted painting rather than layout/highlighting work. The hardware cursor is hidden before painting even when synchronization is unsupported. Terminal cleanup releases synchronization before leaving the alternate screen or invoking caller panic diagnostics. Backend-writer access is enabled solely for this staging seam.

`terminal_colors` intercepts crossterm's key-shaped OSC 11/4 replies before editor dispatch, assembles a bounded RGB background/red/green triple, and preserves unrelated events and opaque bracketed paste. Queries never block input and start after painting, so syntax initialization does not spend their reply deadline. Startup, color-scheme notifications, and focus-regain queries replace cached diff tints atomically. While any rendered pane shows a diff, a one-second fallback probes for silent palette changes or missed notifications; ordinary editor views do not poll. Its injected-time deadline prevents overlapping periodic requests. An unanswered/partial query expires after 250 ms and removes stale tints rather than assuming a dark theme. Valid late replies are consumed without becoming editing commands. The frontend precomputes rounded RGB blends from the original background (18% row, 38% character), propagating them to active, parked, and newly created panes.

`vendor/crossterm` retains Crossterm 0.29.0's upstream source and MIT license, with a small Unix decoder patch exposing `Event::ColorSchemeChanged` for `CSI ? 997 ; 1/2 n`. The report signals a palette refresh, not a choice of hard-coded light/dark colors. Valid fragmented reports and malformed color reports leave following keys intact. Cargo patches both direct and Ratatui dependency paths to this one copy; remove the patch/workspace member once upstream supports these notifications.

The TUI allocates a flexible buffer viewport and optional one-row top/bottom bars, with no reserved prompt/message footer. Both bars derive visibility from configured content: empty content takes no row, and tabs-only content is hidden with a single tab in either position. Both render across ordinary, split, diff, and selector views. Ordered left/center/right groups use full-row centering, active-tab collision priority, internal padding, and independent styled edges. Floating Command/Search input owns the hardware cursor; non-focusable operation/diagnostic notifications anchor bottom-right inside the chrome-free workspace and hide obscured document carets. Higher-priority modal overlays suppress them without changing input state. Wheel hit regions clear each frame and consume reports over these popups. Zero-sized terminals render nothing; minimal-height input never reserves another row. Layout and terminal-cell text mapping remain frontend-owned.

Mouse wheel input uses the last rendered document/panel rectangles for hit-testing. Document offsets and explorer scroll state remain frontend-owned; three-row wheel steps never become document cursor motions. Manual document views persist until logical caret-reveal, caret/selection, mode, revision, or buffer changes; offscreen primary and browsing-selection cursors are not placed. Hover wheel input reuses the existing editor-owned popup scrolling.

Already-ready mouse reports share a redraw: at most 64 reports are applied in their original order before painting, without dropping or summing away wheel steps. Readiness checks do not wait. The first non-mouse event is retained for the next iteration after rendering, so keys, paste, and resizes cannot reuse geometry from before their layout changes. The batch bound keeps continuous mouse input from starving drawing or background polling.

Ratatui's bounded layout cache is enabled: unchanged geometry and constraints reuse solved rectangles during scrolling; resizes and panel-layout changes use their own cache keys.

The buffer viewport includes a fixed left gutter with right-aligned hybrid line numbers: the highlighted primary cursor line shows its one-based absolute number; every other line shows its distance from the primary. Secondary carets do not establish separate numbering origins. Gutter width follows the total line count plus one separator cell, including an empty final row after a trailing newline. Horizontal scrolling affects only text; search/selection highlights and carets never paint over the gutter. Rows beyond the buffer have no number. The gutter is hidden when it would leave no text column.

## Syntax caches

Each buffer has a frontend-owned parser/tree cache. Unchanged revision/path skips comparison and parsing; unchanged text at a later revision also avoids parsing. Actual text changes produce a minimal UTF-8-safe byte edit with newline-aware Tree-sitter Points, edit the prior tree, then parse using that tree for incremental reuse. Grammar changes reset the tree, including TypeScript versus TSX despite their shared display name. Native highlight/local/injection queries resolve capture precedence and scoped definitions into nonoverlapping original-line spans; unchanged injected trees are reused. Buffer switching restores its cache, and closing retires it. Incomplete text and grammar ERROR nodes remain highlightable; genuine language/query/parser failures expose a status error and readable plain text. Full-tree highlight queries still run after incremental parsing—a deliberate ceiling to revisit if measured costly. There is no local semantic inference engine or runtime grammar download.

Diff highlighting lazily owns two instances of the same syntax cache, keyed by the accepted comparison request ID and selected file. Before detects language from the old path when renamed; After uses the new path. Scrolling, focus changes, and explorer toggling reuse parsed spans without copying/reparsing snapshots. A fresh comparison identity prevents stale Working-checkout colors even when labels and paths are unchanged. Closing the view releases snapshot caches. Syntax styles patch foreground/modifiers over diff backgrounds; historical panes never receive live-buffer semantic tokens.

## Clipboard providers

macOS uses fixed JXA/AppKit `NSPasteboardTypeString` access through `osascript`, preserving literal RTF/EPS text rather than treating it as rich clipboard data. Linux supports Wayland with `wl-paste`/`wl-copy`, or X11 with `xclip`, on PATH with the corresponding display environment. Other platforms report unsupported access. Commands have a two-second deadline and bounded output; failures terminate/reap their process group.

## Native LSP

The native module initializes each server, sends `initialization_options` as `initializationOptions`, answers `workspace/configuration` from `settings` (including dotted sections; missing sections return `null`), honors open/change/save capabilities, synchronizes in-memory text including hidden dirty buffers, and sends close events. Incremental servers receive whole-document range replacements. Process/pipe I/O and requests stay on bounded background workers; input and idle diagnostic redraw do not wait for server responses.

Diff snapshots retain a separate immutable document identity, full source text, side-specific path (the old path for renamed Before), and UTF-16 positions. Native definition updates preserve their UTF-16 ranges until the editor resolves the target's actual snapshot, dirty buffer, disk text, or lazily loaded comparison file; generic plugin navigation remains grapheme-based. Target ranges overlapping actual changed rows route within the same comparison and reveal the exact selection, including an unchanged declaration above a changed body. Wholly unchanged/context/omitted targets and files outside its changes open an ordinary tab without changing the original comparison or view. Snapshot-URI targets keep their immutable identity. Freshness includes tab, pane, source buffer/revision/caret/mode, and comparison/side; deferred file-load navigation also checks its originating view before moving focus. Invalid targets fail before opening a tab. Completion remains restricted to writable Working After.

Language configurations can own an ordered server stack. The first matching language wins extension overlap; all its matching servers receive document events, while the first handles hover/definition/completion. The Python preset uses ty then Ruff. LSP merges each worker's latest diagnostic snapshot in assignment order before emitting the unchanged core-owned update. Empty publications/retirement remove only their source; revision/path/root changes and close discard all contributions. Worker snapshots retain identity so queued pre-rename diagnostics cannot attach to a new path with the same text revision. Combined diagnostic message bytes remain bounded to 4 MiB; an overflowing publication retires its worker instead of discarding healthy sibling annotations. Workers are stored in config/root order, avoiding per-poll key cloning/sorting. Shutdown flushes the exit notification and waits for peer termination within the existing bounded grace period before process cleanup.

Semantic tokens belong only to the first assigned server. Initialization advertises standard token types/modifiers, relative encoding, full/range requests, and server refresh support; deltas, overlapping/multiline tokens, and dynamic registration are not advertised. Each buffer has at most one request in flight; changes/refreshes coalesce into the latest snapshot. Full requests are preferred, with whole-document range fallback. A linear UTF-16 decoder validates raw coordinates and legend indices before outward grapheme rounding; overlong ends truncate at EOL, unknown types and invisible spans fall back to syntax. Both wire frames and decoded spans are bounded to 4 MiB. Snapshot identity rejects stale/renamed/closed replies before decoding. Invalid semantic replies clear the overlay and report an error without retiring diagnostics/navigation; primary retirement clears its overlays, and sibling retirement leaves them intact.

Manual completion dispatches the Insert-only `core.lsp.completion` action directly to the session, without the Ex execution path's mode/history transitions. The native worker sends the primary caret as UTF-16 and normalizes results into `CompletionItem { label, detail, primary_edit, edits, snippet }`; each `CompletionEdit` uses original-document, end-exclusive grapheme coordinates. Snippet primary text is expanded and newline-normalized before byte-relative metadata is assigned; additional edits remain plain text. Primary and additional edits form one atomic candidate. Session freshness includes the latest request, buffer/revision, primary caret, Insert source mode, and absence of modal overlays; any intervening input invalidates a pending reply. Decoding/validation errors remain completion-local and preserve healthy diagnostics/semantic tokens. Server commands, indentation adjustment, resolve requests, and automatic triggers are not supported; both frames and aggregate decoded completion text remain bounded.

## Ruby action catalog

`src/editor.rs`'s `CORE_ACTIONS` catalog owns core action names, eligible modes, optional Ex aliases, and prompt policies. It generates the Rust Action enum and protected core command registration. Typed keys and textual Ex aliases share Action-backed execution; the palette has one row per core action and searches its alias without adding duplicate command rows.

Rust supplies name/Ex-alias descriptors before loading configuration or plugin scripts. Ruby generates `config.core` methods and a frozen built-in alias lookup from those descriptors, rejecting built-in string binding targets without a second command list. Dotted identifiers create nested namespaces automatically; each namespace and Action value is frozen.