# vamp

A modal Rust editor with a replaceable frontend and subprocess-isolated Ruby plugins.

## Run

Requires current stable Rust and an interactive terminal. Ruby 2.6+ with its standard-library JSON support is required only for configuration/plugins; no Ruby gems are needed.

```sh
cargo run -- --no-config notes.txt
cargo run -- --config examples/config.rb notes.txt
```

Without a file, vamp opens an unnamed buffer. A nonexistent file opens an empty buffer. Use `:w path` to save it. `cargo run -- --help` lists the command-line options.

### Default editing keys

| Mode | Keys |
| --- | --- |
| All modes | Ctrl+p opens the command palette; type to filter, Ctrl+j/k or arrows select, Enter accepts, Esc/Ctrl+p cancels |
| Normal, Visual | Space Space opens the palette through the default leader |
| Normal | Space w saves; Space b n/p/l/d switches next/previous, lists, or closes buffers |
| Normal, Visual | Space o opens the floating tree in INSERT/filter mode; Space e opens/focuses the docked compact tree |
| Normal | `i` insert before each caret; `a` insert after each caret; `o`/`O` open lines below/above |
| Normal, Visual | `I` (Shift+i) / `A` (Shift+a) insert at first nonblank / line end; Visual splits each touched row into a caret first |
| Normal | `h`/`j`/`k`/`l` or arrows move every caret; `0`/`$` or Home/End |
| Normal | `w`/`b`/`e` move every caret to next word start, previous/current word start, word end; `W`/`B`/`E` for whitespace-delimited WORDs |
| Normal, Visual | Decimal prefixes repeat cursor/word/search motions: `5j`, `3k`, `2w`, `4e`, `2n`; Esc cancels a pending count |
| Normal | `J` (Shift+j) joins each targeted line with the next line |
| Normal | `x`/Delete delete; `u` undo; `U` (Shift+u) redo; `:` enter command mode |
| Normal, Visual | `.` repeats the last successful native edit against the current targets; one undo group |
| Normal | `/` opens search; `n` finds the next match; `N` (Shift+n) finds the previous match |
| Normal | `v` starts Visual selections; `p`/`P` paste internal clipboard after/before each caret; Esc keeps only the primary caret |
| Normal, Visual | Ctrl+k clones above; Ctrl+e clones below |
| Visual | Cursor/word motions and `n`/`N` extend every selection; `y` copies; `d`/`x`/Delete cuts; `c` changes selections; `v`/Esc cancels highlighting |
| Visual | Ctrl+l splits touched rows into Normal carets at first nonblank; Ctrl+n adds the next occurrence; Ctrl+s skips the primary occurrence; Ctrl+a selects all occurrences |
| Insert | Type, Enter, Tab, Backspace/Delete, arrows, Home/End at every caret; Esc returns to Normal, retaining carets |
| Command | Enter executes; Backspace edits; Esc cancels |
| Search | Type a literal query; Enter finds the next match; Backspace edits; Esc cancels |

`J` removes the next line's leading spaces/tabs and preserves existing trailing whitespace. It normally adds one space, two after `.`, `?`, or `!` (Vim's default), and none before `)` or when either side is empty. The cursor lands at the join point; the join is one undo action. On the last line, `J` does nothing.

Word motions separate runs of Unicode letters/numbers/underscore from runs of punctuation or emoji. Classification uses each grapheme's first character; combining sequences and ZWJ emoji stay intact. WORD motions treat any non-whitespace run as one WORD.

`w`/`W` move to the next start. `b`/`B` move to the current start, or the previous start when already at one. `e`/`E` move to the current end when before it, otherwise the next end. Motions cross lines but never wrap. Truly empty lines are stops for start motions; whitespace-only lines are skipped. End motions skip empty lines while looking for a word. With no further target, motions stop at the buffer edge, including trailing whitespace or an empty final line.

These keys type literal text in Insert mode. The corresponding actions can also be bound in Insert mode to move all insertion carets without splitting their undo group. Motions never edit text, add history, or clear an active search highlight.

Counts apply to `h`/`j`/`k`/`l`, arrows, `w`/`b`/`e`, `W`/`B`/`E`, and `n`/`N`, including remapped keys for those actions. Every caret moves independently before duplicate/overlapping targets normalize. Vertical counts preserve the clamping behavior of repeated steps through short rows; horizontal and word motions stop at buffer boundaries. Search counts wrap through the available matches.

Unbound ASCII digits `1`–`9` start a count in Normal/Visual; subsequent digits extend it. `0` retains line-start behavior without a count and extends an existing count when bound to line-start. Explicit digit bindings, including disabled keys, take precedence. Count arithmetic saturates rather than overflowing; large counts stop at motion boundaries or wrap for search, without executing an unbounded repeat loop.

The status bar displays a pending count. Esc cancels it without moving, collapsing carets, or leaving Visual; the next Esc performs its ordinary action. Leader prefixes retain the count until their leaf action resolves. Other commands consume the prefix and execute once, including line-start/end, edits, and plugins. Unknown/disabled keys and bracketed paste clear it; opening the palette clears it, so palette query digits remain literal. Digits also remain literal in Insert and command/search prompts. Counts add no history, and Vim operator grammar such as `3dw` is not supported.

Editing uses an ordered selection set with one primary target. Cursor and word motions apply to every target; Visual motions keep each target's anchor and move its active endpoint. Whole combining sequences and ZWJ emoji remain intact. Visual selection is characterwise and inclusive of the endpoints; its read-only ranges are end-exclusive. `$`/End can select the newline after a non-final row; empty-line newlines are selectable too. Selected newlines appear as a blue blank cell after the line. Blue highlighting overrides yellow search highlighting; secondary carets are magenta, including on empty lines and at line ends. Only the primary owns the hardware cursor and viewport. The status line counts all targets, including offscreen targets.

Ctrl+k/Ctrl+e clone each target to the adjacent row, preserving preferred terminal-cell columns (tabs use four-cell stops); Visual cloning preserves both endpoints. Duplicate carets and truly overlapping selections merge; adjacent ranges remain distinct. Visual Ctrl+l creates one Normal caret at the first nonblank of each touched row. Visual `I`/`A` similarly create one Insert caret per touched row at first nonblank/end. Occurrence actions use the primary selection as a literal, potentially multiline, grapheme-aligned query: Ctrl+n adds the next non-overlapping occurrence and wraps; Ctrl+s moves only the primary to that occurrence; Ctrl+a selects all occurrences.

Copy and cut return to Normal at each selection start; Visual cancellation keeps each active endpoint and removes highlighting. Normal Esc collapses to the primary. `p`/`P` paste after/before each current grapheme, including multiline text. Each caret lands on its last inserted grapheme, or the new row's start when its fragment ends in a newline. Every multi-target edit is planned against the original buffer and committed as one undo action, not one per target. Copy, movement, and cancellation do not add history or clear redo. Undo/redo restore text, the full caret set, and primary identity in Normal mode, not Visual highlighting or the clipboard.

Visual `c` removes all selected text into the internal clipboard and enters Insert at each selection start. Deletion and replacement typing form one undo action when Insert mode is exited, including through explicit command execution. Esc without typing commits the deletion alone. An identical replacement creates no history entry and preserves redo. Changing only empty final-row selections enters Insert without overwriting the clipboard.

Bracketed paste broadcasts the same literal text to all Insert carets in a separate undo group, distinct from typing before/after it. A rejected paste leaves the pending change intact. Normal-mode operator grammar such as `cw` is not supported; `c` types literal text in Insert mode.

The clipboard is internal to the editor session and independent of the system clipboard. Copy/cut store fragments in document order: one fragment broadcasts to every caret; matching fragment/caret counts pair in document order; any other count refuses paste without changing state. Empty clipboard paste does not edit text; copying/cutting only empty final-row selections does not overwrite the clipboard. Open a new search or enter Ex commands after leaving Visual mode. Plugin commands execute once, not once per target: successful text effects collapse to the primary and apply once; rejected or message-only effects preserve the selection set. There is no selection-aware plugin API yet.

### Repeat last edit

`.` repeats the session's last successful native edit in Normal/Visual. Insertion placements (`i`/`I`/`a`/`A`/`o`/`O`), Insert typing and edit-context motions/newline/backspace/delete, Visual change/cut, Normal deletion, clipboard/literal paste, and line joining are recorded as resolved edit operations—not keystrokes, command invocations, or old byte offsets. Remapping keys afterward does not change the recorded operation. Insert `.` and popup query `.` remain literal. A count before dot is consumed and repeats once, consistent with other non-motion commands.

In Normal, Visual change/cut targeting replays its resolved motions and counts at each current caret: `vecitem` followed later by `.` changes a fresh whole word, even if its length differs. If targeting was rebuilt by cloning, occurrence gathering, search, or overlap merging, repeat uses relative whole-grapheme spans instead. Equal spans broadcast; unequal spans require matching target counts. In Visual, the current explicit ranges replace the stored targeting. Target-building commands themselves do not recreate old cursors.

Clipboard paste captures the fragments actually pasted, so a later yank does not change repeat's payload. One fragment broadcasts; equal fragment/target counts pair; mismatches refuse atomically. Other per-target edit data, such as partially effective Insert deletion, obeys the same conservative distribution policy. A refusal or cardinality change during replay leaves text, caret/primary state, clipboard, and history unchanged.

Each repeat returns to Normal and creates one undo entry restoring the full caret set and primary. Original typing/paste/typing boundaries remain separate; dot replays the selected committed group as one transaction. Typed text retains scalar insertion boundaries, preserving combining/ZWJ interactions with surrounding graphemes; bracketed paste remains one bulk literal operation. Trailing Insert movement is not repeated.

The last recipe is session-wide across buffers, but pending Insert groups and undo/redo remain buffer-local. No-op/identical edits, rejected input, navigation, yank, explorer filtering, saving, undo/redo, and plugin effects do not replace it. Successful buffer parking and ordinary explicit Ex execution commit pending native typing at existing boundaries; failed buffer requests do not split that group. Plugins never execute through dot. Repeat does not consume or recursively replace its recipe. Rebind with `config.core.repeat_last_edit`, including Normal/Visual leader routes.

### Search

Search is case-sensitive and single-line, with no regular expressions or Unicode normalization. Matches start and end on whole grapheme boundaries, including combining marks and emoji. Next/previous navigation skips the current position and wraps through the buffer; a sole match wraps back to itself. The active match is highlighted yellow.

Submitting an empty search repeats the last query. Esc cancels without moving the cursor or replacing the previous query/match. A missing match reports the query, clears the highlight, and leaves the cursor unchanged; searching without a previous query also leaves the cursor unchanged. Search never edits text or adds undo history. Buffer edits and undo/redo clear the highlight but retain the query, so subsequent navigation searches the current text again.

Commands: `:w [path]`, `:q`, `:q!`, `:wq [path]`, `:plugins`, and `:plugin-command [arguments]`.

`:q` refuses unsaved changes in any open buffer; `:q!` exits without saving them. `:wq` saves the active buffer and quits only if every buffer is then clean. Saves use a same-directory temporary file and rename, preserve existing permissions, and reject target symlinks. Writing to a path owned by another loaded buffer refuses before modifying the file. UTF-8 text is edited by extended grapheme; tabs render at four-cell stops. LF and trailing-newline structure are preserved; CRLF and CR are normalized to LF. Binary/terminal-control-containing text is rejected. Bracketed paste inserts only in Insert mode and never executes pasted commands in Normal mode.

Paste is backend input: it is ignored in Normal, Command, Search, and Visual modes, and inserts literal text in Insert mode, with CRLF/CR normalization and a 4 MiB limit. Pasted text is one undo action, separate from typing before and after it. Rejected paste reports an error without changing text, cursor, mode, or pending insert history. Internal clipboard actions are separate from `Input::Paste` and use already-validated buffer text.

### Buffers

One buffer is visible at a time. Each retains its text, path, saved state, directed selections and primary, mode, search state, and undo/redo history. The TUI retains separate vertical/horizontal scroll offsets by stable buffer ID, adjusting them only as needed to keep the primary visible after resizing. Clipboard fragments, bindings, plugin hosts, and plugin retirement remain session-wide. Plugin context and effects refer to the active buffer.

| Command | Behavior |
| --- | --- |
| `:edit PATH` | Switch to an already-loaded file, or read and validate a new buffer; a nonexistent file opens empty |
| `:buffers` | List stable IDs and paths; `%` marks active, `+` marks dirty |
| `:buffer N` | Switch to buffer ID `N` |
| `:bnext` / `:bprev` | Switch in ascending-ID order, wrapping at either end |
| `:bdelete [N]` | Close the active or named buffer; refuse unsaved changes |
| `:bdelete! [N]` | Explicitly discard changes and close the active or named buffer |

IDs start at 1 and are never renumbered or reused. Closing the last buffer creates a fresh unnamed clean buffer rather than quitting. Closing the active buffer selects the next remaining ID, with wraparound. Switching does not save, discard, or reload hidden edits. Existing-file aliases resolve to the same loaded buffer; the supplied path spelling remains the save/display path, so opening through a symlink does not bypass save rejection. Paths are relative to the process working directory; the entire `:edit` argument is the path, including spaces, with no shell expansion.

Switching from Insert commits its pending undo group and parks that buffer in Normal. Explicit buffer switching from Visual retains that buffer's directed ranges and Visual mode; switching back restores them. Command/search prompts, palette queries, and pending motion counts are transient, not restored per buffer. The new commands appear in the command palette and can be bound by exact command name in Normal mode. When several buffers are open, status shows the active ID and total count.

### File picker and explorer

Space o opens a floating **Tree** explorer directly in **INSERT/filter** mode, ready for typing; Space e opens or focuses the docked **Tree**, starting in **NORMAL/navigation** mode when new. Both use one catalog and instance. Invoking the other action applies that presentation's configured default while retaining query, selection identities, and surviving folder expansion. Floating Tree invocation enters filtering if not already filtering. These actions are available as `config.core.file_picker` and `config.core.file_explorer` in Normal/Visual and in the command palette.

The dock defaults to the right of the editor workspace. Set `config.file_explorer_side = "left"` (or `"right"`, `"top"`, `"bottom"`) to choose another side. Status and command/search prompts remain full-width; editor text, gutter, highlights, and cursors use the remaining rectangle. Focused panes prioritize their query on tiny terminals; unfocused docks shrink or hide to preserve editing space.

Both view preferences default to `"tree"`: `config.file_picker_view` and `config.file_explorer_view` independently accept `"list"` or `"tree"`. Set the floating preference to `"list"` to retain the old flat picker. Ctrl+t toggles the current focused instance without rescanning. List retains searchable full relative paths. Tree shows folders first, two-cell indentation, and basename-only files. Folder names end in `/` and use cyan text; files use the normal foreground color. Fold-state arrows are omitted. Maximal single-child directory chains share one row, such as `src/client/http/`; a directory containing one file still gets its own row.

Floating Tree opens in explorer **INSERT** mode; a new docked Tree opens in **NORMAL**. Press `i` in NORMAL to resume editing the existing filter; the `i` itself is not added to the query. Typing and Backspace filter full relative paths by case-insensitive whitespace tokens. These are explorer-local modes, not changes to the file buffer's mode. Matching nodes appear with ancestor context, and query changes initially select a direct match. Escape in INSERT changes only to NORMAL: the filter, visible results, highlighted item, and explorer focus remain. NORMAL displays the active filter and navigates that filtered tree. Escape from NORMAL returns focus to the buffer (or closes floating search). List always accepts query typing immediately.

| File-view input | Behavior |
| --- | --- |
| Type / Backspace | Type query text in List/explorer INSERT / remove one whole grapheme; explorer NORMAL uses hjkl for navigation |
| j/k (NORMAL); Ctrl+j/k or Up/Down | Wrap forward/backward through visible rows |
| l (NORMAL); Ctrl+l/Right | NORMAL expands/enters a folder; INSERT selects its visible child without changing the filter |
| h (NORMAL); Ctrl+h/Left | NORMAL collapses/selects parent; INSERT selects its visible parent without changing the filter |
| Enter | Toggle a folder, or open the selected file using existing buffer deduplication |
| `i` (explorer NORMAL) | Enter explorer INSERT/filter mode without inserting `i` |
| Esc | INSERT → NORMAL with the filter and selection retained; NORMAL → buffer focus or floating close |
| Ctrl+u | Clear the filter in NORMAL or INSERT without changing mode/focus; preserve the selected path where possible |
| Tab | Return to editor focus from a dock |
| Ctrl+w | Close either presentation |
| Ctrl+r | Rescan while retaining query, surviving expansion, and selection |
| Ctrl+p | Open the command palette, closing floating search or blurring a dock |
| Ctrl+t | Toggle List/Tree while retaining view state |

Opening a file from a dock leaves it visible and returns focus to the buffer. Space e refocuses it. Choosing a folder during filtering returns to explorer NORMAL and toggles that folder; it never opens a text buffer for a directory. Selections use actual OS-path identities across filtering, view switches, and refresh; a removed or hidden selection falls back to the nearest visible ancestor, then the first row. Query input never edits the underlying buffer; bracketed paste is ignored while file search is focused. Cancellation preserves buffer mode, selections, and pending Insert history. Invalid, binary, unreadable, or disappeared file selections report an error and keep focus without changing the active buffer.

Clearing returns to the full catalog and reveals the selected file's ancestry in NORMAL when needed. With no current result, it uses the last available selection; removed paths fall back to a visible ancestor, then the first row. Clearing an already empty query is harmless. Filtered folders can be collapsed/expanded in NORMAL without losing the query. Temporary filtered collapse overrides survive mode/view changes and refresh of surviving directories; editing or clearing the query resets them so new matches can be revealed. Choosing a directory during filtering transitions to NORMAL and toggles it while retaining the query.

The project root is the working directory captured at startup. Scanning uses the `ignore` crate for nested `.gitignore` rules and negation; parent/global Git ignore rules are disabled. Hidden regular files and directories are included unless ignored, `.git`/`.jj` metadata is always excluded, and symlink files/directories are not followed. Files open using their original OS paths, not sanitized display labels. Root scan failures report an error; descendant/ignore errors retain reachable entries with an explicit incomplete-scan warning. A failed refresh keeps the prior catalog. There is no background watcher: refresh explicitly after external file changes.

### Command palette

Ctrl+p opens a searchable overlay without leaving the current mode. It lists core actions and registered Ex/plugin commands with their owner, effective bindings in the current mode, and eligible modes. Disabled or overridden bindings are not advertised; actions with no key remain available through the palette. Mode-ineligible entries are dimmed and cannot execute. Retired plugin commands disappear.

Search is case-insensitive: every whitespace-separated query token must occur in the command name, human-readable label, or owner. Results have a stable label/name order. Ctrl+j/Down/Ctrl+n select the next result; Ctrl+k/Up select the previous, with wraparound. Backspace removes a whole grapheme. Enter with no match or an ineligible selection leaves the palette open. Bracketed paste is ignored while the palette is open.

Accepting a core action executes it in the underlying mode, including Visual edits and Insert-mode actions. Accepting an Ex/plugin command is available only in Normal mode and opens a prefilled `:` prompt; add arguments if needed, then Enter executes through the usual session dispatch. Choosing `q!` therefore does not immediately discard changes.

Esc or Ctrl+p cancels without changing text, selections, the previous command/search prompt, or pending Insert history. The opening key can be remapped with `config.core.palette`; list navigation uses the shared configurable `selection` context. Other popup controls keep their defaults unless explicitly intercepted by a selection binding. The TUI uses a constraint-based modal panel, keeps the selected result visible, and prioritizes the query on tiny terminals.

### Selection-list bindings

The palette, floating file picker, and focused docked explorer share `config.modes.selection`. It is a binding context, not a buffer editing mode. `config.core.down` moves to the next list item; `config.core.up` moves to the previous. Defaults are Ctrl+j/Down/Ctrl+n for next and Ctrl+k/Up for previous. Remap or disable any single key:

```ruby
config.bind "ctrl+f", config.core.down, mode: config.modes.selection
config.bind "ctrl+b", config.core.up, mode: config.modes.selection
config.bind "ctrl+j", nil, mode: config.modes.selection
```

Selection bindings take precedence while a file or command list is focused. Unbound printable keys filter in List/explorer INSERT, but not explorer NORMAL; a disabled key is consumed without filtering or moving. Only `up`, `down`, and `nil` are accepted—no leader sequences, edits, or plugin commands. Invalid declarations leave existing routes unchanged. Navigation does not change text, carets, history, or the buffer mode. Both list footers show effective keys, including remaps and disabled directions.

Tree views use `config.modes.tree`, accepting `up`, `down`, `left`, `right`, or `nil`. Explorer NORMAL defaults to h/j/k/l for parent/next/previous/child, with the existing control/arrow routes retained. Tree routes override shared selection routes. In explorer INSERT, printable tree keys are not intercepted: h/j/k/l become query text, while control/special-key tree routes still navigate. Ctrl+h/l select visible parents/children in the filtered projection without changing the query or saved folder expansion. Unmatched keys inherit shared selection bindings. Cached hints prioritize plain keys in NORMAL and omit them in INSERT. For example:

```ruby
config.bind "ctrl+f", config.core.right, mode: config.modes.tree
config.bind "ctrl+h", nil, mode: config.modes.tree
```

Ctrl+h is **not** a Backspace alias or default deletion key in any mode. Raw Ctrl+h (0x08) and Backspace (DEL/0x7f) are distinct, as are CSI-u events. In the tree it navigates in NORMAL and INSERT without deleting query text; it never deletes file-buffer Insert text by default. Explicit `config.core.backspace` bindings remain available if desired.

Ctrl+j is distinct from Enter: in the TUI's raw mode, LF is Ctrl+j and CR is Enter; CSI-u control events also work. No enhanced-terminal negotiation is required. Ctrl+m remains an Enter alias. Outside lists, existing editing bindings are unchanged: Ctrl+k still clones above in Normal/Visual, and explicit Ctrl+j defaults insert a newline in Insert or submit Command/Search prompts. Enter and Ctrl+j can now be rebound independently.

### Leader key

Space starts a leader sequence in Normal/Visual when it has no direct binding in that mode. Leader bindings use `leader` followed by whitespace-separated single-key names, for example `config.bind "leader b n", "bnext"`. Nested prefixes wait for the next key without a timeout. The status bar shows the actual pending sequence before the file path; the palette advertises effective sequences alongside ordinary bindings.

Set `config.leader = ","` to change the trigger for every default and configured leader route. Suffix keys stay unchanged: the default palette binding becomes comma then Space, save becomes comma then `w`, and buffer-next becomes comma then `b` then `n`. Choose an unused single key in the existing notation; Escape, ASCII digits, malformed keys, and a new trigger already directly bound in Normal/Visual are rejected without replacing the current choice. A direct binding on the current trigger—including `nil`—takes precedence per mode and hides unreachable leader routes from the palette.

Esc cancels a pending sequence and count without leaving Visual or collapsing carets. Unknown suffixes consume the key and cancel safely, never falling through to an edit. Paste, external command execution, buffer switching, and binding/leader changes clear pending state. A count before a leader motion applies normally; digits inside a sequence are literal suffix keys. Plugins execute once. Outside Normal/Visual, the leader has no prefix behavior, so Space still types normally in Insert and prompts.

Leader bindings require Normal/Visual and the target's existing mode eligibility; Ex/plugin targets remain Normal-only. A sequence cannot be both a complete binding and another binding's prefix: ambiguous declarations are refused atomically. Disabled leaves remain reserved. Only leader-prefixed sequences are supported—not arbitrary multi-key mappings, timers, or macros.

## Module seams

One crate, five modules, no workspace or terminal-coordinate types in the editing backend:

- `editor`: owns buffer lifecycle and per-buffer text, saved state, primary/selection set, modes, search, and undo/redo; session-wide clipboard fragments, action metadata, command-palette and file-picker focus/dispatch, key notation, leader/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.
- `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.
- `session`: `EditorSession` owns the editor and its Ruby hosts together. It loads configuration once, registers eligible plugins before installing shared bindings, executes selected commands against the active buffer, and retires both host and command ownership on invocation or effect-validation failure.
- `tui`: translates terminal events to session input, renders read-only active-buffer state, keeps frontend-owned viewports by stable buffer ID, and advertises `text` and `styled_text` capabilities. It has no plugin lifecycle callback, host storage, 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.

Frontends drive `EditorSession::handle` or `execute` and inspect `editor()`; there is no mutable editor getter that could independently alter plugin registration. 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. A range ending at the next row's column 0 includes the previous row's newline; an empty final-row range contains no text. Selection normalization, clipboard contents, edit planning, and history remain inside the editor module.
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 motion prefix; parsing and counted motion dispatch remain editor-owned.
Frontends inspect `leader_pending()` for the cached display of a pending leader sequence; prefix recognition, cancellation, and dispatch remain editor-owned.
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 `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.

The terminal adapter owns raw mode, alternate-screen state, bracketed paste, 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.

The TUI uses Ratatui constraint-based layout for a flexible buffer viewport, a one-row status bar, and a one-row prompt/message area. Scrolling, clipping, highlights, and cursor placement use the allocated regions, not terminal-wide offsets. Below three rows the status bar is hidden; at one row the buffer remains visible unless an active command/search prompt takes priority. Zero-sized terminals render nothing. Layout and terminal-cell text mapping remain frontend-owned.

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.

Built-in Ex commands register as the protected `core` feature in the same command registry used by plugins. External plugins cannot claim core status, replace existing commands, or disable core. User configuration can override any keybinding without replacing the core implementation. `:plugins` lists active features and frontend capabilities.

A feature declares all capabilities it needs. Registration is atomic: if any requirement is unavailable or any command conflicts, none of its commands are installed. For example, `Vamp.plugin "canvas", requires: ["graphics"]` will be refused by this TUI. Capability names are extensible strings, not a terminal-vs-GUI switch. Capability declarations express compatibility; they are not security permissions.

## Ruby configuration

By default, vamp loads `$XDG_CONFIG_HOME/vamp/config.rb`, or `~/.config/vamp/config.rb` when that environment variable is unset. `--config path` selects a file explicitly; `--no-config` bypasses Ruby entirely. Set `VAMP_RUBY` to select a different Ruby executable.

```ruby
Vamp.configure do |config|
  config.leader = "space"
  config.file_explorer_side = "right"
  config.file_explorer_view = "tree"
  config.file_picker_view = "tree"
  config.bind "ctrl+h", config.core.left, mode: config.modes.tree
  config.bind "ctrl+l", config.core.right, mode: config.modes.tree
  config.plugin "plugins/greeting.rb"
  config.bind "g", "greet"
  config.bind "leader g", "greet"
  config.bind "ctrl+r", config.core.redo
  config.bind "shift+j", config.core.join_lines
  config.bind "ctrl+c", config.core.normal, mode: config.modes.insert
  config.bind "ctrl+f", config.core.search
  config.bind "ctrl+c", config.core.normal, mode: config.modes.search
  config.bind "ctrl+v", config.core.select
  config.bind "ctrl+c", config.core.copy, mode: config.modes.visual
  config.bind "ctrl+x", config.core.cut, mode: config.modes.visual
  config.bind "ctrl+r", config.core.change, mode: config.modes.visual
end
```

Plugin paths resolve relative to the config file, not the shell's working directory. `config.bind key, target, mode: config.modes.normal` overrides one key or leader-prefixed sequence; editing modes are `config.modes.normal`, `config.modes.insert`, `config.modes.command`, `config.modes.search`, and `config.modes.visual`. `config.modes.selection` configures shared list navigation; `config.modes.tree` overrides it in tree browsing. Omitting `mode` selects Normal. The leader defaults to `"space"` and is applied before configured bindings.
`config.file_explorer_side` defaults to `"right"`; other choices are `"left"`, `"top"`, and `"bottom"`. Independent `file_explorer_view` / `file_picker_view` preferences both default to `"tree"` and accept `"list"` as an alternative. Invalid preference strings report notices and retain defaults while valid bindings still install. Non-string/empty values disable the whole configuration like other Ruby type errors.

`config.core` exposes the built-in actions below as immutable `Action` values; `config.modes` exposes immutable `Mode` values. Misspelled methods fail during configuration evaluation, and `bind` rejects the wrong value type. Built-in action strings and mode strings are not accepted. Registered Ex/plugin commands still use exact string names (`"w"`, `"greet"`, etc., without `:` or arguments) and can only be bound in Normal mode. Ruby provides runtime checks, not compile-time checking; the editor still validates action/mode compatibility.

Key notation follows [Herdr's readable style](https://herdr.dev/docs/configuration/#keybindings). Literal non-control Unicode characters are case-sensitive (`n`, `J`, `+`); named keys and modifiers are case-insensitive:

- Named keys: `esc`, `enter`, `backspace`, `delete`, `left`, `right`, `up`, `down`, `home`, `end`, `tab`, `space`.
- Modifiers: `ctrl+a` through `ctrl+z`, and `shift+a` through `shift+z`. `shift+j` and `J` address the same key.
- Named punctuation: `minus`, `comma`, `ampersand`, `plus`, `backtick`. Each addresses the same binding as its literal character.

`ctrl+i` aliases `tab`, and `ctrl+m` aliases `enter`, including inside leader sequences. Ctrl+h and Ctrl+j are distinct control keys, not Backspace/Enter aliases. Only a single modifier on an ASCII letter is supported. Arbitrary non-leader key sequences, Alt/Cmd/Super, combined modifiers, modified special keys, and Vim-style angle-bracket notation are rejected rather than silently treated as another key.

| Available modes | Methods on `config.core` |
| --- | --- |
| Normal | `insert`, `append`, `open_below`, `open_above` |
| Normal, Visual | `insert_first_nonblank`, `append_line_end`, `clone_above`, `clone_below` |
| Normal | `join_lines`, `undo`, `redo`, `command` |
| Normal | `search`, `paste_before`, `paste_after` |
| Normal, Visual | `select`, `search_next`, `search_previous` |
| Normal, Visual | `repeat_last_edit` |
| Normal, Visual | `file_picker`, `file_explorer` |
| Normal, Insert, Visual | `line_start`, `line_end` |
| Normal, Insert, Visual, Tree | `left`, `right` |
| Normal, Insert, Visual, Selection, Tree | `down`, `up` |
| Normal, Insert, Visual | `word_next`, `word_previous`, `word_end`, `big_word_next`, `big_word_previous`, `big_word_end` |
| Normal, Insert | `delete` |
| Visual | `copy`, `cut`, `change`, `select_lines`, `select_next`, `skip_occurrence`, `select_all` |
| Normal, Insert, Command, Search, Visual | `normal`, `palette` |
| Insert, Command, Search | `backspace` |
| Insert | `newline` |
| Command, Search | `submit` |

Adding a binding keeps the original key. Pass `nil` to disable a key, including literal typing in Insert/Command mode:

```ruby
Vamp.configure do |config|
  config.bind "n", config.core.insert
  config.bind "i", nil
  config.bind "space", config.core.command
  config.bind ":", nil
end
```

The last valid declaration for a key/mode wins. Invalid keys, incompatible action/mode pairs, ambiguous leader prefixes, or unknown command names leave that binding unchanged and appear in the status message; other valid bindings still load. An invalid leader key reports a notice and retains Space, while valid bindings still install. Ruby syntax errors, unknown methods, and type errors—including non-string or empty leader values—disable the entire configuration and fall back to defaults. One plugin's load failure does not prevent other plugins loading. Disabling a plugin removes its single-key and leader bindings, without restoring any default keys they replaced.

Bindings are resolved inside the editor module, not the terminal adapter. Bracketed paste remains literal and bypasses keybindings. If configuration disables your keys for leaving Insert/Command/Search/Visual mode or entering commands, restart with `--no-config` to restore defaults.

## Ruby plugins

```ruby
Vamp.plugin "greeting", requires: ["text"]

Vamp.command "greet" do |editor, args|
  name = args.empty? ? "world" : args
  editor.insert "Hello, #{name}!\n"
  editor.message "Greeting inserted by Ruby"
end
```

Run `:greet vamp`, or press `g` with the example configuration. `examples/plugins/greeting.rb` also provides `:upper` to uppercase the buffer.

Callbacks receive an immutable primary-only context snapshot: `editor.text`, `editor.row`, `editor.column`, `editor.mode`, and `editor.path`. Row/column are **one-based grapheme positions**; mode is `NORMAL`; path is a string or `nil`. Arguments are the remaining command text, without surrounding whitespace. Commands run once regardless of target count; successful text effects collapse to the primary before editing once. The plugin API does not expose selections.

`editor.insert(text)`, `editor.replace(text)`, and `editor.message(text)` queue effects. The context remains the pre-command snapshot even after queuing an effect. All effects are validated before the backend changes anything; buffer changes from one successful invocation form one undo action. Exceptions, process exits, timeouts, malformed replies, and invalid effects disable that plugin and discard its effects. Other plugins and built-ins remain available. Plugin `puts`, explicit `STDOUT.write`, and stderr cannot overwrite the TUI; diagnostic output is discarded, while exceptions appear in the status message.

This is crash isolation, **not a security sandbox**: Ruby configuration and plugins have your user account's filesystem/process permissions. Load only trusted scripts. On Unix, hosts run in their own process groups and their groups are killed on shutdown.

### Messaging

Rust and Ruby exchange UTF-8, newline-delimited JSON objects with `version: 1`. Startup returns `manifest` (name, required capabilities, commands) or `config` (plugin paths and bindings). `invoke` requests carry an ID, command, arguments, and context; `result` replies carry the matching ID and typed effects (`insert`, `replace`, `message`). Errors use `error` frames. Unknown fields, wrong versions, and mismatched replies are rejected. Frames and aggregate effect text are bounded to 4 MiB.

JSON uses Ruby's standard library. Protocol Buffers is not installed or required; there is no frontend/network wire protocol yet. The frontend currently calls the Rust library directly.

## Current limits

- One visible buffer at a time; Normal, Insert, Command, Search, and characterwise Visual modes. No system clipboard integration, named registers, line/block selection, Vim operators, splits/tabs, regex/multiline search, LSP, or graphical frontend.
- Undo uses full-buffer snapshots and movement scans the current line. This favors straightforward correctness over large-file performance.
- Plugin invocation is synchronous and may pause input for up to 500 ms before a host timeout. Config/plugin startup has a 2-second deadline per host. Buffer context must fit within a 4 MiB JSON request; a too-large request disables that plugin, not editing.
- Disabling a plugin removes its commands and bindings until the next launch. There is no hot reload.

## Verify

```sh
cargo test
cargo clippy --all-targets -- -D warnings
cargo fmt --check
ruby -c src/ruby_host.rb
```

Regression checks exercise Unicode edits, undo/redo, saving and failed saves, capability/command ownership, effect atomicity, real Ruby execution, protocol errors, crash/timeout recovery, and inherited-pipe cleanup. Backend paste checks cover ignored modes, literal Unicode/newline insertion, rejection atomicity, and typing/paste/typing undo and redo. Session checks join real Ruby execution to capability/collision rejection, complete command/binding retirement after invalid effects or host failure, surviving plugins, core editing/saving, and broken-config fallback. The executable was also exercised in PTY sessions for editing/saving, rejected-effect retirement, plugin crash and hang recovery, modal bracketed paste, rejected-paste feedback, undo/redo, scrolling, resize, and terminal restoration.

Unix terminal-hook checks run in isolated child processes and real PTYs to keep global hooks out of the parallel test runner. They cover entry failure, normal return, I/O error, panic cleanup before caller diagnostics, original panic-payload propagation, and later panics producing no stale terminal-restoration output.