Struct SnippetActiveMode 

pub struct SnippetActiveMode;

active-snippet-mode — a transient minor mode activated while a snippet session is live on a buffer. Contributes the three Insert-mode bindings (<Tab> / <S-Tab> / <Esc>) via Mode::keymap(); K.2.4 registers them at startup under KeymapLayer::MinorMode("active-snippet-mode") and K.1.c gates them to buffers where the mode is active.

SN.2b (2026-06-12): the mode now owns the <Tab> / <S-Tab> placeholder-navigation handler bodies, not just the chord choice. The bodies were Editor::do_snippet_next/prev_ placeholder in lattice-host — the half-migration feedback_mode_owns_its_surface forbids (keymap in the mode, handler in the host). They register here as ActionContext -> Effect closures on the ActionHandlerRegistry substrate (the path the project-search provider already uses), advancing the shared SnippetSession service and returning a cursor effect through the host’s generic effect pipeline (see snippet_group_cursor_effect).

SN.3d.3 (2026-06-15): that cursor effect now consumes Select mode. A placeholder with a non-empty default returns Effect::Many([EnterMode(Select(Charwise)), SelectionChange(span)]) so the default is SELECTED and the next printable key overtypes the whole thing (then drops to Insert). An empty tabstop still returns a bare Effect::SelectionChange cursor. The host’s initial-expand focus (Editor::expand_snippet) mirrors this directly.

SN.3c.2 (2026-06-14): <Esc> (action:snippet-leave) now owns its body here too — a third per-buffer handler that clears the shared session and returns Effect::EnterMode(Normal). The old Editor::dispatch Action::SnippetLeave arm (session clear + modal flip) + Action::SnippetLeave / AppEffect::SnippetLeave are gone (feedback_mode_owns_its_surface).

Replaces the old push_layer / pop_layer push mechanism (MO.3). The host’s sync_keymap_overlays calls activate_minor / deactivate_minor by polling the shared session’s is_active() — when the next-placeholder handler walks off $0 and clears the session, the reconciler deactivates this mode, dropping the Guard (and with it the two ActionHandlerRegistration tokens). (That host poll is itself a snippet-specific seam slated to move into this crate as a typed session-lifecycle event — see the snippet activation slice plan.)

Implementations

impl SnippetActiveMode

pub fn mode_id() -> ModeId

Trait Implementations

impl Mode for SnippetActiveMode

type Guard = SnippetActiveModeGuard

Owned cleanup token returned by [Self::on_activate].

fn id(&self) -> ModeId

Canonical identity. Same value every call.

fn kind(&self) -> ModeKind

Major or minor. Read at registration and on every activation call (activate_major on a minor, or vice versa, is [ModeActivationError::WrongKind]).

fn required_capabilities(&self) -> CapabilitySet

Capabilities the mode requires. Validated at activation; missing capability ⇒ [ModeActivationError::MissingCapability], never silent skip.

fn keymap(&self) -> Keymap

Keymap chord → command additions / overrides.

fn on_activate(&self, ctx: ModeContext) -> LifecycleFuture<'_, Self::Guard>

Lifecycle. Called once per (buffer, activation) cycle after the registry has applied the declarative contributions. Returns an owned Guard carrying every resource the mode allocated. The dispatcher stashes the Guard until deactivation, at which point dropping it performs cleanup via the Guard’s Drop impl.

fn target_buffer_kind(&self) -> Option<BufferKind>

For major modes, the [BufferKind] this mode is the default major for (H.2, 2026-05-31). ModeRegistry::register indexes this so ModeRegistry::find_major_for_kind can dispatch buffer-creation events to the right major without host-side match BufferKind { ... } blocks.

fn target_language(&self) -> Option<&str>

For major modes, the language this mode is the default major for, by canonical name (Lang::name() — "rust", "org") (OM.1). The peer of target_buffer_kind for the dispatch path [BufferKind::Document] takes: language detection rather than kind dispatch.

fn options(&self) -> OptionOverrideSet

Option overrides this mode contributes. Pure declarative (same return value every call); the host merges these into the buffer’s option-resolution layer stack while the mode is active, at the mode’s layer (later-activated minors win ties), and drops them on deactivation. Build with lattice_config::overrides! { lattice_config::Wrap = true, … }.

fn decorations(&self) -> Vec<DecorationProvider>

Decoration providers (gutter / inline / overlay / statusline). Stub — reserved for the WIT plugin path (M.10).

fn gutter_decorations(&self, _ctx: &DecorationCtx<'_>) -> Vec<GutterDecoration>

Gutter sign decorations this mode contributes while active. Called once per pane per frame with a [DecorationCtx] carrying relevant render-state snapshots (diff sign map, LSP diagnostics arc). Returns per-line GutterDecoration values; the renderer partitions them by variant into the appropriate gutter column. Default: empty (no contribution).

fn completion_sources(&self) -> Vec<CompletionSourceContribution>

Insert-mode completion sources this mode contributes while active on a buffer. Empty by default; minors that own a completion source (lsp-completion-mode, snippet-completion-mode, buffer-words-mode, tree-sitter-completion-mode, path-completion-mode, plugin sources) override.

fn action_handlers(&self) -> Vec<ActionHandlerContribution>

Global (buffer-agnostic) action handlers this mode contributes (SN.3c.0). The host walks every registered mode’s action_handlers() once at boot, resolves each action_name → CommandId, registers the handler in the ActionHandlerRegistry, and holds the tokens for the app’s lifetime. Use this for handlers that read the active buffer / cursor / services from the ActionContext at call time and close over no per-buffer state (e.g. snippet expand). Per-buffer, session-scoped handlers register in on_activate instead, so their tokens drop with the Guard. Default: none. See feedback_effect_vocabulary_is_host_boundary.

fn conflicts_with(&self) -> &[ModeId]

Modes this one cannot be active alongside.

fn implies(&self) -> &[ModeId]

Minor modes activating this mode also activates. Used by relative-line-numbers-mode ⇒ line-numbers-mode, and by read-only majors ⇒ read-only-mode.

fn presents_extensions(&self) -> &[&'static str]

File extensions (lowercase, no dot) this major PRESENTS rather than edits — the file is never loaded as text.

fn mirrors_option(&self) -> Option<&'static str>

Declarative mirror hint for “this mode is the on/off switch for a typed option of the same observable state”. Some(canonical_name) ⇒ a host-driven cascade keeps the mode’s active state and the option’s value in sync.

fn invocation_runner(&self) -> Option<ModeId>

Invocation-runner discovery (2026-05-26). Modes that own command-invocation dispatch for their buffer kind (terminal-mode, oil-mode, file-tree-mode, help-mode, …) return their canonical [ModeId]; the host registers a runner function under that id at boot, and Editor::run_invocation looks it up by walking the active modes on the active pane’s buffer (minors first, then major) before falling back to the central grammar Action gate.

fn refresh_action(&self) -> Option<&'static str>

Which of this mode’s own actions refreshes its view, or None (the default) when the mode backs nothing refreshable (RV.1, 2026-08-10).

fn fold_toggle_action(&self) -> Option<&'static str>

Which of this mode’s actions <Tab> fires, and the declaration that pulls in foldable-view-mode — the shared minor owning the chord.

fn refresh_on_open(&self) -> bool

Should re-opening this view re-run its refresh?

fn activation_policy(&self) -> ActivationPolicy

A minor mode’s default auto-activation policy (MA.1; mode-architecture.md §7.4). The host’s minor-activation resolver reads this for every registered minor when a buffer enters a major mode, and activates those whose policy admits the entered major. The default is [ActivationPolicy::Manual] — auto-activate nowhere until the mode or the user opts in. Ignored for major modes (a buffer’s major is chosen by the major resolver, not this allowlist).

fn editable_tail(&self) -> Option<EditableTail>

The mode’s editable tail on an otherwise read-only buffer, or None (the default) for a fully read-only / fully writable buffer (AU‑3).