refactor: add Keymap with default bindings and wire into handle_key

Create keymap.rs with Keymap struct mapping (mode, key) to Cmd trait
objects. Wire into App::handle_key — keymap dispatch is tried first,
falling through to old handlers for unmigrated bindings. Normal mode
navigation, cell ops, mode switches, and Help mode are keymap-driven.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/command/keymap.rs

@@ -0,0 +1,126 @@
+use std::collections::HashMap;
+
+use crossterm::event::{KeyCode, KeyModifiers};
+
+use crate::ui::app::AppMode;
+use crate::ui::effect::Effect;
+
+use super::cmd::{self, Cmd, CmdContext};
+
+/// A key pattern that can be matched against a KeyEvent.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub enum KeyPattern {
+    /// Single key with modifiers
+    Key(KeyCode, KeyModifiers),
+}
+
+/// Identifies which mode a binding applies to.
+/// Uses discriminant matching — mode data (buffers, etc.) is ignored.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub enum ModeKey {
+    Normal,
+    Help,
+    // More modes can be added as we migrate handlers
+}
+
+impl ModeKey {
+    pub fn from_app_mode(mode: &AppMode) -> Option<Self> {
+        match mode {
+            AppMode::Normal => Some(ModeKey::Normal),
+            AppMode::Help => Some(ModeKey::Help),
+            _ => None,
+        }
+    }
+}
+
+pub struct Keymap {
+    bindings: HashMap<(ModeKey, KeyPattern), Box<dyn Cmd>>,
+}
+
+impl Keymap {
+    pub fn new() -> Self {
+        Self {
+            bindings: HashMap::new(),
+        }
+    }
+
+    pub fn bind(&mut self, mode: ModeKey, key: KeyCode, mods: KeyModifiers, cmd: impl Cmd + 'static) {
+        self.bindings
+            .insert((mode, KeyPattern::Key(key, mods)), Box::new(cmd));
+    }
+
+    pub fn lookup(
+        &self,
+        mode: &AppMode,
+        key: KeyCode,
+        mods: KeyModifiers,
+    ) -> Option<&dyn Cmd> {
+        let mode_key = ModeKey::from_app_mode(mode)?;
+        self.bindings
+            .get(&(mode_key, KeyPattern::Key(key, mods)))
+            .map(|c| c.as_ref())
+    }
+
+    /// Execute a keymap lookup and return effects, or None if no binding.
+    pub fn dispatch(
+        &self,
+        ctx: &CmdContext,
+        key: KeyCode,
+        mods: KeyModifiers,
+    ) -> Option<Vec<Box<dyn Effect>>> {
+        let cmd = self.lookup(ctx.mode, key, mods)?;
+        Some(cmd.execute(ctx))
+    }
+
+    /// Build the default keymap with all vim-style bindings.
+    pub fn default_keymap() -> Self {
+        let mut km = Self::new();
+        let none = KeyModifiers::NONE;
+        let ctrl = KeyModifiers::CONTROL;
+
+        // ── Normal mode: Navigation ──────────────────────────────────────
+        km.bind(ModeKey::Normal, KeyCode::Up, none, cmd::MoveSelection { dr: -1, dc: 0 });
+        km.bind(ModeKey::Normal, KeyCode::Down, none, cmd::MoveSelection { dr: 1, dc: 0 });
+        km.bind(ModeKey::Normal, KeyCode::Left, none, cmd::MoveSelection { dr: 0, dc: -1 });
+        km.bind(ModeKey::Normal, KeyCode::Right, none, cmd::MoveSelection { dr: 0, dc: 1 });
+        km.bind(ModeKey::Normal, KeyCode::Char('k'), none, cmd::MoveSelection { dr: -1, dc: 0 });
+        km.bind(ModeKey::Normal, KeyCode::Char('j'), none, cmd::MoveSelection { dr: 1, dc: 0 });
+        km.bind(ModeKey::Normal, KeyCode::Char('h'), none, cmd::MoveSelection { dr: 0, dc: -1 });
+        km.bind(ModeKey::Normal, KeyCode::Char('l'), none, cmd::MoveSelection { dr: 0, dc: 1 });
+
+        // Jump to boundaries
+        km.bind(ModeKey::Normal, KeyCode::Char('G'), KeyModifiers::SHIFT, cmd::JumpToLastRow);
+        km.bind(ModeKey::Normal, KeyCode::Char('0'), none, cmd::JumpToFirstCol);
+        km.bind(ModeKey::Normal, KeyCode::Char('$'), KeyModifiers::SHIFT, cmd::JumpToLastCol);
+
+        // Scroll
+        km.bind(ModeKey::Normal, KeyCode::Char('d'), ctrl, cmd::ScrollRows(5));
+        km.bind(ModeKey::Normal, KeyCode::Char('u'), ctrl, cmd::ScrollRows(-5));
+
+        // ── Normal mode: Cell operations ─────────────────────────────────
+        km.bind(ModeKey::Normal, KeyCode::Char('x'), none, cmd::ClearSelectedCell);
+        km.bind(ModeKey::Normal, KeyCode::Char('p'), none, cmd::PasteCell);
+
+        // ── Normal mode: View ────────────────────────────────────────────
+        km.bind(ModeKey::Normal, KeyCode::Char('t'), none, cmd::TransposeAxes);
+
+        // ── Normal mode: Mode changes ────────────────────────────────────
+        km.bind(ModeKey::Normal, KeyCode::Char('q'), ctrl, cmd::ForceQuit);
+        km.bind(ModeKey::Normal, KeyCode::Char(':'), KeyModifiers::SHIFT, cmd::EnterMode(AppMode::CommandMode { buffer: String::new() }));
+        km.bind(ModeKey::Normal, KeyCode::Char('/'), none, cmd::EnterSearchMode);
+        km.bind(ModeKey::Normal, KeyCode::Char('s'), ctrl, cmd::SaveCmd);
+        km.bind(ModeKey::Normal, KeyCode::F(1), none, cmd::EnterMode(AppMode::Help));
+        km.bind(ModeKey::Normal, KeyCode::Char('?'), KeyModifiers::SHIFT, cmd::EnterMode(AppMode::Help));
+
+        // Two-key sequence starters
+        km.bind(ModeKey::Normal, KeyCode::Char('g'), none, cmd::SetPendingKey('g'));
+        km.bind(ModeKey::Normal, KeyCode::Char('y'), none, cmd::SetPendingKey('y'));
+        km.bind(ModeKey::Normal, KeyCode::Char('Z'), KeyModifiers::SHIFT, cmd::SetPendingKey('Z'));
+
+        // ── Help mode ────────────────────────────────────────────────────
+        km.bind(ModeKey::Help, KeyCode::Esc, none, cmd::EnterMode(AppMode::Normal));
+        km.bind(ModeKey::Help, KeyCode::Char('q'), none, cmd::EnterMode(AppMode::Normal));
+
+        km
+    }
+}