Make side-by-side diff hunk navigation rebindable

Goal

The side-by-side diff view (composite buffer) already supports n/p (and ]/[) for next/prev hunk navigation, but the keys are hardcoded in the CompositeInputRouter. Make them rebindable through the standard keybinding system so they appear in the keybinding editor.

Read CONTRIBUTING.md before starting.

Current Architecture

How it works today

1. Composite router intercepts keys — crates/fresh-editor/src/input/composite_router.rs:112-143 has a route_key_event function that pattern-matches raw KeyEvents:

   rustCopy

   (KeyModifiers::NONE, KeyCode::Char('n')) => RoutedEvent::NavigateHunk(Direction::Next),
   (KeyModifiers::NONE, KeyCode::Char('p')) => RoutedEvent::NavigateHunk(Direction::Prev),
   (KeyModifiers::NONE, KeyCode::Char(']')) => RoutedEvent::NavigateHunk(Direction::Next),
   (KeyModifiers::NONE, KeyCode::Char('[')) => RoutedEvent::NavigateHunk(Direction::Prev),
   

2. Input dispatch calls the router — crates/fresh-editor/src/app/input.rs:4035-4089, try_route_composite_key calls CompositeInputRouter::route_key_event and dispatches RoutedEvent::NavigateHunk to composite_next_hunk/composite_prev_hunk.

3. Hunk nav implementation — crates/fresh-editor/src/app/composite_buffer_actions.rs:299-348, composite_next_hunk searches for the next RowType::HunkHeader row and scrolls to center it at 1/3 from the top.

4. Plugin fallback — crates/fresh-editor/plugins/audit_mode.ts review_next_hunk (line ~1871) also calls editor.compositeNextHunk(bufferId) when activeCompositeDiffState is set, as a plugin-side fallback.

Why this is a problem

The keybinding editor (accessible from the command palette) cannot rebind n/p/]/[ in composite buffer views because these keys are intercepted by the router before the Action-based keybinding system sees them. Users who want different keys (e.g. gn/gp, or Ctrl+Down/Ctrl+Up) cannot customize this.

What to do

Step 1: Add Action variants

In crates/fresh-editor/src/input/keybindings.rs:

• Add CompositeNextHunk and CompositePrevHunk to the Action enum.
• Add entries to the define_action_str_mapping! macro (maps string names ↔ enum variants). Use names "composite_next_hunk" and "composite_prev_hunk".
• Add them to all_action_names() so they appear in the keybinding editor.
• Add translation keys in format_action — use t!("action.composite_next_hunk") / t!("action.composite_prev_hunk").

Step 2: Add translation strings

Add the English strings to the locale file (check crates/fresh-editor/src/i18n/ for the locale YAML/JSON files):

action.composite_next_hunk: "Next Hunk (Side-by-Side Diff)"
action.composite_prev_hunk: "Previous Hunk (Side-by-Side Diff)"

Step 3: Add default keybindings

In crates/fresh-editor/src/input/keybindings.rs, in the default keybinding definitions, add:

n → CompositeNextHunk   (context: composite buffer active)
p → CompositePrevHunk   (context: composite buffer active)
] → CompositeNextHunk   (context: composite buffer active)
[ → CompositePrevHunk   (context: composite buffer active)

These should only activate when a composite buffer is the active view. Check how other context-dependent bindings work (e.g. terminal mode bindings use KeyContext::Terminal). You may need a KeyContext::CompositeBuffer or use a custom context.

Step 4: Handle the actions

In crates/fresh-editor/src/app/input.rs, in handle_action, add cases for Action::CompositeNextHunk and Action::CompositePrevHunk. These should call the existing composite_next_hunk_active / composite_prev_hunk_active methods (defined in composite_buffer_actions.rs).

Step 5: Remove hardcoded keys from router

In crates/fresh-editor/src/input/composite_router.rs:

• Remove the n, p, ], [ → NavigateHunk mappings from route_key_event.
• You can also remove the NavigateHunk variant from RoutedEvent and the Direction enum if no other code uses them, OR keep them for potential plugin-API use.

In crates/fresh-editor/src/app/input.rs:

• Remove the RoutedEvent::NavigateHunk dispatch in try_route_composite_key (since it's now handled by the Action system).
• The router's try_route_composite_key should still run FIRST for non-rebindable composite-specific keys (scroll, pane switch, etc.). Only hunk navigation moves to the Action system.

Step 6: Update the plugin

In crates/fresh-editor/plugins/audit_mode.ts, the review_next_hunk / review_prev_hunk handlers currently call editor.compositeNextHunk() as a fallback. This path is now redundant since the Action system handles it. Remove the composite-buffer fallback from the plugin handlers — when the composite buffer view is active, the review-mode n/p bindings won't fire because the composite buffer's Action bindings take precedence (or the composite buffer isn't a review-mode context).

Verify this: if pressing n in the side-by-side view still goes through the review-mode plugin handler (because review-mode context is active), make sure the plugin handler returns early / doesn't interfere with the Action-based hunk nav. The cleanest approach is to ensure the Action keybinding takes priority over the plugin mode binding when a composite buffer is focused.

Testing

Run existing tests:

cargo test --package fresh-editor --test e2e_tests side_by_side_diff_hunk_nav
cargo test --package fresh-editor --test e2e_tests review_diff_ux_bugs
cargo test --package fresh-editor --test e2e_tests audit_mode

All must pass. The existing side_by_side_diff_hunk_nav tests use direct API calls (composite_next_hunk_active), not keybindings, so they should still pass. Add at least one new e2e test that presses the n key in a composite buffer view opened from Review Diff drill-down and verifies the viewport scrolled to a different hunk.

Files to modify