SidebarSystem migration: Source Control panel

[JDonaghy]

Summary

Migrate the Source Control panel from hand-rolled section navigation, scroll, and collapse state to quadraui::compose::SidebarSystem.

The SC panel has the most state machine code of any sidebar (~641 lines of navigation/input handling). It uses source_control_to_tree_view() with Decoration::Header sections (Staged, Changes, Worktrees, Log). SidebarSystem replaces the core section-walk, scroll, collapse, and selection logic — the domain-specific handlers (stage, commit, push, discard) remain on the engine and dispatch from SidebarEvent matches.

Prereqs

• SidebarSystem: compose helper for MSV + TreeView sidebar panels quadraui#63 — SidebarSystem shipped

Engine fields replaced by SidebarSystem

Field	Purpose	SidebarSystem equivalent
sc_selected	flat row index	per-section selection
sc_sections_expanded: [bool; 4]	collapse state	SidebarSystem internal collapse
sc_has_focus	keyboard focus	SidebarSystem focus state

Fields that remain (domain-specific): sc_file_statuses, sc_worktrees, sc_log, sc_ahead/behind, sc_commit_message, sc_commit_cursor, sc_commit_input_active, sc_button_focused/hovered, sc_branch_picker_*, sc_help_open, sc_diff_rx, sc_diff_pending_win.

Migration steps

1. Define 4 SidebarSectionDefs: "staged", "changes", "worktrees", "log"
2. Each frame: call sidebar.set_rows(section, rows) from source_control_to_tree_view() data
3. Replace the j/k/Tab/Enter navigation in handle_sc_key() with sidebar.handle() + SidebarEvent dispatch
4. Keep domain actions (s stage, d discard, c commit, p push, etc.) as post-event handlers that match on SidebarEvent::RowSelected
5. Remove the 3 engine fields listed above
6. The commit input sub-mode (sc_commit_input_active) is orthogonal — it intercepts before SidebarSystem and stays as-is
7. TUI + GTK: replace bespoke tree paint with sidebar.render(backend, rect)
8. Update tests in source_control.rs

Complexity note

SC has the richest interaction surface: commit input mode, branch picker popup, button bar keyboard nav, and help dialog. These are not sidebar state machine concerns — they are modal overlays that intercept before the sidebar handler runs. The migration only replaces the section/scroll/selection plumbing, which is the duplicated part.

Key files

• src/core/engine/mod.rs — remove sc_selected, sc_sections_expanded, sc_has_focus
• src/core/engine/source_control.rs — replace navigation in handle_sc_key(), keep domain actions
• src/render.rs — adapt source_control_to_tree_view() to feed SidebarSystem::set_rows()
• src/tui_main/panels.rs — replace SC render
• src/main.rs — replace GTK SC render

Reference

See JDonaghy/quadraui#63 for the complete migration guide with code examples.