Phase B.5c — TUI + GTK trait coverage to 100% (master)

[JDonaghy]

Goal

Both TUI and GTK at 100% on quadraui::Backend. After B.5c, every primitive that has runtime usage either has a trait method that's used end-to-end, OR has a documented reason for not (e.g. backend-specific UX that genuinely doesn't fit the cross-backend contract). The runner crates (B.5e) depend on this being clean.

Context

B.5b shipped the GTK runtime migration (closed at #249 after 13 stages on develop), but uncovered concrete trait-coverage gaps that aren't bugs — they're architectural:

1. Trait methods that return () but call sites need hit-region info. Backend::draw_status_bar returns (); call sites in both backends use Vec<StatusBarHitRegion> from the legacy direct shims. Same for draw_tab_bar (returns TabBarHits). Fix: redesign return types — either return the data, or split into draw + query.

2. GTK trait impls that are forward-compat stubs because the rasteriser takes legacy render::Theme. Backend::draw_activity_bar and draw_terminal on GTK currently unimplemented!() because the existing rasterisers in crate::gtk::quadraui_gtk::* take render::Theme instead of quadraui::Theme. Fix: lift those rasterisers into quadraui::gtk::* (see Lift TUI + GTK rasterisers out of vimcode and into the quadraui crate #223).

3. TUI bypasses the trait for half the draws. TUI's draw_frame calls quadraui::tui::draw_* directly. After the return-type redesign in (1), route TUI through the trait method so future generic paint::<B> consumers exercise the same code path GTK does.

4. Primitives that don't have a trait method at all. Tooltip, dialog, context_menu, rich_text_popup, completions, find_replace — all 6 have rasterisers in quadraui::*::* but no Backend::* method. Both backends call the rasterisers directly. Fix: extend the trait per-primitive (some need return types for hit info: dialog needs button rects, rich_text_popup needs link rects).

Suggested stage order

Stage	Goal
B5c.1	Redesign Backend::draw_status_bar to return Vec<StatusBarHitRegion>. Update both backend impls. Migrate all GTK + TUI call sites onto the trait. Validates the return-type pattern before applying to others.
B5c.2	Same shape for draw_tab_bar (returns TabBarHits).
B5c.3	Same shape for draw_text_display (no hit data — straightforward).
B5c.4	TUI draw_tree + draw_form migration onto trait method (no trait change; mechanical mirror of GTK B5b.8).
B5c.5	Lift quadraui_gtk::draw_activity_bar + draw_terminal_cells into quadraui::gtk::* with quadraui::Theme. Wire GTK trait impls to call them.
B5c.6	Trait extension + impls for the 6 currently-trait-less primitives. Group by complexity: text_display already done (B5c.3 reuses); dialog and rich_text_popup need return types; the rest are straightforward.
B5c.7	Final parity sweep + smoke tests on both backends.

Pickup files

• quadraui/src/backend.rs — trait definition.
• quadraui/src/gtk/, quadraui/src/tui/ — rasterisers.
• src/gtk/quadraui_gtk.rs — in-tree shims to lift.
• src/gtk/draw.rs, src/gtk/mod.rs, src/tui_main/render_impl.rs — call sites to migrate.

Why first

The runner-crate work (B.5e) needs every primitive to have a stable cross-backend trait surface. Doing the runner crates first would force the runner API to expose backend-specific hatches, defeating the boilerplate-elimination goal.

PLAN.md "🎯 NEXT FOCUS" section has the full context.

[JDonaghy]

Phase B.5c stages 1–7 shipped on develop (985b087 through 40efa99).

Trait-coverage state for the layout-passthrough primitives is now:

• ✅ status_bar, tab_bar, text_display, tree, list, form, palette, tooltip, context_menu — fully on the Backend trait, both backends.
• ✅ activity_bar, terminal — GTK on the trait; TUI is inline (separate scope).
• ⏭️ dialog, rich_text_popup, completions, find_replace — deferred. See Phase B.5c followup — lift rich_text_popup / completions / find_replace into quadraui::{tui,gtk} #266 (rasteriser lifts) and Phase B.5c followup — Backend::draw_dialog needs dual-Pango-layout handling #267 (dialog dual-Pango handling).

Next: #260 (B.5d setup audit) → #261 (B.5e runner crates) → B.6 Win-GUI rebuild.