Phase L.0 — foundation for the complete retail-style Settings interface
agreed in the 2026-04-26 brainstorm. Splits Phase K's keybind-only F11
panel into a tabbed shell whose first tab wraps the existing keybinds
content unchanged; the other five tabs (Display / Audio / Gameplay /
Chat / Character) render "Coming soon" placeholders so the shape the
user approved is visible immediately and gets filled in over the L.x
sub-phases (Display first per Easy-wins build order).
Why a tab API extension: retail had distinct Options UIs
(gmGameplayOptionsUI / gmChatOptionsUI / gmCharacterSettingsUI per the
PDB at acclient_2013_pseudo_c.txt:170739+) and the existing
IPanelRenderer only exposed CollapsingHeader. ImGui maps
BeginTabBar / BeginTabItem / EndTabItem / EndTabBar 1:1, so the new
primitives stay backend-friendly — the future D.2b custom retail-look
backend implements them via the retail tab UIs without panel changes.
Save / Cancel / Reset-all stay above the tab bar so they remain global
across all tabs (Phase K's UX preserved). FakePanelRenderer grows
matching tab calls + an ActiveTabLabel knob so tests can target a
specific tab's content; default behavior treats the first tab item
seen as active so existing tests keep passing without changes.
5 new SettingsPanelTests assertions: tab bar opens once, six expected
tab labels emitted in order, Keybinds-tab section headers only render
when active, placeholders show "Coming soon" text on inactive-content
tabs, and Save/Cancel buttons render BEFORE the tab bar (regression
guard against accidentally moving them inside a tab item).
dotnet build green (0 warnings); dotnet test 1,227 / 1,227 green
(243 Core.Net + 311 UI.Abstractions + 673 Core).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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