Slice 10 a1: preview pipeline spike — wlr pixels -> RMLUi texture (Fork-B GO)

The keystone for the stage dock. Proves Fork B on the real target (Mesa crocus,
HD 4400): a toplevel's pixels, rendered by the wlr GLES2 renderer into a LINEAR
ARGB8888 dmabuf, import as an EGLImage -> sampled GL texture in the sibling RMLUi
GLES 3.2 context (the slice-3 bridge run in reverse) and composite into an
<img src="unbox-preview://N"> inside a ui surface — upright, color-correct.

Public surface (ui.hpp): class Preview (source_uri/source_width/source_height/
refresh) + UiSubstrate::create_preview(wlr_scene_tree*) -> unique_ptr<Preview>
(nullptr if no GL path; never throws). Kernel-suite probes: ui_preview_import_is_dmabuf,
ui_pixel(x,y). Clean four-resource teardown (URI reg, GL texture, EGLImage, dmabuf);
refresh-after-source-destruction is UB (consumer drops Preview on unmap).

kernel 42 cases/150 assertions green on build + build-asan (asan clean, no new
suppressions). Edits confined to packages/kernel/.

1 files changed, 1 insertions, 0 deletions

diff --git a/packages/kernel/src/server_impl.hpp b/packages/kernel/src/server_impl.hpp
index ef4a479..bcdb693 100644
--- a/packages/kernel/src/server_impl.hpp
+++ b/packages/kernel/src/server_impl.hpp
@@ -184,6 +184,7 @@ public:
     PerExtensionUi(Server::Impl* server, ExtensionId id) : server_(server), id_(id) {}
 
     auto create_surface(const UiSurfaceSpec& spec) -> std::unique_ptr<UiSurface> override;
+    auto create_preview(wlr_scene_tree* source) -> std::unique_ptr<Preview> override;
     auto available() const -> bool override;
     auto touch_mode() const -> bool override;
     void set_touch_mode_override(TouchModeOverride ov) override;