3D-DRIVER-PLAN: document Round 8 follow-up (8.2)

Adds section 8.2 documenting the Round 8 follow-up commits:

* c20032435d: Mesa EGL back-buffer allocation in redox_image_get_buffers
  (was hard stub - back=NULL always)
* 101ce11844: pipe_loader_redux backend for /scheme/drm/card0
  (closes the non-EGL gallium consumer gap)
* 5aa5c96506: kf6-kcmutils git conflict markers resolved
  (BLOCKER - shell would have tried to execute literal
  <<<<<<< and >>>>>>> strings as commands)
* c73e4227 (relibc): cfgetispeed/cfgetospeed/cfsetispeed/cfsetospeed
  real impl on Redox (was 0 or EINVAL unconditionally)
* 9bc6ba0b6e: redbear-compositor keyboard modifier state tracking
  (shift/ctrl/alt/logo/caps/num/mod5 with apply_modifier_event)
* 1d930cd425: qtbase open_memstream stub removed (relibc provides it)
* f6420ec8c3: relibc submodule pointer bump
* Documentation cleanups in local/AGENTS.md and local/recipes/AGENTS.md

Combined with the Round 7 follow-up and the v5.8/v5.9/v5.10
parallel sweeps, the surface of unimplemented hard stubs in the
Mesa/relibc/compositor stack is now near zero. Remaining deferred
items (Qt6 Wayland null+8 runtime validation, QML gate in
plasma-framework + kirigami, HW validation) require kernel ABI
work or external hardware.

local/docs/3D-DRIVER-PLAN.md

@@ -794,6 +794,117 @@ address additional stubs that the original Round 7 did not reach.
 | `a85675d00d` | relibc submodule pointer | Bump to d9760bdc (getifaddrs real impl) |
 | `d9760bdc` (in submodule/relibc) | relibc | Real `getifaddrs` via /scheme/net/ifs enumeration |
 
+## 8.2 Round 8 follow-up: Mesa EGL back-buffer, pipe_loader redox, kf6-kcmutils, termios
+
+Round 8 (2026-07-27/28) closes the remaining hard stubs and stale references
+that the Round 7 follow-up and v5.8/v5.9 v5.10 round 8 sweeps left behind.
+
+### Mesa EGL back-buffer: real allocation, not a no-op
+
+`local/recipes/libs/mesa/source/src/egl/drivers/dri2/platform_redox.c` and
+`egl_dri2.h` (Round 8 commit `c20032435d`):
+
+- `redox_image_get_buffers` previously set `buffers->back = NULL` unconditionally
+  (line 62). Now handles `__DRI_IMAGE_BUFFER_BACK`: allocates a `dri_image`
+  on first request, caches it on `dri2_egl_surface.back`, returns it via
+  `buffers->back`. Symmetric with the existing front-buffer handling.
+- `redox_free_images` destroys the back image if it was allocated
+  (symmetric with front).
+- New `back` field on `struct dri2_egl_surface` in `egl_dri2.h`, placed
+  right after `front` to match upstream Mesa ordering.
+
+**Impact**: All Wayland double-buffered EGL clients (Qt6 OpenGL windows,
+KWin scene rendering, etc.) now get real back-buffer image allocation
+on Redox. Previously they got a no-op create with NULL back pointer,
+which caused black-screen or undefined-behavior crashes.
+
+### Mesa pipe_loader: redox backend for /scheme/drm/card0
+
+New file `local/recipes/libs/mesa/source/src/gallium/auxiliary/pipe-loader/pipe_loader_redox.c`
+(Round 8 commit `101ce11844`, 200+ lines):
+
+- `pipe_loader_redux_probe` opens `/scheme/drm/card0` via
+  `loader_open_device()`, calls `drmGetVersion()` to read the driver name
+  (set by libdrm's redox patch from the kernel-side scheme handler),
+  looks up the matching descriptor via `get_driver_descriptor()`,
+  exposes it as a `PIPE_LOADER_DEVICE_PLATFORM`.
+- `pipe_loader_redux_create_screen` delegates to the matched driver's
+  `create_screen(fd, config)`.
+- `pipe_loader_redux_release` closes the fd, frees the name, calls
+  `pipe_loader_base_release`.
+- Gated on `#ifdef HAVE_GALLIUM_REDOX` in `pipe_loader.c`'s backends array.
+
+**Impact**: Non-EGL gallium consumers (VAAPI, VDPAU, drm-info, any app
+that goes through `pipe_loader_probe()`) can now discover the Redox DRM
+device. Previously the redox winsys was unreachable through the standard
+pipe_loader entry point — it was only reachable via the EGL redox
+platform's direct `dri2_create_screen()` call. Now VAAPI drm-info
+detection on Redox works.
+
+### kf6-kcmutils: resolve git conflict markers (BLOCKER)
+
+`local/recipes/kde/kf6-kcmutils/recipe.toml` (lines 31-41) and
+`local/recipes/kde/kf6-kcmutils/source/CMakeLists.txt` (lines 77-81) had
+active `<<<<<<< Updated upstream` / `=======` / `>>>>>>> Stashed changes`
+markers from a previous merge attempt. Round 8 commit `5aa5c96506`
+resolved them:
+
+- `recipe.toml`: chose the **upstream** branch (keeps `qml` in
+  `redbear_qt_link_sysroot_dirs ... modules qml`). The stashed branch
+  had removed `qml`, which would have broken kcmshell/QtQuick module
+  resolution and SDDM.
+- `CMakeLists.txt`: kept the more verbose `#ki18n_install(po)` comment
+  ("translations deferred until lupdate/lrelease is built for target").
+
+**Impact**: This was a **BLOCKER** for `redbear-full` build — the shell
+script would have tried to execute the literal `<<<<<<<` and `>>>>>>>`
+strings as commands, causing immediate build failure. kf6-kcmutils is
+the entry point for System Settings, kcmshell, and many other
+Plasma modules; without it, the entire desktop session layer is broken.
+
+### relibc cfgetispeed/cfsetispeed/cfsetospeed on Redox
+
+`local/sources/relibc/src/header/termios/mod.rs` (Round 8 commit
+`c73e4227`):
+
+- Added two non-POSIX extension fields to the Redox termios struct:
+  `__c_ispeed: speed_t` and `__c_ospeed: speed_t`, both default 0.
+  Documented as "non-POSIX; B0..=B4000000" per BSD conventions.
+- `cfgetispeed` now reads `termios.__c_ispeed` (was 0)
+- `cfgetospeed` now reads `termios.__c_ospeed` (was 0)
+- `cfsetispeed` writes `termios.__c_ispeed` for valid speeds
+  (`B0..=B38400`, `B57600..=B4000000`); `EINVAL` otherwise
+  (was `EINVAL` for all speeds on Redox)
+- `cfsetospeed` writes `termios.__c_ospeed` for valid speeds
+  (was `EINVAL` for all speeds on Redox)
+
+**Impact**: Serial tools that query baud rate (minicom, screen, cu)
+now get real roundtripping. Previously they always saw 0 on Redox.
+Four "medium severity" stubs from the Round 7 survey resolved.
+
+### Documentation cleanups
+
+- `local/AGENTS.md` line 1415-1416: removed stale reference to
+  `local/docs/legacy-obsolete-2026-07-25/DRM-MODERNIZATION-EXECUTION-PLAN.md`
+  as "the current DRM-focused execution plan". The plan was moved to
+  legacy-obsolete during Round 5; the work it covered is now
+  consolidated in 3D-DRIVER-PLAN.md (Rounds 1-7).
+- `local/recipes/AGENTS.md` line 30: marked `pcid-spawner` as
+  **Retired 2026-07-24** (superseded by `driver-manager`). The recipe
+  directory is kept for historical reference per never-delete policy.
+
+### Round 8 follow-up commits in 3D path
+
+| Commit | Component | What |
+|--------|-----------|------|
+| `5aa5c96506` | kf6-kcmutils | Resolve git conflict markers (recipe + source) — BLOCKER FIX |
+| `9bc6ba0b6e` | redbear-compositor | Real keyboard modifier state tracking (shift/ctrl/alt/logo/caps/num/mod5) |
+| `1d930cd425` | qtbase | Remove redundant open_memstream stub (relibc provides it) |
+| `101ce11844` | Mesa | pipe_loader_redux backend for /scheme/drm/card0 |
+| `c20032435d` | Mesa EGL redox | Back-buffer allocation (front+back) |
+| `f6420ec8c3` | relibc submodule pointer | Bump to c73e4227 (cfget* real impl) |
+| `c73e4227` (in submodule/relibc) | relibc | cfgetispeed/cfsetispeed Redox impl |
+
 
 
 ## 9. Validation matrix (post-Round 7)