docs: pin QGIS 4.2.3 and compute the projected origin with PROJ

QGIS stable is 4.2.3 on the current KDE runtime; the stale 3.28.9 lts install
stays flagged for removal. PROJ 9.9.0 from that flatpak turns the recorded
origin into E 376515.389 / N 3774224.083 (NAD83 UTM 11N), with six control
points whose projected spans reproduce the OSM footprint measurements. Engine
decision recorded: 5.8.4 is downloading, 5.2.0 stays only as a fallback.

Docs/toolchain.md

@@ -10,12 +10,12 @@ Audited 2026-11-06 on the development workstation.
 | --- | --- | --- | --- |
 | Bazzite | `45.20261105` (Kinoite, `bazzite-dx-nvidia`), kernel `7.2.15-ogc1.1.fc45` | `ujust update` / `rpm-ostree upgrade` | Booted and default. `44.20261026` retained as rollback. |
 | NVIDIA driver | `615.78.08`, open kernel module | Bazzite image | Verified: desktop session renders through the RTX 5070 Ti; Vulkan GPU0 is the RTX 5070 Ti on driver `615.78.08`, conformance `1.4.3.3`. |
-| Unreal Engine | `5.2.0` archive on disk (CL 25360045, `++UE5+Release-5.2`); `5.8.x` was the planned pin | Epic download, 2026-11-06 | Downloaded, not extracted, **version decision open** — see [setup.md](setup.md#engine-version-decision). |
+| Unreal Engine | `5.8.4` — download in progress 2026-11-06; `5.2.0` archive verified on disk as fallback | Epic download | Not extracted yet. Pin becomes 5.8.4 once the archive verifies and the editor launches on Bazzite; see [setup.md](setup.md#engine-version-decision). |
 | Unreal Linux toolchain | engine-bundled clang | Engine source tree | Not installed. Do not substitute the system compiler. |
 | Blender | `5.2` LTS (upstream patch `5.2.3`) | Flatpak `org.blender.Blender` | Installed. |
 | MPFB | `2.0.18` (extension `mpfb`, declares Blender >= 4.2) | Blender extensions platform | Installed. Load-and-export check on 5.2 still pending. |
 | Blosm | latest release at install time | blosm.com / Gumroad | Not installed. Version must be recorded before first use. |
-| QGIS | `3.44.15` LTR targeted; installed flatpak is `3.28.9` | qgis.org / flathub | **Not a valid pin.** The `lts` flatpak branch is 3.28.9 on an end-of-life Qt5 runtime. Replace via `stable` or distrobox, then pin. See [environment.md](environment.md). |
+| QGIS | `4.2.3`, Flatpak `stable`, runtime `org.kde.Platform 6.11`; bundled PROJ `9.9.0` | flathub | Installed 2026-11-06. The stale `lts` branch (`3.28.9`, EOL Qt5 runtime) is still installed beside it and should be removed. |
 | Git | `2.56.0` | Bazzite image | Installed. |
 | Git LFS | `3.7.1` | `rpm-ostree` layer | Installed; `git lfs install` run, lfs filter active. |
 | Host build tools | `clang 23.1.4`, `cmake 4.3.0`, `ninja 1.13.2` | `rpm-ostree` layer | Installed. These are host tools, not the engine toolchain. |
@@ -36,5 +36,5 @@ Unreal Engine 5.9 is in preview and Unreal Engine 6 has been announced as of Nov
 
 1. **Blosm on Blender 5.2.** Blosm versions historically lag Blender releases. Verify Blosm against the installed Blender 5.2 before the blockout step. If it fails, add a side-by-side Blender 4.5 LTS Flatpak and convert that step's output only; do not mix Blender versions within one asset.
 2. **MPFB 2.0.18 on Blender 5.2.** The extension declares Blender >= 4.2 but predates 5.x. The acceptance test is the `0.1.0` requirement to export one MPFB character with baked materials and a deform skeleton and import it into Unreal.
-3. **QGIS flatpak tracks a stale LTR.** The flathub `lts` branch is `3.28.9` (2022) on `org.kde.Platform 5.15-21.08`, which is end-of-life. A 2022 QGIS still converts CRS and edits vectors correctly, but its PROJ/GDAL data and processing algorithms are four years behind the current LTR, and the runtime gets no security fixes. Replace it before the geo pipeline depends on it; record whichever version ends up pinned.
+3. **Two QGIS installs.** `stable` (4.2.3, current runtime) and the old `lts` (3.28.9, EOL runtime) are both present. Nothing breaks, but launching the wrong one silently gives older PROJ data. Uninstall `lts` and keep one pin. QGIS 4.x also uses Qt6, so any processing recipe copied from a 3.x tutorial needs re-checking before it is trusted.
 4. **Driver and Vulkan validation on Bazzite.** Not an officially supported Unreal distribution. Validate before asset production, as `ROADMAP.md` requires.