bootstrap: finish project bootstrap — scale test, MPFB character, build docs

- Static-mesh scale test passes: 1 m = 100.00 cm, origin preserved, axis
  mapping east→+X / north→−Y / up→+Z (named presets ue_metric_v1 both sides).
- MPFB 2.0.18 acceptance passes: generated human + standard 137-bone rig
  with weights + v2 skin baked to 1024² diffuse; imports as SkeletalMesh
  with Skeleton, Material, and Texture2D in /Game/Test/Character.
- MPFB headless requires XDG_CONFIG_HOME at the Flatpak config tree;
  documented in Art/blender/README.md, probe in Tools/addon_compat_probe.py.
- Docs/build.md completed: fresh-checkout build, packaging, headless checks.
- Docs/setup.md reconciled with reality; ROADMAP/bootstrap closed out.

Docs/build.md

@@ -1,6 +1,6 @@
 # Build
 
-Fresh-checkout build procedure. To be completed once the pinned engine is installed and a blank project has been packaged — see [setup.md](setup.md). Until then this file records only the constraints that are already known.
+Fresh-checkout build procedure. Completed 2026-11-07 after the pinned engine was installed and a blank `Game/GigLine` build was packaged and launch-tested.
 
 ## Constraints
 
@@ -8,14 +8,72 @@ Fresh-checkout build procedure. To be completed once the pinned engine is instal
 - Build output (`Binaries/`, `Intermediate/`, `Saved/`, `DerivedDataCache/`) is never committed.
 - Large content is LFS-tracked, so a fresh clone needs `git lfs install && git lfs pull` before any build.
 
-## Procedure (placeholder)
+## Engine
+
+Pinned install: **Unreal Engine 5.8.4** (CL 58902052, promoted build) at
+`/run/media/system/DATA/Engines/UE_5.8.4`. The engine bundles **no** Linux clang; the system clang (23.1.4, Fedora 45) is the game-code toolchain. Game targets must use `BuildSettingsVersion.V7` to share the installed editor's build environment.
+
+## Fresh-checkout build
 
 ```bash
 git clone <remote> gig-line && cd gig-line
 git lfs install && git lfs pull
-# engine path, project generation, build, and packaging commands — fill in after setup
+Tools/check-lfs.sh                 # must pass before any content build
+
+# Compile the project's editor target (first build also proves the toolchain)
+cd /run/media/system/DATA/Engines/UE_5.8.4
+Engine/Build/BatchFiles/Linux/Build.sh GigLineEditor Linux Development \
+  -project="$PWD/../../Documents/06-games/gig-line/Game/GigLine/GigLine.uproject" \
+  -WaitMutex
+# Expected tail: "Result: Succeeded"; module binary lands in
+# Game/GigLine/Binaries/Linux/libUnrealEditor-GigLine.so
+
+# Open in the editor (GUI, Vulkan)
+./Engine/Binaries/Linux/UnrealEditor \
+  /run/media/system/DATA/Documents/06-games/gig-line/Game/GigLine/GigLine.uproject
 ```
 
+Adapt the `-project=` path to the actual checkout location.
+
+## Package a Linux build
+
+```bash
+cd /run/media/system/DATA/Engines/UE_5.8.4
+Engine/Build/BatchFiles/RunUAT.sh BuildCookRun \
+  -project="/run/media/system/DATA/Documents/06-games/gig-line/Game/GigLine/GigLine.uproject" \
+  -noP4 -platform=Linux -clientconfig=Development \
+  -cook -allmaps -build -stage -pak \
+  -archive -archivedirectory="/run/media/system/DATA/Builds/GigLine" \
+  -unattended
+# Expected: "BUILD SUCCESSFUL" (~1 min for the blank project; archive ~1.1 GiB)
+# Launch test: /run/media/system/DATA/Builds/GigLine/Linux/GigLine.sh
+```
+
+The archive directory is deliberately **outside** the repository; never archive into the checkout.
+
+## Headless content checks
+
+Both content-acceptance tests run headless and are the template for all asset import verification:
+
+```bash
+# Static-mesh scale test (Blender export -> Unreal import -> measure)
+#   Blender: Tools/scale_test_export.py, Unreal: Tools/ue_scale_test_import.py
+# MPFB character (generate -> rig -> bake -> export -> skeletal import)
+#   Blender: Tools/mpfb_character_export.py, Unreal: Tools/ue_character_import.py
+
+# Unreal side of any test:
+./Engine/Binaries/Linux/UnrealEditor-Cmd \
+  /run/media/system/DATA/Documents/06-games/gig-line/Game/GigLine/GigLine.uproject \
+  -run=pythonscript -script=<repo>/Tools/<script>.py -nullrhi -unattended -nopause -stdout
+# Note: 5.8 swallows Python print() in the commandlet; scripts write result files to /tmp.
+```
+
+## Known engine quirks (2026-11-07)
+
+- One handled `PSOPrecache` ensure fires at packaged-build exit only; not blocking.
+- Interchange 5.8 does not create material/texture assets for skeletal FBX imports — `Tools/ue_character_import.py` finishes that chain explicitly.
+- Android Turnkey status errors and datarouter DNS warnings in logs are benign.
+
 ## Packaged Linux build
 
-Record here: the packaging command, output path, size, and the controls document path. The packaged build must launch and quit cleanly on the development workstation before `v0.1.0` is tagged.
+- 2026-11-07: blank `Game/GigLine` Development build packaged via the command above; 1.1 GiB archive at `/run/media/system/DATA/Builds/GigLine/Linux`; `GigLine.sh` launched on the desktop session, Vulkan swapchain created, 759 frames rendered across a 60 s smoke test. Controls document to be written with the first playable (`0.1.0` Gameplay section).