docs: crossing done pending review; record LFS-lockable and normals traps

MEMORY.md

@@ -147,3 +147,19 @@ Scope: facts and traps that cost time to establish. Planned work lives in [TODO.
 - **A per-pixel `struct.pack` loop over `img.pixels` is catastrophic in headless Blender** (256² took 25 s). Blender ships numpy: read `img.pixels[:]` once into a float array, reshape `(h,w,4)`, clip→uint8, reverse rows for PNG top-down, then zlib-compress. Whole 1024² encode ≈ 0.3 s.
 - **MPFB's v2-skin node tree does not resolve to a simple base colour**, so a Cycles DIFFUSE bake returns black. Since the FBX export material replaces the node tree anyway, synthesize the diffuse directly (`make_diffuse`): warm skin body + a darker shorts-suggestive bottom band.
 - **A read-only `.umap` silently makes `save_map` return `False` with no error** (already recorded); re-hit in the review pipeline — `chmod u+w` the maps before rebuilding, otherwise the new character material never appears in shots.
+
+## 2026-11-07 — Blender skill packs: discovery depth
+
+- **The 94 packs were never registered with the `skill` tool**, only readable as files. The loader resolves `<skills-root>/<pack>/SKILL.md` one level down; `.agents/skills/blender-skills/` is a *container* of 94 packs, so it was skipped silently (no warning, no error). Symptom: `skill("archviz")` unresolvable even though `archviz/SKILL.md` exists.
+- **Fix applied:** 94 symlinks in `~/.agents/skills/<pack>` → `<repo>/.agents/skills/blender-skills/<pack>/`. The catalog then lists all of them (verified by calling `skill` on `collision-proxy`: base dir resolves through the link). `references/` stays unlinked — it is a shared folder with no `SKILL.md`, not a pack.
+- **The AGENTS.md "MCP-driven" caveat is overstated.** 41 of 94 SKILL.md mention MCP, mostly only in the `description` line; the bodies are method guides (naming, proportions, validation checklists) that work headless. Do not skip a pack because it advertises MCP.
+- **Skill names in AGENTS.md/TODO.md all resolve** except `references`, which is the folder above, not a pack.
+- Symlinks are user-level: a fresh machine needs the same 94 links before the packs are loadable by name.
+
+
+## 2026-11-07 — Street visibility and the LFS lockable trap
+
+- **Every street surface (road, sidewalks, kerbs, markings) had 100 % downward face normals** — `strip()`'s natural winding (rows along +s, cols along +normal) faces the ground. Invisible in engine for as long as the terrain covered them; the corridor cut exposed the black trench. Fixed by reversing the winding in `strip()`, `kerb_faces()` and `crossing_band()`.
+- **`*.blend` and `*.umap` are LFS-lockable in `.gitattributes`** — Git LFS checks them out read-only (444). `bpy.ops.wm.save_as_mainfile` then fails ("path is not writable") and `EditorLoadingAndSavingUtils.save_map` silently returns False. All Blender builders now chmod u+w before saving and treat a failed save as fatal; the UE map builders chmod the .umap first. A failed save used to leave downstream steps building from stale files — that produced a degenerate-mesh FBX (all-same vertex indices from an index-arithmetic bug) that cost an hour to trace.
+- **FBX SDK refuses to triangulate the crown-twisted crossing quads** ("unable to triangulate mesh ... will be omitted") — emit triangles from the builder, and make sure per-stripe vertex indices advance (`len(verts)` must be captured before the loop, not per-corner).
+- Demo-map coordinate note: UE Y is south-positive; the facade at Y −1450 and the player start at Y −3500 are on opposite sides of the road (Y −1382..+1047) — arrangement is correct; the Sidewalk_North/South mesh names are swapped relative to their physical sides (documented in export_site_fbx.py).