feat(pocket3d): character-widget substrate + pocket-vrm crate

[doodlewind]

What

Generic engine support for desktop character widgets (transparent, always-on-top, VRM-animated) — the reusable half of the pocket-character runtime (pocket-stack/pocket-character, the airi-parity 3D digital-human widget).

pocket3d

• Morph targets: sparse CPU deltas + per-instance overlay vertex buffer, flushed lazily on weight change — an idle face costs zero; draws redirect via base_vertex, shared index buffer untouched.
• Explicit poses: Skeleton::sample_locals / globals_from_locals split + ModelInstance::pose, so hosts inject look-at/physics edits between clip sampling and the hierarchy walk.
• Widget window mode: AppConfig transparent / decorations / always_on_top / resizable / max_fps (frame-paced sleeping loop) / drag_window; non-opaque surface alpha; Scene::transparent_clear.
• Per-instance alpha-test cutout; Input::cursor(); capture-on-click gated on capture_mouse; joint window 128 → 512 mat4s (VRoid rigs carry ~270 joints).
• load_glb_opts + ModelLoadOptions { max_texture_dim }: skip unreferenced glTF images (VRM thumbnails), box-filter cap authoring-resolution textures — the single biggest memory lever (931 → 518 MB footprint on the widget).

pocket-vrm (new crate)

VRM 0.x parsing (humanoid / blend shapes / springs / MToon info / look-at), UniVRM-semantics spring-bone verlet solver (allocation-free, deterministic), VRMA retargeting (channel-unit hips rescale + re-anchor + VRM1 +Z → VRM0 −Z yaw conjugation — the arms-up bug otherwise), bone-type eye look-at. Fixtures downloaded, never committed (VRoid sample license).

Validation

• pocket3d workspace cargo test green; pocket-vrm: 21 tests incl. real-model parse/retarget/spring stability.
• Rendered verification in the satellite repo: AvatarSample_A + airi's idle_loop.vrma posed correctly, blink morph closes the eyes, transparent widget window composites over the desktop.
• Measured (M3 Max, ≥60 s steady-state, full process tree): pocket-character = 1 process, 118 MB RSS, 3.9 % of one core at 60 fps (2.1 % at 30 fps), 518 MB phys_footprint — vs airi v0.11.0 VRM stage on the same machine: 8 processes, 2184 MB RSS, 44.4 % CPU, ~1870 MB footprint. Full report: pocket-character/REPORT.md.

🤖 Generated with Claude Code

Try it (manual verification, from scratch)

The satellite repo is the end-to-end harness for everything in this PR:

git clone --recurse-submodules https://github.com/pocket-stack/pocket-character
cd pocket-character
bun run setup        # vendored bun install + symlinks + model assets (not committed)
bun run widget       # build guest bundle + release binary, launch the widget (Ctrl-C to quit)

# once built:
target/release/pocket-character                 # 60 fps widget
target/release/pocket-character --max-fps 30    # low-power variant (~2% of one core)
target/release/pocket-character --headless-shot shot.png --ticks 90   # no-window render, alpha preserved
bun scripts/measure.ts                          # reproduce the RSS/%CPU measurement

Engine-only checks in this repo: cd pocket3d && cargo test -p pocket3d -p pocket-vrm (pocket-vrm integration tests fetch fixtures per crates/pocket-vrm/fixtures/README.md; they skip when absent).