Phase 7 — Runtime Services

Authoritative spec. See also the phase index, perf-dod, and testing-strategy. Live issue numbers: pinned master #810.

Phase 7 — Runtime Services (W5) — concurrent with Phases 5, 6

Goal: The built-but-unwired services become real: async assets, mipmaps, one audio stack, one 2D physics, retained UI, multi-window. 6 issues.

ID	Title	Grp	Effort	Blocked by
ENG2-P7-01	Wire async asset pipeline into the runtime; background decode incl. RGB→RGBA off main thread	A	M	Phase 4 gate
ENG2-P7-02	Mipmap generation + trilinear sampling in the wgpu texture path	B	M	—
ENG2-P7-03	Unify the dual rodio audio stacks onto the provider architecture	C	M	—

P7-01: assets/server/async_operations.rs:44-104 (load_async + process_loads) has ZERO non-test native callers; the live path is blocking operations.rs:14-53 incl. per-pixel RGB→RGBA on the main thread (texture.rs:59-70) — violates assets/CLAUDE.md’s own rule. Call process_loads() once per frame in the instance runtime; decode on rayon.
P7-02: mip_level_count: 1 everywhere (texture.rs:41, init.rs:160, sdl/xbox init) with MipmapFilterMode::Nearest and no chain — aliasing + wasted bandwidth at distance.
P7-03: assets/audio_manager/ (2832 LOC) vs libs/providers/impls/rodio_audio.rs:118-138 — two full rodio wrappers, two unsafe Send/Sync blocks; keep the provider-trait one, bridge asset data through it.

ID	Title	Grp	Effort	Blocked by
ENG2-P7-04	Consolidate 2D physics on rapier2d; delete the custom ECS solver	A	M	P3-07
ENG2-P7-05	UI v2: retained command buffer, dirty-subtree relayout, string interning; absolute positioning (#553)	B	L	—
ENG2-P7-06	Multi-window support (WindowId-keyed window collection)	C	M	—

P7-04: Custom solver (ecs/physics_world/simulation.rs, 397 LOC) coexists with the rapier2d provider — divergence risk; rapier2d becomes canonical (“no legacy code kept”).
P7-05: manager/render.rs:12-20 rebuilds the full command Vec + clones label/font/path strings per frame; single global layout_dirty flag relayouts the whole tree (layout.rs:16-33); HashMap node storage (manager.rs:44). Retain commands, dirty subtrees, interned strings/slotmap; ship #553’s absolute-positioning mode as part of the layout rework.
P7-06: winit_platform.rs:37-48 holds one Option<Arc<Window>>; needed for Phase 9 editor/tools.

Load burst (100 × 2048² textures) during S1 ⇒ no frame > 20 ms.
Textures upload with full mip chains (mip_level_count > 1 asserted in test); trilinear default.
Exactly one audio stack and one 2D physics backend in-tree.
UI: 1k-widget tree, single label change ⇒ relayout+rebuild ≤ 0.3 ms (bench).
Two windows render simultaneously in an example.