Retain original local ShaderEffect capture frames

[wieslawsoltes]

Scope

Stacked on #277 (feat/native-shader-capture-padding), preserving its source union of #267/#270/#271. No dependency repin, runtime staging or capability admission.

• Add exact version-4 retained local ShaderEffect capture metadata; v1–v3 layouts/readers/integral behavior stay unchanged.
• Retain real request-root DPI and each source visual float transform/offset history. Independently floor/ceil scale-space edges, preserve full input/UV/derivative/sampler extent, and require exact integral residual placement.
• Preserve original aliased output coverage separately from allocation, including original 28.4 edge conversion, actual own/local/parent float operation order, source clip intersection and exact physical clip transport.
• Keep complete descriptor ownership/cache identity and shared native provider execution. No new compositor or renderer fallback.
• Author eighteen actual-source paired pixel cases, ordinary input baselines, cold/warm/independent counters, legacy wire and raw fractional-clip rejection, invalid metadata and real unsupported source-history controls. Padding variant 9 becomes an actual v4 positive case with its original input bytes/counters retained.

Evidence and remaining gates

Major implementation was committed before bounded checks. Strict C++20 syntax passed for the actual MIL implementation/tests, scene validator/builder, shared renderer with the cached Dawn ABI, and fully instantiated shared GPU fixture. Protocol/coverage, native ownership inventory, all seven generated contracts, both Unicode verifiers and three inline-array generator tests pass. Generated C# source parses. No native library/test executable, GPU/VM or full graph build was run locally.

Independent original Microsoft reference #280 at e611aae3fdf3366085475094d11156676f4141a3 passed Windows reference workflow https://github.com/wieslawsoltes/ProGPU/actions/runs/37045784511 (x64 pixels, separate ARM64 unavailable control). That is source evidence, not native pixel qualification. Hardware pixel-center UV remains distinct from original SoftwareOnly integer-phase UV.

The first inverse proof is internally bounded to exact power-of-two accumulated axes in [1/256,256]; this is not a new public policy or completion claim. Non-dyadic/full inverse, fractional final placement, fractional source clips, anti-aliased output coverage and actual WPF source integration remain required implementation/qualification contracts. Native CPU, both-provider GPU, Windows/package and exact whole producer Build gates are pending. Root coordinates a single hosted dispatch; no Build was manually dispatched by this worker.

Detailed contract and receipts: docs/native-shader-local-capture-frame.md.