[SunSi12138]

Goal

Implements the explicit 3.0 Codec API retirement decision in #801. Generated Contract/assembly-owned [RpcCodec] / Adapter / Route policies remain the authoritative RPC binding path. No standalone dynamic resolver, per-Context explicit AddCodec registration, or endpoint Server serializer override.

Production code

• Delete SharpLinkRuntimeContextBuilder.AddCodec<T> and UseCodecResolver, SharpLinkServerBuilder.UseSerializer, and Client's old internal UseSerializer.
• Remove the dynamic resolver, explicit override cache/priority, fallback ResolvedCodec state, and related immutable build-plan data from Runtime. Preserve owner-generated manifest registrations, snapshot publication, dependency checks, builtins, enums, 3.0 ABI validation and fail-closed behavior.
• Update the reviewed 3.0.0 public API baseline, deleting the two Runtime and one Server signatures.
• Adjust 3.0 UnsafeBlit / Codec migration guidance. Direct non-RPC serialization uses an explicitly instantiated IRpcCodec<T>; generated RPC uses its owning manifest.
• Migrate direct Codec injection in test/bench code to a test-project-only generated Codec fixture. Remove obsolete fallback-specific tests and benchmark cases.

Branch and order

Built directly on dev after #799 was merged at a1f9ee2a7addfdf2bc86ae0598d99d5e5596cfe5. This PR contains only #801 cleanup differences, and does not change #799.

Verification

Draft — under active validation; do not merge yet.

• Branch Release / UnitTests / Generator / Integration CI must be completely green.
• Verify 3.0 public API baseline, external NuGet package clients, native AOT and Trim across supported platforms.
• Check all test/bench-only callers are either migrated to generated bindings or removed as intentionally obsolete; no production fallback must be reintroduced to satisfy tests.

Related: #801 (Codec surface and dead-code retirement); #805 (remaining public/internal + sealed 3.0 audit); #799 (merged native AOT/Trim implementation).

[SunSi12138]

Exact-head evidence for the Codec API retirement

Source at c16a22185c17ec0f0bc740b7eebfdc1e0ea744d7, based on merged #799 (dev @ a1f9ee2a). This is the actual PR source, not an ephemeral deletion probe.

• Release + UnitTests + Generator + Integration + reviewed 3.0 public API snapshot — success. Full Release build 0 warnings/errors; UnitTests 2034/2034, Generator 271/271, Integration 453/453. All eight packages' full public/protected signatures (including SDK type forwards) match the newly reviewed 3.0.0 API baseline.
• PR Fast — success: formatting, maintainability, Release, Unit/Generator, managed allocation gate.
• PR Package Smoke — success: ProjectReference full/partial Trim, isolated Linux x64 NativeAOT, all eight 3.0.0 NuGet package contracts, packaged consumers, partial/late Trim configuration, packaged NativeAOT, QuickStart and ProductionTemplate.
• Windows x64 and macOS ARM64 native publish + execute — both success. Complete solution Release 0W/0E and the original native TCP/shared-memory transport + topology, generated service, SharpPack sidecar and pre-credit streaming cases pass on both. Raw proof: Windows, macOS.
• CodeQL — success; Codec padding-security — success; Pending/codec regression — success.

Still in progress: Android/iOS CoreCLR matrix and UnsafeBlit mobile/layout evidence. PR remains Draft until these results are reviewed.

Net result: public SharpLinkRuntimeContextBuilder.AddCodec<T>, UseCodecResolver, Server UseSerializer, Client internal UseSerializer, plus actual dynamic resolver and explicit-override backing state have been removed. Generated owner Codec/Adapter binding, AOT ABI capability, and runtime Core/Session ownership remain.