Remove the binding request FFI exports

[Gudge (MGudgin)]

This PR removes the deprecated private binding-request FFI surface now that
Node and .NET call the exact JSON exports directly. The mxc_ffi crate keeps the
shared run result, output conversion, streaming handle, and lifecycle surfaces,
while deleting the old request parser, binding fixtures, stale docs, and codegen
inventory entries.

Details

• Removed mxc_run_request, mxc_spawn_request, their helpers, and request.rs.
• Retargeted retained FFI tests and ignored real-host smoke tests to
  mxc_run_json and mxc_spawn_json with exact 1.0.0 documents.
• Deleted the binding-request goldens and updated tests/policy documentation to
  describe only SDK v1 goldens and state-aware exact fixtures.
• Updated native C# binding codegen checks to require only JSON entry points.

Tests

• cargo fmt --all -- --check; cargo check --workspace --all-targets
  --all-features; cargo clippy --workspace --all-targets --all-features --
  -D warnings.
• cargo test -p mxc_ffi --all-features: 80 passed, 4 ignored, doc 0.
• cargo test -p mxc_engine --all-features: 139 passed.
• cargo test -p mxc-sdk --all-features: 55 passed, 5 ignored.
• RUSTDOCFLAGS=-D warnings cargo doc -p mxc_ffi -p mxc-sdk --no-deps
  --all-features.
• npm run build; npm test: 350 passed, 20 skipped; npm run typecheck.
• dotnet test --solution Microsoft.Mxc.Sdk.slnx: 260 succeeded, 27 skipped.
• node scripts/check-dotnet-bindings-codegen.js: 37 entry points.
• node scripts/check-dotnet-api-parity.js: 7 one-shot backends, 8 discovery
  backends, 5 capabilities.
• node scripts/check-dotnet-errorcode-parity.js: 17 codes.
• node scripts/versioning/check-contract-codegen.js: 3 artifact sets.
• node scripts/versioning/validate-configs.js: 414 configs, 15 exempt.
• node scripts/versioning/check-tests-present.js: 7 test files.
• git diff --check.

Microsoft Reviewers: Open in CodeFlow

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[Copilot]

Copilot review overview

🟡 Changes recommended

Retargeted host tests now share the default container identity, risking cross-test policy and cleanup interference.

Review effort: Balanced
Findings: 2 · 1

Open (3)

• Preserve isolated container IDs in retargeted tests · New
• Add a fresh container ID to preserve test isolation · New
• Include lifecycle exec handles in the safety contract · New

What changed in this PR

Removes the deprecated private binding-request FFI after SDK migration to exact-version JSON ingress.

Changes:

• Removes legacy request exports, parser, fixtures, and tests.
• Retargets FFI tests and documentation to exact JSON APIs.
• Updates C# binding checks for retained JSON entry points.

File	Description
tests/​policy/​request-wslc.json	Removes legacy WSLC fixture.
tests/​policy/​request-process-container.json	Removes legacy ProcessContainer fixture.
tests/​policy/​request-directional-network.json	Removes legacy networking fixture.
tests/​policy/​README.md	Documents retained fixture families.
src/​ffi/​mxc_ffi/​tests/​ffi.rs	Retargets FFI tests to exact JSON.
src/​ffi/​mxc_ffi/​src/​streaming.rs	Removes legacy spawn export and updates tests/docs.
src/​ffi/​mxc_ffi/​src/​state_aware.rs	Updates retained handle references.
src/​ffi/​mxc_ffi/​src/​request.rs	Deletes private request parser.
src/​ffi/​mxc_ffi/​src/​lib.rs	Removes legacy run export and parser wiring.
scripts/​check-dotnet-bindings-codegen.js	Drops removed signatures from checks.

---

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[Copilot]

Copilot review overview

🔵 Needs a closer look

Unsafe handle documentation incorrectly excludes handles returned by the retained state-aware execution API.

Review effort: Balanced
Findings: 2 · 1

Open (3)

• Add a fresh container ID to preserve test isolation
• Preserve isolated container IDs in retargeted tests
• Include lifecycle exec handles in the safety contract