[Gopalakrishnan Nallasamy (GopalakrishnanN)]

Description

Adds Rust bindings for the stable EPContext data read callback APIs in #32265.

• Provides transactional registration/clearing, Arc-backed callback ownership, explicit callback errors, and an unwind-contained allocator-safe trampoline.
• Uses API 31 callback/state-only native registration and retrieval. max_data_size stays in Rust callback state and is enforced before native output allocation; allocations inside the callback remain application-owned policy.
• Preserves the newer fix from 97d3907fdc: the environment lock is released before native session creation, so callbacks can reenter environment APIs without deadlocking.
• Merges Promote EPContext data callbacks to stable API #32265 at e0cc266cdefef4e27104b14e4091a9d61f75a214, including its main-branch update, retained-NHWC READ-support validation, and provider-specific callback preflight before capability-time I/O.
• Fixes the resulting Rust E0004 build failure from the newly merged FLOAT6 enum variants by adding both to the existing unsupported-output dispatch. Extends unsupported-type conversion tests for both variants; this does not add FLOAT6 tensor support.
• The stable callback signatures remain unchanged; preflight remains core-owned.

Motivation and Context

This independent binding PR remains stacked on #32265. Rust applications retain bounded, application-managed EPContext reads and safe callback ownership while following the stable transport ABI. Rust currently has no model-compilation/write-callback surface.

The latest core checks provider-specific callback requirements before capability discovery, including AOT, NHWC, and ORT-format paths, rather than relying solely on checks immediately before Compile(). Its main-branch merge also requires the explicit FLOAT6 compatibility cases so regenerated Rust bindings compile.

Retarget to main after #32265 lands.

Testing

Revalidated on Windows with Rust 1.99.0, libclang 18, regenerated bindings from current source headers, and the runtime freshly built from e0cc266cde.

• cargo fmt --manifest-path .\rust\Cargo.toml --all -- --check — passed, with existing warnings for nightly-only rustfmt settings.
• With ORT_RUST_STRATEGY=system, ORT_RUST_LIB_LOCATION pointing to the fresh import-library prefix, and RUST_ONNXRUNTIME_LIBRARY_PATH pointing to the freshly rebuilt DLL: cargo test --manifest-path rust\Cargo.toml -j 4 -p onnxruntime --lib -- --test-threads=1 — 33 passed, 0 failed/ignored.
• This includes the environment-lock regression, registration/replacement/clearing, ownership, concurrency, size boundaries, allocator failures, panic/error handling, and both new unsupported FLOAT6 conversion cases.
• git diff --check e0cc266cdefef4e27104b14e4091a9d61f75a214 HEAD — passed for the binding PR delta.

Non-Windows, 32-bit execution, and hardware-provider-specific callback/preflight paths were not run. Existing compiler warnings outside this compatibility fix remain unchanged.

[Tianlei Wu (tianleiwu)]

Reviewed the isolated stacked diff against GopalakrishnanN/stable-epcontext-data-api. The callback trampoline contains panics, enforces the configured size bound before native allocation, maps failures explicitly, and retains callback state safely across session creation and teardown. The registration/clearing and compatibility paths are well covered, and all reported CI checks pass.

[Copilot]

Copilot review overview

🔵 Needs a closer look

The unsafe cross-language callback and lifetime behavior warrants final human review, especially for untested non-Windows and 32-bit targets.

Review effort: Balanced
Findings: None

What changed in this PR

Adds safe Rust bindings for stable EPContext data-read callbacks, including ownership, error handling, and API compatibility. No actionable issues identified.

Changes:

• Adds bounded, concurrent, panic-contained callback registration.
• Preserves callback lifetime and lock-free session creation.
• Updates bindings generation and unsupported tensor-type handling.

File	Description
rust/​BUILD.md	Documents header and version overrides.
rust/​onnxruntime-sys/​build.rs	Improves header discovery and release selection.
rust/​onnxruntime/​src/​environment.rs	Validates C API availability safely.
rust/​onnxruntime/​src/​error.rs	Adds callback and API-version errors.
rust/​onnxruntime/​src/​lib.rs	Exports callback errors and tests FLOAT6 handling.
rust/​onnxruntime/​src/​memory.rs	Reorders imports.
rust/​onnxruntime/​src/​session.rs	Implements callback registration, trampoline, ownership, and tests.
rust/​onnxruntime/​src/​tensor/​ort_output_tensor.rs	Handles newly generated unsupported enum variants.

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The base branch was changed.