[nihalpasham]

Summary

Move cuda-oxide from a pinned daily nightly toolchain (nightly-2026-10-11) to official stable Rust 1.99.1, unifying the entire monorepo (cuda-core, cutile-rs, and cuda-oxide) on stable Rust releases:

Before: cuda-oxide/rust-toolchain.toml -> channel = "nightly-2026-10-11" (daily snapshot)
After:  cuda-oxide/rust-toolchain.toml -> channel = "1.99.1"             (official stable release + RUSTC_BOOTSTRAP=1)

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Before vs. After

• Before (nightly pin): cuda-oxide pinned a moving daily nightly snapshot while the root host workspace and cutile-rs used stable Rust. Any mid-cycle nightly bump (such as pulling in an upstream rustc_public addition) forced an unscheduled compiler upgrade with unrelated daily churn across 1,500+ files.
• After (Stable 1.99.1 pin): cuda-oxide pins official stable Rust 1.99.1, which has already completed Rust's 12-week nightly and beta stabilization cycle and ships LLVM 23 (23.1.1) with an NVPTX backend and TableGen intrinsic definitions identical to nightly-2026-10-11.

Why This Works on Official Stable Rust

1. Stable rustc and Nightly rustc are the same binary: Official stable rustc builds do not strip out -Z flags (-Z codegen-backend=..., -Z mir-enable-passes=-JumpThreading, -Z always-encode-mir) or #![feature(rustc_private)]. They gate them behind RUSTC_BOOTSTRAP=1 (the environment variable rustc uses when bootstrapping core and std on stable).
2. rustup ships rustc-dev and rustc_public on stable releases: Running rustup component add rustc-dev on stable 1.99.1 provides librustc_driver.so, librustc_public.rlib, and librustc_public_bridge.rlib out of the box.
3. Production precedent: This follows the same model used by Microsoft's rustc_codegen_utc and Ferrocene (building a CodegenBackend against a vetted stable Rust release tag rather than tracking daily nightlies).

Upstreaming to rustc_public on the Stable Cycle

Because rustc_public only wraps data that already exists inside rustc_middle and rustc_abi, crates/mir-importer/src/translator/facts.rs acts as our quarantine boundary when we upstream new rustc_public queries (such as rust-lang/rust#163242):

• Day 1: Land the feature immediately on the current stable pin by reading the underlying rustc_middle / rustc_target field in facts.rs via rustc_internal::internal(tcx, ...), while upstreaming the rustc_public getter in parallel.
• Next scheduled stable release: Swap the temporary internal read in facts.rs to the upstreamed rustc_public method call.

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Changes in This PR

• Pin 1.99.1 across all SIMT toolchain surfaces: cuda-oxide/rust-toolchain.toml, cargo oxide new (scaffold.rs), .devcontainer/devcontainer.json, intrinsics/upstream.lock, and the book/README install commands.
• Configure RUSTC_BOOTSTRAP=1 automatically: Set in cuda-oxide/.cargo/config.toml, cuda-oxide/Justfile, cargo-oxide (backend.rs, codegen_env.rs, fmt.rs, host_cargo.rs), and the example CI loops so -Z compiler flags, #![feature(rustc_private)], #![feature(f16)], and cargo-features = ["profile-rustflags"] work transparently on stable 1.99.1.
• Adapt to 1.99.1 compiler APIs (~12 lines):
  • cuda-host: Use core::intrinsics::type_id::<T>() in type_id_u128.
  • mir-importer: Query tcx.fn_abi_of_instance inside facts.rs (reference_param_validity) for typed ArgAttributes (NoAlias, NoFree, pointee_size), and match ValueAbi::Scalar in types.rs.
  • rustc-codegen-cuda: Match 1.99.1's CodegenBackend (init, target_config, CompiledModule), ShimKind::FnPtrAddr, and layout.peel_transparent_wrappers.
• Update cuda-oxide-book: Add the toolchain stabilization, facts.rs upstreaming workflow, and standalone bundle sections with four SVG diagrams under cuda-oxide-book/compiler/images/.

Validation

• just check & just book: fmt-check, clippy (workspace + backend + all 258 example/model manifests), test, test-cuda, check-guards, check-intrinsics (all 1,042 routes / 2,427 target probes on LLVM version 23.1.1-rust-1.99.1-stable), doc-check, and Sphinx HTML book build (-W) all pass.
• SIMT examples (scripts/smoketest.sh on RTX 5090): 240 / 240 pass.
• cute-rs-preview examples and models: 16 / 16 pass (all 12 sm_120a workloads execute and pass on RTX 5090; all 4 sm_100a workloads compile to validated direct-ABI cubins via CUTLASS 4.7).

Checklist

• All commits signed off (git commit -s)
• SPDX headers on new source files

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