Define a package contract for multi-dispatch execution graphs

[NripeshN]

Problem

Compiler packages describe compiled artifacts, reflection, validation, and source metadata, but they cannot represent an operation that dispatches multiple artifacts over shared resources with explicit ordering and visibility requirements.

Repository runtimes commonly sequence initialization, transformation, reduction, scan, FFT, and aggregation kernels through temporary buffers. Treating each artifact as an independent package entry loses the resource lifetime, dependency, and synchronization contract needed by package verification and downstream runtime tooling.

Expected behavior

• Define a versioned, target-neutral execution graph document that can be embedded in or referenced by a compiler package.
• Represent graph-scoped external inputs, external outputs, and temporary resources with logical type, physical layout, allocation size/alignment, and lifetime.
• Represent dispatch, copy, fill, and barrier nodes with stable IDs and explicit dependency edges.
• Resolve dispatch nodes to packaged artifact identity, entry point, specialization values, resource binding coordinates, and dispatch geometry.
• Express resource access and memory visibility without encoding one target API's barrier enum.
• Permit conditional or repeated execution only when the control resource and finite bound are explicit; arbitrary host callbacks remain outside the portable contract.
• Preserve source/provenance metadata for graph nodes and referenced artifacts.
• Extend package verification and inspection to reject missing artifacts, missing interfaces, incompatible resource layouts, invalid ranges, dependency cycles, unordered conflicting accesses, and unsupported graph capabilities.

Acceptance criteria

• The public package schema and C++ data model round-trip a deterministic two-dispatch graph.
• Package verification checks every referenced artifact, entry point, resource binding, and physical layout before reporting the graph ready.
• Validation tests cover missing references, duplicate IDs, dependency cycles, unsafe barriers, invalid temporary lifetimes, and bounded-control errors.
• Package inspection reports graph/node/resource counts, readiness, and structured diagnostics.
• A compatibility fixture demonstrates that a single packaged compute artifact can be represented as a one-node graph without changing existing package consumers.
• The contract is documented as metadata and verification; it does not claim a built-in host scheduler or native runtime executor.

Real-world driver

At MLX commit 4367c73b60541ddd5a266ce4644fd93d20223b6e, operations including reductions, scans, FFTs, split-kernel matrix multiplication, and quantized paths sequence multiple compute pipelines and temporary allocations. CrossTL issue CrossGL/crosstl#1736 is implementing the translator-side repository-neutral graph and runtime validation needed to exercise these paths on DirectX and OpenGL. A compiler package contract would let both repositories exchange the same artifact and graph identities without making the translator depend on a compiler release.