Add executable provider runtime artifact contract

[i386]

Experimental stacked change

This is the 2A provider artifact layer of the experimental Apple runtime roadmap in #1246.

• Stacked on Add experimental Apple runtime #1249; review and merge that PR first.
• Base branch: jd/experimental-apple-runtime
• This is experimental and is not connected to production model gossip, mesh routing, or the public OpenAI frontend.
• Trying the Apple runtime requires Apple silicon, macOS Golden Gate (macOS 27), full Xcode 27 selected with xcode-select, Apple Intelligence enabled, and the system model downloaded.

Why this layer exists

MeshLLM already has native runtime artifacts for backend libraries selected against the Skippy ABI. An Apple system-model integration is a different shape: it is a signed executable provider with its own process boundary, protocol version, model identities, platform requirements, entitlements, and lifecycle.

This PR gives executable providers a provider-neutral package, resolution, verification, download, and immutable-cache contract before the host supervisor and SDK bindings are added. Apple is the first consumer, but the contract does not embed Foundation Models semantics.

What changes

• Adds the publishable mesh-llm-provider-runtime crate.
• Defines schema-v1 provider-runtime.json bundle manifests and provider-runtimes.json release indexes.
• Selects artifacts by OS/architecture/minimum OS, artifact/provider/protocol/model selector, semantic version, and source priority.
• Supports in-place bundles, immutable cache installs, and verified HTTP ZIP downloads.
• Enforces safe relative paths, payload and ZIP symlink rejection, SHA-256 verification, executable entrypoints, bounded archives, unique coordinates/model IDs, and exact release-index/payload agreement.
• Keeps cache coordinates immutable at <cache>/<artifact-id>/<version>/<os>-<arch>/.
• Updates Apple packaging to emit and validate the shared contract, ZIP/checksum sidecars, a release index, and descriptive signing metadata.
• Proves that the same artifact survives CLI, Swift bundle, Node package, and JVM resource carrier layouts.
• Routes the new crate through affected-crate, Clippy, SDK-smoke, publication, Docker/Fly, and CI consistency inventories.
• Documents the contract in docs/design/PROVIDER_RUNTIMES.md.

This layer deliberately does not launch or supervise the provider, bind it into SDK lifecycle APIs, or advertise it across a mesh. Those are the next stacked changes.

Try it

From the repository root:

1. Confirm the Golden Gate developer environment:

   xcode-select -p
   xcodebuild -version
   xcrun --sdk macosx --show-sdk-version

   The selected path must be full Xcode/Xcode beta and the SDK must be 27.x.

2. Build the carrier-neutral Apple provider artifact:

   just apple::package

3. Validate provider-runtime.json, every declared file digest, and the executable bit using the shared Rust contract:

   just apple::contract

4. Exercise the same artifact in every planned SDK carrier layout:

   just apple::carriers

   Expected summary:

   {
     "carriers": [
       "cli_runtimes_apple",
       "jvm_ai_meshllm_apple-runtime_macos-arm64_runtime",
       "node_node_modules__mesh-llm_apple-runtime-darwin-arm64_runtime",
       "swift_MeshLLMAppleRuntime.bundle_Contents_Resources_runtime"
     ],
     "status": "pass"
   }

5. To exercise the experimental parent runtime itself:

   just apple::run status
   just apple::run serve --port 11435

   In another terminal:

   curl -s http://127.0.0.1:11435/v1/models | jq
   just apple::rest

   The parent PR's providers/apple/README.md includes captured Golden Gate output for a buffered completion, SSE streaming, usage accounting, and a REST tool execution.

Generated artifacts are under target/apple-runtime/package/, including the bundle, ZIP, SHA-256 sidecars, and provider-runtimes.json.

Validation

• just build
• just with-lld cargo fmt --all -- --check
• just with-lld cargo test -p mesh-llm-provider-runtime — 11 passed
• just with-lld cargo clippy -p mesh-llm-provider-runtime --all-targets -- -D warnings
• just with-lld cargo package -p mesh-llm-provider-runtime --allow-dirty --no-verify
• just apple::carriers — CLI, Swift, Node, and JVM carrier layouts passed
• actionlint -config-file .github/actionlint.yaml
• shellcheck providers/apple/Packaging/package.sh providers/apple/QA/carriers.sh
• repo-consistency: ci-crate-lists, publish-crates, and release-targets
• python3 scripts/tests/test_publish_crates.py — 9 passed

Next stack

2B will add the Rust host supervisor: resolve the artifact, enforce platform signing policy, launch and health-check the sidecar, forward requests, drain it, and terminate it with the owning MeshLLM instance. Later changes will bind that lifecycle into Rust, Swift, Node/Electron, and Kotlin/JVM before private-mesh routing is enabled.

Closes no issue; advances #1246.

[github-actions]

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