[jbwinters]

Adds an SDK layer to the Rust crate (jacquard_host::sdk), comparable to the Python, TypeScript, and Go SDKs, and runs the four example projects through it. The crate still uses only the standard library.

SDK

• Runtime::prepare checks, hashes, and installs .jac (or .jqd) sources with Core's public check, hash, and run commands into a verified cache. The cache key covers source bytes, Core executable bytes, every prelude file, and the protocol. A changed cache entry is refused. The --version check and prelude discovery run once per key across clones and threads. Each Core command runs in its own process group with a timeout and bounded output.
• Data mapping through Encode and Decode traits. They cover integers, f64, text, Hash, bool, Vec (List), Option, (), tuples, and protocol::Value.
  • record! and variants! declare application structs and enums as constructors.
  • Dynamic handles untyped values by public name.
  • Encoded arguments are checked against the function's checked signature, the selected limits, and the frame size before any worker starts.
• Operations binds closures to exact operation identities. A closure may take a leading &HandlerContext, and its parameters decode into their Rust types.
  • It returns Result<T, HandlerError>; any other error raised with ?, or a panic, becomes completion unknown.
  • Every operation of each checked effect must be bound, and names that are not operations are refused.
• Function::call, invoke, and map_batches (explicit batches, every batch validated first, nothing retried), each with a Cancel variant.
• Invocation provides decode, value, render, and owner-only save.
• All failures are one sdk::Error. A result-mapping failure keeps the successful raw result.

Projects: cargo run --example jacquard-examples -- <project> runs quickstart, planner, triage, and fulfillment. It reads the rules from examples/ and supports the same --inspect, --fault, and --deliver-pending recovery paths as the Go command.

Low-level change: HandlerError gains From<E: std::error::Error>, mapping any such error to Unknown.

Docs:

• rust/README.md is rewritten around the SDK and keeps the low-level host section.
• Also updated: root README, examples README, CONTRIBUTING, LIMITS (two Rust SDK rows replace "protocol-level only"), EVIDENCE, and CHANGELOG (Unreleased).

Verification (local, Linux 7.0, Rust 1.99.1)

• Offline: 10 new unit tests and 7 new doctests. They use synthetic identities and, on Unix, a fake Core. One fake-Core test checks that a failing command returns promptly while a descendant holds Core's output.
• Live against jacquard-core-0.3.0, with JACQUARD_REQUIRE_LIVE=1 and no skips:
  • 12 SDK tests, ported from the Go SDK suite, including the 25-case planner oracle and the 64-row triage oracle;
  • 2 project tests: all four commands, and three fault-and-recovery runs across restart;
  • the existing 4 adapter tests and the 21-recording replay.
• Rust 1.88: clippy and offline tests pass.
• clippy is clean for aarch64-apple-darwin and x86_64-pc-windows-gnu, but those targets are only type-checked.
• scripts/core_pin.py check, the offline Python suite, and scripts/check_distribution.py pass.