Linux: ship public Rust embedder SDK for GTK and CLI clients

[enricopiovesan]

Summary

Ship the public Rust embedder SDK required by reference-apps #117.

Depends on

• Spec 068 approval.

Definition of Done

• Versioned public Rust crate exposes every Spec 068 embedder operation, including compatible-capability start/stop/kill, with stable public types.
• It loads bundled runtime/manifests/capabilities and has no production dependency on traverse-cli serve.
• It forwards runtime-owned output, state, and structured errors without UI/business-rule duplication.
• It includes rustdoc, compatibility policy, and deterministic test double.
• It passes shared conformance plus Linux/GTK/CLI package tests.
• GTK and CLI reference-app integration executes a bundled workflow without a sidecar.
• Release evidence records crate version, runtime-WASM digest, and conformance version.

Unblocks

• reference-apps Standardize local Traverse runtime home #117 after Template executable capability package manifests and deterministic build commands #111 and Document adapter responsibilities versus core runtime responsibilities #112 are also complete.

[enricopiovesan]

Unblocked (2026-07-13): Spec 068 was approved and merged in PR #651. This implementation ticket is now Ready.

[enricopiovesan]

Blocked after pre-flight (2026-07-13): this ticket explicitly depends on Spec 068 approval, but current main contains no specs/068-* artifact and no approved-spec registry entry for 068. Unblock by landing and approving Spec 068 with the public Rust API, packaging/digest, conformance, and compatibility commitments.

[enricopiovesan]

Board correction (2026-07-13): Spec 068 is approved and present on main via PR #651. The earlier blocker report was stale. This ticket is Ready; its Definition of Done now correctly cites Spec 068 and the complete embedder lifecycle.