feat: declare runtime backing and hold the artifact to the manifest

[lr00rl]

What

This plugin's service now carries "backing": "runtime" in its re-signed manifest, and a new conformance_test.go holds the artifact to what the manifest promises.

Why

This plugin genuinely serves its own methods — but nothing proved it. Elsewhere in the fleet, a manifest could declare interface methods its artifact could not answer, with lattice-server quietly answering them from an in-core handler instead. A contract that lied, invisible to CI, because every suite covered what the artifact does and never what the manifest claims.

Declaring runtime explicitly means who serves a method is a signed fact, not something the host infers from a publisher string.

The conformance test is the real deliverable

It walks every declared method and probes the artifact:

• backing: runtime → the artifact must answer it. A payload-validation error counts as an answer; unsupported method does not.
• backing: core → the artifact must not answer it (the engine lives in lattice-server).

The probe uses an empty payload, which is rejected before any host call, and a stub host that fails the test if the dispatcher reaches for the broker or network — so checking which methods exist can never have a side effect.

On the three façade plugins, flipping their declarations to runtime turns the build red on every declared method. That is the gap this gate exists to catch.

Safety of this change

• Artifact untouched. bundle.digest_sha256 and version are unchanged — only the manifest's signed metadata differs, so CI's rebuild-and-compare digest gate still passes without a rebuild.
• Signature parity verified against the real key: re-signing an unmodified manifest reproduces its previously committed signature byte-for-byte, confirming backing is omitempty and does not perturb existing signed manifests.

⚠️ Deployment ordering

Deploy the server first. The loader uses DisallowUnknownFields, so a server without backing support rejects this manifest outright: decode manifest: json: unknown field "backing". It fails closed (the plugin does not load) rather than degrading.

Requires: LatticeNet/lattice-server#8.

Test plan

• go test ./... -race -count=1 in system-go — green
• Conformance gate green; stub host proves the probe reaches neither broker nor network
• gofmt clean
• Bundle digest unchanged → CI digest gate unaffected

Part of the 2026-07-14 plugin-boundary architecture review (§4.1).

https://claude.ai/code/session_01FzYExyy6G7Cb7QpXoUEY78

[lr00rl]

Closed as landed — zeus, Olympus TASK-0007 (2026-07-26, rules/01 §8.5): this branch's commit (3c3571f) IS the integration branch tip — the backing declaration + conformance test are the integration baseline. Not in main, but main's design-15 manifest (0.3.2-alpha.4) independently carries backing: runtime, verified 2026-07-26, so the declaration survives the pending integration↔main reconciliation in both directions. Closing, not rejecting.