Generate Target-IR-bound Echo registration and invocation helpers

[flyingrobots]

Purpose

Generate the first Echo-owned Rust/API helpers carried as provider output roles, bound to the exact Target IR and contract bundle identities rather than to mutable application names.

Acceptance criteria

• Generated registration and invocation descriptors name exact Target IR and bundle digests plus required Echo ABI/schema versions.
• The helper constructs an opaque provider-generic package/registry proposal whose private mutation handler uses Echo's existing scheduler-owned contract-handler shape, without exposing raw rule mutation, scheduler tick, WAL, recovery, or package-install authority to application code.
• The minimal Target IR operation maps to one explicit host-supplied executor or observer.
• Wrong Target IR, bundle, codec, schema, operation, footprint, or profile identity refuses before registration or mutation.
• Output is deterministic, namespaced, schema-validated, and emitted only when requested.
• Review projection and generated source are release artifacts; neither becomes a new semantic source of truth.
• Consumer tests compile and exercise the generated API against the pinned minimal fixture.

Runtime installation boundary

This goalpost ends at a pure, opaque provider proposal. The proposal is not an InstalledContractPackage, does not implement the legacy GraphQL/Wesley RegistryProvider facade, and grants no artifact admission, installation, scheduling, execution, durability, receipt, or observation authority.

A trusted Echo runtime must independently authenticate/select the callback implementation and consume the proposal during native provider admission. Equality between generated and host-claimed implementation identities proves cross-binding only; it does not prove arbitrary callback semantics. Native admission/invocation remains tracked by #583, with the end-to-end Jedit execution gate in #589.

Prerequisites #652 and #653 are complete.
Parent: #650
Downstream app-safe delivery remains tracked by #516.

[coderabbitai]

🔗 Related PRs

#365 - feat(wesley): emit query observer host helpers [merged]
#671 - feat(echo-wesley-gen): generate canonical Edict provider artifacts [merged]
#672 - Implement Echo Edict provider lowerer [merged]
#673 - Implement the Echo Target IR semantic verifier [merged]
#674 - Assemble digest-locked Edict provider package [open]

---

📝 Issue Planner

_{Check the box below or use the @coderabbitai plan command to generate an implementation plan and prompts that you can use with your favorite coding assistant.}

• Create Plan

---

🧪 Issue enrichment is currently in open beta.

You can configure auto-planning by selecting labels in the issue_enrichment configuration.

To disable automatic issue enrichment, add the following to your .coderabbit.yaml:

issue_enrichment:
  auto_enrich:
    enabled: false

💬 Have feedback or questions? Drop into our discord!