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 the existing installed-contract package/registry 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.

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]

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