[sudo-tee]

Summary

• Expose registration and unregistration for custom completion sources, including async results, metadata, selection callbacks, and isolated failures.
• Document a GitHub issue completion recipe that expands selected issue details into the visible draft.
• Add focused completion and public API tests.

Closes #554

Validation

• make check (typecheck completed with existing warnings)
• make topology-check
• Headless recipe expansion and draft-change tests

[github-actions]

🏗️ Architecture check

Checks that require() calls between modules follow the layer rules in scripts/dependency-topology/topology.jsonc (entry → dispatch → services/UI → server/protocols; shared helpers usable everywhere).

Compared origin/main → HEAD.

	Before	After	Δ
Imports breaking layer rules	0	0	+0
Import loops	0	0	+0
Modules in largest loop	0	0	+0
Modules without a layer	0	0	+0

Imports between modules: +2 / -0

✅ No new problems

_{Run locally: make topology-check}