[sudo-tee]

Summary

• Add public tool formatter registration and removal APIs with explicit built-in override opt-in.
• Preserve core rendering policy and fall back to built-in formatter when custom formatter fails.
• Document formatter contract and add opencode-pty recipe.

Closes #552

Validation

• make test
• make format-check
• make topology-check
• make typecheck (completed with existing warnings)

[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: +5 / -1

✅ No new problems

_{Run locally: make topology-check}