_build_registry built one capabilities dict from the global default_model and
attached it to every entry, so any agent with an `agents.<name>.model` or
`model_capabilities` override was advertised under the wrong model — even
though server.py applies those overrides at startup. Resolve capabilities per
agent, mirroring _register_unknown_models.
Also stop emitting null context_window / max_output_tokens when
model_capabilities is absent: _register_one_model registers the model with
131072 / 16384, so the registry now advertises those effective values. The
defaults are hoisted to module constants in server.py so the two cannot drift.
Verified against mentor's config: capabilities go from
{"context_window": null, "max_output_tokens": null} to {131072, 16384}, model
name unchanged. No checked-in deployment uses per-agent overrides today, so no
currently-published model changes.
Adds tests/test_registry.py (9 tests, first coverage for registry.py) and
documents agents.<name>.model / model_capabilities, which the agents.yaml
field table omitted entirely.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Robert Helewka
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