POST /api/combos and PUT /api/combos/[id] had zero validation or
observability when a combo name collided with a real model id, and
sseModelService.getComboForModel() always resolves the combo first. That
combo-first precedence is not a bug: #6940 documents a combo named after a
bare model id (e.g. `gpt-5.5`) as the supported mechanism for per-model
provider fallback, reusing the #3227/#3233 machinery and covered by
tests/unit/responses-combo-resolution-3227.test.ts and
tests/unit/combo-name-codex-responses-rewrite.test.ts. Hard-rejecting a
colliding name (as #8530's literal acceptance criteria requested) would
regress that documented workflow.
Instead, both routes now attach a non-blocking `warning` field
(`COMBO_NAME_SHADOWS_MODEL`) to the create/rename response when the name
collides with a real model id, and a new boot-time scan
(scanComboModelNameCollisionsAtBoot in src/instrumentation-node.ts) logs a
startup warning enumerating existing collisions — so an operator who hits
this by accident has a signal, while the #6940-sanctioned pattern keeps
working exactly as before.
New tests/unit/combo-model-name-collision-8530.test.ts proves both: the
sanctioned shapes (create/rename to a colliding name) still return
201/200 with the warning attached, and non-colliding names get no warning
field at all.
Co-authored-by: ikelvingo <im.kelvinwong@gmail.com>
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