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fix(providers): keep protocol types narrow and unwrap PEP 695 aliases - #20
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Two type-erasure defects found while a strict downstream host consumed the
provider substrate. Both are silent: the annotation reads correctly at the
call site and the wrong type only shows up further downstream.
`protocol_of` and `thinking_format_for_protocol` were extracted with `-> str`
and `-> str | None`, widening what the host they came from declared. Their
outputs feed `ModelProfile.protocol` / `.thinking_format`, which are `Literal`
unions, so a value this module had just validated with `is_wire_protocol` was
no longer assignable to the very field it was validated for. This file is
checked at `basic` level, so nothing here caught it; a strict host did, with
four errors in code it had not touched.
`_schema_for_type` mapped a PEP 695 `type Alias = ...` straight to
`{"type": "string"}`: a TypeAliasType is not a primitive, has no origin, and is
not a Pydantic model, so it reached the `Any` floor. That floor is a deliberate
choice for under-annotated parameters — an alias is the opposite, and a tool
author who names a union to describe a parameter precisely got a schema
claiming it was a string. Unwrap `__value__` instead. `agent_core` uses `type`
statements itself (pause_check, openai_chat), so this was live.
Validation:
- uv run ruff check agent_core tests
- uv run pyright agent_core (0 errors)
- uv run pytest -q (1054 passed)
- both new alias tests fail with the unwrap removed
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Summary
Two silent type-erasure defects found while a strict downstream host consumed the provider substrate (FrontierAgent #104).
protocol_of/thinking_format_for_protocolwere widened tostrduring extraction. Their outputs feedModelProfile.protocol/.thinking_format, which areLiteralunions — so a value this module had just validated withis_wire_protocolwas no longer assignable to the very field it was validated for.protocol_client.pyis checked atbasiclevel, so nothing here caught it; the strict host did, with 4 pyright errors in code it had not touched. Restores the narrow aliases the host declared before extraction. Signatures only, no body changes._schema_for_typemapped a PEP 695type Alias = ...to{"type": "string"}. ATypeAliasTypeis not a primitive, has no origin, and is not a Pydantic model, so it fell through to theAnyfloor. That floor is a deliberate choice for under-annotated parameters — an alias is the opposite: a tool author who names a union to describe a parameter precisely got a schema claiming it was a string, with the annotation looking correct in the source. Now unwraps__value__.agent_coreusestypestatements itself (runtime/pause_check.py,providers/openai_chat.py), so this was live rather than hypothetical.Validation
uv run ruff check agent_core testsuv run pyright agent_core— 0 errorsuv run pytest -q— 1054 passed