fix(server): separate the Codex reasoning summary capability

[eugenn]

Problem

Codex reads route capabilities from GET /v1/models. Switchyard derives
reasoning summary support from the general reasoning capability. Some models
accept reasoning effort but reject reasoning.summary, which causes HTTP 400
responses.

Codex also renamed the capability, so publishing one name only leaves one
Codex version reading nothing and sending reasoning.summary anyway.

Change

• Add an optional reasoning_summaries route capability. It defaults to
  reasoning when unset, so existing configurations are unaffected.
• Publish it under both Codex capability names: the legacy
  supports_reasoning_summaries and the current
  supports_reasoning_summary_parameter.
• Keep the benchmark harness model card in sync.
• Document and test a route that supports reasoning effort but not summaries.

Configuration

reasoning = true
reasoning_summaries = false

Compatibility

Codex 0.144.x reads supports_reasoning_summaries and gates its whole
reasoning control on it, so disabling summaries also stops reasoning effort.
Codex 0.145+ reads supports_reasoning_summary_parameter, keeps reasoning
effort, and omits only reasoning.summary.

Validation

• cargo fmt --all --check
• cargo test -p switchyard-runner
• cargo test -p switchyard-server
• cargo clippy --workspace --all-targets -- -D warnings
• uv run ruff check .

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Walkthrough

The change adds optional route-level reasoning_summaries configuration, stores it in Route, exposes model routes through Runner, and propagates the setting into Codex model metadata. Tests and TOML schema documentation cover enabled and disabled summary support.

Changes

Reasoning Summary Metadata

Layer / File(s)	Summary
Route configuration and state crates/switchyard-runner/src/config.rs, crates/switchyard-runner/src/route.rs, docs/reference/toml_schema.md	Routes parse and store optional reasoning_summaries values. Route construction applies the setting. The TOML schema documents its default and Codex behavior.
Model discovery metadata crates/switchyard-runner/src/runner.rs, crates/switchyard-server/src/lib.rs	Model discovery iterates over model routes and passes resolved reasoning-summary capability into Codex metadata fields.
Metadata integration validation crates/switchyard-server/tests/server.rs	Integration tests cover routes with and without reasoning summaries and preserve reasoning-level metadata.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to da1e6

This change adds independent route configuration for reasoning summaries and correctly documents the version-specific Codex behavior. No current merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 55.56% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 18 functions across 5 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: separating Codex reasoning summary capability from general reasoning capability.

Full details: Docstring Coverage

Explanation

Docstring coverage is 55.56% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 18 functions across 5 files. (1 skipped: 1 unsupported.)

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---

_{A rabbit reads the route with care
Optional summaries now live there
Models share the setting bright
Codex fields report it right
Tests watch both on and off
Documentation seals the loft}

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Actionable comments posted: 2

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Inline comments:
In `@crates/switchyard-runner/src/config.rs`:
- Around line 603-604: Add a concise Rust comment near the test configuration
identifying that reasoning and reasoning_summaries are independent route
settings; leave the existing reasoning and reasoning_summaries values unchanged.

In `@docs/reference/toml_schema.md`:
- Line 116: Update the reasoning_summaries schema documentation to state both
version-specific behaviors: Codex 0.144.x disables reasoning effort when
summaries are disabled, while Codex 0.145+ retains reasoning effort and omits
reasoning.summary.

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📒 Files selected for processing (6)

• crates/switchyard-runner/src/config.rs
• crates/switchyard-runner/src/route.rs
• crates/switchyard-runner/src/runner.rs
• crates/switchyard-server/src/lib.rs
• crates/switchyard-server/tests/server.rs
• docs/reference/toml_schema.md

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[messiaen]

Thanks for the PR!

The config is only required for reasoning models that reject reasoning.summary. But users must know:

What each model accepts.
What its provider accepts.
Which Codex version interprets the metadata.
Whether every target in a route has the same support.
Ideally that knowledge should live in Switchyard, not route configuration.
Can we discover capability from provider metadata?