[codex] Add tool schema cleaning helpers

[senamakel]

Summary

Adds provider-oriented JSON Schema cleaning helpers to harness::tool so tool schemas can be normalized for model tool-calling compatibility before provider dispatch.

This ports the OpenHuman SchemaCleanr behavior into TinyAgents with crate-native errors and tests. The cleaner resolves local $refs, strips provider-unsupported keywords, flattens literal unions, removes nullable variants, converts const to enum, and breaks circular local refs safely.

Validation

• cargo fmt --check
• timeout 180s cargo clippy --all-targets -- -D warnings
• timeout 120s cargo test schema_

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📥 Commits

Reviewing files that changed from the base of the PR and between e72036d and 83008a6.

📒 Files selected for processing (3)

• src/harness/tool/mod.rs
• src/harness/tool/schema.rs
• src/harness/tool/schema_test.rs

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Infer literal enum types instead of abandoning const-only unions

When a schema generator emits a literal union as anyOf/oneOf variants containing only const values, this ? returns None, so clean_for_gemini leaves the union shape in place after merely converting each const to a single-value enum. Const-only literal unions are valid and common JSON Schema for string literals, so Gemini-normalized tool schemas can still contain unsimplified unions and be rejected or become less useful; infer the type from the literal value or flatten without requiring a redundant type.

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