fix(strict-schema): preserve chained $ref during sibling-key expansion

[adityasingh2400]

Summary

When a $ref pointing to an alias definition (a $ref-only schema that itself points to another definition) had sibling keys like description, ensure_strict_json_schema silently dropped the inner $ref and lost the underlying type. The merge {**resolved, **json_schema} ran while json_schema still contained its own $ref, so the resolved schema's $ref was overwritten by the original (now-stale) $ref, and the subsequent pop("$ref") then removed it entirely.

This is a small, surgical fix: pop the original $ref from the schema before the merge so the resolved schema's $ref (if any) survives into the recursive expansion call. The recursive call then fully resolves the chain.

Repro (failed before fix)

schema = {
    "$defs": {
        "Inner": {"type": "string"},
        "Outer": {"$ref": "#/$defs/Inner"},
    },
    "type": "object",
    "properties": {"a": {"$ref": "#/$defs/Outer", "description": "desc"}},
}
ensure_strict_json_schema(schema)
# Before: properties.a == {"description": "desc"}    -- type lost
# After:  properties.a == {"description": "desc", "type": "string"}

This pattern arises naturally when Pydantic models reference other models that are themselves thin aliases (e.g. RootModel, generic aliases, type aliases that emit single-key $ref definitions).

Test plan

• New regression test test_chained_ref_with_sibling_keys_is_resolved in tests/test_strict_schema.py fails before the fix and passes after.
• All existing tests/test_strict_schema.py and tests/test_strict_schema_oneof.py tests still pass (19 passed).
• Broader related suites unaffected: tests/test_function_schema.py, tests/test_agent_runner.py, tests/test_function_tool.py, tests/mcp/test_mcp_util.py (305 total passed, 0 failed).

[seratch]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Can't wait for the next one!

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