This is a comment left during a code review.
Path: src/agentex/_client.py
Line: 137

Comment:
**Non-mapping `default_headers` silently dropped**

When `AGENTEX_CUSTOM_HEADERS` is set and the caller passes `default_headers` as a list of `(name, value)` tuples (a valid `HeadersLike` form), `is_mapping_t` returns `False`, the explicit headers are silently ignored, and only the env-derived headers survive. Any caller using tuple-style headers would lose them without warning.

Consider handling the sequence-of-tuples case explicitly, or at minimum documenting that `default_headers` must be a mapping when the env var is active.

How can I resolve this? If you propose a fix, please make it concise.

---

This is a comment left during a code review.
Path: tests/test_files.py
Line: 134

Comment:
**Assertion weakened — field-name keys no longer verified**

The previous assertion `extracted == [("items[][file]", file1), ("items[][file]", file2)]` checked both the field name and the file value. The new assertion only checks values and silently ignores whatever keys `extract_files` emits. If the key logic ever regresses (e.g., produces `"items[file]"` or `""` instead of `"items[][file]"`), this test would still pass.

Consider restoring the key check alongside the existing value check:
```suggestion
        assert extracted == [("items[][file]", file1), ("items[][file]", file2)]
```

How can I resolve this? If you propose a fix, please make it concise.