fix: handle tuples in deepcopy_minimal to prevent dict mutation

[giulio-leone]

Summary

Fixes #1202 — deepcopy_minimal does not recurse into tuples, causing files.beta.upload to mutate the caller's headers dict in-place.

Root Cause

deepcopy_minimal only handles dict and list, returning everything else as-is. When a FileTypes tuple like (name, content, mime, headers_dict) is passed, the tuple is shared by reference, so any downstream mutation of the headers dict (element [3]) leaks back to the caller.

Fix

Add tuple handling to deepcopy_minimal:

if isinstance(item, tuple):
    return cast(_T, tuple(deepcopy_minimal(entry) for entry in item))

This ensures dicts (and lists) nested inside tuples are recursively copied.

Tests

• Updated existing tuple test (was asserting obj3 is obj4 identity, now checks proper copy)
• Added test_tuple_with_nested_dict — verifies the exact FileTypes scenario from Use of deepcopy_minimal in files.beta.upload mutates dict in place #1202: mutating the copy's headers dict does not affect the original
• All 8 tests pass

[giulio-leone]

Friendly ping — CI is green, tests pass, rebased on latest. Ready for review whenever convenient. Happy to address any feedback. 🙏

[giulio-leone]

Added a real runtime validation pass for this fix using the public Anthropic(...).beta.files.upload(file=...) path against a local HTTP server (no mocks/stubs in the reproduction itself).

Results:

• On upstream/main, the caller-owned headers dict was mutated in place by the upload call: {'X-Original': '1'} became {'X-Original': '1', 'Content-Type': 'text/plain'} after the request completed.\n- On this branch, the exact same upload call returned a valid FileMetadata response and left the original headers dict unchanged.\n- Targeted regression suite still passes locally: .venv/bin/python -m pytest tests/test_deepcopy.py -q -> 8 passed.\n\nSo this is now backed by both the focused tests and a real before/after reproduction of the public upload flow from issue Use of deepcopy_minimal in files.beta.upload mutates dict in place #1202.