[DawnofGenX]

Summary

Adds regression tests for the breadcrumb-truncation _meta annotation described in #3996.

The runtime behavior itself already exists (merged in 5147ab9 / #4007): when breadcrumbs exceed max_breadcrumbs, the SDK tracks the number dropped on the scope and attaches event["_meta"]["breadcrumbs"] = {"": {"len": <original total>}} to captured events. However, the original PR shipped with no dedicated tests (its only test change was an adjustment to tests/test_scrubber.py caused by the new annotation), so nothing in the suite guards this protocol behavior today.

This PR adds three tests to tests/test_client.py next to the existing test_max_breadcrumbs_option:

1. test_breadcrumbs_truncated_meta — 10 breadcrumbs with max_breadcrumbs=3 → event carries 3 crumbs and _meta records the original total (10).
2. test_breadcrumbs_not_truncated_no_meta — exactly at the limit → no breadcrumbs entry under _meta.
3. test_breadcrumbs_truncated_meta_from_child_scope — breadcrumbs added in a child scope accumulate correctly across scope merging (Scope._merge_into).

Test plan / evidence

Fails without the fix (I temporarily reverted the _meta attachment block in sentry_sdk/client.py):

tests/test_client.py::test_breadcrumbs_truncated_meta FAILED
tests/test_client.py::test_breadcrumbs_not_truncated_no_meta PASSED
tests/test_client.py::test_breadcrumbs_truncated_meta_from_child_scope FAILED

E   KeyError: '_meta'  (test_client.py:1091, test_breadcrumbs_truncated_meta)
E   KeyError: '_meta'  (test_client.py:1121, test_breadcrumbs_truncated_meta_from_child_scope)
=========== 2 failed, 1 passed, 88 skipped, 2329 deselected in 2.53s ===========

Passes with the fix restored (full tests/test_client.py):

========== 2246 passed, 174 skipped, 126 warnings in 77.52s (0:01:17) ==========
  py3.14-common: OK

Commands:

• uv run tox -e py3.14-common -- -k "breadcrumbs_truncated_meta or breadcrumbs_not_truncated_no_meta"
• uv run tox -e py3.14-common -- tests/test_client.py
• uv run ruff check --fix tests/test_client.py / uv run ruff format tests/test_client.py (clean)

Fixes #3996

[alexander-alderman-webb]

Going to close this because we don't have capacity to review the 5 PRs you've opened.
If you'd like to contribute dedicate your time towards making one good PR. Thanks.