mcp(test[middleware]): Fix caplog double-capture on pytest 9.1.0

[tony]

Summary

• Fix test_tool_error_result_logs_at_error_log_level, which fails on pytest 9.1.0 because caplog records each error-log emit twice (assert [30, 30] == [30]). This reds main and any branch carrying the dev-dependency bump.
• Remove the obsolete propagate=True workaround suite-wide — the failing test plus two sister tests (test_send_keys_batch_schema_validation_redacts_inputs, test_expected_tool_error_logs_warning_through_server) all forced fastmcp logger propagation so caplog could see records. pytest 9.1.0 captures non-propagating loggers natively, making the workaround dead weight that double-captures each emit.
• Floor pytest>=9.1.0 in the dev and testing groups so the suite's reliance on that capture behavior is a declared contract, not an implicit one.

Root cause

fastmcp keeps its fastmcp logger non-propagating (it owns a Rich handler). The tests compensated by forcing fastmcp.propagate = True so caplog — which historically only listened at the root logger — could see the records.

pytest 9.1.0 shipped #3697 "Logging capture now works for non-propagating loggers": catching_logs.__enter__ now attaches its LogCaptureHandler directly to every non-propagating logger at setup, including fastmcp. A record emitted on fastmcp.errors reaches caplog by propagating up to fastmcp (where the handler now lives); re-enabling propagation to root captures the same emit a second time.

The error is logged once — only the capture was doubled:

Test setup	Records caplog sees
With propagate=True workaround (before)	2
Without the workaround (after)	1

test_tool_error_result_logs_at_error_log_level asserts an exact record count, so it failed outright. The two sister tests assert on log content, so the duplication was silent — but the workaround was equally obsolete there.

Changes by area

• tests/test_middleware.py: Drop the propagate=True workaround (and now-unused monkeypatch arg) from test_tool_error_result_logs_at_error_log_level and test_send_keys_batch_schema_validation_redacts_inputs; caplog captures fastmcp's logger natively.
• tests/test_utils.py: Drop the same workaround from test_expected_tool_error_logs_warning_through_server, including the docstring paragraph that described it.
• pyproject.toml / uv.lock: Floor pytest>=9.1.0 in dev and testing; relock.
• CHANGES: Add a ### Development entry.

Verification

The workaround is fully removed from the test suite (the monkeypatch.setattr(..., "propagate", ...) target):

rg -n '"propagate"' tests/

The floor is declared in both dependency groups:

rg -n 'pytest>=9\.1\.0' pyproject.toml

Test plan

• test_tool_error_result_logs_at_error_log_level (all parametrizations) passes with --reruns 0
• test_send_keys_batch_schema_validation_redacts_inputs and test_expected_tool_error_logs_warning_through_server pass without the workaround
• uv run ruff check . and uv run ruff format --check .
• uv run mypy
• Full suite green with uv run pytest --reruns 0
• just build-docs

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.73%. Comparing base (188784b) to head (8d43f6c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #83      +/-   ##
==========================================
+ Coverage   84.67%   84.73%   +0.06%     
==========================================
  Files          43       43              
  Lines        3197     3197              
  Branches      438      438              
==========================================
+ Hits         2707     2709       +2     
+ Misses        360      359       -1     
+ Partials      130      129       -1     

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[tony]

Code review

No issues found. Checked for bugs and AGENTS.md compliance.

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