fix: resolve mypy shape-type error in _frames_to_mono_i16

[munkhorgil]

What

Fixes a mypy failure in _recorder.py that broke CI:

src/roark_analytics_python_livekit/_recorder.py:46: error: Incompatible types in assignment (expression has type "ndarray[tuple[int, int], ...]", variable has type "ndarray[tuple[int], ...]")  [assignment]

numpy's shape-parameterized stubs track array rank in the type. In _frames_to_mono_i16, arr starts as a 1-D int16 array from np.frombuffer, so reassigning the 2-D reshape(-1, num_channels) result back onto it is a rank conflict.

Changes

• Move the multi-channel 2-D view into its own multi variable so arr stays 1-D throughout. No runtime behavior change — still averages interleaved channels down to mono int16.

Verification

• uv run mypy src/roark_analytics_python_livekit → Success: no issues found in 6 source files
• uv run ruff check . → clean
• uv run pytest → 34 passed

[claude]

Claude finished @munkhorgil's task in 1m 23s —— View job

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Code Review Summary

Category	Score	Notes
Code Quality	5/5	Minimal, correct fix — keeps arr rank-stable by introducing multi for the 2-D view
Security	5/5	No security surface touched
Performance	5/5	No behavior/perf change — same numpy ops, no extra copies
Testing	5/5	Existing test_frames_to_mono_stereo_averages_channels in tests/test_recorder.py already exercises this exact multi-channel path and passes unchanged
Documentation	5/5	N/A — no public API/behavior change
Overall	5/5

Findings

None. The change in src/roark_analytics_python_livekit/_recorder.py:46-47:

multi = arr.reshape(-1, f.num_channels)
arr = (multi.astype(np.int32).sum(axis=1) // f.num_channels).astype(np.int16)

correctly resolves the mypy shape-rank conflict (numpy's shape-parameterized stubs treat arr.reshape(-1, n) as a different rank than the original 1-D arr, so reassigning onto the same variable was a type error) by giving the intermediate 2-D view its own name. arr stays 1-D int16 throughout, matching the function's declared return type. Confirmed reshape is used nowhere else in the codebase, so this was the only site affected.

Nice, surgical fix — appropriately scoped to just the mypy failure with no unrelated changes.