refactor(macos): extract the fail-soft degrade-and-return pattern in presentation.py

[dhruvbatra]

What

MacOSPresentationController.show_thumbnail, .before_capture, .after_capture, and .encode_observation each wrapped their entire body in an identical shape:

try:
    ...
    return <success value>
except Exception as error:  # noqa: BLE001 - presentation is fail-soft
    await self._degrade(reason, error)
    return <default value>

This pulls that shape into a single _fail_soft(reason, default) decorator (module-level, functools.wraps-preserving) so each of the four methods keeps only its distinct body plus its own reason/default. Net: four duplicated try/except blocks become one shared helper, applied via decorator.

Why this is safe / no public behavior change

• Purely an internal implementation detail of yutori/navigator/macos/presentation.py — no function signatures, return types, or observable behavior change. functools.wraps keeps __name__/__doc__/introspection intact.
• The decorator wraps the entire method body, including the existing early-return guard clauses — since those don't raise, they execute identically to before (no try was ever wrapped around them either way).
• self._degrade is still resolved dynamically via self at call time, so existing tests that monkeypatch controller._degrade on the instance continue to work unchanged.
• present and _present_status were deliberately left alone — they interleave multiple branches and must re-raise asyncio.CancelledError before degrading, so they don't fit this single-exit shape and keep their own inline try/except.
• I did not touch the two methods that have that different CancelledError-first shape (present, _present_status), and did not touch any other file.

What I verified

• ruff check . and ruff format --check pass on the changed file (repo-wide ruff format --check reports 13 pre-existing unrelated files with drift, none of which is this one — confirmed via git diff that only presentation.py changed).
• pytest tests/test_navigator_macos_presentation.py tests/test_navigator_macos_computer.py -v — 109/109 pass, including the existing fail-soft/degrade coverage (test_capture_ids_are_monotonic_and_a_stale_transition_degrades, test_status_mode_thumbnail_rejection_degrades_fail_soft, etc.) unmodified.
• Full suite: pytest -m "not slow" — 862 passed, 9 skipped (pre-existing), 1 deselected (slow marker).

🤖 Generated with Claude Code

https://claude.ai/code/session_01F9iAjBxPM94GjhCENMjXP8

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Generated by Claude Code

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Note

Low Risk
Internal refactor in one file with no signature or observable behavior change; existing presentation fail-soft tests cover the same paths.

Overview
Introduces a module-level _fail_soft(reason, default) async decorator that centralizes the shared “catch any exception → await self._degrade(reason, error) → return default” pattern used by macOS presentation operations.

show_thumbnail, before_capture, after_capture, and encode_observation now use the decorator instead of four copy-pasted try/except blocks; each method keeps its guard clauses and success-path logic unchanged. present and _present_status are intentionally unchanged because they must re-raise asyncio.CancelledError before degrading.

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