Schedule: Add unit tests to services/anthropic/trim_messages.py

[gitauto-ai]

Resolves #1978

Summary

Add comprehensive unit tests for services/anthropic/trim_messages.py to achieve full line/statement/function coverage and exercise previously uncovered branch logic.

Test Patterns

• No-op passthrough when messages are already within the limit
• Trimming to fit a strict limit while preserving required ordering/invariants
• Retaining the most recent exchange and dropping older context as needed
• Empty input and single-message input handling
• Mixed roles and content structures (e.g., string vs segmented content) preserved after trimming
• Invalid inputs (missing role/content, unsupported role/type, non-list input) raise expected errors
• Boundary conditions where the budget is exactly met
• Behavior when every message individually exceeds the budget (minimal viable output or expected error path)
• Exercises both sides of the previously uncovered if branch at line 32 (block 0) and the opposite path

git fetch origin
git checkout gitauto/issue-1978-20251017-000101-bp4l
git pull origin gitauto/issue-1978-20251017-000101-bp4l

[gitauto-ai]

Finished fixing the build check run error!