Scenario 1 (Test 1): Deep nesting → LibraryCall

A → B → C → LibraryCall → Error
✗   ✗   ✓   ✓ (filter intermediates, keep last CallContract + LibraryCall)

Reasoning: LibraryCall is where the real error occurred, C's traceback shows the transition point.

Scenario 2 (Test 2): Alternating calls with LibraryCalls

A → LibraryCall → B → LibraryCall → Error
✓   ✓             ✓   ✓ (keep all - each transition is meaningful)

Reasoning: Each CallContract→LibraryCall transition represents a meaningful execution boundary.

Scenario 3 (Test 3): Pure CallContract chain to error

A → B → StringFrame Error
✓   ✓   (keep all - no LibraryCall, full chain context needed)

Reasoning: Without LibraryCall, the CallContract chain itself IS the error story. Removing A's traceback would lose critical context about how we got to B.