The Bug

  Both Full() (sync.go:236-241) and Incremental() (incremental.go:46-51) used a defer to catch panics and record the failure in the
  database, but then re-threw the panic with panic(r). This crashed the entire program instead of returning a graceful error to the
  caller.

  The Fix

  Three changes per function (identical pattern in both files):

  1. Named return values: Changed (*gmail.SyncSummary, error) to (summary *gmail.SyncSummary, err error) so the defer can set the
  return values
  2. summary := → summary =: Assign to the named return variable instead of shadowing it
  3. panic(r) → summary = nil; err = fmt.Errorf("sync panicked: %v", r): Return an error instead of crashing

  Changes Made

  - internal/sync/sync.go: Named returns, summary =, replace panic(r) with error (3 lines changed)
  - internal/sync/incremental.go: Same 3 changes
  - internal/sync/sync_test.go: Added panicOnBatchAPI wrapper and TestFullSync_PanicReturnsError test (24 lines)