Read-only execution-lineage timeline for one inbound record, chronological.
Sibling of MailglassAdmin.Operator.Timeline (D-48-13). Rows are
ExecutionRun projections (Pitfall 7 — the lineage schema, NOT the replay-run
schema) from MailglassInbound.Internal.Operator.Timeline, each carrying
source (:fresh/:replay), mailbox, outcome, outcome_reason,
executed_at, and the run id.