seedFromCheckpointMessages

Seed discovery from a checkpoint's root messages array (as returned by client.threads.getState().values.messages) so deep agent cards render on thread refresh without waiting for SSE replay.

Drives the existing root values path via a synthetic event so it reuses task discovery + completion marking with no new parsing logic. Root namespace [] keeps namespaces at the default tools:<toolCallId>; the always-on root pump (and applyExecutionNamespace) promote them to the execution namespace later. Idempotent by construction: re-driving root values for already-discovered tasks is a no-op (the FIFO taskInput queue is only populated on first discovery), so no snapshot.size guard is needed.