Attach to the SSE stream for a session and print events.

A point with NO chart_id lands with chart_id="default" on a single-chart session.

Metric ``recall`` exists in chart A, not B. Targeting B with it → 400 unknown_metric.

A client_ts 10 minutes in the future must be rejected with clock_skew.

Invoking without --chart stamps chart_id='default' on every ref.

--chart recall applies to ALL --group flags in the same invocation.

complete_groups can carry CompletionRef objects with explicit chart_id.

A point with an explicit chart_id persists that chart_id.

A live datapoint SSE event preserves the point's chart_id.

dataset_complete events preserve chart_id so chart-specific pills flip.

Pending when no data; running when data but no completion; complete when completion row exists.

A benchmark with 2 charts × 2 groups yields 4 DatasetState entries.

A JSONL line without chart_id and no --chart flag → chart_id='default'.

A JSONL line without chart_id inherits the --chart flag value.

A JSONL line with its own chart_id wins over --chart and the default.

Without --chart, single-mode emits a DataPoint with chart_id='default'.

--chart recall stamps chart_id='recall' on the single-mode DataPoint.

Points inserted with explicit chart_ids round-trip through storage.

Out-of-order client_ts: newer-by-client_ts must win even when inserted later.

Two points with the same (group, metric) but different chart_ids are isolated cells.

Out-of-order client_ts still picks the newest per (chart, group, metric).

Multi-chart benchmark reports chart_count>1 and better=None.

Marking (chart=a, group=g) complete must not affect (chart=b, group=g).

Omitting client_ts should be rejected — Pydantic returns 422.

Multi-chart snapshot: every points entry and every datasets entry has chart_id.

The --chart flag supplies a default for lines that omit their own chart.

A control line's own ``chart`` field wins over the --chart flag default.

POST with a chart_id that doesn't exist in the session's config → 400.

Insert or update a benchmark row keyed by ``session_id``. Serialises the full ``BenchmarkConfig`` into ``config_json``; denormalises ``title`

Upsert metadata for one or more (chart, group) pairs. Returns a list of ``(chart_id, group_key, merged_data)`` for each entry so the caller c