Follow a record into its fields, name the metrics, name the version

Three things the first export pass got wrong for a real study.

**Dotted paths.** A node returns a record, not a scalar — the numbers arrive
inside `final_metrics` — so `--metrics final_metrics.train_loss` yielded an
empty column and `--metrics final_metrics` yielded the whole record in one
cell. Both sides of the wide table now take dotted paths, and the defaults
reach the same depth: every number a result carries is a column named by its
path, and inputs are compared leaf by leaf, so two configurations differing in
one field give that field as the axis rather than two blobs that are merely
not equal. Lists stay whole — a curve belongs in the long table.

**`--list`.** Metric names are flow-qualified, so `--name train_loss` matched
nothing and said only that. `fluksio export metrics --list` prints the names
the selection carries, and an empty export made with `--name` points at it.

**A version to compare.** The CLI ships ahead of the engine and a stale one
answered a flat 404 with nothing anywhere in the API to tell how old it was.
The engine reports `version` on `/observability/summary`, `fluksio status`
prints it, and a 404 from export now names both versions — or says "older"
when the field itself predates the engine. Bumped to 0.1.5, which is what
makes the number worth reading.

Also formats `flow/metrics.py`, which had been committed unformatted and was
the last `ruff format --check` failure.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A9Hdrmf2cwNABCnE5x9UJa

docs/code/cli.md

@@ -307,7 +307,8 @@ of them are finished and exits non-zero if any failed.
 ### `fluksio export`
 
 ```sh
-fluksio export metrics --flow train --name train_loss,val_loss --stride 10 -o curves.csv
+fluksio export metrics --flow train --list
+fluksio export metrics --flow train --name train.train_loss --stride 10 -o curves.csv
 fluksio export runs    --flow train --status ok > arms.csv
 ```
 
@@ -323,6 +324,18 @@ runs — the axis of the sweep, which is what a comparison is read along —
 unless `--params lr,seed` names them. `--metrics` narrows the final numbers
 the same way.
 
+A node usually returns a record rather than a scalar, so both sides take
+dotted paths into one: `--metrics final_metrics.train_loss,test_metrics.known.perfect`
+selects three fields rather than two blobs, and `--params model.ansatz` does
+the same for an input. The defaults reach the same depth — every number a
+result carries becomes a column wherever it sits, and inputs are compared
+leaf by leaf, so two configurations differing in one field give that field
+rather than two records that are merely not equal.
+
+Metric names are flow-qualified — a node of `train` writing `train_loss`
+records `train.train_loss` — so `--list` prints the names the selected runs
+carry when the spelling is not obvious.
+
 Both take `--flow`, `--run ID` (repeat it), `--group`, `--status`, `--since`,
 `--until` and `--local`, and both put the run id on every row: it is the join
 back to the run page and to what the run made.