SDK: artifacts work outside a node, run --follow prints status and queue waits, fluksio cancel

save_artifact/load_artifact outside a node use the worker's own store code in
$FLUKSIO_ARTIFACT_DIR or <tmp>/fluksio-artifacts, so a node can be called by
hand. --follow prints status changes and each node's resource wait; the
placer's waiting snapshot now carries the run. fluksio cancel <run>...

docs/code/cli.md

@@ -206,7 +206,7 @@ warnings. Use `--sync PATH` to choose a target explicitly.
 | Flag | Purpose |
 |---|---|
 | `--wait` | Wait for completion; exit non-zero if the run fails |
-| `--follow` | Wait and print emitted metrics |
+| `--follow` | Wait and print emitted metrics, status changes and what a queued node waits for |
 | `--timeout SECONDS` | Stop waiting after this long; leave the run active |
 | `--seed N` | Record the seed and fill a declared input named `seed` |
 | `--defaults` | Use declared input defaults without prompting |
@@ -217,7 +217,8 @@ warnings. Use `--sync PATH` to choose a target explicitly.
 
 With no parameters at a terminal, the command prompts for each input.
 Press Enter to keep its default. Scripted commands do not prompt.
-Ctrl-C while waiting cancels the run and exits with status 130.
+Ctrl-C while waiting cancels the run and exits with status 130. A run started
+without `--wait` is stopped with [`fluksio cancel`](#fluksio-cancel).
 
 A seed does not initialize your libraries' random number generators. Declare
 a `seed` input and pass it to your code if it controls randomness.
@@ -256,6 +257,15 @@ fluksio runs --flow train --limit 10
 Lists recent runs, newest first. Omit `--flow` for all flows.
 `--local` reads the local instance.
 
+### `fluksio cancel`
+
+```sh
+fluksio cancel <run-id> [<run-id> ...]
+```
+
+Stops the runs and their active node processes. A run already past its last
+node is left as it finished, and its status is printed.
+
 ### `fluksio retry`
 
 ```sh

docs/code/nodes.md

@@ -110,8 +110,10 @@ def process():
 ```
 
 Another node can read it with `fluksio.load_artifact(report)`, which returns
-a local file path. These two helpers require a running node; for tests,
-keep the underlying calculation in ordinary Python functions.
+a local file path. Called directly, outside a node, the two helpers store the
+bytes in `$FLUKSIO_ARTIFACT_DIR` or, when that is unset, in `fluksio-artifacts`
+under the temporary directory. The reference has the same shape as inside the
+engine, so a test can pass what one node returns to the next.
 
 Artifacts are stored by their SHA-256 digest, so identical bytes share storage.
 Use [`fluksio artifacts`](cli.md#fluksio-artifacts) to list and download a