history: one Flux script per chart, and rows are json

Two things the installation found that the checks did not.

A script with three `from()` statements in it produces three results all
called `_result`, and InfluxDB refuses that outright — so the measurements go
into one filter and the rows come back tagged with which one they are.

And the answer a database node hands back holds a *list* of rows, which a
record may not: a record is flat scalars. It was declared one, so every chart
failed on the type check the moment a real answer arrived.

The second one is now caught before anything is pushed: the preflight runs
each sample shape past the port that would receive it, which is what turns
"expected record, got dict" from a runtime surprise into a line of output.

Also records the two engine faults this seeding session surfaced.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/tinyhouse/__main__.py

@@ -176,7 +176,15 @@ def _check_sources(flows: list[Flow]) -> list[str]:
             ports = {}
             for spec in node.get("requires", []):
                 port = spec.get("port") or spec["name"]
-                ports[port] = SHAPES.get(port, SAMPLE.get(spec["dtype"]))
+                sample = SHAPES.get(port, SAMPLE.get(spec["dtype"]))
+                # The shape a node is written against has to be one its port
+                # would actually accept. A payload with a list inside it is
+                # `json`, not `record` — and the difference only shows when a
+                # real answer arrives, which is far too late.
+                bad = _rejects(spec, sample)
+                if bad:
+                    problems.append(f"{where} port '{port}': {bad}")
+                ports[port] = sample
             try:
                 result = process(**ports, **node.get("params", {}))
             except Exception as exc:  # noqa: BLE001 - reported, not raised
@@ -283,6 +291,23 @@ def _check_widgets(known: set[str]) -> list[str]:
 # ── pushing it ───────────────────────────────────────────────────────────
 
 
+def _rejects(spec: dict[str, Any], sample: Any) -> str:
+    """Why this port would refuse the shape it is being written against."""
+    if sample is None:
+        return ""
+    try:
+        from fluksio.flow.messages import MessageSpec
+    except ImportError:
+        return ""
+    try:
+        MessageSpec(**{k: v for k, v in spec.items() if k != "port"}).check(sample)
+    except TypeError as exc:
+        return str(exc)
+    except Exception:  # noqa: BLE001 - a spec we cannot build says nothing
+        return ""
+    return ""
+
+
 def _check_schemas(flows: list[Flow]) -> list[str]:
     """Hand every node to the engine's own models before the API sees them.