`the_header_measurement_table_is_the_measurement` went red on one row of
twenty-five: M4's site read `Types.ck:468` while the run measured `:467`.
Nothing about the measurement changed — the value is still 4 fields, still
the named-tuple TYPE at `fn from_literal(g: (| lat, latd, lon, lond |))`.
The corpus moved under it when `Types.ck` lost a line above that point.

The gate is machine-produced on both sides for exactly this reason: the
header is a claim about the corpus, so when they disagree the corpus wins
and the header is the defect.

@@ -377,0 +514,4 @@
+/// optional `--stdlib <path>` (used only for a directory), and `--opt
+/// <none|speed>`. A second positional, an unknown flag, an unknown `--opt`
+/// value, or a missing path is an error.
+fn parse_build_args(args: &[String]) -> Result<BuildArgs, String> {

@@ -157,0 +218,4 @@
+        let linked = matches!(self.built, Built::Linked);
+        let (exit, stdout, stderr) = match &self.built {
+            Built::NotAttempted => return Some(format!("`{app}`: nothing was attempted")),
+            Built::Refused { rendered } => (1, String::new(), rendered.clone()),