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+---
+status: resolved
+opened: 2026-08-31
+located-in: [mesh-lab]
+fixed-by: mesh-lab — a command with no marker is a failure, not a success
+amended-design:
+---
+
+# 015 — A command that said nothing was read as having succeeded
+
+## Symptom
+
+The end-to-end harness runs a command on a machine and reads its exit status from a marker it
+appends to the output. When the marker was absent, the parse produced `Number("")`, which is `0`,
+and **the command was reported as having succeeded.**
+
+The marker went missing whenever a command contained a heredoc. Everything was wrapped on a single
+line — `<cmd> 2>&1; echo "__exit=$?"` — so a heredoc's terminator line became
+`MARKER 2>&1; echo "__exit=$?"`, matched nothing, and the heredoc consumed the rest of the script,
+the marker included.
+
+## Why this matters
+
+**This is the harness lying in the one direction a harness must never lie.** Everything else in
+this repository is arranged around the principle that absence must never be indistinguishable from
+success — the host says so about a service that does not exist, the builder says so about a build
+that failed, the control plane says so about an empty list. The thing that checks all of that had
+the fault itself.
+
+Its reach is every heredoc in the suite, which is how large files are written to machines: a
+substrate bundle, a certificate authority, a listener script. Each was written with trailing
+junk from the swallowed wrapper, each reported success, and each happened to be tolerated by
+whatever read it — until one was a Python script, which did not run, and the test failed on its own
+setup. **That failure read exactly like the thing being tested working.**
+
+## What was done
+
+`exec 2>&1` on its own first line, so nothing is appended to the command's last line and a heredoc
+terminates where it says it does. A missing marker is now a failure, returning whatever was said
+so the reason is visible rather than inferred.
+
+*Checked by the firewall test, whose listener is written with a heredoc: it could not have started
+before this, and the assertion that it is reachable before any rule set exists is what makes the
+rest of that test mean anything.*