Issue 015: the harness read a swallowed answer as success

2026-08-31 00:48:16 +02:00
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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:
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 # 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.*