skills: a sixth instance, found by the repo owner within the hour

Claimed "## Unreleased is a new convention in this repo" after reading
CHANGELOG.md once — minutes after b615571 had renamed that very section to
`## v1.8.11`. 33 commits touch the heading; the convention is that new entries
land under Unreleased and the heading is renamed at tag time, exactly as it
was renamed out from under my snapshot.

Same root cause as the five instances the section above already records: an
absence observed in one frame, promoted to a fact about the world, with no
second measurement. `git log -S'## Unreleased' -- CHANGELOG.md` was the oracle
and costs one command.

The generalisation is worth more than the instance, so it goes in the habits
block: to learn a repeating PROCESS, read history, not the file. A file's
current content is one frame of a cycle, and the frame you catch may be the one
where the thing you are looking for has just been consumed.

rootfs/usr/local/share/pi-devbox/skills/pi-devbox-environment/SKILL.md

@@ -146,6 +146,7 @@ mine:
 | "the credential is not in the palace" | scanned `embedding_metadata.string_value` only. Drawer **text** lives in `embedding_fulltext_search_content.c0`; 554k metadata rows proved nothing. |
 | "this token is dead — 401" | probed it against the **wrong issuer**. A 401 from an instance that never issued the credential is not evidence about the credential. |
 | "that host is unreachable, can't test" | tried ports 443 and 80. It was on **3000**, and the env var I already held (`GITEA_EGL_HOST`) stated the scheme and port. |
+| "this repo has no `## Unreleased` convention" | read `CHANGELOG.md` **once**, minutes after a release commit had renamed that section to a version heading. 33 commits touch `## Unreleased`. A snapshot cannot show you a cycle. |
 
 Habits that would have caught all three:
 
@@ -158,6 +159,11 @@ ssh -F "$HOME/.ssh-local/config" mac 'command -v docker || ls /usr/local/bin/doc
 
 # match a process's ACTUAL argv, not the name you imagine
 ps -eo pid,etime,args | grep -Ei 'mux|mosh|ssh'
+
+# to learn a repeating PROCESS or convention, read history, not the file. A
+# file's current content is one frame of a cycle, and the frame you happen to
+# catch may be the one where the thing you are looking for was just consumed.
+git log -S'## Unreleased' -- CHANGELOG.md         # not `head -60 CHANGELOG.md`
 ```
 
 Absence has to be *earned*, so spend the extra command there.