feat(s010): plan_check rule 12 parses every workflow and Dependabot file

Red demonstrated on the exact defect PR #7 fixed, planted in the working
tree and reverted; green on the clean tree; both outputs in NOTES.md. The
population derives from git ls-files over .github; a missing YAML parser is
a FAIL, never a skip. G1 line 1.

Signed-off-by: Ayla Croft <aylacroft@proton.me>

Author: HackTuah

scripts/plan_check.sh

@@ -202,6 +202,21 @@ case "$branch" in
     ;;
 esac
 
+section "12. Every workflow and Dependabot file parses as YAML"
+# Found at slice 010 G1, from PR #7: an em dash replaced by a bare colon inside a step name made
+# .github/workflows/package.yml unparseable. GitHub reported a run named after the file path with
+# zero jobs, Dependabot's updater failed on the same file, and the gate stayed green because
+# nothing in it reads those files. The ubuntu runner and the developer machine both carry the
+# Python YAML module; if it is absent the rule says so and fails rather than passing quietly.
+if ! python3 -c 'import yaml' >/dev/null 2>&1; then
+  report "FAIL rule 12: python3 with the yaml module is required to parse the workflow files, and it is absent"
+else
+  for f in $(git ls-files '.github/*.yml' '.github/*.yaml' '.github/**/*.yml' '.github/**/*.yaml' | sort -u); do
+    err=$(python3 -c 'import sys, yaml; yaml.safe_load(open(sys.argv[1]))' "$f" 2>&1 >/dev/null | tail -1)
+    [ -n "$err" ] && report "FAIL $f: not parseable as YAML: $err"
+  done
+fi
+
 printf '\n'
 if [ "$fail" -eq 0 ]; then echo "plan_check: PASS"; else echo "plan_check: FAIL"; fi
 exit "$fail"

slices/010-core-domain-persistence/NOTES.md

@@ -43,3 +43,25 @@ Manual verification queue: none. Every criterion is `[auto]`.
 Deviations from SLICE.md, stated before building: line 3 adds `postgrex` as `optional: true` rather than a
 default dependency, so the standalone desktop build carries no Postgres driver; line 5 writes the UUIDv7
 generator in-tree rather than adding `uniq`, and proposes nothing new for VERSIONS.md.
+
+## Line 1, 2026-09-20: plan_check rule 12, red then green
+
+Planted the exact defect PR #7 fixed (the quotes removed from the step name at
+`.github/workflows/package.yml:173`, working tree only, reverted after):
+
+```
+$ ./scripts/plan_check.sh | grep -E '== 12|FAIL .github|plan_check:'
+== 12. Every workflow and Dependabot file parses as YAML ==
+FAIL .github/workflows/package.yml: not parseable as YAML:   in ".github/workflows/package.yml", line 173, column 25
+plan_check: FAIL
+exit=1
+
+$ git checkout -- .github/workflows/package.yml && ./scripts/plan_check.sh | grep -E '== 12|FAIL|plan_check:'
+== 12. Every workflow and Dependabot file parses as YAML ==
+plan_check: PASS
+exit=0
+```
+
+The population is `git ls-files '.github/*.yml' '.github/*.yaml' '.github/**/*.yml' '.github/**/*.yaml'`, three
+files today. The parser is Python's yaml module (6.0.1 here, present on the ubuntu runner); its absence is a
+FAIL, not a skip.