diff --git a/skills/adr/SKILL.md b/skills/adr/SKILL.md
index b9058d0..596c61e 100644
--- a/skills/adr/SKILL.md
+++ b/skills/adr/SKILL.md
@@ -58,8 +58,8 @@ adr:           0004
 title:         <the decision, as a sentence — not "database choice">
 status:        proposed | accepted | superseded | amended
 date:          2026-08-29
-deciders:      <who accepted it, by name — or "pending: <name>" while proposed>
-supersedes:    <adr number, or ->
+deciders:      <who accepted it, by name — or "pending: <name>" (QUOTED) while proposed>
+supersedes:    <adr number, or null>
 ---
 
 # ADR-0004 — <same title>
@@ -97,6 +97,25 @@ the condition that fires a revisit. An ADR with no validation section is a prefe
 with a template around it.
 ```
 
+### The frontmatter must actually parse
+
+It exists to be machine-read, so a block that does not load is worse than no block at
+all: it drops that ADR silently out of every "what is still open?" query, while looking
+correct. Two shapes this template used to suggest are invalid YAML, and both were found
+live in the estate on 2026-09-05 — `openbanking-api` ADR-0001 and `infra` ADR-0019, each
+copied verbatim from here:
+
+| Wrong | Why | Right |
+|---|---|---|
+| `supersedes:    -` | a bare dash is a YAML *sequence entry*, not a string | `supersedes:    null` |
+| `deciders:      pending: Mathias` | the second, unquoted colon reads as a nested mapping | `deciders:      "pending: Mathias"` |
+
+Check before committing:
+
+```sh
+python3 -c "import yaml,sys;yaml.safe_load(open(sys.argv[1]).read().split('---')[1]);print('ok')" docs/adr/0004-*.md
+```
+
 ## Preserving a productive tension
 
 Some tradeoffs are not unresolved because nobody thought hard enough. They are