fix(ce-compound): quote YAML array items starting with reserved indicators (#613)

Co-authored-by: Nathan Vale <hi@nathanvale.com>

plugins/compound-engineering/skills/ce-compound/references/schema.yaml

@@ -228,3 +228,4 @@ validation_rules:
   - "date must match YYYY-MM-DD format"
   - "rails_version, if provided, must match X.Y.Z format and only applies to bug-track docs"
   - "tags should be lowercase and hyphen-separated"
+  - "Array-of-strings frontmatter items (symptoms, applies_when, tags, related_components, or any future array field) must be wrapped in double quotes when the value starts with a YAML reserved indicator (`, [, *, &, !, |, >, %, @, ?) or contains the substring `: ` — otherwise strict YAML parsers reject the file"

plugins/compound-engineering/skills/ce-compound/references/yaml-schema.md

@@ -89,3 +89,30 @@ Docs created before the track system may have `symptoms`/`root_cause`/`resolutio
 7. Array fields must respect min/max item counts.
 8. `date` must match `YYYY-MM-DD`.
 9. `rails_version`, if present, must match `X.Y.Z` and only applies to bug-track docs.
+
+## YAML Safety Rules
+
+Strict YAML 1.2 parsers (`yq`, `js-yaml` strict, PyYAML) reject array items
+that start with a reserved indicator character as unquoted scalars. When
+writing items for any array-of-strings field (`symptoms`, `applies_when`,
+`tags`, `related_components`, or any future array field), wrap the value in
+double quotes if it starts with any of:
+
+`` ` ``, `[`, `*`, `&`, `!`, `|`, `>`, `%`, `@`, `?`
+
+Also quote if the value contains the substring `": "` — that punctuation
+confuses flow-style parsers.
+
+Example — before (breaks strict YAML):
+
+    symptoms:
+      - `sudo dscacheutil -flushcache` does not restore in-container mDNS
+
+Example — after (parses cleanly):
+
+    symptoms:
+      - "`sudo dscacheutil -flushcache` does not restore in-container mDNS"
+
+This rule applies to all array-of-strings frontmatter fields. Scalar string
+fields like `description:` have their own quoting rules (see plugin
+`AGENTS.md` under "YAML Frontmatter").