fix

AGENTS.md

@@ -121,6 +121,15 @@ util/rm-mac-geom  # reset the app's saved window geometry
   otherwise the build fails on `F.<field>` being unresolved.
 - `dialect.swift` is generated — edits there are overwritten on the next
   `util/build-mac`. Change the source (`dialect.yml` / `components/`) instead.
+- **Validate `dialect.yml` after edits** (e.g. `ruby -ryaml -e 'YAML.load_file("dialect.yml")'`).
+  Every should-branch label (`1. Upon each ...`) MUST end with a colon — the
+  parser (`components/yml/ymlFun.swift`) blindly `dropLast()`s it, so a missing
+  colon silently eats the label's last character in the generated `about`
+  comment. Note the file can never pass a *strict* YAML parser: condition and
+  reaction lines (under `if:` / `then:`) contain unquoted `: ` (e.g.
+  `c.countText = "Count: '\(c.count)'"`), which standard YAML rejects. So treat
+  a parser complaint pointing *inside* an `if:`/`then:` block as expected; any
+  complaint elsewhere (like a missing branch-label colon) is a real bug.
 
 ## Swift 6