M6: form_fill warns when a value does not fit its field (#4018)

With a fixed font size, a text field's appearance cuts a long value at
the edge of its box, but form_fill only answered "filled": n. A person
sees the cut; an agent filling forms through the CLI or MCP did not.

The text appearance builder now notes when the text it lays out does
not fit: one line wider than the box, or wrapped lines below it.
forms::appearance::value_overflow asks that for a field's widget,
Document::field_overflow for a field by name, and form_fill adds a
warning for each filled field that is cut off. The value is still saved
whole and drawn as before; auto-sized fields shrink to fit and are not
reported.

The automation tests' inline PDF builder moves to a shared pdf_of.

Fixes #4018

crates/engine/src/lib.rs

@@ -843,6 +843,14 @@ impl Document {
         matches!(f.kind, FormFieldKind::CheckBox | FormFieldKind::Radio).then(|| pdfcraft_forms::check_style(&e.cos, f))
     }
 
+    /// Whether text field `name`'s value is cut off by its box at the field's font size (#4018):
+    /// the page (0-based) of the first widget that cuts it, and how.
+    pub fn field_overflow(&self, name: &str) -> Option<(Option<usize>, pdfcraft_forms::appearance::Overflow)> {
+        let e = self.editor.as_ref()?;
+        let f = self.form.iter().find(|f| f.name == name)?;
+        f.widgets.iter().find_map(|w| pdfcraft_forms::appearance::value_overflow(&e.cos, f, w).map(|o| (w.page, o)))
+    }
+
     /// Remove Hidden Information: what each category would remove.
     pub fn hidden_info(&self) -> Vec<(Hidden, usize)> {
         self.editor.as_ref().map(|e| pdfcraft_redact::sanitize::scan(&e.cos)).unwrap_or_default()