M5: a callout given its arrow point alone keeps its knee (#1152)

comment_edit with one point on a callout whose /CL has six numbers built
the new line from that point and the end only, so the knee was dropped
without a word. An agent moving just the arrow lost the knee.

place_text_box now keeps the old knee when only the arrow point is given;
two points still set both, and a four-number /CL still gains a knee only
when one is sent. The points schema says so.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pq7HyCfwzyRXj4VfQAVVdv

crates/annot/src/modify.rs

@@ -413,7 +413,7 @@ pub fn set_points(doc: &mut Document, page: usize, index: usize, points: &[[f64;
     }
     if d.name(b"Subtype") == Some(b"FreeText") && callout_line(doc, &d).is_some() {
         // A callout's points: its arrow point, then optionally its knee (a four-number `/CL`
-        // gains one; ISO 32000-2 Table 177 allows both forms).
+        // gains one; ISO 32000-2 Table 177 allows both forms). The arrow point alone keeps a knee.
         if !matches!(points.len(), 1 | 2) || !finite(&points.concat()) {
             return Err(AnnotError::Invalid("a callout has an arrow point and, optionally, a knee".into()));
         }
@@ -545,6 +545,15 @@ fn place_text_box(doc: &mut Document, r: ObjRef, rect: [f64; 4], lead: Option<&[
     let old_line = callout_line(doc, &d);
     let old_box = callout_text_box(doc, &d);
     let old_end = old_line.as_deref().and_then(<[[f64; 2]]>::last).copied();
+    // An arrow point alone moves the arrow: a knee the line has stays where it is.
+    let kept: [[f64; 2]; 2];
+    let lead = match (lead, old_line.as_deref()) {
+        (Some([point]), Some([_, knee, _])) => {
+            kept = [*point, *knee];
+            Some(&kept[..])
+        }
+        _ => lead,
+    };
     let line: Option<Vec<[f64; 2]>> = match (lead, old_line.as_deref()) {
         (Some(lead @ [.., toward]), _) => {
             let side = callout_side(rect, *toward);

crates/annot/src/tests.rs

@@ -2446,3 +2446,17 @@ fn summaries_give_no_callout_points_without_a_text_box() {
         assert_eq!((s.points.len(), s.text_box), (0, None), "/RD {rd:?}");
     }
 }
+
+/// Review on #4094: a callout given its arrow point alone keeps its knee. The new line was built
+/// from the one point and the end, so a six-number `/CL` silently became four.
+#[test]
+fn a_callouts_arrow_point_alone_keeps_its_knee() {
+    let (mut doc, c) = callout_fixture();
+    let before = nums(&list(&doc, 0)[c], b"CL");
+    assert_eq!(before.len(), 6, "{before:?}");
+    set_points(&mut doc, 0, c, &[[190.0, 500.0]], &meta("p")).unwrap();
+    let after = nums(&list(&doc, 0)[c], b"CL");
+    assert_eq!(after.len(), 6, "the knee stays: {after:?}");
+    assert_eq!(after[..2], [190.0, 500.0], "the arrow point moved");
+    assert_eq!(after[2..], before[2..], "the knee and the end are where they were");
+}

crates/automation/src/tools.rs

@@ -916,7 +916,7 @@ pub fn tools() -> Vec<ToolDef> {
                 "font_size": { "type": "number", "minimum": 1, "maximum": 400, "description": "Font size in points of a text box, typewriter text or callout; the box grows to hold the text." },
                 "rect": { "type": "array", "items": { "type": "number" }, "minItems": 4, "maxItems": 4 },
                 "move": point(),
-                "points": { "type": "array", "items": point(), "minItems": 1, "description": "A line's two ends, every corner of connected lines, a polygon or a cloud, or a callout's arrow point and (optionally) knee, in page coordinates." },
+                "points": { "type": "array", "items": point(), "minItems": 1, "description": "A line's two ends, every corner of connected lines, a polygon or a cloud, or a callout's arrow point and (optionally) knee, in page coordinates. A callout given its arrow point alone keeps the knee it has." },
             })),
             &["doc"],
         )),