transcript-ui: log selection begin/extend, for on-device verification

Selection has no accessibility label of its own yet, so a logcat line at
begin/extend is the smallest way to confirm a real long-press-then-drag
reached DragArbiter/Selection on-device. Driven with the new ui-trace
holddrag action against iris-android-app's transcript screen: produced
"iris selection: begin at row ..." then a sequence of "... extend to row
..." lines, and a screenshot right after shows the expected highlighted
selection spanning multiple rows.

New `log = "0.4.28"` dependency (matching iris-android-app's own pin) --
transcript-ui had no logging facility before this.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

iris/Cargo.lock

@@ -3651,6 +3651,7 @@ dependencies = [
  "client-core",
  "event-model",
  "iris",
+ "log",
  "pulldown-cmark",
 ]
 

iris/android-app/Cargo.lock

@@ -3867,6 +3867,7 @@ dependencies = [
  "client-core",
  "event-model",
  "iris",
+ "log",
  "pulldown-cmark",
 ]
 

iris/transcript-ui/Cargo.toml

@@ -18,3 +18,9 @@ iris = { path = ".." }
 client-core = { path = "../../client-core" }
 event-model = { path = "../../event-model" }
 pulldown-cmark = { workspace = true }
+# Selection has no accessibility label of its own yet (IRIS_TODO.md's
+# "Row-level accessibility names"), so a logcat line at
+# begin/extend is the smallest way to confirm a real long-press-then-drag
+# reached `Selection` on-device (RUST.md's I5 box, "Measurements taken"
+# (c)) -- version pinned to match `iris-android-app`'s own dependency.
+log = "0.4.28"

iris/transcript-ui/src/selection.rs

@@ -189,8 +189,19 @@ impl Selection {
         match outcome {
             DragOutcome::Undecided => {}
             DragOutcome::Pan(dy) => list(ui).scroll(-dy),
-            DragOutcome::SelectStart => self.begin(ui, key, pos_row, size),
-            DragOutcome::SelectExtend => self.extend(ui, key, pos_row, size),
+            DragOutcome::SelectStart => {
+                // Grep-able on "iris selection" the way the frame report is
+                // on "iris frame report" -- selection has no accessibility
+                // label of its own yet, so this is the smallest way to
+                // confirm a real on-device long-press-then-drag actually
+                // reached here (RUST.md's I5 box, "Measurements taken" (c)).
+                log::info!("iris selection: begin at row {key:?}");
+                self.begin(ui, key, pos_row, size);
+            }
+            DragOutcome::SelectExtend => {
+                log::info!("iris selection: extend to row {key:?}");
+                self.extend(ui, key, pos_row, size);
+            }
         }
     }