Merge remote-tracking branch 'origin/main'

# Conflicts:
#	app/androidApp/src/main/kotlin/com/example/aiapp/SessionScreen.kt

server/src/session/echo.rs

@@ -25,6 +25,9 @@
 //! This is exactly the event vocabulary the real drivers produce, so a UI
 //! that renders echo sessions correctly renders the real thing.
 //!
+//! - `/stream N` -- one long answer in N small pieces, 50ms apart: the
+//!   shape a real model's reply arrives in, and the one where the row a
+//!   reader is anchored to is the row that keeps changing height.
 //! - `/mixed N` -- N beats of an interleaved transcript: paragraphs of
 //!   different lengths, single tool calls, runs of adjacent ones, images
 //!   and a peer message. Rows of every shape and height the app draws, in
@@ -338,6 +341,9 @@ impl EchoDriver {
         // rather than trusted: this is a test affordance, and a session
         // pinned running for an hour by a typo is a worse outcome than a
         // short wait.
+        let stream = text
+            .strip_prefix("/stream")
+            .map(|rest| rest.trim().parse::<usize>().unwrap_or(400).clamp(1, 4000));
         let mixed = text
             .strip_prefix("/mixed")
             .map(|rest| rest.trim().parse::<usize>().unwrap_or(12).clamp(1, 400));
@@ -423,6 +429,23 @@ impl EchoDriver {
                 return;
             }
 
+            // One long answer arriving in small pieces, which is what a real
+            // model does and what `/slow` does not: `/slow` emits a line a
+            // second, so its message grows in steps a reader can watch one
+            // at a time. A jump caused by the *anchor row itself* changing
+            // height needs growth that is continuous.
+            if let Some(pieces) = stream {
+                for i in 0..pieces {
+                    let len = 3 + (i * 7) % 14;
+                    send(Event::AssistantText {
+                        delta: format!("{i}{} ", "x".repeat(len)),
+                    });
+                    tokio::time::sleep(Duration::from_millis(50)).await;
+                }
+                finish();
+                return;
+            }
+
             if let Some(beats) = mixed {
                 for beat in 1..=beats {
                     write_beat(&sink, &dir, beat).await;