Streams: list / switch / merge down / copy up

- Tools -> Streams: list server streams, switch the workspace to a stream,
  merge down from parent / copy up to parent (into a pending changelist)
- Backend p4 streams, client -s -S, merge/copy -S

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -1867,6 +1867,52 @@ async fn p4_latest_change(state: State<'_, AppState>, scope: String) -> Result<V
     Ok(v.into_iter().next().unwrap_or(Value::Null))
 }
 
+/// List streams on the server.
+#[tauri::command]
+async fn p4_streams(state: State<'_, AppState>) -> Result<Vec<Value>, String> {
+    let conn = current(&state)?;
+    run_json(&conn, &["streams", "-m", "300"])
+}
+
+/// Switch the current workspace to a stream (`p4 client -s -S <stream>`), then
+/// return the refreshed `p4 info`. The workspace View is rebuilt from the stream.
+#[tauri::command]
+async fn p4_switch_stream(state: State<'_, AppState>, stream: String) -> Result<Value, String> {
+    let conn = current(&state)?;
+    let stream = stream.trim();
+    if stream.is_empty() {
+        return Err("No stream".into());
+    }
+    run_text(&conn, &["client", "-s", "-S", stream])?;
+    let info = run_json(&conn, &["info"])?;
+    let info = info.into_iter().next().unwrap_or(Value::Null);
+    let root = info.get("clientRoot").and_then(|r| r.as_str()).unwrap_or("").to_string();
+    state.0.lock().unwrap_or_else(|e| e.into_inner()).root = root;
+    Ok(info)
+}
+
+/// Stream integration: direction "down" merges from the parent into the stream
+/// (merge down), "up" copies the stream to its parent (copy up). Opens the work
+/// into a fresh changelist; resolve (if needed) and submit as usual.
+#[tauri::command]
+async fn p4_stream_integ(state: State<'_, AppState>, stream: String, direction: String) -> Result<String, String> {
+    let conn = current(&state)?;
+    let stream = stream.trim();
+    if stream.is_empty() {
+        return Err("No stream".into());
+    }
+    let (verb, extra, label) = if direction == "up" {
+        ("copy", vec!["-r"], "copy up")
+    } else {
+        ("merge", vec![], "merge down")
+    };
+    let cl = create_changelist(&conn, &format!("{label} {stream}"))?;
+    let mut args: Vec<&str> = vec![verb, "-S", stream, "-c", &cl];
+    args.extend(extra);
+    let out = run_text(&conn, &args).unwrap_or_default();
+    Ok(format!("CL {cl}\n{}", out.trim()))
+}
+
 /// Get a workspace (client) spec as editable text. An unknown name returns a
 /// fresh template — used to create a new workspace.
 #[tauri::command]
@@ -2107,6 +2153,9 @@ pub fn run() {
             p4_labels,
             p4_label_tag,
             p4_branch_op,
+            p4_streams,
+            p4_switch_stream,
+            p4_stream_integ,
             p4_client_spec,
             p4_client_save,
             uasset_thumbnail,