Add Pending changelists view (option B)

The Changes tab now shows committed-but-not-submitted changelists as cards
above the working set: expandable to their files (click to preview), each
with per-CL Submit, plus Edit description / Uncommit (reopen -c default) /
Discard in a ⋯ menu, and a Submit-all button. Backend adds p4_reopen_default
and p4_set_desc; a small text-prompt modal edits descriptions. Preview panel
now shows either the working selection or a clicked pending-CL file.

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

src-tauri/src/lib.rs

@@ -480,6 +480,69 @@ async fn p4_submit_change(state: State<'_, AppState>, change: String) -> Result<
     run_stream(&conn, &["submit", "-c", &change], "submit")
 }
 
+/// "Uncommit": move files back into the default changelist (like `git reset`).
+/// The now-empty numbered changelist is cleaned up on the next `p4_changes`.
+#[tauri::command]
+async fn p4_reopen_default(state: State<'_, AppState>, files: Vec<String>) -> Result<String, String> {
+    let conn = current(&state)?;
+    if files.is_empty() {
+        return Ok(String::new());
+    }
+    let mut args: Vec<&str> = vec!["reopen", "-c", "default"];
+    for f in &files {
+        args.push(f.as_str());
+    }
+    run_text(&conn, &args)
+}
+
+/// Edit the description of a pending changelist, preserving its file list.
+#[tauri::command]
+async fn p4_set_desc(state: State<'_, AppState>, change: String, description: String) -> Result<String, String> {
+    let conn = current(&state)?;
+    let spec = run_text(&conn, &["change", "-o", &change])?;
+    // rebuild the spec, replacing only the Description field's indented body
+    let mut out = String::new();
+    let mut lines = spec.lines().peekable();
+    let mut replaced = false;
+    while let Some(line) = lines.next() {
+        if !replaced && line.starts_with("Description:") {
+            out.push_str("Description:\n");
+            for dl in description.trim().lines() {
+                out.push('\t');
+                out.push_str(dl);
+                out.push('\n');
+            }
+            // consume the old (indented / blank) description body
+            while let Some(p) = lines.peek() {
+                if p.starts_with('\t') || p.starts_with(' ') || p.is_empty() {
+                    lines.next();
+                } else {
+                    break;
+                }
+            }
+            replaced = true;
+        } else {
+            out.push_str(line);
+            out.push('\n');
+        }
+    }
+    let mut child = p4_cmd(&conn, false)
+        .args(["change", "-i"])
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
+        .spawn()
+        .map_err(|e| format!("Failed to start p4: {e}"))?;
+    if let Some(si) = child.stdin.as_mut() {
+        si.write_all(out.as_bytes()).map_err(|e| e.to_string())?;
+    }
+    let res = child.wait_with_output().map_err(|e| e.to_string())?;
+    if !res.status.success() {
+        return Err(String::from_utf8_lossy(&res.stderr).trim().to_string());
+    }
+    Ok(String::from_utf8_lossy(&res.stdout).trim().to_string())
+}
+
 /// Submit the selected files with a description.
 #[tauri::command]
 async fn p4_submit(
@@ -895,6 +958,8 @@ pub fn run() {
             p4_submit,
             p4_commit,
             p4_submit_change,
+            p4_reopen_default,
+            p4_set_desc,
             p4_add,
             p4_edit,
             p4_delete,