feat(webui): add zoom to the session menu

crates/daemon/assets/index.html

@@ -4160,6 +4160,8 @@
                 id="sessionMenuSplitHBtn">split horizontal</button>
         <button type="button" role="menuitem" data-menu-action="split-vertical"
                 id="sessionMenuSplitVBtn">split vertical</button>
+        <button type="button" role="menuitem" data-menu-action="zoom"
+                id="sessionMenuZoomBtn">zoom</button>
         <button type="button" role="menuitem" data-menu-action="close-split"
                 id="sessionMenuCloseSplitBtn">close split</button>
         <button type="button" role="menuitem" data-menu-action="restart">restart</button>
@@ -8514,6 +8516,9 @@ <h2 id="operatorViewTitle"></h2>
       // between viewports.
       "split-horizontal": splitLayoutAvailable(),
       "split-vertical": splitLayoutAvailable(),
+      // Zoom fills the grid with the focused pane, so it needs panes to
+      // hide — with one pane there is nothing to zoom.
+      zoom: splitLayoutActive(),
       "close-split": splitLayoutActive(),
       restart: !!sel && terminal && !archived,
       archive: isUserSession,
@@ -8524,6 +8529,11 @@ <h2 id="operatorViewTitle"></h2>
       const on = enabledByAction[btn.dataset.menuAction];
       btn.disabled = on === false;
     }
+    // Unlike the TUI — whose zoomed layout is borderless, with no title bar
+    // to reopen the menu from — a zoomed pane here keeps its head, so the
+    // row is the way back out and has to say so.
+    const zoomItem = $("sessionMenuZoomBtn");
+    if (zoomItem) zoomItem.textContent = state.paneZoom ? "unzoom" : "zoom";
     const pinItem = $("sessionMenuPinItem");
     if (pinItem) pinItem.textContent = pinned ? "unpin" : "pin";
     const archiveItem = $("sessionMenuArchiveItem");
@@ -14514,6 +14524,9 @@ <h2 id="operatorViewTitle"></h2>
   if (!leaves.some((l) => l.id === state.focusedPaneId)) {
     state.focusedPaneId = leaves.length ? leaves[0].id : null;
   }
+  // A collapsed layout has nothing to zoom. Drop the per-client flag so the
+  // next split doesn't come back pre-zoomed with no visible way out.
+  if (leaves.length <= 1) state.paneZoom = false;
   renderPaneGrid();
   pushLayout(next);
 }
@@ -19302,6 +19315,14 @@ <h2 id="operatorViewTitle"></h2>
   $("sessionMenuBtn").setAttribute("aria-expanded", open ? "true" : "false");
 });
 
+/** Fill the pane grid with the focused pane, or restore the split layout.
+ *  Shared by `C-x z` and the session menu's zoom row. Per-client state
+ *  (spec 0118), so it never round-trips to the daemon. */
+function togglePaneZoom() {
+  state.paneZoom = !state.paneZoom;
+  renderPaneGrid();
+}
+
 $("sessionMenu").addEventListener("click", (ev) => {
   const btn = ev.target.closest("[data-menu-action]");
   if (!btn || btn.disabled) return;
@@ -19311,6 +19332,7 @@ <h2 id="operatorViewTitle"></h2>
   // through the session-action path.
   if (action === "split-horizontal") return splitFocusedPane("right");
   if (action === "split-vertical") return splitFocusedPane("below");
+  if (action === "zoom") return togglePaneZoom();
   if (action === "close-split") return closePane(state.focusedPaneId);
   handleRowAction(action, state.currentId);
 });
@@ -20252,8 +20274,7 @@ <h2 id="operatorViewTitle"></h2>
         showChordEcho("C-x z — nothing to zoom", true);
         return;
       }
-      state.paneZoom = !state.paneZoom;
-      renderPaneGrid();
+      togglePaneZoom();
       return;
     case "new-session":
       openNewSessionDialog();

crates/e2e/tests/split_layout.rs

@@ -575,6 +575,8 @@ async fn shared_split_layout_renders_wide_and_is_read_only_narrow() {
         "the session menu pill belongs in the pane title bar once one exists"
     );
 
+    let before_close_baseline = d.client.layout().await.expect("layout").version;
+
     // ...and that menu is what now offers the split/close actions.
     let menu_actions: String = page
         .evaluate(
@@ -586,16 +588,63 @@ async fn shared_split_layout_renders_wide_and_is_read_only_narrow() {
         .ok()
         .and_then(|r| r.into_value::<String>().ok())
         .unwrap_or_default();
-    for action in ["split-horizontal", "split-vertical", "close-split"] {
+    for action in ["split-horizontal", "split-vertical", "zoom", "close-split"] {
         assert!(
             menu_actions.contains(action),
             "session menu must offer {action}, got {menu_actions}"
         );
     }
 
+    // Zoom fills the grid with the focused pane and — unlike the TUI, whose
+    // zoomed layout is borderless — the pane head survives, so the same row
+    // is the way back out and must relabel itself.
+    assert_eq!(
+        zoom_menu_label(&page).await,
+        "zoom",
+        "an unzoomed split offers zoom"
+    );
+    page.evaluate(
+        "(() => { document.getElementById('sessionMenuZoomBtn').click(); return true; })()",
+    )
+    .await
+    .ok();
+    assert!(
+        wait_for_bool(
+            &page,
+            "document.getElementById('paneGrid').classList.contains('is-zoomed')",
+        )
+        .await,
+        "the menu's zoom row must zoom the pane grid"
+    );
+    // Zoom is per-client (spec 0118): it hides panes, it does not rewrite the
+    // shared tree, so no layout edit is published.
+    let after_zoom = d.client.layout().await.expect("layout");
+    assert_eq!(
+        after_zoom.version, before_close_baseline,
+        "zoom is client-local and must not publish a layout edit"
+    );
+    assert_eq!(
+        zoom_menu_label(&page).await,
+        "unzoom",
+        "a zoomed pane's menu is the way back out"
+    );
+    page.evaluate(
+        "(() => { document.getElementById('sessionMenuZoomBtn').click(); return true; })()",
+    )
+    .await
+    .ok();
+    assert!(
+        wait_for_bool(
+            &page,
+            "!document.getElementById('paneGrid').classList.contains('is-zoomed')",
+        )
+        .await,
+        "clicking unzoom must restore the split layout"
+    );
+
     // Closing a split through the menu really collapses the layout, and the
     // collapse is published like any other layout edit.
-    let before_close = d.client.layout().await.expect("layout").version;
+    let before_close = before_close_baseline;
     page.evaluate(
         "(() => { document.querySelector('#sessionMenu [data-menu-action=\"close-split\"]').click(); return true; })()",
     )
@@ -1015,6 +1064,21 @@ async fn set_viewport(page: &Page, (w, h): (u32, u32)) {
     tokio::time::sleep(Duration::from_millis(350)).await;
 }
 
+/// Open the session menu (so its items refresh against current state) and
+/// read what the zoom row currently offers: "zoom" or "unzoom".
+async fn zoom_menu_label(page: &Page) -> String {
+    page.evaluate(
+        "(() => {
+           document.getElementById('sessionMenuBtn').click();
+           return document.getElementById('sessionMenuZoomBtn').textContent.trim();
+         })()",
+    )
+    .await
+    .ok()
+    .and_then(|r| r.into_value::<String>().ok())
+    .unwrap_or_default()
+}
+
 async fn eval_number(page: &Page, js: &str) -> f64 {
     page.evaluate(js)
         .await

specs/0145-webui-session-controls.md

@@ -19,8 +19,11 @@ Scope: Where the web UI's per-session controls live and how session reorder work
   of the session view (next to the terminal scroll controls), mirroring
   the TUI's session-title menu: rename, pin/unpin, fork conversation,
   restart, archive/unarchive, merge and archive (enabled only for forks,
-  visible otherwise so the menu teaches the workflow), delete. TUI-only
-  entries that manage split panes are omitted — the web UI has no splits.
+  visible otherwise so the menu teaches the workflow), delete. It also
+  carries the pane actions for the web UI's own split layout — split
+  horizontal, split vertical, zoom/unzoom, close split — shown but
+  disabled when the viewport or the current layout cannot offer them, so
+  the menu keeps a stable shape.
 - Client-side preferences (currently the theme) live in a settings sheet
   opened by activating the matrix-rain connection badge in the header,
   which doubles as the settings button.
@@ -47,4 +50,3 @@ single menu matching the TUI keep both clients teaching the same model.
 
 - Cross-region drops (e.g. dragging into a different project group) are
   not reorder semantics; grouping stays a separate operation.
-- The TUI's split-pane management stays TUI-only.