From 159b7ecd6e5d37b8b425c5ec749581db4f3b4abe Mon Sep 17 00:00:00 2001
From: naps62-yolo <yolo-git-naps-pt@naps62.com>
Date: Mon, 22 Jun 2026 09:20:57 +0000
Subject: [PATCH] =?UTF-8?q?feat(maestro):=20multi-view=20web=20UI=20?=
 =?UTF-8?q?=E2=80=94=20splits,=20tabs,=20drag-dock,=20highlights?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Render the content pane as tabs of nested split trees, each session leaf a live
attach mounted through the multi-mount pool:
- #30 arbitrarily-nested H/V splits with mouse-resizable dividers; per-pane
  ⏻/▥/▤/✕ tools; closing a pane collapses its parent split.
- #31 tabs, each holding its own tree; add / switch / close.
- #32 drag-to-dock: drag a pane title or a sidebar session onto a pane for a
  5-zone dock (edges split, centre swaps/replaces); a sidebar drag moves an
  already-open session.
- #33 focused pane at full strength, others dim; sidebar shows focused (loud)
  vs open-elsewhere (quiet) with a stable per-session colour mapping rows to
  panes.

Opening a session fills the focused pane (single-pane parity by default);
multi-pane is opt-in via split / drag / tabs. Panes auto-close when their
session ends (guarded against eviction and intentional close). The steady
"connected" label is hidden as noise.

Closes #30, #31, #32, #33. Part of epic #37.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 web/src/attach.ts       |   7 +
 web/src/catalog.ts      |  73 ++++--
 web/src/connections.ts  |   8 +-
 web/src/layout.ts       | 104 +++++++-
 web/src/main.ts         | 109 ++++----
 web/src/multiview.ts    | 536 ++++++++++++++++++++++++++++++++++++++++
 web/src/sessioncolor.ts |  23 ++
 web/src/styles.css      | 318 ++++++++++++++++++++++++
 8 files changed, 1100 insertions(+), 78 deletions(-)
 create mode 100644 web/src/multiview.ts
 create mode 100644 web/src/sessioncolor.ts

diff --git a/web/src/attach.ts b/web/src/attach.ts
index e019e57..ef7c4b5 100644
--- a/web/src/attach.ts
+++ b/web/src/attach.ts
@@ -30,6 +30,10 @@ export interface AttachConnection {
 export interface AttachOptions {
   /** Invoked when the user clicks the view's explicit "disconnect" control. */
   onRequestClose?: (sessionId: Uuid) => void;
+  /** Invoked when the socket closes on its own — the session ended or the link
+   *  dropped — but NOT on an intentional `dispose()` (eviction / user close). The
+   *  shell uses this to auto-close the pane rather than leave a dead one. */
+  onClosed?: (sessionId: Uuid) => void;
 }
 
 /** What the header shows about the session (name / command / host). Optional —
@@ -242,6 +246,9 @@ export function createAttachConnection(
 
   ws.onclose = (ev) => {
     setState(`closed (${ev.code})`, "closed");
+    // Only bubble up server/network closes — an intentional dispose has already
+    // set `disposed`, and eviction/user-close handle their own pane teardown.
+    if (!disposed) opts.onClosed?.(sessionId);
   };
 
   // PTY input: every keystroke goes out as a binary frame. A pending key-bar
diff --git a/web/src/catalog.ts b/web/src/catalog.ts
index 07ef274..3adc557 100644
--- a/web/src/catalog.ts
+++ b/web/src/catalog.ts
@@ -337,12 +337,24 @@ export function renderTopbar(store: CatalogStore): HTMLElement {
   return header;
 }
 
+/** Two-tier sidebar highlight state (issue #33): which sessions are open in some
+ *  pane (quiet), which one is focused (loud), and a stable per-session colour so
+ *  a row maps to its pane. */
+export interface SidebarHighlights {
+  open: Set<string>;
+  focused: string | null;
+  colors: Map<string, string>;
+}
+
 /** Live handle to the persistent sidebar (built once, survives navigation). */
 export interface SidebarHandle {
   /** The `<aside>` element to mount into the shell. */
   el: HTMLElement;
-  /** Highlight the row for `id` (or clear it with `null`) as the open session. */
+  /** Highlight the row for `id` (or clear it with `null`) as the focused session.
+   *  Back-compat shim over {@link setHighlights}. */
   setActive(id: string | null): void;
+  /** Apply the full open/focused/colour highlight state. */
+  setHighlights(h: SidebarHighlights): void;
   /** Tear down the store subscription + listeners. */
   dispose(): void;
 }
@@ -354,7 +366,13 @@ export interface SidebarHandle {
  * while the content pane swaps between sessions — so the store subscription and
  * scroll position survive navigation. The active session is highlighted.
  */
-export function renderSidebar(store: CatalogStore): SidebarHandle {
+export interface SidebarOptions {
+  /** Pointerdown on a session row — the multi-view controller decides drag vs
+   *  tap (issue #32). Tap falls through to the row's normal click (open). */
+  onLeafDrag?: (sessionId: string, e: PointerEvent) => void;
+}
+
+export function renderSidebar(store: CatalogStore, opts: SidebarOptions = {}): SidebarHandle {
   const el = document.createElement("aside");
   el.className = "sidebar";
 
@@ -378,6 +396,21 @@ export function renderSidebar(store: CatalogStore): SidebarHandle {
   treeHost.className = "tree";
   el.appendChild(treeHost);
 
+  // Drag a session row into the canvas (issue #32). Delegated so it survives
+  // tree re-renders; the controller handles drag-vs-tap (tap still navigates).
+  treeHost.addEventListener("pointerdown", (e) => {
+    if (e.button !== 0 || !opts.onLeafDrag) return;
+    const leaf = (e.target as HTMLElement).closest<HTMLElement>(".tree-leaf");
+    const id = leaf?.dataset.sessionId;
+    if (id) opts.onLeafDrag(id, e);
+  });
+  // The rows are <a> elements, so the browser's native link drag-and-drop would
+  // otherwise hijack pointermove and our live drop-zone preview wouldn't show
+  // until release. Suppress it so the pointer-based drag runs from the start.
+  treeHost.addEventListener("dragstart", (e) => {
+    if ((e.target as HTMLElement).closest(".tree-leaf")) e.preventDefault();
+  });
+
   // Drag-to-resize handle on the sidebar's right edge. Persists the chosen
   // width as a :root CSS var the shell grid reads; clamped to a sane range.
   const SIDEBAR_W_KEY = "maestro-sidebar-w";
@@ -425,16 +458,18 @@ export function renderSidebar(store: CatalogStore): SidebarHandle {
     refresh();
   });
 
-  let activeId: string | null = null;
-  const applyActive = () => {
-    for (const n of treeHost.querySelectorAll(".tree-leaf.is-active")) {
-      n.classList.remove("is-active");
-    }
-    if (activeId) {
-      const row = treeHost.querySelector(
-        `.tree-leaf[data-session-id="${CSS.escape(activeId)}"]`,
-      );
-      row?.classList.add("is-active");
+  let highlights: SidebarHighlights = { open: new Set(), focused: null, colors: new Map() };
+  const applyHighlights = () => {
+    for (const n of treeHost.querySelectorAll<HTMLElement>(".tree-leaf")) {
+      const id = n.dataset.sessionId;
+      if (!id) continue;
+      const focused = highlights.focused === id;
+      const open = highlights.open.has(id);
+      n.classList.toggle("is-active", focused);
+      n.classList.toggle("is-open", open && !focused);
+      const color = highlights.colors.get(id);
+      if (color && (open || focused)) n.style.setProperty("--mv-color", color);
+      else n.style.removeProperty("--mv-color");
     }
   };
 
@@ -455,7 +490,7 @@ export function renderSidebar(store: CatalogStore): SidebarHandle {
     if (tree.kind === "folder") {
       for (const child of tree.children) treeHost.appendChild(renderNode(child, 0));
     }
-    applyActive();
+    applyHighlights();
   };
 
   const rerenderHandler = () => refresh();
@@ -484,8 +519,16 @@ export function renderSidebar(store: CatalogStore): SidebarHandle {
   return {
     el,
     setActive(id: string | null) {
-      activeId = id;
-      applyActive();
+      highlights = {
+        open: id ? new Set([id]) : new Set(),
+        focused: id,
+        colors: new Map(),
+      };
+      applyHighlights();
+    },
+    setHighlights(h: SidebarHighlights) {
+      highlights = h;
+      applyHighlights();
     },
     dispose() {
       document.removeEventListener("catalog-rerender", rerenderHandler);
diff --git a/web/src/connections.ts b/web/src/connections.ts
index ac72ada..a99605b 100644
--- a/web/src/connections.ts
+++ b/web/src/connections.ts
@@ -21,6 +21,9 @@ export interface PoolOptions {
   /** Fired when a view's explicit disconnect control is used; the embedder
    *  decides how to update the layout/route (then typically calls `close`). */
   onRequestClose?: (id: Uuid) => void;
+  /** Fired when a connection's socket closes on its own (session ended/dropped),
+   *  not via an intentional close/eviction. The embedder closes the pane. */
+  onClosed?: (id: Uuid) => void;
 }
 
 /**
@@ -76,7 +79,10 @@ export class ConnectionPool {
     } else {
       conn = createAttachConnection(
         id,
-        { onRequestClose: (sid) => this.opts.onRequestClose?.(sid) },
+        {
+          onRequestClose: (sid) => this.opts.onRequestClose?.(sid),
+          onClosed: (sid) => this.opts.onClosed?.(sid),
+        },
         info,
       );
       this.cache.set(id, conn);
diff --git a/web/src/layout.ts b/web/src/layout.ts
index 0e632e0..51a2ec5 100644
--- a/web/src/layout.ts
+++ b/web/src/layout.ts
@@ -1,15 +1,18 @@
 // Multi-view layout model. The layout tree is the single source of truth for
 // what's on screen: a set of tabs, each holding a binary split tree whose leaves
-// are sessions. Desktop renders the tree as nested splits; mobile projects its
-// leaves to tabs. (Splits/tabs UI land in later issues — see epic #37. This
-// issue introduces the model and renders a single-leaf tree at parity.)
+// hold a session (or nothing yet). Desktop renders the tree as nested splits;
+// mobile (issue #35) projects its leaves to tabs.
+//
+// A session lives in at most one leaf at a time (the connection pool is
+// one-socket-per-session), so a leaf's `sessionId` is unique across the whole
+// layout — or null for a freshly-split, not-yet-filled pane.
 
 import type { Uuid } from "./types.js";
 
 export type Dir = "row" | "col";
 
 export type Node =
-  | { kind: "leaf"; id: string; sessionId: Uuid }
+  | { kind: "leaf"; id: string; sessionId: Uuid | null }
   | { kind: "split"; dir: Dir; a: Node; b: Node; ratio: number };
 
 export type Leaf = Extract<Node, { kind: "leaf" }>;
@@ -19,7 +22,7 @@ export interface Tab {
   title: string;
   /** The split tree, or null for an empty tab. */
   root: Node | null;
-  /** Which leaf has keyboard focus / drives the sidebar highlight. */
+  /** Which leaf has focus (drives keyboard input + the strong highlight). */
   focusedLeafId: string | null;
 }
 
@@ -29,8 +32,6 @@ export interface Layout {
 }
 
 let seq = 0;
-/** Monotonic id for tabs and leaves (not persisted across reloads — restore
- *  assigns fresh ids). */
 export function freshId(prefix = "n"): string {
   return `${prefix}${++seq}`;
 }
@@ -50,8 +51,97 @@ export function activeTab(layout: Layout): Tab {
   return layout.tabs.find((t) => t.id === layout.activeTabId) ?? layout.tabs[0];
 }
 
+/** Distinct sessions shown in any pane of any tab. */
+export function openSessions(layout: Layout): Set<Uuid> {
+  const out = new Set<Uuid>();
+  for (const t of layout.tabs) {
+    for (const l of leaves(t.root)) if (l.sessionId) out.add(l.sessionId);
+  }
+  return out;
+}
+
+/** Find the tab + leaf currently showing `sessionId`, if any. */
+export function locateSession(
+  layout: Layout,
+  sessionId: Uuid,
+): { tab: Tab; leaf: Leaf } | null {
+  for (const tab of layout.tabs) {
+    const leaf = leaves(tab.root).find((l) => l.sessionId === sessionId);
+    if (leaf) return { tab, leaf };
+  }
+  return null;
+}
+
 /** A layout with one empty tab. */
 export function emptyLayout(): Layout {
   const tab: Tab = { id: freshId("t"), title: "Tab 1", root: null, focusedLeafId: null };
   return { tabs: [tab], activeTabId: tab.id };
 }
+
+// ---- mutations (return the affected leaf id where useful) ----
+
+/** Replace `targetId` with a split of [target, fresh] (or reversed when
+ *  `after` is false). Returns the new leaf's id. */
+export function splitLeaf(
+  tab: Tab,
+  targetId: string,
+  sessionId: Uuid | null,
+  dir: Dir,
+  after: boolean,
+): string {
+  const fresh: Leaf = { kind: "leaf", id: freshId("l"), sessionId };
+  const rec = (n: Node): Node => {
+    if (n.kind === "leaf") {
+      if (n.id !== targetId) return n;
+      return { kind: "split", dir, ratio: 0.5, a: after ? n : fresh, b: after ? fresh : n };
+    }
+    n.a = rec(n.a);
+    n.b = rec(n.b);
+    return n;
+  };
+  tab.root = tab.root ? rec(tab.root) : fresh;
+  return fresh.id;
+}
+
+/** Remove a leaf, collapsing its parent split into the sibling. */
+export function removeLeaf(tab: Tab, leafId: string): void {
+  const rec = (n: Node): Node | null => {
+    if (n.kind === "leaf") return n.id === leafId ? null : n;
+    const a = rec(n.a);
+    const b = rec(n.b);
+    if (!a) return b;
+    if (!b) return a;
+    n.a = a;
+    n.b = b;
+    return n;
+  };
+  tab.root = tab.root ? rec(tab.root) : null;
+}
+
+export function addTab(layout: Layout): Tab {
+  const tab: Tab = {
+    id: freshId("t"),
+    title: `Tab ${layout.tabs.length + 1}`,
+    root: null,
+    focusedLeafId: null,
+  };
+  layout.tabs.push(tab);
+  layout.activeTabId = tab.id;
+  return tab;
+}
+
+export function closeTab(layout: Layout, tabId: string): void {
+  if (layout.tabs.length <= 1) {
+    // Keep at least one tab; just empty it.
+    const t = layout.tabs[0];
+    t.root = null;
+    t.focusedLeafId = null;
+    return;
+  }
+  const i = layout.tabs.findIndex((t) => t.id === tabId);
+  if (i < 0) return;
+  layout.tabs.splice(i, 1);
+  if (layout.activeTabId === tabId) {
+    layout.activeTabId = layout.tabs[Math.max(0, i - 1)].id;
+  }
+}
diff --git a/web/src/main.ts b/web/src/main.ts
index 218e85a..242d6e2 100644
--- a/web/src/main.ts
+++ b/web/src/main.ts
@@ -3,15 +3,8 @@ import { ConnectionPool } from "./connections.js";
 import { installHudKeybind } from "./debug.js";
 import { CatalogStore } from "./events.js";
 import { mountHud, type Hud } from "./hud.js";
-import {
-  activeTab,
-  emptyLayout,
-  findLeaf,
-  freshId,
-  leaves,
-  type Layout,
-  type Node,
-} from "./layout.js";
+import { emptyLayout, type Layout, openSessions } from "./layout.js";
+import { createMultiView, type MultiView } from "./multiview.js";
 import { openSpawnModal } from "./spawn.js";
 import { initTheme } from "./theme.js";
 import { sessionName } from "./types.js";
@@ -67,7 +60,13 @@ const shellEl = document.createElement("div");
 shellEl.className = "app-shell";
 shellEl.dataset.route = "catalog";
 
-const sidebar = renderSidebar(store);
+// Forward-declared so the sidebar's drag hook can reach the controller (created
+// after the welcome renderer). The hook only fires on user interaction, by which
+// point `mv` is assigned.
+let mv: MultiView;
+const sidebar = renderSidebar(store, {
+  onLeafDrag: (id, e) => mv?.beginSessionDrag(id, e),
+});
 const content = document.createElement("section");
 content.className = "content";
 
@@ -79,27 +78,35 @@ root.replaceChildren(renderTopbar(store), shellEl);
 // It can mount several panes at once — the layout tree decides how many. For now
 // the tree only ever holds a single leaf (splits/tabs arrive in epic #37); this
 // routes the existing single-session view through that model.
+// `mv` is forward-declared above (the sidebar drag hook needs it); the pool's
+// disconnect callback below also references it.
 let hud: Hud | undefined;
 const pool = new ConnectionPool({
-  onFocusChange: (id) => {
-    sidebar.setActive(id);
+  onFocusChange: () => {
+    // Sidebar highlighting is driven by the multi-view controller; the pool only
+    // nudges the HUD here.
     hud?.refresh();
   },
-  onRequestClose: (id) => {
-    pool.close(id);
-    // Drop back to the welcome pane via the router.
-    if (location.hash !== "#/" && location.hash !== "") location.hash = "#/";
-  },
+  // Both the explicit disconnect (⏻) and a session ending on its own close the
+  // pane — drop its leaf (collapsing the split) and tear down the socket. A dead
+  // pane is never left lying around.
+  onRequestClose: (id) => closePane(id),
+  onClosed: (id) => closePane(id),
 });
 
+function closePane(id: string): void {
+  pool.close(id);
+  mv?.closeSession(id);
+  updateShellRoute();
+}
+
 // Debug HUD (#20): a fixed-corner overlay on the active session's inferred
 // fields, off by default (Ctrl+Shift+D, or `?hud` in dev).
 hud = mountHud(root, store, () => pool.focused());
 
 // ---- layout state ----
-// Single source of truth for what's mounted. Today it's derived from the hash
-// route (one leaf per `#/attach/:id`); future issues let the user build splits
-// and tabs on top of the same model.
+// Single source of truth for what's mounted: tabs of split trees. The hash route
+// is just a deep-link into it (`#/attach/:id` focuses/opens a session).
 const layout: Layout = emptyLayout();
 
 function infoFor(sessionId: string) {
@@ -107,32 +114,10 @@ function infoFor(sessionId: string) {
   return s ? { name: sessionName(s), command: s.command, daemon: s.daemon_id } : undefined;
 }
 
-/** Show a single session in the active tab. */
-function openInLayout(sessionId: string): void {
-  const tab = activeTab(layout);
-  const leaf: Node = { kind: "leaf", id: freshId("l"), sessionId };
-  tab.root = leaf;
-  tab.focusedLeafId = leaf.id;
-}
-
-/** Empty the active tab (welcome / not-found). */
-function clearLayout(): void {
-  const tab = activeTab(layout);
-  tab.root = null;
-  tab.focusedLeafId = null;
-}
-
-/** Reconcile the pool's visible panes + focus with the active tab's tree. */
-function renderLayout(): void {
-  const tab = activeTab(layout);
-  if (!tab.root) {
-    pool.parkActive();
-    return;
-  }
-  const ls = leaves(tab.root);
-  pool.setVisible(ls.map((l) => ({ id: l.sessionId, pane: content, info: infoFor(l.sessionId) })));
-  const focusLeaf = tab.focusedLeafId ? findLeaf(tab.root, tab.focusedLeafId) : ls[0];
-  pool.setFocus(focusLeaf?.sessionId ?? null);
+/** Drive the shell's responsive layout off whether any pane is open. */
+function updateShellRoute(): void {
+  const hasPanes = openSessions(layout).size > 0;
+  shellEl.dataset.route = hasPanes ? "attach" : "catalog";
 }
 
 function renderWelcome(): HTMLElement {
@@ -168,6 +153,19 @@ function renderNotFound(raw: string): HTMLElement {
   return el;
 }
 
+// The multi-view controller renders tabs + splits inside the content pane and
+// mounts a live attach into each session leaf.
+mv = createMultiView({ pool, layout, sidebar, infoFor, onDisconnect: closePane, renderWelcome });
+let contentShowsMv = false;
+function showMultiView(): void {
+  if (!contentShowsMv) {
+    content.replaceChildren(mv.el);
+    contentShowsMv = true;
+  }
+  mv.render();
+  updateShellRoute();
+}
+
 type Route =
   | { kind: "catalog" }
   | { kind: "attach"; sessionId: string }
@@ -185,21 +183,22 @@ function dispatch(): void {
   const route = parseRoute();
   switch (route.kind) {
     case "attach":
-      shellEl.dataset.route = "attach";
-      openInLayout(route.sessionId);
-      renderLayout();
+      // Deep-link: open/focus the session, then show the layout.
+      showMultiView();
+      mv.openSession(route.sessionId);
+      updateShellRoute();
       return;
     case "not-found":
       shellEl.dataset.route = "notfound";
-      clearLayout();
-      renderLayout();
+      pool.setVisible([]);
+      pool.setFocus(null);
       content.replaceChildren(renderNotFound(route.raw));
+      contentShowsMv = false;
       return;
     case "catalog":
-      shellEl.dataset.route = "catalog";
-      clearLayout();
-      renderLayout();
-      content.replaceChildren(renderWelcome());
+      // Show the current layout (welcome if empty) — navigating to #/ no longer
+      // tears panes down.
+      showMultiView();
       return;
   }
 }
diff --git a/web/src/multiview.ts b/web/src/multiview.ts
new file mode 100644
index 0000000..85b59cd
--- /dev/null
+++ b/web/src/multiview.ts
@@ -0,0 +1,536 @@
+// The multi-view renderer/controller (issues #30 splits, #31 tabs, #33
+// highlights). Owns the tab bar + canvas inside the content pane, builds the
+// active tab's split tree into DOM, and mounts a live AttachConnection into each
+// session leaf via the pool. Empty leaves (freshly split, not yet filled) show a
+// placeholder. Drag-to-dock is a later issue (#32); mobile projection is #35.
+
+import type { SidebarHandle } from "./catalog.js";
+import type { ConnectionPool } from "./connections.js";
+import {
+  activeTab,
+  addTab,
+  closeTab,
+  findLeaf,
+  type Dir,
+  type Layout,
+  leaves,
+  locateSession,
+  type Node,
+  openSessions,
+  removeLeaf,
+  splitLeaf,
+} from "./layout.js";
+import { sessionColor } from "./sessioncolor.js";
+import type { AttachInfo } from "./attach.js";
+
+export interface MultiViewOptions {
+  pool: ConnectionPool;
+  layout: Layout;
+  sidebar: SidebarHandle;
+  /** Header text for a session's pane / attach view. */
+  infoFor: (sessionId: string) => AttachInfo | undefined;
+  /** Disconnect a session (the ⏻ tool): tear down its socket and close the pane. */
+  onDisconnect: (sessionId: string) => void;
+  /** Welcome content for an empty tab. */
+  renderWelcome: () => HTMLElement;
+}
+
+export interface MultiView {
+  el: HTMLElement;
+  /** Bring a session into the layout: focus it if already open, else fill the
+   *  focused pane (or open the first pane in an empty tab). */
+  openSession: (sessionId: string) => void;
+  /** Drop the pane showing `sessionId` (the session was disconnected/killed). */
+  closeSession: (sessionId: string) => void;
+  /** Start dragging a sidebar session into the canvas (issue #32). The
+   *  controller owns drag-vs-tap: a tap lets the row's normal click open it, a
+   *  drag shows drop zones to place it. */
+  beginSessionDrag: (sessionId: string, e: PointerEvent) => void;
+  /** Rebuild the view from the current layout. */
+  render: () => void;
+  focusedSessionId: () => string | null;
+}
+
+export function createMultiView(opts: MultiViewOptions): MultiView {
+  const { pool, layout, sidebar, infoFor, onDisconnect, renderWelcome } = opts;
+
+  const el = document.createElement("div");
+  el.className = "mv";
+  const tabBar = document.createElement("div");
+  tabBar.className = "mv-tabs";
+  const canvas = document.createElement("div");
+  canvas.className = "mv-canvas";
+  el.append(tabBar, canvas);
+
+  // ---- highlight helpers ----
+
+  function colorMap(): Map<string, string> {
+    const m = new Map<string, string>();
+    for (const id of openSessions(layout)) m.set(id, sessionColor(id));
+    return m;
+  }
+
+  function focusedLeafSession(): string | null {
+    const tab = activeTab(layout);
+    const fl = tab.focusedLeafId ? findLeaf(tab.root, tab.focusedLeafId) : null;
+    return fl?.sessionId ?? null;
+  }
+
+  /** Update focus styling + pool focus + sidebar highlights without rebuilding
+   *  the DOM (cheap path for click-to-focus). */
+  function syncFocus(): void {
+    const tab = activeTab(layout);
+    for (const pane of canvas.querySelectorAll<HTMLElement>(".mv-pane")) {
+      pane.classList.toggle("is-focused", pane.dataset.leafId === tab.focusedLeafId);
+    }
+    pool.setFocus(focusedLeafSession());
+    sidebar.setHighlights({
+      open: openSessions(layout),
+      focused: focusedLeafSession(),
+      colors: colorMap(),
+    });
+  }
+
+  function focusLeaf(leafId: string): void {
+    const tab = activeTab(layout);
+    if (tab.focusedLeafId === leafId) return;
+    tab.focusedLeafId = leafId;
+    syncFocus();
+  }
+
+  // ---- pane + split DOM ----
+
+  function buildPane(leaf: Extract<Node, { kind: "leaf" }>): {
+    el: HTMLElement;
+    host: HTMLElement;
+    sessionId: string | null;
+  } {
+    const pane = document.createElement("div");
+    pane.className = "mv-pane";
+    pane.dataset.leafId = leaf.id;
+    if (leaf.sessionId) {
+      pane.dataset.sessionId = leaf.sessionId;
+      pane.style.setProperty("--mv-color", sessionColor(leaf.sessionId));
+    }
+
+    const host = document.createElement("div");
+    host.className = "mv-pane-host";
+    if (!leaf.sessionId) {
+      host.innerHTML = `<div class="mv-pane-empty">Empty pane — pick a session from the sidebar.</div>`;
+    }
+
+    const tools = document.createElement("div");
+    tools.className = "mv-pane-tools";
+    const mkBtn = (label: string, title: string, fn: () => void) => {
+      const b = document.createElement("button");
+      b.type = "button";
+      b.className = "mv-tool";
+      b.title = title;
+      b.textContent = label;
+      b.addEventListener("pointerdown", (e) => e.stopPropagation());
+      b.addEventListener("click", (e) => {
+        e.stopPropagation();
+        fn();
+      });
+      return b;
+    };
+    // Order: disconnect (⏻) leftmost, then split-right / split-down / close.
+    if (leaf.sessionId) {
+      const off = mkBtn("⏻", "Disconnect", () => onDisconnect(leaf.sessionId!));
+      off.classList.add("mv-tool-off");
+      tools.appendChild(off);
+    }
+    tools.append(
+      mkBtn("▥", "Split right", () => splitFocused(leaf.id, "row")),
+      mkBtn("▤", "Split down", () => splitFocused(leaf.id, "col")),
+      mkBtn("✕", "Close pane", () => closePane(leaf.id)),
+    );
+
+    pane.append(host, tools);
+    pane.addEventListener(
+      "pointerdown",
+      (e) => {
+        focusLeaf(leaf.id);
+        // Drag a pane by its title bar (not its buttons or the terminal body).
+        const t = e.target as HTMLElement;
+        if (t.closest(".attach-header") && !t.closest("button, a, .mv-tool")) {
+          runDrag({ kind: "pane", leafId: leaf.id }, e, { deferred: true });
+        }
+      },
+      true,
+    );
+    return { el: pane, host, sessionId: leaf.sessionId };
+  }
+
+  function wireDivider(
+    divider: HTMLElement,
+    split: Extract<Node, { kind: "split" }>,
+    slotA: HTMLElement,
+    slotB: HTMLElement,
+    container: HTMLElement,
+  ): void {
+    divider.addEventListener("pointerdown", (e) => {
+      e.preventDefault();
+      e.stopPropagation();
+      divider.classList.add("is-dragging");
+      divider.setPointerCapture(e.pointerId);
+      const rect = container.getBoundingClientRect();
+      const move = (ev: PointerEvent) => {
+        const frac =
+          split.dir === "row"
+            ? (ev.clientX - rect.left) / rect.width
+            : (ev.clientY - rect.top) / rect.height;
+        split.ratio = Math.max(0.1, Math.min(0.9, frac));
+        slotA.style.flexGrow = String(split.ratio);
+        slotB.style.flexGrow = String(1 - split.ratio);
+      };
+      const up = (ev: PointerEvent) => {
+        divider.classList.remove("is-dragging");
+        try {
+          divider.releasePointerCapture(ev.pointerId);
+        } catch {
+          /* already released */
+        }
+        divider.removeEventListener("pointermove", move);
+        divider.removeEventListener("pointerup", up);
+      };
+      divider.addEventListener("pointermove", move);
+      divider.addEventListener("pointerup", up);
+    });
+  }
+
+  /** Build the tree DOM, collecting each session leaf's mount host. */
+  function buildTree(node: Node, hosts: { id: string; host: HTMLElement; info?: AttachInfo }[]): HTMLElement {
+    if (node.kind === "leaf") {
+      const pane = buildPane(node);
+      if (node.sessionId) {
+        hosts.push({ id: node.sessionId, host: pane.host, info: infoFor(node.sessionId) });
+      }
+      return pane.el;
+    }
+    const container = document.createElement("div");
+    container.className = `mv-split ${node.dir}`;
+    const slotA = document.createElement("div");
+    slotA.className = "mv-slot";
+    slotA.style.cssText = `flex:${node.ratio} 1 0`;
+    const divider = document.createElement("div");
+    divider.className = "mv-divider";
+    const slotB = document.createElement("div");
+    slotB.className = "mv-slot";
+    slotB.style.cssText = `flex:${1 - node.ratio} 1 0`;
+    slotA.appendChild(buildTree(node.a, hosts));
+    slotB.appendChild(buildTree(node.b, hosts));
+    container.append(slotA, divider, slotB);
+    wireDivider(divider, node, slotA, slotB, container);
+    return container;
+  }
+
+  // ---- tab bar ----
+
+  function renderTabs(): void {
+    tabBar.replaceChildren();
+    for (const t of layout.tabs) {
+      const tab = document.createElement("button");
+      tab.type = "button";
+      tab.className = "mv-tab" + (t.id === layout.activeTabId ? " is-active" : "");
+      const n = leaves(t.root).filter((l) => l.sessionId).length;
+      const label = document.createElement("span");
+      label.textContent = t.title + (n ? ` · ${n}` : "");
+      tab.appendChild(label);
+      tab.addEventListener("click", () => {
+        if (layout.activeTabId !== t.id) {
+          layout.activeTabId = t.id;
+          render();
+        }
+      });
+      if (layout.tabs.length > 1) {
+        const close = document.createElement("span");
+        close.className = "mv-tab-close";
+        close.textContent = "✕";
+        close.title = "Close tab";
+        close.addEventListener("click", (e) => {
+          e.stopPropagation();
+          closeTab(layout, t.id);
+          render();
+        });
+        tab.appendChild(close);
+      }
+      tabBar.appendChild(tab);
+    }
+    const add = document.createElement("button");
+    add.type = "button";
+    add.className = "mv-tab-add";
+    add.textContent = "+";
+    add.title = "New tab";
+    add.addEventListener("click", () => {
+      addTab(layout);
+      render();
+    });
+    tabBar.appendChild(add);
+  }
+
+  // ---- mutations ----
+
+  function splitFocused(leafId: string, dir: Dir): void {
+    const tab = activeTab(layout);
+    tab.focusedLeafId = splitLeaf(tab, leafId, null, dir, true);
+    render();
+  }
+
+  function closePane(leafId: string): void {
+    const tab = activeTab(layout);
+    removeLeaf(tab, leafId);
+    if (tab.focusedLeafId === leafId) {
+      tab.focusedLeafId = leaves(tab.root)[0]?.id ?? null;
+    }
+    render();
+  }
+
+  function openSession(sessionId: string): void {
+    const loc = locateSession(layout, sessionId);
+    if (loc) {
+      layout.activeTabId = loc.tab.id;
+      loc.tab.focusedLeafId = loc.leaf.id;
+      render();
+      return;
+    }
+    const tab = activeTab(layout);
+    if (!tab.root) {
+      const id = splitLeaf(tab, "", sessionId, "row", true); // root from empty
+      tab.focusedLeafId = id;
+      render();
+      return;
+    }
+    // Fill the focused pane (VS Code style: open replaces the active group).
+    const target = (tab.focusedLeafId && findLeaf(tab.root, tab.focusedLeafId)) || leaves(tab.root)[0];
+    target.sessionId = sessionId;
+    tab.focusedLeafId = target.id;
+    render();
+  }
+
+  // ---- top-level render ----
+
+  function render(): void {
+    renderTabs();
+    canvas.replaceChildren();
+    const tab = activeTab(layout);
+
+    if (!tab.root) {
+      pool.setVisible([]);
+      pool.setFocus(null);
+      canvas.appendChild(renderWelcome());
+      sidebar.setHighlights({ open: openSessions(layout), focused: null, colors: colorMap() });
+      return;
+    }
+
+    // Keep focus pointing at a real leaf.
+    if (!tab.focusedLeafId || !findLeaf(tab.root, tab.focusedLeafId)) {
+      tab.focusedLeafId = leaves(tab.root)[0]?.id ?? null;
+    }
+
+    const hosts: { id: string; host: HTMLElement; info?: AttachInfo }[] = [];
+    canvas.appendChild(buildTree(tab.root, hosts));
+    pool.setVisible(hosts.map((h) => ({ id: h.id, pane: h.host, info: h.info })));
+    syncFocus();
+  }
+
+  function closeSession(sessionId: string): void {
+    const loc = locateSession(layout, sessionId);
+    if (!loc) return;
+    removeLeaf(loc.tab, loc.leaf.id);
+    if (loc.tab.focusedLeafId === loc.leaf.id) {
+      loc.tab.focusedLeafId = leaves(loc.tab.root)[0]?.id ?? null;
+    }
+    render();
+  }
+
+  // ---- drag-to-dock (issue #32) ----
+  // Drag a pane's title bar, or a session from the sidebar, onto another pane:
+  // edge zones split that pane, centre swaps (pane source) or replaces (session
+  // source). Sidebar drags move the session if it's already open elsewhere.
+  type Zone = "left" | "right" | "top" | "bottom" | "center";
+  type DragSource = { kind: "pane"; leafId: string } | { kind: "session"; sessionId: string };
+  let drag: {
+    source: DragSource;
+    ghost: HTMLElement;
+    overlay: HTMLElement | null;
+    targetLeafId: string | null;
+    zone: Zone | null;
+  } | null = null;
+
+  function dragSessionId(src: DragSource): string | null {
+    if (src.kind === "session") return src.sessionId;
+    return findLeaf(activeTab(layout).root, src.leafId)?.sessionId ?? null;
+  }
+  /** The leaf in the ACTIVE tab the source occupies (skip it as a drop target). */
+  function dragSelfLeaf(src: DragSource): string | null {
+    if (src.kind === "pane") return src.leafId;
+    const loc = locateSession(layout, src.sessionId);
+    return loc && loc.tab.id === layout.activeTabId ? loc.leaf.id : null;
+  }
+  function dragLabel(src: DragSource): string {
+    const sid = dragSessionId(src);
+    if (!sid) return "empty pane";
+    return infoFor(sid)?.name ?? sid;
+  }
+
+  function makeGhost(src: DragSource): HTMLElement {
+    const g = document.createElement("div");
+    g.className = "mv-drag-ghost";
+    g.textContent = `⠿ ${dragLabel(src)}`;
+    document.body.appendChild(g);
+    return g;
+  }
+
+  function runDrag(src: DragSource, e: PointerEvent, opts: { deferred: boolean }): void {
+    const sx = e.clientX;
+    const sy = e.clientY;
+    let started = !opts.deferred;
+    if (started) drag = { source: src, ghost: makeGhost(src), overlay: null, targetLeafId: null, zone: null };
+    const place = (ev: PointerEvent) => {
+      if (drag) {
+        drag.ghost.style.left = `${ev.clientX + 12}px`;
+        drag.ghost.style.top = `${ev.clientY + 12}px`;
+      }
+    };
+    if (started) place(e);
+    const move = (ev: PointerEvent) => {
+      if (!started) {
+        if (Math.hypot(ev.clientX - sx, ev.clientY - sy) < 5) return;
+        started = true;
+        document.body.style.userSelect = "none";
+        drag = { source: src, ghost: makeGhost(src), overlay: null, targetLeafId: null, zone: null };
+      }
+      place(ev);
+      updateDock(ev);
+    };
+    const up = () => {
+      window.removeEventListener("pointermove", move);
+      window.removeEventListener("pointerup", up);
+      if (!started) return;
+      document.body.style.userSelect = "";
+      suppressNextClick();
+      finishDrag();
+    };
+    window.addEventListener("pointermove", move);
+    window.addEventListener("pointerup", up);
+  }
+
+  /** Eat the click that follows a real drag (so a dragged sidebar row doesn't
+   *  also navigate, and a dragged pane title doesn't trigger anything). */
+  function suppressNextClick(): void {
+    const kill = (e: MouseEvent) => {
+      e.preventDefault();
+      e.stopPropagation();
+      window.removeEventListener("click", kill, true);
+    };
+    window.addEventListener("click", kill, true);
+  }
+
+  function paneUnder(x: number, y: number): HTMLElement | null {
+    for (const node of document.elementsFromPoint(x, y)) {
+      const pane = (node as HTMLElement).closest?.(".mv-pane") as HTMLElement | null;
+      if (pane && canvas.contains(pane)) return pane;
+    }
+    return null;
+  }
+
+  function clearOverlay(): void {
+    drag?.overlay?.remove();
+    if (drag) drag.overlay = null;
+  }
+
+  function updateDock(ev: PointerEvent): void {
+    if (!drag) return;
+    clearOverlay();
+    const pane = paneUnder(ev.clientX, ev.clientY);
+    const self = dragSelfLeaf(drag.source);
+    if (!pane || pane.dataset.leafId === self) {
+      drag.targetLeafId = null;
+      drag.zone = null;
+      return;
+    }
+    const r = pane.getBoundingClientRect();
+    const fx = (ev.clientX - r.left) / r.width;
+    const fy = (ev.clientY - r.top) / r.height;
+    const edges = { left: fx, right: 1 - fx, top: fy, bottom: 1 - fy };
+    const nearest = (Object.keys(edges) as (keyof typeof edges)[]).reduce((m, k) =>
+      edges[k] < edges[m] ? k : m,
+    );
+    const zone: Zone = edges[nearest] < 0.28 ? nearest : "center";
+    drag.targetLeafId = pane.dataset.leafId!;
+    drag.zone = zone;
+
+    const ov = document.createElement("div");
+    ov.className = "mv-dock-overlay";
+    const hot = document.createElement("div");
+    hot.className = "mv-dock-zone";
+    const css: Record<Zone, string> = {
+      left: "left:0;top:0;width:50%;height:100%",
+      right: "left:50%;top:0;width:50%;height:100%",
+      top: "left:0;top:0;width:100%;height:50%",
+      bottom: "left:0;top:50%;width:100%;height:50%",
+      center: "inset:14%",
+    };
+    hot.style.cssText = "position:absolute;" + css[zone];
+    ov.appendChild(hot);
+    pane.appendChild(ov);
+    drag.overlay = ov;
+  }
+
+  function finishDrag(): void {
+    if (!drag) return;
+    const { source, targetLeafId, zone, ghost } = drag;
+    ghost.remove();
+    clearOverlay();
+    drag = null;
+    if (!targetLeafId || !zone) return;
+
+    const tab = activeTab(layout);
+    const self = dragSelfLeaf(source);
+    if (targetLeafId === self) return; // dropped on its own pane
+    const target = findLeaf(tab.root, targetLeafId);
+    if (!target) return;
+    const sessionId = dragSessionId(source);
+
+    if (zone === "center") {
+      if (source.kind === "pane" && self) {
+        const dragged = findLeaf(tab.root, self)!;
+        [dragged.sessionId, target.sessionId] = [target.sessionId, dragged.sessionId];
+        tab.focusedLeafId = target.id;
+      } else if (sessionId) {
+        const loc = locateSession(layout, sessionId);
+        if (loc) removeLeaf(loc.tab, loc.leaf.id);
+        const t2 = findLeaf(tab.root, targetLeafId);
+        if (t2) {
+          t2.sessionId = sessionId;
+          tab.focusedLeafId = t2.id;
+        }
+      }
+      render();
+      return;
+    }
+
+    // edge zone → split the target, placing the source beside it
+    const dir: Dir = zone === "left" || zone === "right" ? "row" : "col";
+    const after = zone === "right" || zone === "bottom";
+    const loc = sessionId ? locateSession(layout, sessionId) : null;
+    if (source.kind === "pane" && self) removeLeaf(tab, self);
+    else if (loc) removeLeaf(loc.tab, loc.leaf.id);
+    tab.focusedLeafId = splitLeaf(tab, targetLeafId, sessionId, dir, after);
+    render();
+  }
+
+  function beginSessionDrag(sessionId: string, e: PointerEvent): void {
+    runDrag({ kind: "session", sessionId }, e, { deferred: true });
+  }
+
+  return {
+    el,
+    openSession,
+    closeSession,
+    beginSessionDrag,
+    render,
+    focusedSessionId: focusedLeafSession,
+  };
+}
diff --git a/web/src/sessioncolor.ts b/web/src/sessioncolor.ts
new file mode 100644
index 0000000..a61caab
--- /dev/null
+++ b/web/src/sessioncolor.ts
@@ -0,0 +1,23 @@
+// Stable per-session accent colour, used to map a sidebar row to the pane
+// showing that session (issue #33). Hash the session id into a fixed OKLCH
+// palette tuned to the maestro tokens; collisions are tolerated when there are
+// more open sessions than hues — the colour is a hint, not an identity.
+
+import type { Uuid } from "./types.js";
+
+const PALETTE = [
+  "oklch(0.80 0.13 152)", // green (the house accent)
+  "oklch(0.80 0.12 90)", // amber
+  "oklch(0.76 0.13 30)", // coral
+  "oklch(0.78 0.11 210)", // teal
+  "oklch(0.74 0.13 265)", // blue
+  "oklch(0.76 0.14 320)", // magenta
+  "oklch(0.80 0.11 60)", // gold
+  "oklch(0.78 0.12 185)", // cyan
+];
+
+export function sessionColor(id: Uuid): string {
+  let h = 0;
+  for (let i = 0; i < id.length; i++) h = (h * 31 + id.charCodeAt(i)) >>> 0;
+  return PALETTE[h % PALETTE.length];
+}
diff --git a/web/src/styles.css b/web/src/styles.css
index ec34074..8895722 100644
--- a/web/src/styles.css
+++ b/web/src/styles.css
@@ -1899,3 +1899,321 @@ textarea {
   color: var(--accent);
   border-color: var(--accent);
 }
+
+/* =========================================================================
+   multi-view (#30 splits, #31 tabs, #33 highlights)
+   Tabs of nested split trees; each session leaf hosts a live .attach. The
+   focused pane reads at full strength, the rest recede — and the sidebar row
+   for the focused session matches it (loud), open-elsewhere rows stay quiet.
+   ========================================================================= */
+.mv {
+  flex: 1;
+  min-height: 0;
+  display: flex;
+  flex-direction: column;
+}
+
+/* tab bar */
+.mv-tabs {
+  display: flex;
+  align-items: stretch;
+  gap: 2px;
+  height: var(--bar-h);
+  padding: 0 var(--sp-2);
+  background: var(--surface);
+  border-bottom: 1px solid var(--border);
+  overflow-x: auto;
+  scrollbar-width: none;
+  flex: none;
+}
+.mv-tab {
+  display: inline-flex;
+  align-items: center;
+  gap: var(--sp-2);
+  padding: 0 var(--sp-3);
+  align-self: center;
+  height: calc(var(--bar-h) - 8px);
+  border-radius: var(--r-1);
+  font: 500 var(--fs-12) / 1 var(--font-mono);
+  color: var(--muted);
+  background: transparent;
+  border: 1px solid transparent;
+  cursor: pointer;
+  white-space: nowrap;
+}
+.mv-tab:hover {
+  background: var(--surface-2);
+  color: var(--ink);
+}
+.mv-tab.is-active {
+  background: var(--surface-3);
+  color: var(--ink);
+  border-color: var(--border);
+}
+.mv-tab-close {
+  opacity: 0.5;
+  font-size: var(--fs-13);
+  line-height: 1;
+}
+.mv-tab-close:hover {
+  opacity: 1;
+  color: var(--danger);
+}
+.mv-tab-add {
+  align-self: center;
+  width: 24px;
+  height: 24px;
+  border-radius: var(--r-1);
+  color: var(--muted);
+  font-size: var(--fs-15);
+  background: transparent;
+  border: none;
+  cursor: pointer;
+}
+.mv-tab-add:hover {
+  background: var(--surface-2);
+  color: var(--ink);
+}
+
+/* canvas + welcome */
+.mv-canvas {
+  position: relative;
+  flex: 1;
+  min-height: 0;
+  overflow: hidden;
+  background: var(--bg);
+}
+.mv-canvas > .mv-split,
+.mv-canvas > .mv-pane {
+  position: absolute;
+  inset: var(--sp-2);
+}
+.mv-canvas > .content-welcome {
+  position: absolute;
+  inset: 0;
+  margin: auto;
+  height: max-content;
+}
+
+/* splits + dividers */
+.mv-split {
+  display: flex;
+  width: 100%;
+  height: 100%;
+  min-width: 0;
+  min-height: 0;
+}
+.mv-split.row {
+  flex-direction: row;
+}
+.mv-split.col {
+  flex-direction: column;
+}
+.mv-split > .mv-slot {
+  min-width: 0;
+  min-height: 0;
+  display: flex;
+}
+.mv-split > .mv-slot > * {
+  flex: 1;
+  min-width: 0;
+  min-height: 0;
+}
+.mv-divider {
+  flex: none;
+  position: relative;
+  z-index: 2;
+}
+.mv-split.row > .mv-divider {
+  width: 6px;
+  cursor: col-resize;
+}
+.mv-split.col > .mv-divider {
+  height: 6px;
+  cursor: row-resize;
+}
+.mv-divider::after {
+  content: "";
+  position: absolute;
+  inset: 0;
+  margin: auto;
+  background: var(--border);
+}
+.mv-split.row > .mv-divider::after {
+  width: 1px;
+  height: 100%;
+}
+.mv-split.col > .mv-divider::after {
+  height: 1px;
+  width: 100%;
+}
+.mv-divider:hover::after,
+.mv-divider.is-dragging::after {
+  background: var(--accent);
+}
+
+/* a single pane = wrapper around a live .attach (or an empty placeholder) */
+.mv-pane {
+  position: relative;
+  display: flex;
+  min-width: 0;
+  min-height: 0;
+  border: 1px solid var(--border);
+  border-radius: var(--r-2);
+  overflow: hidden;
+  background: var(--term-bg);
+}
+.mv-pane-host {
+  flex: 1;
+  min-width: 0;
+  min-height: 0;
+  display: flex;
+}
+.mv-pane-host > .attach {
+  flex: 1;
+  min-width: 0;
+  min-height: 0;
+}
+/* per-session colour strip — maps a pane to its sidebar row */
+.mv-pane::before {
+  content: "";
+  position: absolute;
+  inset: 0 0 auto 0;
+  height: 2px;
+  background: var(--mv-color, transparent);
+  z-index: 3;
+  pointer-events: none;
+}
+/* focused pane: accent ring + glow, full strength */
+.mv-pane.is-focused {
+  border-color: var(--accent);
+  box-shadow: inset 0 0 0 1px var(--accent), 0 0 22px -8px var(--accent-ring);
+}
+/* unfocused panes recede so the eye finds the live one */
+.mv-pane:not(.is-focused) {
+  border-color: color-mix(in oklab, var(--border) 70%, transparent);
+}
+.mv-pane:not(.is-focused) .attach-body {
+  opacity: 0.45;
+}
+.mv-pane:not(.is-focused) .attach-header {
+  opacity: 0.7;
+}
+/* per-pane back button is meaningless in multi-view (use Close pane instead) */
+.mv-pane .attach-header .back {
+  display: none;
+}
+
+.mv-pane-empty {
+  flex: 1;
+  display: grid;
+  place-items: center;
+  padding: var(--sp-4);
+  color: var(--faint);
+  font: var(--fs-12) / 1.5 var(--font-mono);
+  text-align: center;
+}
+
+/* pane tools cluster (disconnect / split / close), top-right corner. The attach
+   header's own disconnect button is hidden — ⏻ lives here as the leftmost tool. */
+.mv-pane-tools {
+  position: absolute;
+  top: 6px;
+  right: 4px;
+  z-index: 4;
+  display: flex;
+  gap: 2px;
+  opacity: 0;
+  pointer-events: none;
+  transition: opacity var(--dur-fast) var(--ease-out);
+}
+.mv-pane .attach-header .disconnect {
+  display: none;
+}
+.mv-tool-off:hover {
+  background: var(--danger-tint);
+  color: var(--danger);
+}
+.mv-pane:hover .mv-pane-tools {
+  opacity: 1;
+  pointer-events: auto;
+}
+/* The tools share the header's right corner with the connection-state label, so
+   hide that label while hovering (tools showing) — no overlap. */
+.mv-pane:hover .attach-state {
+  visibility: hidden;
+}
+/* "connected" is noise — a streaming terminal already shows it's connected. Only
+   the transient/meaningful states surface (connecting/error); a closed session
+   auto-closes its pane, so "closed" is rarely seen. */
+.attach-state[data-state="open"] {
+  display: none;
+}
+.mv-tool {
+  display: inline-grid;
+  place-items: center;
+  width: 22px;
+  height: 22px;
+  border-radius: var(--r-1);
+  border: 1px solid var(--border);
+  background: var(--surface-2);
+  color: var(--muted);
+  font-size: var(--fs-12);
+  cursor: pointer;
+}
+.mv-tool:hover {
+  background: var(--surface-3);
+  color: var(--ink);
+}
+
+/* drag-to-dock (issue #32): a cursor-following ghost + the target pane's drop
+   zone highlight. */
+.mv-drag-ghost {
+  position: fixed;
+  z-index: var(--z-toast);
+  pointer-events: none;
+  padding: 2px 10px;
+  border-radius: var(--r-2);
+  background: var(--surface-3);
+  border: 1px solid var(--accent);
+  color: var(--ink);
+  font: 600 var(--fs-12) / 1.4 var(--font-mono);
+  box-shadow: var(--shadow-2);
+}
+.mv-dock-overlay {
+  position: absolute;
+  inset: 0;
+  z-index: 5;
+  pointer-events: none;
+}
+.mv-dock-zone {
+  background: color-mix(in oklab, var(--accent) 30%, transparent);
+  border: 1px solid var(--accent);
+  border-radius: var(--r-1);
+}
+
+/* sidebar two-tier highlight + colour dot (issue #33).
+   .is-active = focused pane (loud, from existing rule); .is-open = open
+   elsewhere (quiet). The dot uses the session's colour so a row maps to a pane. */
+.tree-leaf.is-open {
+  background: color-mix(in oklab, var(--accent) 6%, transparent);
+}
+.tree-leaf.is-open::after,
+.tree-leaf.is-active::after {
+  content: "";
+  position: absolute;
+  right: 9px;
+  top: 50%;
+  width: 7px;
+  height: 7px;
+  margin-top: -3.5px;
+  border-radius: 50%;
+  background: var(--mv-color, var(--accent));
+  pointer-events: none;
+}
+.tree-leaf.is-open::after {
+  opacity: 0.7;
+}
+.tree-leaf.is-active::after {
+  box-shadow: 0 0 8px var(--mv-color, var(--accent-ring));
+}