diff --git a/app/src-tauri/Cargo.lock b/app/src-tauri/Cargo.lock
index c607a07c..4c95c2dd 100644
--- a/app/src-tauri/Cargo.lock
+++ b/app/src-tauri/Cargo.lock
@@ -26,6 +26,7 @@ dependencies = [
  "tauri-plugin-process",
  "tauri-plugin-single-instance",
  "tauri-plugin-updater",
+ "tauri-plugin-window-state",
  "tempfile",
 ]
 
@@ -4099,6 +4100,21 @@ dependencies = [
  "zip",
 ]
 
+[[package]]
+name = "tauri-plugin-window-state"
+version = "2.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73736611e14142408d15353e21e3cca2f12a3cfb523ad0ce85999b6d2ef1a704"
+dependencies = [
+ "bitflags 2.13.0",
+ "log",
+ "serde",
+ "serde_json",
+ "tauri",
+ "tauri-plugin",
+ "thiserror 2.0.18",
+]
+
 [[package]]
 name = "tauri-runtime"
 version = "2.11.3"
diff --git a/app/src-tauri/Cargo.toml b/app/src-tauri/Cargo.toml
index 574654bd..008d8d5d 100644
--- a/app/src-tauri/Cargo.toml
+++ b/app/src-tauri/Cargo.toml
@@ -24,6 +24,7 @@ tauri-plugin-dialog = "2"
 tauri-plugin-updater = "2"
 tauri-plugin-process = "2"
 tauri-plugin-single-instance = "2"
+tauri-plugin-window-state = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 # Terminal-embedded core: own agent PTYs (spawn + read + write + inject) and
diff --git a/app/src-tauri/src/lib.rs b/app/src-tauri/src/lib.rs
index debf4d49..c92322d1 100644
--- a/app/src-tauri/src/lib.rs
+++ b/app/src-tauri/src/lib.rs
@@ -498,6 +498,11 @@ pub fn run() {
         .plugin(tauri_plugin_dialog::init())
         .plugin(tauri_plugin_updater::Builder::new().build())
         .plugin(tauri_plugin_process::init())
+        // Restores the main window's size/position/maximized state on
+        // launch and saves it on move/resize/close — fully automatic, no
+        // frontend involvement needed (unlike zoom/view-visibility, which
+        // are app-specific state the frontend also reads/writes).
+        .plugin(tauri_plugin_window_state::Builder::default().build())
         // Built in English first — the frontend doesn't get a chance to
         // report its actual language until after the webview loads and
         // i18next resolves it, so set_menu_language rebuilds this shortly
diff --git a/app/src/App.css b/app/src/App.css
index 18e29b66..262469ff 100644
--- a/app/src/App.css
+++ b/app/src/App.css
@@ -3,6 +3,11 @@
   --panel: #11151f;
   --panel-2: #161b27;
   --border: #232a3a;
+  /* One step brighter than --border, specifically for the pane frame
+     (koit: --border alone was too faint to read as a visible box at
+     rest). Its own variable, not a --border change, so the other 27
+     places --border is used elsewhere in the UI stay as-is. */
+  --pane-border: #3a4660;
   --fg: #c5c8c6;
   --muted: #6b7280;
   --accent: #7aa2f7;
@@ -1029,7 +1034,7 @@ body.resizing-row {
   font-size: 11px;
   color: var(--muted);
   background: var(--panel);
-  border: 1px solid var(--border);
+  border: 1px solid var(--pane-border);
   border-bottom: none;
   border-radius: 6px 6px 0 0;
 }
@@ -1123,7 +1128,11 @@ body.resizing-row {
 .pane-divider-h::before {
   content: "";
   position: absolute;
-  background: var(--border);
+  /* Invisible at rest now that the gap itself is a full terminal cell
+     (koit) — a static hairline sitting in the middle of that gap read as
+     a redundant, always-on divider line. Shows only on hover/while
+     actively dragging (below), same as before. */
+  background: transparent;
 }
 .pane-divider-v::before {
   top: 0;
@@ -1139,13 +1148,15 @@ body.resizing-row {
   height: 1px;
   transform: translateY(-50%);
 }
-.pane-divider-v:hover::before {
+.pane-divider-v:hover::before,
+.pane-divider-v.pane-divider-dragging::before {
   left: 0;
   width: 100%;
   transform: none;
   background: var(--accent);
 }
-.pane-divider-h:hover::before {
+.pane-divider-h:hover::before,
+.pane-divider-h.pane-divider-dragging::before {
   top: 0;
   height: 100%;
   transform: none;
@@ -1268,7 +1279,7 @@ body.resizing-row {
   min-height: 0;
   width: 100%;
   height: auto;
-  border: 1px solid var(--border);
+  border: 1px solid var(--pane-border);
   border-top: none;
 }
 
diff --git a/app/src/App.tsx b/app/src/App.tsx
index ec9bb036..f4a59b34 100644
--- a/app/src/App.tsx
+++ b/app/src/App.tsx
@@ -18,6 +18,8 @@ import {
   AgentModal,
   AppUserModal,
   ConfirmModal,
+  MAX_TERMINAL_FONT_SIZE,
+  MIN_TERMINAL_FONT_SIZE,
   NewTeamModal,
   RenameModal,
   SettingsModal,
@@ -28,6 +30,7 @@ import {
   clampRatio,
   collectDividers,
   computeRects,
+  dividerDragKey,
   insertAsNewLeaf,
   insertBeside,
   leaves,
@@ -102,7 +105,7 @@ type DropPreview = { paneId: string; zone: ReturnType<typeof classifyDrop> };
 type Modal =
   | { kind: "team"; firstRun: boolean }
   | { kind: "agent" }
-  | { kind: "appuser" }
+  | { kind: "appuser"; auto: boolean }
   | { kind: "rename"; current: string }
   | { kind: "leave"; name: string }
   | { kind: "settings" }
@@ -119,6 +122,22 @@ const ROOM_PAGE_SIZE = 30;
 // enough for now; panes always start fresh each launch anyway (they're
 // live PTYs, not something a restart could restore even if we tried).
 const LAST_TEAM_KEY = "agmsg-app-last-team";
+// Persists the two View menu toggles below. See the seeding useEffect for
+// why restoring these pushes INTO Rust (set_team_room_visible/
+// set_user_chat_visible) rather than reading view_visibility unconditionally.
+const SHOW_TEAM_ROOM_KEY = "agmsg-app-show-team-room";
+const SHOW_USER_CHAT_KEY = "agmsg-app-show-user-chat";
+// Persists the sidebar's icon-only-rail collapse toggle.
+const SIDEBAR_COLLAPSED_KEY = "agmsg-app-sidebar-collapsed";
+// Persists the terminal font size (Settings modal). xterm.js default is 15;
+// this app has always hardcoded 12 (a bit denser), so that's the fallback.
+const TERMINAL_FONT_SIZE_KEY = "agmsg-app-terminal-font-size";
+const DEFAULT_TERMINAL_FONT_SIZE = 12;
+// "Don't show this again" for the auto-triggered app-user prompt (see the
+// team-change effect below) — adding an app-user is always reachable from
+// the chat's "Add one" link, so a user who dismisses the auto-prompt once
+// shouldn't be re-asked on every future team switch.
+const SUPPRESS_APPUSER_PROMPT_KEY = "agmsg-app-suppress-appuser-prompt";
 // Custom drag-and-drop MIME type for pane-swap drags (see PANE_DRAG_MIME
 // usages below) — a made-up type, not text/plain, so a stray OS file drag
 // or an unrelated drag elsewhere on the page never accidentally matches a
@@ -166,10 +185,24 @@ export default function App() {
   const [spawnTypes, setSpawnTypes] = useState<AgentType[]>([]);
   const [sidebarWidth, setSidebarWidth] = useState(200);
   const [chatHeight, setChatHeight] = useState(160);
+  // Terminal font size, adjustable from the Settings modal and persisted
+  // across restarts (see TERMINAL_FONT_SIZE_KEY). Validated against the same
+  // range the Settings <input> enforces — a stray/corrupted localStorage
+  // value (NaN, Infinity, out of range) would otherwise reach xterm as-is
+  // and persist itself right back on the next write.
+  const [terminalFontSize, setTerminalFontSize] = useState(() => {
+    const stored = Number(localStorage.getItem(TERMINAL_FONT_SIZE_KEY));
+    return Number.isFinite(stored) && stored >= MIN_TERMINAL_FONT_SIZE && stored <= MAX_TERMINAL_FONT_SIZE
+      ? stored
+      : DEFAULT_TERMINAL_FONT_SIZE;
+  });
   // Collapses the team sidebar to an icon-only rail so panes get more width.
-  // Session-only (no persistence needed) — spawning/messaging a member isn't
-  // offered from the collapsed rail; expand to get back to the full list.
-  const [sidebarCollapsed, setSidebarCollapsed] = useState(false);
+  // Persisted across restarts (see SIDEBAR_COLLAPSED_KEY) — spawning/
+  // messaging a member isn't offered from the collapsed rail; expand to get
+  // back to the full list.
+  const [sidebarCollapsed, setSidebarCollapsed] = useState(
+    () => localStorage.getItem(SIDEBAR_COLLAPSED_KEY) === "true",
+  );
   // Popup the collapsed rail's team-icon button opens — team switching, the
   // one thing the full sidebar's team <select> offers that needs a menu
   // instead of a direct icon action at rail width. Settings is a direct
@@ -178,9 +211,23 @@ export default function App() {
   // Toggled from the native "View > Show Team Room" menu item — when off,
   // the room tab itself disappears from the tab bar (not just its
   // content), matching Show User Chat's own toggle just below it.
-  const [showTeamRoom, setShowTeamRoom] = useState(true);
-  // Toggled from the native "View > Show User Chat" menu item.
-  const [showUserChat, setShowUserChat] = useState(true);
+  // Lazily restored from localStorage (see SHOW_TEAM_ROOM_KEY) rather than
+  // always starting `true` and correcting via an effect — the mount-time
+  // seeding effect below still exists, but only to push this already-
+  // correct initial value INTO Rust, not to setState a second time (that
+  // would race the persist effect just below it: a persist effect keyed on
+  // [showTeamRoom] captures the value AS OF THE RENDER IT WAS DECLARED IN,
+  // so if this state started `true` and got corrected by a later setState,
+  // the initial-render persist effect would already have fired and written
+  // the stale `true` back to localStorage before the correction landed).
+  const [showTeamRoom, setShowTeamRoom] = useState(
+    () => localStorage.getItem(SHOW_TEAM_ROOM_KEY) !== "false",
+  );
+  // Toggled from the native "View > Show User Chat" menu item. See
+  // showTeamRoom just above for why this is lazily restored.
+  const [showUserChat, setShowUserChat] = useState(
+    () => localStorage.getItem(SHOW_USER_CHAT_KEY) !== "false",
+  );
   // The app-user chat pane's 3 states (session-only, like sidebarCollapsed):
   // "normal" (today's layout), "minimized" (collapses the history away,
   // leaving just the composer row — the team room becomes the only log,
@@ -324,6 +371,26 @@ export default function App() {
     setPaneStatus((current) => applyStateChange(current, paneId, state));
   }, []);
 
+  // Cell size in CSS px. The ref is for snapping a divider drag to whole
+  // terminal rows/cols — read once at drag-start, doesn't need a re-render
+  // on every fit. The state twin drives the gap BETWEEN panes below (koit:
+  // should be a full terminal cell per axis, herdr-style, not an arbitrary
+  // fixed px value) — that one has to be real React state since it feeds
+  // rendered CSS. Every pane uses the same fixed font today, so any one of
+  // them reporting is representative of them all.
+  const cellSizeRef = useRef<{ w: number; h: number } | null>(null);
+  const [cellSize, setCellSize] = useState<{ w: number; h: number } | null>(null);
+  const handleCellSize = useCallback((w: number, h: number) => {
+    cellSizeRef.current = { w, h };
+    setCellSize((prev) => (prev && prev.w === w && prev.h === h ? prev : { w, h }));
+  }, []);
+
+  // Which divider (by dividerDragKey, below) is currently being dragged —
+  // state, not a captured DOM element, so the highlight survives a
+  // grid-segment transpose remounting the divider mid-drag (co1 review,
+  // PR #390).
+  const [draggingDividerKey, setDraggingDividerKey] = useState<string | null>(null);
+
   // The app user = the member registered with the agmsg-app type (one per team).
   const appUserMember = members.find(
     (m) => m.source_id === "local" && m.types.includes(APP_USER_TYPE),
@@ -440,19 +507,35 @@ export default function App() {
     invoke<string>("agmsg_command_name").then(setCmdName).catch(() => {});
   }, []);
 
-  // Rust holds the only durable copy of these two flags (see view_visibility
-  // in lib.rs) — seed our state from there on mount rather than guessing
-  // `true`. Without this, a webview remount that doesn't restart the Rust
-  // process (Vite HMR during `tauri dev`, or any future webview reload)
-  // would reset these back to `true` while the native menu checkbox and
-  // Rust's own state kept whatever was last set, silently disagreeing.
+  // showTeamRoom/showUserChat are already correctly seeded from localStorage
+  // by their useState initializers above — this effect's only job is to
+  // PUSH that initial value into Rust (set_team_room_visible/
+  // set_user_chat_visible, which also resyncs the native menu checkbox), so
+  // Rust doesn't sit at its own process-default `true` while the frontend
+  // shows something else. No setState here: doing so would re-introduce the
+  // write-then-correct race this replaced (a persist effect below, keyed on
+  // showTeamRoom/showUserChat, would capture the stale initial-render value
+  // and write it back to localStorage before a corrective setState's
+  // re-render could fix it).
+  //
+  // Falls back to Rust's own view_visibility only when localStorage has
+  // nothing stored yet (true first run) — this also covers a webview
+  // remount that doesn't restart the Rust process (Vite HMR during
+  // `tauri dev`), where Rust may hold a value localStorage hasn't caught
+  // up to yet.
   useEffect(() => {
-    invoke<{ team_room: boolean; user_chat: boolean }>("view_visibility")
-      .then((v) => {
-        setShowTeamRoom(v.team_room);
-        setShowUserChat(v.user_chat);
-      })
-      .catch(() => {});
+    const storedTeamRoom = localStorage.getItem(SHOW_TEAM_ROOM_KEY);
+    const storedUserChat = localStorage.getItem(SHOW_USER_CHAT_KEY);
+    if (storedTeamRoom !== null) void invoke("set_team_room_visible", { visible: storedTeamRoom === "true" });
+    if (storedUserChat !== null) void invoke("set_user_chat_visible", { visible: storedUserChat === "true" });
+    if (storedTeamRoom === null || storedUserChat === null) {
+      invoke<{ team_room: boolean; user_chat: boolean }>("view_visibility")
+        .then((v) => {
+          if (storedTeamRoom === null) setShowTeamRoom(v.team_room);
+          if (storedUserChat === null) setShowUserChat(v.user_chat);
+        })
+        .catch(() => {});
+    }
   }, []);
 
   // Native "View > Show Team Room" menu checkbox toggles the room tab itself.
@@ -467,6 +550,21 @@ export default function App() {
     return () => void p.then((u) => u());
   }, []);
 
+  // Persist the two View toggles and the sidebar collapse state across
+  // restarts (see their _KEY constants above).
+  useEffect(() => {
+    localStorage.setItem(SHOW_TEAM_ROOM_KEY, String(showTeamRoom));
+  }, [showTeamRoom]);
+  useEffect(() => {
+    localStorage.setItem(SHOW_USER_CHAT_KEY, String(showUserChat));
+  }, [showUserChat]);
+  useEffect(() => {
+    localStorage.setItem(SIDEBAR_COLLAPSED_KEY, String(sidebarCollapsed));
+  }, [sidebarCollapsed]);
+  useEffect(() => {
+    localStorage.setItem(TERMINAL_FONT_SIZE_KEY, String(terminalFontSize));
+  }, [terminalFontSize]);
+
   // Spawnable agent types (for the Add-agent type picker). spawnMember
   // re-fetches this itself right before spawning — see there for why.
   useEffect(() => {
@@ -579,8 +677,16 @@ export default function App() {
     void loadInitialHistory();
     loadMembers(team)
       .then((loaded) => {
-        if (!loaded.some((member) => member.source_id === "local" && member.types.includes(APP_USER_TYPE))) {
-          setModal((current) => current ?? { kind: "appuser" });
+        // Only a local app user satisfies the prompt: the composer writes to
+        // the local source, so a member carrying APP_USER_TYPE on a read-only
+        // remote source cannot stand in for one here.
+        if (
+          !loaded.some(
+            (member) => member.source_id === "local" && member.types.includes(APP_USER_TYPE),
+          ) &&
+          localStorage.getItem(SUPPRESS_APPUSER_PROMPT_KEY) !== "true"
+        ) {
+          setModal((current) => current ?? { kind: "appuser", auto: true });
         }
       })
       .catch(console.error);
@@ -1287,10 +1393,18 @@ export default function App() {
     // own doc).
     const MIN_PANE_PX = 120;
     const cursorClass = axis === "col" ? "resizing-col" : "resizing-row";
+    // koit: prefers the divider snapping to whole terminal cells over a
+    // free pixel drag (herdr-inspired, though herdr itself had nothing
+    // reusable here — this is agmsg's own design). Every pane shares the
+    // same fixed font, so one representative cell size (captured by any
+    // TerminalPane's fit) is enough regardless of which panes flank this
+    // specific divider.
+    const cellPx = axis === "col" ? cellSizeRef.current?.w : cellSizeRef.current?.h;
     const onMove = (ev: MouseEvent) => {
       const totalPx = axis === "col" ? parentPx.width : parentPx.height;
       const raw = axis === "col" ? (ev.clientX - parentPx.left) / totalPx : (ev.clientY - parentPx.top) / totalPx;
-      const ratio = clampRatio(raw, MIN_PANE_PX, totalPx);
+      const snapped = cellPx ? (Math.round((raw * totalPx) / cellPx) * cellPx) / totalPx : raw;
+      const ratio = clampRatio(snapped, MIN_PANE_PX, totalPx);
       setWindows((prev) =>
         prev.map((w) => (w.id === windowId ? { ...w, root: updateRatioAtPath(w.root, dragPath, ratio) } : w)),
       );
@@ -1299,9 +1413,15 @@ export default function App() {
       document.removeEventListener("mousemove", onMove);
       document.removeEventListener("mouseup", onUp);
       document.body.classList.remove(cursorClass);
+      setDraggingDividerKey(null);
     };
     document.addEventListener("mousemove", onMove);
     document.addEventListener("mouseup", onUp);
+    // dragPath.join(".") is this divider's identity on BOTH sides of the
+    // grid-segment transpose queued above (see dividerDragKey's doc) — key
+    // off that, not a captured DOM element, so the highlight survives even
+    // if this transpose swaps in a differently-shaped divider set.
+    setDraggingDividerKey(dragPath.join(".") || "root");
     document.body.classList.add(cursorClass);
   }, []);
 
@@ -1846,6 +1966,17 @@ export default function App() {
                     top: `${rect.top}%`,
                     width: `${rect.width}%`,
                     height: `${rect.height}%`,
+                    // The gap between two adjacent panes is each side's own
+                    // padding added together, so half a cell per side makes
+                    // a full terminal cell of gap at the shared seam
+                    // (koit/herdr: the gap should read as "one cell", not
+                    // an arbitrary fixed px value — falls back to the old
+                    // fixed padding before any pane has fit and reported
+                    // its real cell size).
+                    paddingLeft: cellSize ? cellSize.w / 2 : undefined,
+                    paddingRight: cellSize ? cellSize.w / 2 : undefined,
+                    paddingTop: cellSize ? cellSize.h / 2 : undefined,
+                    paddingBottom: cellSize ? cellSize.h / 2 : undefined,
                   }}
                   onDragOver={(e) => {
                     // Gate on dataTransfer.types, NOT React state: dragover
@@ -1970,30 +2101,40 @@ export default function App() {
                     cmd={p.cmd}
                     args={p.args}
                     cwd={p.cwd}
+                    fontSize={terminalFontSize}
                     onAgentState={applyAgentState}
+                    onCellSize={handleCellSize}
                   />
                 </div>
               );
             })}
 
             {active !== "room" &&
-              activeDividers.map((d) => (
-                <div
-                  key={
-                    d.kind === "single"
-                      ? `single:${d.path.join(".") || "root"}`
-                      : `grid:${d.basePath.join(".") || "root"}:${d.segmentPath.join(".")}`
-                  }
-                  className={d.axis === "col" ? "pane-divider-v" : "pane-divider-h"}
-                  style={{
-                    left: `${d.rect.left}%`,
-                    top: `${d.rect.top}%`,
-                    width: `${d.rect.width}%`,
-                    height: `${d.rect.height}%`,
-                  }}
-                  onMouseDown={(e) => startPaneDividerDrag(e, active, d)}
-                />
-              ))}
+              activeDividers.map((d) => {
+                const isDragging = draggingDividerKey !== null && dividerDragKey(d) === draggingDividerKey;
+                return (
+                  <div
+                    key={
+                      d.kind === "single"
+                        ? `single:${d.path.join(".") || "root"}`
+                        : `grid:${d.basePath.join(".") || "root"}:${d.segmentPath.join(".")}`
+                    }
+                    className={[
+                      d.axis === "col" ? "pane-divider-v" : "pane-divider-h",
+                      isDragging && "pane-divider-dragging",
+                    ]
+                      .filter(Boolean)
+                      .join(" ")}
+                    style={{
+                      left: `${d.rect.left}%`,
+                      top: `${d.rect.top}%`,
+                      width: `${d.rect.width}%`,
+                      height: `${d.rect.height}%`,
+                    }}
+                    onMouseDown={(e) => startPaneDividerDrag(e, active, d)}
+                  />
+                );
+              })}
           </section>
 
           {showUserChat && chatPaneState === "normal" && (
@@ -2064,7 +2205,7 @@ export default function App() {
                 {!appUser && team && (
                   <div className="empty">
                     {t("chat.emptyState.noUser")}
-                    <button className="link" onClick={() => setModal({ kind: "appuser" })}>
+                    <button className="link" onClick={() => setModal({ kind: "appuser", auto: false })}>
                       {t("chat.emptyState.addOne")}
                     </button>
                   </div>
@@ -2129,7 +2270,18 @@ export default function App() {
         />
       )}
       {modal?.kind === "appuser" && (
-        <AppUserModal onAdd={onAddAppUser} onClose={() => setModal(null)} browseDir={browseDir} />
+        <AppUserModal
+          onAdd={onAddAppUser}
+          onClose={() => {
+            // Dismissing the auto-prompt (vs. the "Add one" link's manual
+            // open) means the user doesn't want to add one right now — an
+            // app-user is always reachable from the chat link, so don't
+            // re-ask on every future team switch (see SUPPRESS_APPUSER_PROMPT_KEY).
+            if (modal.auto) localStorage.setItem(SUPPRESS_APPUSER_PROMPT_KEY, "true");
+            setModal(null);
+          }}
+          browseDir={browseDir}
+        />
       )}
       {modal?.kind === "agent" && (
         <AgentModal
@@ -2153,7 +2305,13 @@ export default function App() {
           onClose={() => setModal(null)}
         />
       )}
-      {modal?.kind === "settings" && <SettingsModal onClose={() => setModal(null)} />}
+      {modal?.kind === "settings" && (
+        <SettingsModal
+          onClose={() => setModal(null)}
+          terminalFontSize={terminalFontSize}
+          onTerminalFontSizeChange={setTerminalFontSize}
+        />
+      )}
       {modal?.kind === "closeWindow" &&
         (() => {
           const win = windows.find((w) => w.id === modal.windowId);
diff --git a/app/src/TerminalPane.tsx b/app/src/TerminalPane.tsx
index 7150d8e4..e46ac17a 100644
--- a/app/src/TerminalPane.tsx
+++ b/app/src/TerminalPane.tsx
@@ -12,7 +12,11 @@ type Props = {
   cmd: string;
   args?: string[];
   cwd?: string;
+  fontSize?: number;
   onAgentState?: (id: string, state: "idle" | "working" | "blocked" | "unknown") => void;
+  /** Reported on every fit — the pane's current cell size in CSS px, so a
+   * divider drag elsewhere can snap to whole terminal rows/cols. */
+  onCellSize?: (widthPx: number, heightPx: number) => void;
 };
 
 function b64ToBytes(b64: string): Uint8Array {
@@ -26,19 +30,29 @@ function b64ToBytes(b64: string): Uint8Array {
  * One embedded agent terminal: an xterm.js view bound to a backend PTY session.
  * Output streams in via `pty-output` events; keystrokes go back via `pty_write`.
  */
-export function TerminalPane({ id, cmd, args = [], cwd, onAgentState }: Props) {
+export function TerminalPane({ id, cmd, args = [], cwd, fontSize = 12, onAgentState, onCellSize }: Props) {
   const ref = useRef<HTMLDivElement>(null);
+  // Live handles to the current terminal/fit addon, for the font-size effect
+  // below to reach — that effect must NOT be a dependency of the main effect
+  // (a fontSize change would otherwise kill and respawn the PTY, losing the
+  // running process).
+  const termRef = useRef<Terminal | null>(null);
+  const fitRef = useRef<FitAddon | null>(null);
+  const idRef = useRef(id);
+  idRef.current = id;
   const { t } = useTranslation();
 
   useEffect(() => {
     let disposed = false;
     const term = new Terminal({
-      fontSize: 12,
+      fontSize,
       fontFamily: "Menlo, Monaco, 'Courier New', monospace",
       cursorBlink: true,
       theme: { background: "#0b0e14", foreground: "#c5c8c6" },
     });
+    termRef.current = term;
     const fit = new FitAddon();
+    fitRef.current = fit;
     term.loadAddon(fit);
     term.open(ref.current!);
 
@@ -63,6 +77,10 @@ export function TerminalPane({ id, cmd, args = [], cwd, onAgentState }: Props) {
         lastCols = term.cols;
         void invoke("pty_resize", { id, rows: term.rows, cols: term.cols });
       }
+      // Every pane uses the same fixed font today, so any one of them
+      // reporting its cell size is representative of them all — a divider
+      // drag doesn't need to know which specific panes it's between.
+      onCellSize?.(el.offsetWidth / term.cols, el.offsetHeight / term.rows);
     };
 
     const unlisteners: Array<() => void> = [];
@@ -119,8 +137,40 @@ export function TerminalPane({ id, cmd, args = [], cwd, onAgentState }: Props) {
       unlisteners.forEach((u) => u());
       void invoke("pty_kill", { id });
       term.dispose();
+      termRef.current = null;
+      fitRef.current = null;
     };
-  }, [id, cmd, cwd, onAgentState]);
+  }, [id, cmd, cwd, onAgentState, onCellSize]);
+
+  // Apply a fontSize change live, without recreating the terminal (which
+  // would kill and respawn the PTY). Skips its very first run — at that
+  // point termRef was *just* created above with this same fontSize value
+  // (passed to the Terminal constructor), so re-fitting would be a no-op
+  // re-resize racing the pty_spawn call still in flight in the effect above.
+  const skipInitialFontSizeEffect = useRef(true);
+  useEffect(() => {
+    if (skipInitialFontSizeEffect.current) {
+      skipInitialFontSizeEffect.current = false;
+      return;
+    }
+    const term = termRef.current;
+    const fit = fitRef.current;
+    const el = ref.current;
+    if (!term || !fit || !el || el.offsetWidth === 0 || el.offsetHeight === 0) return;
+    term.options.fontSize = fontSize;
+    try {
+      fit.fit();
+    } catch {
+      return;
+    }
+    void invoke("pty_resize", { id: idRef.current, rows: term.rows, cols: term.cols });
+    // A font size change resizes xterm's internal cell geometry without
+    // resizing the .term-pane container itself, so the ResizeObserver in
+    // the main effect above never fires for it — re-report cell size here,
+    // or divider snap/gap sizing (see onCellSize's doc comment) silently
+    // stays pinned to whatever font was active on last container resize.
+    onCellSize?.(el.offsetWidth / term.cols, el.offsetHeight / term.rows);
+  }, [fontSize, onCellSize]);
 
   return <div className="term-pane" ref={ref} />;
 }
diff --git a/app/src/i18n/locales/de.json b/app/src/i18n/locales/de.json
index 4f440b3d..a9b1048b 100644
--- a/app/src/i18n/locales/de.json
+++ b/app/src/i18n/locales/de.json
@@ -170,7 +170,10 @@
     "label": "Sprache"
   },
   "settings": {
-    "title": "Einstellungen"
+    "title": "Einstellungen",
+    "terminalFontSize": {
+      "label": "Terminal-Schriftgröße"
+    }
   },
   "nativeMenu": {
     "about": "Über {{name}}",
diff --git a/app/src/i18n/locales/en.json b/app/src/i18n/locales/en.json
index 5a58d39c..cb6416d3 100644
--- a/app/src/i18n/locales/en.json
+++ b/app/src/i18n/locales/en.json
@@ -7,7 +7,10 @@
     "projectDirLabel": "Project dir"
   },
   "settings": {
-    "title": "Settings"
+    "title": "Settings",
+    "terminalFontSize": {
+      "label": "Terminal font size"
+    }
   },
   "startupError": {
     "installing": "Installing agmsg…",
diff --git a/app/src/i18n/locales/es.json b/app/src/i18n/locales/es.json
index a88667a1..b1311419 100644
--- a/app/src/i18n/locales/es.json
+++ b/app/src/i18n/locales/es.json
@@ -170,7 +170,10 @@
     "label": "Idioma"
   },
   "settings": {
-    "title": "Configuración"
+    "title": "Configuración",
+    "terminalFontSize": {
+      "label": "Tamaño de fuente de la terminal"
+    }
   },
   "nativeMenu": {
     "about": "Acerca de {{name}}",
diff --git a/app/src/i18n/locales/fr.json b/app/src/i18n/locales/fr.json
index c06b0f83..6fb759a4 100644
--- a/app/src/i18n/locales/fr.json
+++ b/app/src/i18n/locales/fr.json
@@ -170,7 +170,10 @@
     "label": "Langue"
   },
   "settings": {
-    "title": "Paramètres"
+    "title": "Paramètres",
+    "terminalFontSize": {
+      "label": "Taille de police du terminal"
+    }
   },
   "nativeMenu": {
     "about": "À propos de {{name}}",
diff --git a/app/src/i18n/locales/ja.json b/app/src/i18n/locales/ja.json
index 05c02478..059c959c 100644
--- a/app/src/i18n/locales/ja.json
+++ b/app/src/i18n/locales/ja.json
@@ -170,7 +170,10 @@
     "label": "言語"
   },
   "settings": {
-    "title": "設定"
+    "title": "設定",
+    "terminalFontSize": {
+      "label": "ターミナルのフォントサイズ"
+    }
   },
   "nativeMenu": {
     "about": "{{name}} について",
diff --git a/app/src/i18n/locales/ko.json b/app/src/i18n/locales/ko.json
index ad13b5bd..eb3c88f7 100644
--- a/app/src/i18n/locales/ko.json
+++ b/app/src/i18n/locales/ko.json
@@ -170,7 +170,10 @@
     "label": "언어"
   },
   "settings": {
-    "title": "설정"
+    "title": "설정",
+    "terminalFontSize": {
+      "label": "터미널 글꼴 크기"
+    }
   },
   "nativeMenu": {
     "about": "{{name}} 정보",
diff --git a/app/src/i18n/locales/pt-BR.json b/app/src/i18n/locales/pt-BR.json
index 2f8db077..f41cac97 100644
--- a/app/src/i18n/locales/pt-BR.json
+++ b/app/src/i18n/locales/pt-BR.json
@@ -170,7 +170,10 @@
     "label": "Idioma"
   },
   "settings": {
-    "title": "Configurações"
+    "title": "Configurações",
+    "terminalFontSize": {
+      "label": "Tamanho da fonte do terminal"
+    }
   },
   "nativeMenu": {
     "about": "Sobre o {{name}}",
diff --git a/app/src/i18n/locales/zh-CN.json b/app/src/i18n/locales/zh-CN.json
index 76ff1965..b3b3ee7b 100644
--- a/app/src/i18n/locales/zh-CN.json
+++ b/app/src/i18n/locales/zh-CN.json
@@ -170,7 +170,10 @@
     "label": "语言"
   },
   "settings": {
-    "title": "设置"
+    "title": "设置",
+    "terminalFontSize": {
+      "label": "终端字体大小"
+    }
   },
   "nativeMenu": {
     "about": "关于 {{name}}",
diff --git a/app/src/i18n/locales/zh-TW.json b/app/src/i18n/locales/zh-TW.json
index d25c29ea..b88b5a30 100644
--- a/app/src/i18n/locales/zh-TW.json
+++ b/app/src/i18n/locales/zh-TW.json
@@ -170,7 +170,10 @@
     "label": "語言"
   },
   "settings": {
-    "title": "設定"
+    "title": "設定",
+    "terminalFontSize": {
+      "label": "終端機字型大小"
+    }
   },
   "nativeMenu": {
     "about": "關於 {{name}}",
diff --git a/app/src/modals.tsx b/app/src/modals.tsx
index af917ae2..a26e7563 100644
--- a/app/src/modals.tsx
+++ b/app/src/modals.tsx
@@ -364,10 +364,17 @@ export function ConfirmModal(props: {
   );
 }
 
-// The only setting today is language, so this is a single dropdown rather
-// than a full preferences panel — expand into sections here as more
-// settings show up instead of adding separate modals per setting.
-export function SettingsModal(props: { onClose: () => void }) {
+// Exported so App.tsx can validate a localStorage-restored value against the
+// same range this modal's <input> enforces (see terminalFontSize's lazy
+// useState initializer).
+export const MIN_TERMINAL_FONT_SIZE = 8;
+export const MAX_TERMINAL_FONT_SIZE = 24;
+
+export function SettingsModal(props: {
+  onClose: () => void;
+  terminalFontSize: number;
+  onTerminalFontSizeChange: (size: number) => void;
+}) {
   const { t, i18n } = useTranslation();
   return (
     <Modal title={t("modal.settings.title")} onClose={props.onClose}>
@@ -384,6 +391,21 @@ export function SettingsModal(props: { onClose: () => void }) {
           ))}
         </select>
       </label>
+      <label>
+        {t("settings.terminalFontSize.label")}
+        <input
+          type="number"
+          min={MIN_TERMINAL_FONT_SIZE}
+          max={MAX_TERMINAL_FONT_SIZE}
+          value={props.terminalFontSize}
+          onChange={(e) => {
+            const n = Number(e.target.value);
+            if (n >= MIN_TERMINAL_FONT_SIZE && n <= MAX_TERMINAL_FONT_SIZE) {
+              props.onTerminalFontSizeChange(n);
+            }
+          }}
+        />
+      </label>
       <div className="modal-actions">
         <button type="button" className="primary" onClick={props.onClose}>
           {t("common.close")}
diff --git a/app/src/paneTree.test.ts b/app/src/paneTree.test.ts
index bd26b335..a4d6813c 100644
--- a/app/src/paneTree.test.ts
+++ b/app/src/paneTree.test.ts
@@ -5,6 +5,7 @@ import {
   clampRatio,
   collectDividers,
   computeRects,
+  dividerDragKey,
   insertAsNewLeaf,
   insertBeside,
   leaves,
@@ -655,3 +656,31 @@ describe("transposeGrid", () => {
     expect(rects.get("4")!.height).toBeCloseTo(50, 6);
   });
 });
+
+describe("dividerDragKey", () => {
+  it("stays the same across a grid-segment transpose (regression, co1 review PR #390)", () => {
+    // A 3-column aligned grid: transposing a grid-segment divider from one
+    // of these turns the OTHER segments' dividers from "grid-segment" into
+    // "single" (a 2x2 grid stays grid-shaped either way — this needed 3+
+    // columns to reproduce). App.tsx keys its drag-highlight off this
+    // identity precisely because the divider's own DOM node can get
+    // unmounted by that shape change mid-drag.
+    const row = (leftId: string, rest: SplitNode) => split("col", 0.4, leaf(leftId), rest);
+    const tree = split(
+      "row",
+      0.5,
+      row("1", split("col", 0.6, leaf("2"), leaf("3"))),
+      row("4", split("col", 0.6, leaf("5"), leaf("6"))),
+    );
+    const before = collectDividers(tree);
+    const grabbed = before.find((d) => d.kind === "grid-segment")!;
+    expect(grabbed.kind).toBe("grid-segment");
+    const keyBefore = dividerDragKey(grabbed);
+
+    // Mirrors startPaneDividerDrag: transpose at the grabbed divider's own
+    // basePath, exactly as grabbing it does.
+    const transposed = applyAtPath(tree, (grabbed as Extract<DividerInfo, { kind: "grid-segment" }>).basePath, transposeGrid);
+    const after = collectDividers(transposed);
+    expect(after.some((d) => dividerDragKey(d) === keyBefore)).toBe(true);
+  });
+});
diff --git a/app/src/paneTree.ts b/app/src/paneTree.ts
index 8f9b948a..1d649dfc 100644
--- a/app/src/paneTree.ts
+++ b/app/src/paneTree.ts
@@ -207,6 +207,21 @@ export function collectDividers(node: SplitNode, rect: PaneRect = FULL_RECT, pat
   return [...thisSeam, ...collectDividers(node.a, rectA, [...path, "a"]), ...collectDividers(node.b, rectB, [...path, "b"])];
 }
 
+/**
+ * A divider's identity across a grid-segment transpose (co1 review, PR
+ * #390): grabbing a grid-segment divider transposes its aligned grid at
+ * drag-start (see transposeGrid's own doc), and for 3+ segment grids that
+ * changes collectDividers' shape from "grid" divider keys to "single"
+ * ones — a DOM node keyed on the pre-transpose divider gets unmounted
+ * mid-drag. `[...basePath, ...segmentPath]` (or `path` directly for an
+ * already-single divider) stays the correct path to the same split node on
+ * both sides of that transpose, so App.tsx keys its drag-highlight off
+ * this instead of a captured DOM reference.
+ */
+export function dividerDragKey(d: DividerInfo): string {
+  return (d.kind === "single" ? d.path : [...d.basePath, ...d.segmentPath]).join(".") || "root";
+}
+
 function zipPairs(a: SplitNode, b: SplitNode, pairAxis: SplitAxis, pairRatio: number): SplitNode {
   if (a.kind === "leaf" && b.kind === "leaf") {
     return { kind: "split", axis: pairAxis, ratio: pairRatio, a, b };