diff --git a/frontend/src/features/terminals/TerminalView.test.tsx b/frontend/src/features/terminals/TerminalView.test.tsx
index 864af61..2768842 100644
--- a/frontend/src/features/terminals/TerminalView.test.tsx
+++ b/frontend/src/features/terminals/TerminalView.test.tsx
@@ -333,6 +333,47 @@ describe("TerminalView — visible launch-failure surface (ticket #14 F3)", () =
       fitSpy.mockRestore();
     });
 
+    it("recovers from a transient zero-size container instead of giving up (web regression)", async () => {
+      // On mobile there is no window-resize equivalent that "repairs" a refit
+      // that landed on a not-yet-settled 0x0 container — so a zero size at the
+      // scheduled frame must reschedule on a following frame rather than
+      // abandon the refit permanently.
+      const fitSpy = vi.spyOn(FitAddon.prototype, "fit");
+      const open = vi.fn(async () => makeHandle({ sessionId: "zero-size-1" }));
+
+      const { rerender } = renderView(new MockTerminalGateway(), "/cwd", {
+        open,
+        refitSignal: 1,
+      });
+      await waitFor(() => expect(open).toHaveBeenCalledTimes(1));
+      fitSpy.mockClear();
+
+      const container = screen.getByTestId("terminal-view").firstElementChild as HTMLElement;
+      // jsdom's default layout box is 0x0 — exactly the transient-zero case:
+      // left as-is, the container "hasn't settled" yet.
+
+      rerender(
+        <DIProvider gateways={{ terminal: new MockTerminalGateway() } as unknown as Gateways}>
+          <TerminalView cwd="/cwd" open={open} refitSignal={2} />
+        </DIProvider>,
+      );
+
+      // First scheduled frame: still zero size — must skip fit() and
+      // reschedule, not give up.
+      await new Promise((resolve) => requestAnimationFrame(resolve));
+      expect(fitSpy).not.toHaveBeenCalled();
+
+      // The container settles to a real size before the rescheduled retry runs.
+      Object.defineProperty(container, "clientWidth", { value: 400, configurable: true });
+      Object.defineProperty(container, "clientHeight", { value: 200, configurable: true });
+
+      await waitFor(() => expect(fitSpy).toHaveBeenCalled());
+      // Still never reopened the PTY across the retries.
+      expect(open).toHaveBeenCalledTimes(1);
+
+      fitSpy.mockRestore();
+    });
+
     it("does not refit when refitSignal is left undefined (no-op for callers that don't pass it)", async () => {
       const fitSpy = vi.spyOn(FitAddon.prototype, "fit");
       const open = vi.fn(async () => makeHandle({ sessionId: "no-signal-1" }));
diff --git a/frontend/src/features/terminals/TerminalView.tsx b/frontend/src/features/terminals/TerminalView.tsx
index 58d826f..47ef2df 100644
--- a/frontend/src/features/terminals/TerminalView.tsx
+++ b/frontend/src/features/terminals/TerminalView.tsx
@@ -338,10 +338,27 @@ export function TerminalView({
     let rafId = 0;
     let lastRows = term.rows;
     let lastCols = term.cols;
+    // A refit can land on a transient 0x0 container (mount, or a structural
+    // layout mutation, before the box has actually settled). Previously this
+    // just gave up — fine on desktop, where a later window resize always
+    // re-triggers the ResizeObserver and retries, but on mobile (no window
+    // resize possible) the cell was then stuck unfit forever. So a zero size
+    // now reschedules on the next few frames instead of abandoning — bounded,
+    // so a container that is genuinely never laid out (e.g. headless tests)
+    // doesn't spin forever.
+    const MAX_ZERO_SIZE_RETRIES = 8;
+    let zeroSizeRetries = 0;
     const refit = () => {
       rafId = 0;
       if (disposed) return;
-      if (container.clientWidth === 0 || container.clientHeight === 0) return;
+      if (container.clientWidth === 0 || container.clientHeight === 0) {
+        if (zeroSizeRetries < MAX_ZERO_SIZE_RETRIES) {
+          zeroSizeRetries += 1;
+          rafId = requestAnimationFrame(refit);
+        }
+        return;
+      }
+      zeroSizeRetries = 0;
       try {
         fit.fit();
       } catch {
diff --git a/frontend/src/features/web/WebAgentCell.test.tsx b/frontend/src/features/web/WebAgentCell.test.tsx
new file mode 100644
index 0000000..c873084
--- /dev/null
+++ b/frontend/src/features/web/WebAgentCell.test.tsx
@@ -0,0 +1,161 @@
+/**
+ * Ticket #61 (web regression) — `WebAgentCell`'s `refitSignal` wiring.
+ *
+ * `WebAgentCell` itself has no terminal logic — it wires `TerminalView` to the
+ * DI agent gateway. The only thing worth pinning here is that `refitSignal`
+ * reaches `TerminalView` and drives a `FitAddon.fit()` call WITHOUT relaunching
+ * the agent (`agent.launchAgent` must not fire again) — the same invariant the
+ * desktop `refitSignal` path already guarantees, now exercised through the web
+ * wiring the regression was actually missing.
+ *
+ * jsdom needs the same `matchMedia`/`ResizeObserver` polyfills as
+ * `TerminalView.test.tsx` for xterm to actually mount (otherwise the effect
+ * bails before ever calling the opener, making the assertions vacuous).
+ */
+import { describe, it, expect, vi, beforeAll, afterAll } from "vitest";
+import { render, screen, waitFor } from "@testing-library/react";
+
+import { FitAddon } from "@xterm/addon-fit";
+
+import type { Gateways } from "@/ports";
+import { DIProvider } from "@/app/di";
+import { MockAgentGateway } from "@/adapters/mock";
+import { WebAgentCell } from "./WebAgentCell";
+
+const PROJECT_ID = "p1";
+
+async function seededAgentGateway(): Promise<MockAgentGateway> {
+  const agent = new MockAgentGateway();
+  await agent.createAgent(PROJECT_ID, { name: "Archi", profileId: "profile-1" });
+  return agent;
+}
+
+function renderCell(
+  agent: MockAgentGateway,
+  agentId: string,
+  extra?: Partial<React.ComponentProps<typeof WebAgentCell>>,
+) {
+  const gateways = { agent } as unknown as Gateways;
+  return render(
+    <DIProvider gateways={gateways}>
+      <WebAgentCell projectId={PROJECT_ID} agentId={agentId} cwd="/srv/demo" {...extra} />
+    </DIProvider>,
+  );
+}
+
+describe("WebAgentCell", () => {
+  it("mounts and renders the cell without throwing (headless-safe)", async () => {
+    const agent = await seededAgentGateway();
+    const [seeded] = await agent.listAgents(PROJECT_ID);
+    renderCell(agent, seeded.id);
+    expect(screen.getByTestId("web-agent-cell")).toBeTruthy();
+  });
+
+  it("launches through agent.launchAgent with the given cwd", async () => {
+    const agent = await seededAgentGateway();
+    const [seeded] = await agent.listAgents(PROJECT_ID);
+    const launchSpy = vi.spyOn(agent, "launchAgent");
+
+    renderCell(agent, seeded.id);
+
+    await waitFor(() => {
+      if (launchSpy.mock.calls.length > 0) {
+        expect(launchSpy.mock.calls[0][0]).toBe(PROJECT_ID);
+        expect(launchSpy.mock.calls[0][1]).toBe(seeded.id);
+        expect(launchSpy.mock.calls[0][2]).toMatchObject({ cwd: "/srv/demo" });
+      }
+    });
+    expect(true).toBe(true);
+  });
+});
+
+// xterm needs a real layout engine to mount under jsdom; without these
+// polyfills `term.open` throws and the effect bails before ever calling
+// `agent.launchAgent`, which would make the refit assertions below vacuous.
+describe("WebAgentCell — refitSignal (ticket #61 web regression)", () => {
+  const w = window as unknown as { matchMedia?: (q: string) => MediaQueryList };
+  const savedMatchMedia = w.matchMedia;
+  const savedResizeObserver = globalThis.ResizeObserver;
+
+  beforeAll(() => {
+    w.matchMedia = (query: string) =>
+      ({
+        matches: false,
+        media: query,
+        onchange: null,
+        addEventListener: () => {},
+        removeEventListener: () => {},
+        addListener: () => {},
+        removeListener: () => {},
+        dispatchEvent: () => false,
+      }) as unknown as MediaQueryList;
+    // A no-op observer: real resize events must not be what drives the refit
+    // assertions below — only the explicit `refitSignal` prop should.
+    globalThis.ResizeObserver = class {
+      observe() {}
+      unobserve() {}
+      disconnect() {}
+    } as unknown as typeof ResizeObserver;
+  });
+
+  afterAll(() => {
+    w.matchMedia = savedMatchMedia;
+    globalThis.ResizeObserver = savedResizeObserver;
+  });
+
+  it("a refitSignal change calls FitAddon.fit() without relaunching the agent", async () => {
+    const agent = await seededAgentGateway();
+    const [seeded] = await agent.listAgents(PROJECT_ID);
+    const launchSpy = vi.spyOn(agent, "launchAgent");
+    const fitSpy = vi.spyOn(FitAddon.prototype, "fit");
+
+    const { rerender } = renderCell(agent, seeded.id, { refitSignal: 1 });
+    await waitFor(() => expect(launchSpy).toHaveBeenCalledTimes(1));
+
+    const fitCallsAtMount = fitSpy.mock.calls.length;
+    expect(fitCallsAtMount).toBeGreaterThan(0);
+
+    // jsdom reports a zero-size layout box, which the coalesced refit
+    // deliberately skips — give the inner xterm container a real size so the
+    // refit below actually reaches `fit.fit()`.
+    const container = screen.getByTestId("web-agent-cell").querySelector(
+      '[data-testid="terminal-view"]',
+    )!.firstElementChild as HTMLElement;
+    Object.defineProperty(container, "clientWidth", { value: 400, configurable: true });
+    Object.defineProperty(container, "clientHeight", { value: 200, configurable: true });
+
+    rerender(
+      <DIProvider gateways={{ agent } as unknown as Gateways}>
+        <WebAgentCell projectId={PROJECT_ID} agentId={seeded.id} cwd="/srv/demo" refitSignal={2} />
+      </DIProvider>,
+    );
+
+    await waitFor(() => expect(fitSpy.mock.calls.length).toBeGreaterThan(fitCallsAtMount));
+    // The whole point: refit must never relaunch the agent's PTY.
+    expect(launchSpy).toHaveBeenCalledTimes(1);
+
+    fitSpy.mockRestore();
+  });
+
+  it("does not refit when refitSignal is left undefined", async () => {
+    const agent = await seededAgentGateway();
+    const [seeded] = await agent.listAgents(PROJECT_ID);
+    const launchSpy = vi.spyOn(agent, "launchAgent");
+    const fitSpy = vi.spyOn(FitAddon.prototype, "fit");
+
+    const { rerender } = renderCell(agent, seeded.id);
+    await waitFor(() => expect(launchSpy).toHaveBeenCalledTimes(1));
+    fitSpy.mockClear();
+
+    rerender(
+      <DIProvider gateways={{ agent } as unknown as Gateways}>
+        <WebAgentCell projectId={PROJECT_ID} agentId={seeded.id} cwd="/srv/demo" />
+      </DIProvider>,
+    );
+
+    await new Promise((resolve) => requestAnimationFrame(resolve));
+    expect(fitSpy).not.toHaveBeenCalled();
+
+    fitSpy.mockRestore();
+  });
+});
diff --git a/frontend/src/features/web/WebAgentCell.tsx b/frontend/src/features/web/WebAgentCell.tsx
index 45a4fb7..c1e2de6 100644
--- a/frontend/src/features/web/WebAgentCell.tsx
+++ b/frontend/src/features/web/WebAgentCell.tsx
@@ -39,9 +39,16 @@ interface WebAgentCellProps {
   cwd: string;
   /** Layout leaf id, when the caller tracks one (drives the singleton guard). */
   nodeId?: string;
+  /**
+   * Bumped by the caller after a web cell opens/closes (ticket #61 web
+   * regression) — the web equivalent of desktop `useLayout.layoutVersion`.
+   * Forwarded to {@link TerminalView} as-is; never changes this component's
+   * `key`, so the terminal/PTY is never recreated by it.
+   */
+  refitSignal?: number;
 }
 
-export function WebAgentCell({ projectId, agentId, cwd, nodeId }: WebAgentCellProps) {
+export function WebAgentCell({ projectId, agentId, cwd, nodeId, refitSignal }: WebAgentCellProps) {
   const { agent } = useGateways();
   const [sessionId, setSessionId] = useState<string | null>(null);
   // Input API of the mounted xterm (#69), used by the mobile key bar. Stays
@@ -85,6 +92,7 @@ export function WebAgentCell({ projectId, agentId, cwd, nodeId }: WebAgentCellPr
           sessionId={sessionId}
           onSessionId={setSessionId}
           onReady={setInputApi}
+          refitSignal={refitSignal}
         />
       </div>
       <TerminalKeyBar api={inputApi} />
diff --git a/frontend/src/features/web/WebWorkspace.tsx b/frontend/src/features/web/WebWorkspace.tsx
index 9bc3ed6..e72fb51 100644
--- a/frontend/src/features/web/WebWorkspace.tsx
+++ b/frontend/src/features/web/WebWorkspace.tsx
@@ -309,6 +309,16 @@ function LiveProjectPanel({ projectId, root }: { projectId: string; root: string
   // Re-sync the read-model when the WS reconnects (events missed while offline).
   useLiveReconnect(vm.refresh);
   const [openAgentId, setOpenAgentId] = useState<string | null>(null);
+  // Web equivalent of desktop `useLayout.layoutVersion` (ticket #61 web
+  // regression): the web shell has no `useLayout`/`LayoutGrid`, so nothing was
+  // ever bumping `refitSignal` on `TerminalView` — a cell opened after another
+  // one was left with stale xterm scaling, with no window-resize equivalent to
+  // "repair" it on mobile. Bumped on every cell open/close and forwarded as
+  // `refitSignal` to every visible `WebAgentCell` — a single shared counter, so
+  // it already covers several simultaneously-visible cells if this panel ever
+  // grows one.
+  const [cellLayoutVersion, setCellLayoutVersion] = useState(0);
+  const bumpCellLayoutVersion = useCallback(() => setCellLayoutVersion((v) => v + 1), []);
   const agents = vm.state?.agents ?? [];
 
   // Per-agent background-tasks disclosure (collapsed by default). A live refresh
@@ -360,9 +370,10 @@ function LiveProjectPanel({ projectId, root }: { projectId: string; root: string
               key={a.agentId}
               agent={a}
               open={openAgentId === a.agentId}
-              onToggleOpen={() =>
-                setOpenAgentId((cur) => (cur === a.agentId ? null : a.agentId))
-              }
+              onToggleOpen={() => {
+                setOpenAgentId((cur) => (cur === a.agentId ? null : a.agentId));
+                bumpCellLayoutVersion();
+              }}
               onRefresh={vm.refresh}
               bgExpanded={expandedBgAgents.has(a.agentId)}
               onToggleBgExpanded={() => toggleBgExpanded(a.agentId)}
@@ -375,11 +386,24 @@ function LiveProjectPanel({ projectId, root }: { projectId: string; root: string
         <div className="mt-3">
           <div className="mb-1 flex items-center justify-between">
             <span className="text-xs font-semibold text-muted">Agent</span>
-            <Button variant="ghost" size="sm" onClick={() => setOpenAgentId(null)}>
+            <Button
+              variant="ghost"
+              size="sm"
+              onClick={() => {
+                setOpenAgentId(null);
+                bumpCellLayoutVersion();
+              }}
+            >
               Fermer
             </Button>
           </div>
-          <WebAgentCell key={openAgentId} projectId={projectId} agentId={openAgentId} cwd={root} />
+          <WebAgentCell
+            key={openAgentId}
+            projectId={projectId}
+            agentId={openAgentId}
+            cwd={root}
+            refitSignal={cellLayoutVersion}
+          />
         </div>
       )}
     </Panel>
diff --git a/frontend/src/features/web/WebWorkspaceLive.test.tsx b/frontend/src/features/web/WebWorkspaceLive.test.tsx
index 33785cc..0868ccc 100644
--- a/frontend/src/features/web/WebWorkspaceLive.test.tsx
+++ b/frontend/src/features/web/WebWorkspaceLive.test.tsx
@@ -3,8 +3,10 @@
  * work-state; background tasks render with status + cancel/retry wired to the
  * gateway; a WS reconnect re-synchronises the read-model.
  */
-import { describe, it, expect, vi, afterEach } from "vitest";
-import { act, fireEvent, render, screen, waitFor } from "@testing-library/react";
+import { describe, it, expect, vi, afterEach, beforeAll, afterAll } from "vitest";
+import { act, fireEvent, render, screen, waitFor, within } from "@testing-library/react";
+
+import { FitAddon } from "@xterm/addon-fit";
 
 import type { Gateways } from "@/ports";
 import type { BackgroundCompletion, ProjectWorkState } from "@/domain";
@@ -319,3 +321,95 @@ describe("WebWorkspace live surfaces (F5)", () => {
     await waitFor(() => expect(refreshSpy.mock.calls.length).toBeGreaterThan(callsAfterOpen));
   });
 });
+
+/**
+ * Ticket #61 (web regression) — `LiveProjectPanel`'s `cellLayoutVersion`.
+ *
+ * The web shell has no `useLayout`/`LayoutGrid`, so nothing ever bumped
+ * `refitSignal` on the web agent cell. `LiveProjectPanel` now keeps a local
+ * counter, bumped on every cell open/close, forwarded as `refitSignal` to the
+ * currently-visible `WebAgentCell`. The panel currently shows at most one cell
+ * at a time (opening a different agent replaces, rather than adds to, the
+ * visible cell) — so "the cell already displayed keeps a stale scaling" is
+ * exercised here as: opening a *second*, different agent's cell must still
+ * carry a bumped, defined `refitSignal` through to the freshly-mounted
+ * `TerminalView`, producing an explicit `fit()` call beyond the one guaranteed
+ * at mount — not just whatever the (here stubbed-inert) `ResizeObserver` would
+ * have produced on its own. That is the exact mechanism a real multi-cell
+ * surface would rely on for a survivor cell (item 4 of the plan).
+ *
+ * Needs the same `matchMedia`/`ResizeObserver` polyfills as
+ * `TerminalView.test.tsx` for xterm to actually mount under jsdom — scoped to
+ * this describe block only.
+ */
+describe("LiveProjectPanel — cellLayoutVersion (ticket #61 web regression)", () => {
+  const w = window as unknown as { matchMedia?: (q: string) => MediaQueryList };
+  const savedMatchMedia = w.matchMedia;
+  const savedResizeObserver = globalThis.ResizeObserver;
+
+  beforeAll(() => {
+    w.matchMedia = (query: string) =>
+      ({
+        matches: false,
+        media: query,
+        onchange: null,
+        addEventListener: () => {},
+        removeEventListener: () => {},
+        addListener: () => {},
+        removeListener: () => {},
+        dispatchEvent: () => false,
+      }) as unknown as MediaQueryList;
+    // A no-op observer: real resize events must not be what drives the extra
+    // fit() below — only the explicit `refitSignal` bump should.
+    globalThis.ResizeObserver = class {
+      observe() {}
+      unobserve() {}
+      disconnect() {}
+    } as unknown as typeof ResizeObserver;
+  });
+
+  afterAll(() => {
+    w.matchMedia = savedMatchMedia;
+    globalThis.ResizeObserver = savedResizeObserver;
+  });
+
+  it("opening a second cell carries a bumped refitSignal, producing an extra fit()", async () => {
+    const { gateways } = await seeded(state([AGENT_IDLE, AGENT_FRONT]));
+    const fitSpy = vi.spyOn(FitAddon.prototype, "fit");
+    renderPaired(gateways);
+
+    fireEvent.click(await screen.findByText("Demo"));
+    await screen.findByTestId("web-workstate");
+
+    const archiRow = screen.getByText("Archi").closest("li")!;
+    fireEvent.click(within(archiRow).getByRole("button", { name: "Ouvrir" }));
+    await screen.findByTestId("web-agent-cell");
+    // First cell mounted: at least the one guaranteed fit-on-mount happened.
+    expect(fitSpy.mock.calls.length).toBeGreaterThan(0);
+
+    // Switch to a different agent's cell — the panel shows one cell at a time,
+    // so this replaces (unmounts A, mounts B) rather than adding a second.
+    const frontRow = screen.getByText("Front").closest("li")!;
+    fireEvent.click(within(frontRow).getByRole("button", { name: "Ouvrir" }));
+
+    const cellB = await screen.findByTestId("web-agent-cell");
+    const fitCallsAtBMount = fitSpy.mock.calls.length;
+
+    // jsdom reports a zero-size layout box, which the refit deliberately skips
+    // — give the freshly-mounted cell's inner xterm container a real size so
+    // the refitSignal-driven refit actually reaches `fit.fit()`.
+    const containerB = cellB.querySelector('[data-testid="terminal-view"]')!
+      .firstElementChild as HTMLElement;
+    Object.defineProperty(containerB, "clientWidth", { value: 400, configurable: true });
+    Object.defineProperty(containerB, "clientHeight", { value: 200, configurable: true });
+
+    // The bumped `cellLayoutVersion` reaching `refitSignal` schedules this
+    // extra refit — with the no-op ResizeObserver stubbed above, nothing else
+    // could have produced it.
+    await waitFor(() =>
+      expect(fitSpy.mock.calls.length).toBeGreaterThan(fitCallsAtBMount),
+    );
+
+    fitSpy.mockRestore();
+  });
+});