FN-6110: fix Reliability view flex sizing on mobile

Keep the Reliability view filling its flex parent across mobile and desktop states.

- add flex growth and min-width safeguards to the Reliability view, loading, and error containers
- add desktop and mobile regression coverage for loading, populated, and error rendering states

Files changed:
 packages/dashboard/app/components/ReliabilityView.css  |  6 +++
 packages/dashboard/app/components/__tests__/ReliabilityView.test.tsx | 59 ++++++++++++++++++++++
 2 files changed, 65 insertions(+)

Fusion-Task-Id: FN-6110

Fusion-Task-Lineage: 5fe1e5a7-f13a-4316-8c4e-b5c85a51ce86

packages/dashboard/app/components/ReliabilityView.css

@@ -1,9 +1,11 @@
 .reliability-view {
   display: flex;
+  flex: 1 1 auto;
   flex-direction: column;
   gap: var(--space-lg);
   height: 100%;
   min-height: 0;
+  min-width: 0;
   overflow-y: auto;
   -webkit-overflow-scrolling: touch;
 }
@@ -17,20 +19,24 @@
 
 .reliability-loading {
   display: flex;
+  flex: 1 1 auto;
   flex-direction: column;
   align-items: center;
   justify-content: center;
   gap: var(--space-md);
+  min-width: 0;
   padding: var(--space-2xl);
   color: var(--text-muted);
 }
 
 .reliability-error {
   display: flex;
+  flex: 1 1 auto;
   flex-direction: column;
   align-items: center;
   justify-content: center;
   gap: var(--space-md);
+  min-width: 0;
   padding: var(--space-2xl);
   text-align: center;
 }

packages/dashboard/app/components/__tests__/ReliabilityView.test.tsx

@@ -32,6 +32,27 @@ const baseResponse = {
   mergeAttempts: { mean: 1.2, max: 2, histogram: { "1": 1 } },
 };
 
+function renderInProjectContent() {
+  return render(
+    <div data-testid="project-content" style={{ display: "flex", width: "100%" }}>
+      <ReliabilityView />
+    </div>,
+  );
+}
+
+function setViewportWidth(width: number) {
+  Object.defineProperty(window, "innerWidth", { configurable: true, value: width });
+  window.dispatchEvent(new Event("resize"));
+}
+
+function expectFlexFill(element: HTMLElement) {
+  const computed = getComputedStyle(element);
+  expect(computed.flexGrow).toBe("1");
+  expect(computed.flexShrink).toBe("1");
+  expect(computed.flexBasis).toBe("auto");
+  expect(computed.minWidth).toBe("0px");
+}
+
 describe("ReliabilityView", () => {
   afterEach(() => {
     vi.useRealTimers();
@@ -58,6 +79,44 @@ describe("ReliabilityView", () => {
     expect(screen.queryByRole("heading", { name: "Reliability" })).not.toBeInTheDocument();
   });
 
+  it.each([
+    ["desktop", 1024],
+    ["mobile", 375],
+  ])("fills flex parent width in %s loading state", (_label, width) => {
+    setViewportWidth(width);
+    vi.spyOn(globalThis, "fetch").mockReturnValue(new Promise<Response>(() => {}));
+
+    renderInProjectContent();
+
+    expectFlexFill(screen.getByTestId("reliability-loading"));
+  });
+
+  it.each([
+    ["desktop", 1024],
+    ["mobile", 375],
+  ])("fills flex parent width in %s populated state", async (_label, width) => {
+    setViewportWidth(width);
+    vi.spyOn(globalThis, "fetch").mockResolvedValue({ ok: true, json: async () => baseResponse } as Response);
+
+    const { container } = renderInProjectContent();
+
+    await waitFor(() => expect(container.querySelector(".reliability-view")).not.toBeNull());
+    expectFlexFill(container.querySelector(".reliability-view") as HTMLElement);
+  });
+
+  it.each([
+    ["desktop", 1024],
+    ["mobile", 375],
+  ])("fills flex parent width in %s error state", async (_label, width) => {
+    setViewportWidth(width);
+    vi.spyOn(globalThis, "fetch").mockRejectedValue(new Error("Network unavailable"));
+
+    renderInProjectContent();
+
+    await waitFor(() => expect(screen.getByTestId("reliability-error")).toBeInTheDocument());
+    expectFlexFill(screen.getByTestId("reliability-error"));
+  });
+
   it("shows data after successful load even if loading refresh is pending", async () => {
     vi.useFakeTimers();
     const fetchSpy = vi.spyOn(globalThis, "fetch")