fix(ui): fall back to plain write when block exceeds terminal height

The cursor-up escape that repositions the header only works when the
block fits on screen without scrolling. With a tall next-steps body
(~27 lines for deploy), a short terminal scrolls the buffer and the
cursor-up no longer lands on the header, corrupting the output.

Guard against this by comparing rowsBelow against process.stderr.rows
before entering the animation path.

Author: rafa-thayto

packages/cli-core/src/lib/gradient.test.ts

@@ -199,4 +199,25 @@ describe("animateHeader (interactive gating)", () => {
     await run();
     expect(captured.err).toContain("\r");
   });
+
+  test("falls back to a plain write when the block is taller than the terminal", async () => {
+    const savedRows = process.stderr.rows;
+    try {
+      Object.defineProperty(process.stderr, "rows", { value: 5, configurable: true });
+      await animateHeader({
+        prefix: "",
+        label: "Hi",
+        fallback: bold,
+        // 5 newlines → rowsBelow = 6, which exceeds rows = 5
+        body: "a\nb\nc\nd\ne\n",
+        frames: 2,
+        intervalMs: 1,
+      });
+      expect(captured.err).not.toContain("\r");
+      expect(captured.err).not.toContain("\x1b[?25l");
+      expect(captured.err).toContain("a");
+    } finally {
+      Object.defineProperty(process.stderr, "rows", { value: savedRows, configurable: true });
+    }
+  });
 });

packages/cli-core/src/lib/gradient.ts

@@ -149,6 +149,14 @@ export async function animateHeader(options: AnimateHeaderOptions): Promise<void
   // header's own newline plus every newline inside the body.
   const rowsBelow = 1 + (body.match(/\n/g)?.length ?? 0);
 
+  // The cursor-up escape only lands on the header when the block fits on screen
+  // without scrolling. Fall back to a plain write on short terminals where the
+  // scroll would push the header out of reach.
+  if (process.stderr.rows != null && rowsBelow >= process.stderr.rows) {
+    write(`${prefix}${fallback(label)}\n${body}`);
+    return;
+  }
+
   hideCursor();
   try {
     // Print the whole block first so the body is visible immediately, then step