test(pi-tui): add regression tests for slash command TUI interactions

Add 3 new tests covering editor↔selector/input component swaps that
happen during /gsd prefs, /gsd migrate, and /gsd setup:

- editor-to-selector swap: verifies cursor tracking when editor with
  CURSOR_MARKER is replaced by a selector without one
- selector-to-editor swap: verifies cursor restores to CURSOR_MARKER
  position when editor returns after selector dismissal
- input component swap: verifies typing in prefs wizard text input
  produces correct cursor movement without jumps

All tests confirm hardwareCursorRow baseline computes correct movement
deltas for these interactive component transitions.

src/tests/tui-content-cursor-desync.test.ts

@@ -101,6 +101,182 @@ describe("TUI cursor tracking regression (#3764)", () => {
     );
   });
 
+  it("handles editor-to-selector swap without cursor corruption", () => {
+    // Simulates /gsd prefs: editor with CURSOR_MARKER is replaced by
+    // a selector component (no CURSOR_MARKER) that has different line count.
+    const terminal = new MockTTYTerminal();
+    const tui = new TUI(terminal, false);
+
+    // Initial state: chat + editor with cursor marker (typical idle state)
+    const chatLines = Array.from({ length: 15 }, (_, i) => `chat line ${i}`);
+    const editorComponent = new DynamicLinesComponent([
+      ...chatLines,
+      `> ${CURSOR_MARKER}`,  // editor input line with cursor
+    ]);
+
+    tui.addChild(editorComponent);
+    (tui as any).doRender();
+
+    // Cursor should be at the CURSOR_MARKER line (row 15)
+    assert.strictEqual(
+      (tui as any).hardwareCursorRow,
+      15,
+      "hardwareCursorRow should be at editor cursor position (row 15)",
+    );
+
+    // Now swap editor for selector (simulating showExtensionSelector)
+    terminal.writtenData = [];
+    editorComponent.lines = [
+      ...chatLines,
+      "─── Select preference ───",
+      "→ Model routing",
+      "  Timeouts",
+      "  Budget",
+      "  Cancel",
+      "─────────────────────────",
+    ];
+
+    (tui as any).doRender();
+
+    assert.ok(terminal.writtenData.length >= 1, "selector render should produce output");
+
+    const buffer = terminal.writtenData[0];
+    // Verify no extremely large cursor jumps that would cause visual corruption
+    const hugeJump = buffer.match(/\x1b\[(\d{2,})A/);
+    if (hugeJump) {
+      const jumpSize = parseInt(hugeJump[1], 10);
+      assert.ok(
+        jumpSize < 20,
+        `cursor jump of ${jumpSize} rows is too large — likely a baseline desync, got: ${JSON.stringify(buffer.slice(0, 200))}`,
+      );
+    }
+
+    // hardwareCursorRow should NOT be at old IME position
+    // since there's no CURSOR_MARKER in the selector
+    const hwRow = (tui as any).hardwareCursorRow;
+    assert.ok(
+      hwRow >= 15 && hwRow <= 20,
+      `hardwareCursorRow should be at rendered content (${hwRow}), not stuck at old IME position`,
+    );
+
+    // Now simulate user pressing ↓ in selector (one line changes)
+    terminal.writtenData = [];
+    editorComponent.lines = [
+      ...chatLines,
+      "─── Select preference ───",
+      "  Model routing",
+      "→ Timeouts",
+      "  Budget",
+      "  Cancel",
+      "─────────────────────────",
+    ];
+
+    (tui as any).doRender();
+
+    if (terminal.writtenData.length > 0) {
+      const navBuffer = terminal.writtenData[0];
+      // The differential render should only update the 2 changed lines (16 and 17)
+      // Verify no large upward jumps from wrong baseline
+      const navJump = navBuffer.match(/\x1b\[(\d{2,})A/);
+      if (navJump) {
+        const jumpSize = parseInt(navJump[1], 10);
+        assert.ok(
+          jumpSize < 20,
+          `navigation caused jump of ${jumpSize} rows — cursor baseline may be wrong`,
+        );
+      }
+    }
+  });
+
+  it("handles selector-to-editor swap restoring cursor correctly", () => {
+    // After dismissing a selector, the editor returns with CURSOR_MARKER.
+    // The cursor must move to the new marker position without corruption.
+    const terminal = new MockTTYTerminal();
+    const tui = new TUI(terminal, false);
+
+    const chatLines = Array.from({ length: 10 }, (_, i) => `chat ${i}`);
+    const component = new DynamicLinesComponent([
+      ...chatLines,
+      "─── Selector ───",
+      "→ Option A",
+      "  Option B",
+      "────────────────",
+    ]);
+
+    tui.addChild(component);
+    (tui as any).doRender();
+
+    // No CURSOR_MARKER → cursor stays at last rendered line
+    const hwRowAfterSelector = (tui as any).hardwareCursorRow;
+
+    // Swap back to editor with CURSOR_MARKER
+    terminal.writtenData = [];
+    component.lines = [
+      ...chatLines,
+      `> ${CURSOR_MARKER}`,
+    ];
+
+    (tui as any).doRender();
+
+    // CURSOR_MARKER is at row 10 — cursor should be positioned there
+    assert.strictEqual(
+      (tui as any).hardwareCursorRow,
+      10,
+      "hardwareCursorRow should move to editor cursor after selector dismiss",
+    );
+  });
+
+  it("handles input component swap (prefs wizard text input)", () => {
+    // Simulates /gsd prefs input step: selector replaced by text input with cursor
+    const terminal = new MockTTYTerminal();
+    const tui = new TUI(terminal, false);
+
+    const chatLines = Array.from({ length: 8 }, (_, i) => `msg ${i}`);
+    const component = new DynamicLinesComponent([
+      ...chatLines,
+      "─── Enter value ───",
+      `Value: ${CURSOR_MARKER}`,
+      "───────────────────",
+    ]);
+
+    tui.addChild(component);
+    (tui as any).doRender();
+
+    assert.strictEqual(
+      (tui as any).hardwareCursorRow,
+      9,
+      "hardwareCursorRow should be at input cursor (row 9)",
+    );
+
+    // Simulate typing in the input
+    terminal.writtenData = [];
+    component.lines = [
+      ...chatLines,
+      "─── Enter value ───",
+      `Value: hello${CURSOR_MARKER}`,
+      "───────────────────",
+    ];
+
+    (tui as any).doRender();
+
+    assert.ok(terminal.writtenData.length >= 1, "typing should trigger render");
+
+    const buffer = terminal.writtenData[0];
+    // Should not jump to wrong row — only line 9 changed
+    const upJump = buffer.match(/\x1b\[(\d+)A/);
+    if (upJump) {
+      const jumpSize = parseInt(upJump[1], 10);
+      // Cursor was at row 9 (IME), need to go to row 9 (changed line) = no jump needed
+      assert.ok(jumpSize <= 1, `typing in input caused unexpected up-jump of ${jumpSize}`);
+    }
+
+    assert.strictEqual(
+      (tui as any).hardwareCursorRow,
+      9,
+      "hardwareCursorRow should stay at input cursor after typing",
+    );
+  });
+
   it("hardwareCursorRow tracks actual terminal position through IME and shrink", () => {
     const terminal = new MockTTYTerminal();
     const tui = new TUI(terminal, false);