fix(cli): scroll the /model picker viewport so long catalogs aren't clipped

The /model picker rendered every choice into a prompt_toolkit Window
with no max height. Providers with many models (e.g. Ollama Cloud's 36+)
overflowed the terminal, clipping the bottom border and the last items.

- Add HermesCLI._compute_model_picker_viewport() to slide a scroll
  offset that keeps the cursor on screen, sized from the live terminal
  rows minus chrome reserved for input/status/border.
- Render only the visible slice in _get_model_picker_display() and
  persist the offset on _model_picker_state across redraws.
- Bind ESC (eager) to close the picker, matching the Cancel button.
- Cover the viewport math with 8 unit tests in
  tests/hermes_cli/test_model_picker_viewport.py.

cli.py

@@ -4514,6 +4514,32 @@ class HermesCLI:
         self._restore_modal_input_snapshot()
         self._invalidate(min_interval=0.0)
 
+    @staticmethod
+    def _compute_model_picker_viewport(
+        selected: int,
+        scroll_offset: int,
+        n: int,
+        term_rows: int,
+        chrome_reserve: int = 14,
+    ) -> tuple[int, int]:
+        """Resolve (scroll_offset, visible_count) for the /model picker panel.
+
+        ``term_rows - chrome_reserve`` caps how many rows the panel may use for
+        items; when the list overflows we slide the offset to keep ``selected``
+        on screen. The position counter sits in the bottom border, so no extra
+        row is reserved for it.
+        """
+        max_visible = max(3, term_rows - chrome_reserve)
+        if n <= max_visible:
+            return 0, n
+        visible = max_visible
+        if selected < scroll_offset:
+            scroll_offset = selected
+        elif selected >= scroll_offset + visible:
+            scroll_offset = selected - visible + 1
+        scroll_offset = max(0, min(scroll_offset, n - visible))
+        return scroll_offset, visible
+
     def _apply_model_switch_result(self, result, persist_global: bool) -> None:
         if not result.success:
             _cprint(f"  ✗ {result.error_message}")
@@ -8693,6 +8719,13 @@ class HermesCLI:
             state["selected"] = min(max_idx, state.get("selected", 0) + 1)
             event.app.invalidate()
 
+        @kb.add('escape', filter=Condition(lambda: bool(self._model_picker_state)), eager=True)
+        def model_picker_escape(event):
+            """ESC closes the /model picker."""
+            self._close_model_picker()
+            event.app.current_buffer.reset()
+            event.app.invalidate()
+
         # --- History navigation: up/down browse history in normal input mode ---
         # The TextArea is multiline, so by default up/down only move the cursor.
         # Buffer.auto_up/auto_down handle both: cursor movement when multi-line,
@@ -9494,6 +9527,22 @@ class HermesCLI:
 
             box_width = _panel_box_width(title, [hint] + choices, min_width=46, max_width=84)
             inner_text_width = max(8, box_width - 6)
+            selected = state.get("selected", 0)
+
+            # Scrolling viewport: the panel renders into a Window with no max
+            # height, so without limiting visible items the bottom border and
+            # any items past the available terminal rows get clipped on long
+            # provider catalogs (e.g. Ollama Cloud's 36+ models).
+            try:
+                from prompt_toolkit.application import get_app
+                term_rows = get_app().output.get_size().rows
+            except Exception:
+                term_rows = shutil.get_terminal_size((80, 24)).lines
+            scroll_offset, visible = HermesCLI._compute_model_picker_viewport(
+                selected, state.get("_scroll_offset", 0), len(choices), term_rows,
+            )
+            state["_scroll_offset"] = scroll_offset
+
             lines = []
             lines.append(('class:clarify-border', '╭─ '))
             lines.append(('class:clarify-title', title))
@@ -9501,8 +9550,8 @@ class HermesCLI:
             _append_blank_panel_line(lines, 'class:clarify-border', box_width)
             _append_panel_line(lines, 'class:clarify-border', 'class:clarify-hint', hint, box_width)
             _append_blank_panel_line(lines, 'class:clarify-border', box_width)
-            selected = state.get("selected", 0)
-            for idx, choice in enumerate(choices):
+            for idx in range(scroll_offset, scroll_offset + visible):
+                choice = choices[idx]
                 style = 'class:clarify-selected' if idx == selected else 'class:clarify-choice'
                 prefix = '❯ ' if idx == selected else '  '
                 for wrapped in _wrap_panel_text(prefix + choice, inner_text_width, subsequent_indent='  '):

tests/hermes_cli/test_model_picker_viewport.py

@@ -0,0 +1,63 @@
+"""Tests for the prompt_toolkit /model picker scroll viewport.
+
+Regression for: when a provider exposes many models (e.g. Ollama Cloud's
+36+), the picker rendered every choice into a Window with no max height,
+clipping the bottom border and any items past the terminal's last row.
+The viewport helper now caps visible items and slides the offset to keep
+the cursor on screen.
+"""
+from cli import HermesCLI
+
+
+_compute = HermesCLI._compute_model_picker_viewport
+
+
+class TestPickerViewport:
+    def test_short_list_no_scroll(self):
+        offset, visible = _compute(selected=0, scroll_offset=0, n=5, term_rows=30)
+        assert offset == 0
+        assert visible == 5
+
+    def test_long_list_caps_visible_to_chrome_budget(self):
+        # 36 models, 30 terminal rows, chrome_reserve=14 → max_visible=16.
+        # Position counter lives in the bottom border, no row reserved.
+        offset, visible = _compute(selected=0, scroll_offset=0, n=36, term_rows=30)
+        assert visible == 16
+        assert offset == 0
+
+    def test_cursor_past_window_scrolls_down(self):
+        offset, visible = _compute(selected=20, scroll_offset=0, n=36, term_rows=30)
+        assert visible == 16
+        assert 20 in range(offset, offset + visible)
+
+    def test_cursor_above_window_scrolls_up(self):
+        offset, visible = _compute(selected=3, scroll_offset=15, n=36, term_rows=30)
+        assert offset == 3
+        assert 3 in range(offset, offset + visible)
+
+    def test_offset_clamped_to_bottom(self):
+        # Selected on last item — offset must keep visible window full, not
+        # walk past the end of the list.
+        offset, visible = _compute(selected=35, scroll_offset=0, n=36, term_rows=30)
+        assert offset + visible == 36
+        assert 35 in range(offset, offset + visible)
+
+    def test_tiny_terminal_uses_minimum_visible(self):
+        # term_rows below chrome_reserve falls back to the floor of 3 rows.
+        _, visible = _compute(selected=0, scroll_offset=0, n=20, term_rows=10)
+        assert visible == 3  # max(3, 10 - 14) == 3
+
+    def test_offset_recovers_after_stage_switch(self):
+        # When the user backs out of the model stage and re-enters with
+        # selected=0, a stale offset from the previous stage must collapse.
+        offset, visible = _compute(selected=0, scroll_offset=25, n=36, term_rows=30)
+        assert offset == 0
+        assert 0 in range(offset, offset + visible)
+
+    def test_full_navigation_keeps_cursor_visible(self):
+        offset = 0
+        for cursor in list(range(36)) + list(range(35, -1, -1)):
+            offset, visible = _compute(cursor, offset, n=36, term_rows=30)
+            assert cursor in range(offset, offset + visible), (
+                f"cursor={cursor} out of view: offset={offset} visible={visible}"
+            )