feat(dashboard): x stops a dashboard-owned bottle (PRD 0020 chunk 4)

Final PRD 0020 chunk. `x` on a focused agents-pane row tears
down the selected bottle if the dashboard owns it (started via
the chunk-2 `n` flow): pops `(cm, bottle, identity)` from the
main loop's bottles map, snapshots the transcript best-effort,
calls `cm.__exit__(None, None, None)` to drive the existing
compose-down + network-remove sequence, then `settle_state` to
honor any pre-existing preserve marker.

On a non-owned slug (discovered via `list_active_slugs` but not
in the dashboard's bottles dict — i.e., previous-dashboard or
external `./cli.py start` bottle), `x` is a no-op with a status
hint pointing at `./cli.py cleanup`. Matches the PRD's
cross-dashboard re-attach model: the dashboard can re-attach
either kind, but can only tear down its own.

The PRD's chunk 5 ("quit-cleanup") is satisfied by the existing
no-op behavior of `q` — per the user's resolved-question
answer, quit leaves bottles running unchanged. No code change
needed for that.

Footer surfaces `[x] stop`. 465 unit tests pass (1 new for the
non-owned no-op path; the owned path is integration territory
because it drives a real compose-down).

claude_bottle/cli/dashboard.py

@@ -650,6 +650,46 @@ def _bottle_for_slug(
     return synth, (prompt_path or "")
 
 
+def _stop_bottle_flow(
+    stdscr: "curses._CursesWindow",
+    bottles: dict,
+    slug: str,
+) -> str:
+    """Explicit per-bottle teardown (PRD 0020 chunk 4). Pops the
+    (cm, bottle, identity) tuple from the dashboard's bottles
+    map, snapshots the transcript best-effort, drives the launch
+    context's __exit__ (compose down + network remove), and
+    settles the state dir. A non-owned slug is a no-op with a
+    hint pointing at `./cli.py cleanup`."""
+    if slug not in bottles:
+        return (
+            f"[{slug}] not dashboard-owned — use ./cli.py cleanup"
+        )
+    cm, _bottle, identity = bottles.pop(slug)
+    # compose-down writes to stderr; drop curses so the lines
+    # render cleanly. Same pattern as the attach handoff.
+    curses.endwin()
+    try:
+        # Best-effort snapshot before teardown so the operator
+        # can still inspect the agent's last state via the
+        # preserved transcript dir even after explicit stop.
+        # exit_code=0 → no auto-preserve; the operator's
+        # existing preserve marker (if any) is honored by
+        # settle_state below.
+        try:
+            capture_session_state(identity, exit_code=0)
+        except BaseException:
+            pass
+        try:
+            cm.__exit__(None, None, None)
+        except BaseException:
+            pass
+    finally:
+        stdscr.refresh()
+    settle_state(identity)
+    return f"[{slug}] stopped"
+
+
 def _attach_to_bottle(
     stdscr: "curses._CursesWindow",
     bottle,
@@ -927,10 +967,8 @@ def _main_loop(stdscr: "curses._CursesWindow") -> None:
 
         if focus == PANE_AGENTS:
             # j/k/arrow navigate the agents list. Enter re-attaches
-            # to the focused bottle (PRD 0020 chunk 3) — works for
-            # both dashboard-owned bottles and bottles discovered
-            # via `list_active_slugs` (the synth path resolves the
-            # in-container claude target from the slug).
+            # (PRD 0020 chunk 3); `x` explicitly stops a
+            # dashboard-owned bottle (chunk 4).
             if key in (curses.KEY_DOWN, ord("j")):
                 selected_agent = min(selected_agent + 1, max(0, len(agents) - 1))
             elif key in (curses.KEY_UP, ord("k")):
@@ -943,6 +981,14 @@ def _main_loop(stdscr: "curses._CursesWindow") -> None:
                     manifest = manifest_cache[0]  # may be None; that's ok
                     bottle, _hint = _bottle_for_slug(target.slug, bottles, manifest)
                     status_line = _attach_to_bottle(stdscr, bottle, target.slug)
+            elif key == ord("x"):
+                target = _selected_agent(focus, agents, selected_agent)
+                if target is None:
+                    status_line = "no agent selected"
+                else:
+                    status_line = _stop_bottle_flow(
+                        stdscr, bottles, target.slug,
+                    )
             continue
 
         if not pending:
@@ -1082,7 +1128,7 @@ def _render(
 
     footer = (
         "[n] new  [Tab] switch  [j/k] move  "
-        "[Enter] view/attach  [a/m/r] proposal  [e/p] edit  [q] quit"
+        "[Enter] view/attach  [x] stop  [a/m/r] proposal  [e/p] edit  [q] quit"
     )
     stdscr.hline(h - 2, 0, curses.ACS_HLINE, w)
     stdscr.addnstr(h - 1, 0, footer, w - 1, curses.A_DIM)

tests/unit/test_dashboard_active_agents.py

@@ -379,6 +379,24 @@ class TestBottleForSlug(unittest.TestCase):
         self.assertEqual("", hint)
 
 
+class TestStopBottleFlow(unittest.TestCase):
+    """Explicit per-bottle stop (PRD 0020 chunk 4). The non-owned
+    path is the one safe to test without curses + docker — the
+    owned path drives `cm.__exit__` against a real launch context
+    and belongs in integration tests."""
+
+    def test_non_owned_returns_cleanup_hint(self):
+        # stdscr is None here on purpose — the non-owned branch
+        # returns before any curses call.
+        msg = dashboard._stop_bottle_flow(
+            stdscr=None,  # type: ignore[arg-type]
+            bottles={},
+            slug="ghost-zzz",
+        )
+        self.assertIn("not dashboard-owned", msg)
+        self.assertIn("./cli.py cleanup", msg)
+
+
 class TestOperatorEditFlowGuards(_FakeHomeMixin, unittest.TestCase):
     """Chunk-4 contract: the edit flow refuses when the selected
     agent doesn't have the required sidecar running. The discover-