fix(dashboard): use os._exit on quit so bottles survive the dashboard

The `bottles` dict held `@contextmanager`-wrapped launch contexts.
On normal Python interpreter shutdown those context managers'
generators got GC'd, which raised GeneratorExit at the yield
point and ran the `finally` block — invoking each bottle's
teardown and tearing down the compose project. Net effect: `q`
WAS implicitly stopping every dashboard-launched bottle even
though the keypress handler just `return`'d.

`os._exit(0)` skips all Python-level cleanup (GC, atexit, etc.),
so the docker compose projects survive the dashboard exit
untouched. Curses gets explicit `endwin()` first because the
brutal exit skips curses.wrapper's normal terminal restoration.

Matches PRD 0020's resolved-question answer (`q` does NOT tear
down bottles; teardown is always explicit via `x` or
`./cli.py cleanup`).

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,
@@ -957,10 +997,8 @@ 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
+            # (PRD 0020 chunk 3); `x` explicitly stops a
-            # both dashboard-owned bottles and bottles discovered
+            # dashboard-owned bottle (chunk 4).
-            # via `list_active_slugs` (the synth path resolves the
-            # in-container claude target from the slug).
             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")):
@@ -973,6 +1011,14 @@ 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:
@@ -1112,7 +1158,7 @@ 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-