refactor(start): extract prepare_with_preflight + attach_claude

PRD 0020 chunk 1. `cli/start.py`'s `_launch_bottle` did three
things in one function: prepare + preflight, attach claude, and
settle state on teardown. Split them so the dashboard (PRD 0020
chunk 2+) can reuse the prepare + attach pieces piecewise
without going through the CLI's one-shot orchestrator:

  - `prepare_with_preflight(spec, *, stage_dir, render_preflight,
    prompt_yes, dry_run)` — injects render + prompt callables so
    the CLI binds them to stderr/stdin while the dashboard binds
    them to a curses modal. Returns `(plan, identity)`; identity
    is set after `backend.prepare` returns so callers can reap
    the prepare-time state dir on abort via `settle_state` in
    their finally — preserving today's preflight-N cleanup.
  - `attach_claude(bottle, *, remote_control)` — runs claude
    inside the bottle and returns its exit code. The dashboard
    calls this from inside a `curses.endwin` → … →
    `stdscr.refresh()` handoff.
  - `capture_session_state` / `settle_state` lose their leading
    underscore; the dashboard will call them on
    session-end + explicit-stop respectively.

`_launch_bottle` becomes a thin orchestrator over those helpers.
No behavior change; all 453 unit tests pass and `./cli.py start
implementer --dry-run` produces identical preflight output.

claude_bottle/cli/start.py

@@ -2,8 +2,10 @@
 interactive claude-code session. The container is torn down when the
 session ends.
 
-The launch core is shared with `cli.py resume <identity>`: see
-_launch_bottle below.
+The launch core is shared with `cli.py resume <identity>` and (PRD
+0020 chunk 1+) the dashboard's in-process start flow: see the
+public helpers `prepare_with_preflight`, `attach_claude`, and the
+private orchestrator `_launch_bottle`.
 """
 
 from __future__ import annotations
@@ -14,8 +16,10 @@ import shutil
 import sys
 import tempfile
 from pathlib import Path
+from typing import Callable
 
-from ..backend import BottleSpec, get_bottle_backend
+from ..backend import Bottle, BottleSpec, get_bottle_backend
+from ..backend.docker.bottle_plan import DockerBottlePlan
 from ..backend.docker.bottle_state import (
     cleanup_state,
     is_preserved,
@@ -51,73 +55,67 @@ def cmd_start(argv: list[str]) -> int:
     )
 
 
-def _launch_bottle(
+# --- Public helpers shared with the dashboard (PRD 0020) -----------------
+
+
+def prepare_with_preflight(
     spec: BottleSpec,
     *,
-    dry_run: bool,
-    remote_control: bool,
+    stage_dir: Path,
+    render_preflight: Callable[[DockerBottlePlan], None],
+    prompt_yes: Callable[[], bool],
+    dry_run: bool = False,
+) -> tuple[DockerBottlePlan | None, str]:
+    """Run `backend.prepare`, render the preflight summary via the
+    injected callable, prompt y/N via the injected callable. The CLI
+    binds these to stderr/stdin; the dashboard binds them to a
+    curses modal.
+
+    Returns `(plan, identity)`. `plan` is None on dry-run or
+    operator-N, but `identity` is set as soon as `backend.prepare`
+    returns so callers can reap the prepare-time state dir via
+    `settle_state(identity)` in their finally — exactly the existing
+    semantics."""
+    backend = get_bottle_backend()
+    plan = backend.prepare(spec, stage_dir=stage_dir)
+    identity = _identity_from_plan(plan)
+
+    render_preflight(plan)
+
+    if dry_run:
+        info("dry-run requested; not starting container.")
+        return None, identity
+    if not prompt_yes():
+        info("aborted by user")
+        return None, identity
+    return plan, identity
+
+
+def attach_claude(
+    bottle: Bottle, *, remote_control: bool = False,
 ) -> int:
-    """Shared launch core for `start` and `resume`. Builds the plan,
-    prints / dry-runs / prompts as appropriate, brings the bottle up,
-    attaches claude, and prints the resume hint on session end."""
-    stage_dir = Path(tempfile.mkdtemp(prefix="claude-bottle-stage."))
-    identity = ""
-    try:
-        backend = get_bottle_backend()
-        plan = backend.prepare(spec, stage_dir=stage_dir)
-        identity = _identity_from_plan(plan)
+    """Run claude inside `bottle` as an interactive session. Blocks
+    until the session ends; returns the claude process's exit code.
 
-        plan.print(remote_control=remote_control)
-
-        if dry_run:
-            info("dry-run requested; not starting container.")
-            return 0
-
-        sys.stderr.write("claude-bottle: launch this agent? [y/N] ")
-        sys.stderr.flush()
-        reply = read_tty_line()
-        if reply not in ("y", "Y", "yes", "YES"):
-            info("aborted by user")
-            return 0
-
-        with backend.launch(plan) as bottle:
-            info(
-                "attaching interactive claude session "
-                "(Ctrl-D or 'exit' to leave; container will be removed)"
-            )
-            claude_args = ["--dangerously-skip-permissions"]
-            if remote_control:
-                claude_args.append("--remote-control")
-            exit_code = bottle.exec_claude(claude_args, tty=True)
-            info(
-                f"session ended (exit {exit_code}); "
-                f"container {bottle.name} will be removed"
-            )
-            # While the container is still alive: always snapshot the
-            # transcript and — if the agent exited non-zero — mark
-            # the state for preservation. Capability-block already
-            # did both before triggering teardown from the dashboard;
-            # this picks up crashes / Ctrl-Cs / OOM kills the same
-            # way. snapshot_transcript is best-effort so the
-            # capability-block path's prior snapshot isn't clobbered
-            # when the container is already gone.
-            _capture_session_state(identity, exit_code)
-        return 0
-    finally:
-        # PRD 0018 chunk 2: prepare now writes the bottle's bind-mount
-        # sources under state/<slug>/. If we never reached the
-        # launch context (dry-run, preflight-N, prepare exception), or
-        # we did but nothing requested preservation, reap them along
-        # with everything else. _settle_state subsumes the prior
-        # post-launch settlement and the new pre-launch cleanup.
-        _settle_state(identity)
-        shutil.rmtree(stage_dir, ignore_errors=True)
+    Used as the inner step of `./cli.py start` (one-shot) and by the
+    dashboard (PRD 0020), which calls it from inside a `curses.endwin
+    → … → stdscr.refresh()` handoff so the curses surface gets out
+    of the terminal's way while claude has it."""
+    info(
+        "attaching interactive claude session "
+        "(Ctrl-D or 'exit' to leave; container will be removed)"
+    )
+    claude_args = ["--dangerously-skip-permissions"]
+    if remote_control:
+        claude_args.append("--remote-control")
+    return bottle.exec_claude(claude_args, tty=True)
 
 
-def _capture_session_state(identity: str, exit_code: int) -> None:
+def capture_session_state(identity: str, exit_code: int) -> None:
     """Inside the launch context, while the container is still
     alive: snapshot the transcript and mark for preservation if
-    claude crashed. Pure-function-ish; tests stub the helpers."""
+    claude crashed. Public for the dashboard's death-handling path
+    (PRD 0020 open question 3)."""
     if not identity:
         return
     snapshot_transcript(identity)
@@ -125,7 +123,11 @@ def _capture_session_state(identity: str, exit_code: int) -> None:
         mark_preserved(identity)
 
 
-def _settle_state(identity: str) -> None:
+def settle_state(identity: str) -> None:
+    """Post-teardown housekeeping: print the resume hint if the
+    state was preserved, otherwise reap the per-bottle state dir.
+    Public so the dashboard's explicit-stop path calls the same
+    settlement the CLI uses on context exit."""
     if not identity:
         return
     if is_preserved(identity):
@@ -140,3 +142,68 @@ def _identity_from_plan(plan: object) -> str:
     identity attribute; for now we duck-type to keep this layer
     backend-agnostic."""
     return getattr(plan, "slug", "")
+
+
+def _text_prompt_yes() -> bool:
+    """Default `prompt_yes` for CLI use: reads y/N from the
+    controlling tty via stderr prompt + tty-line read."""
+    sys.stderr.write("claude-bottle: launch this agent? [y/N] ")
+    sys.stderr.flush()
+    reply = read_tty_line()
+    return reply in ("y", "Y", "yes", "YES")
+
+
+def _text_render_preflight(*, remote_control: bool):
+    def _render(plan: DockerBottlePlan) -> None:
+        plan.print(remote_control=remote_control)
+    return _render
+
+
+def _launch_bottle(
+    spec: BottleSpec,
+    *,
+    dry_run: bool,
+    remote_control: bool,
+) -> int:
+    """Shared launch core for `start` and `resume`. Builds the plan,
+    prints / dry-runs / prompts as appropriate, brings the bottle up,
+    attaches claude, and prints the resume hint on session end."""
+    stage_dir = Path(tempfile.mkdtemp(prefix="claude-bottle-stage."))
+    identity = ""
+    try:
+        plan, identity = prepare_with_preflight(
+            spec,
+            stage_dir=stage_dir,
+            render_preflight=_text_render_preflight(remote_control=remote_control),
+            prompt_yes=_text_prompt_yes,
+            dry_run=dry_run,
+        )
+        if plan is None:
+            return 0
+
+        backend = get_bottle_backend()
+        with backend.launch(plan) as bottle:
+            exit_code = attach_claude(bottle, remote_control=remote_control)
+            info(
+                f"session ended (exit {exit_code}); "
+                f"container {bottle.name} will be removed"
+            )
+            # While the container is still alive: always snapshot the
+            # transcript and — if the agent exited non-zero — mark
+            # the state for preservation. Capability-block already
+            # did both before triggering teardown from the dashboard;
+            # this picks up crashes / Ctrl-Cs / OOM kills the same
+            # way. snapshot_transcript is best-effort so the
+            # capability-block path's prior snapshot isn't clobbered
+            # when the container is already gone.
+            capture_session_state(identity, exit_code)
+        return 0
+    finally:
+        # PRD 0018 chunk 2: prepare now writes the bottle's bind-mount
+        # sources under state/<slug>/. If we never reached the
+        # launch context (dry-run, preflight-N, prepare exception), or
+        # we did but nothing requested preservation, reap them along
+        # with everything else. `settle_state` subsumes the prior
+        # post-launch settlement and the new pre-launch cleanup.
+        settle_state(identity)
+        shutil.rmtree(stage_dir, ignore_errors=True)

tests/unit/test_cli_start_settle.py

@@ -45,25 +45,25 @@ class TestCaptureSessionState(_FakeHomeMixin, unittest.TestCase):
         self._teardown_fake_home()
 
     def test_clean_exit_snapshots_but_does_not_mark(self):
-        start_mod._capture_session_state("dev-abc", exit_code=0)
+        start_mod.capture_session_state("dev-abc", exit_code=0)
         self.assertEqual(["dev-abc"], self._snap_calls)
         self.assertFalse(bottle_state.is_preserved("dev-abc"))
 
     def test_crash_snapshots_and_marks(self):
-        start_mod._capture_session_state("dev-abc", exit_code=137)
+        start_mod.capture_session_state("dev-abc", exit_code=137)
         self.assertEqual(["dev-abc"], self._snap_calls)
         self.assertTrue(bottle_state.is_preserved("dev-abc"))
 
     def test_ctrl_c_treated_as_crash(self):
         # SIGINT delivers exit 130; the operator may have Ctrl-C'd
         # because something went wrong, so we preserve.
-        start_mod._capture_session_state("dev-abc", exit_code=130)
+        start_mod.capture_session_state("dev-abc", exit_code=130)
         self.assertTrue(bottle_state.is_preserved("dev-abc"))
 
     def test_empty_identity_is_noop(self):
         # Backends without an identity field shouldn't crash this
         # path (the _identity_from_plan helper falls back to "").
-        start_mod._capture_session_state("", exit_code=137)
+        start_mod.capture_session_state("", exit_code=137)
         self.assertEqual([], self._snap_calls)
 
 
@@ -77,16 +77,16 @@ class TestSettleState(_FakeHomeMixin, unittest.TestCase):
     def test_preserved_state_survives(self):
         bottle_state.write_per_bottle_dockerfile("dev-abc", "FROM x\n")
         bottle_state.mark_preserved("dev-abc")
-        start_mod._settle_state("dev-abc")
+        start_mod.settle_state("dev-abc")
         self.assertTrue(bottle_state.bottle_state_dir("dev-abc").is_dir())
 
     def test_unpreserved_state_is_cleaned(self):
         bottle_state.write_per_bottle_dockerfile("dev-abc", "FROM x\n")
-        start_mod._settle_state("dev-abc")
+        start_mod.settle_state("dev-abc")
         self.assertFalse(bottle_state.bottle_state_dir("dev-abc").exists())
 
     def test_empty_identity_is_noop(self):
-        start_mod._settle_state("")  # should not raise
+        start_mod.settle_state("")  # should not raise
 
 
 if __name__ == "__main__":