refactor(bottles): rename DockerBottleSpec to BottleSpec

The spec is intent-only and platform-agnostic — only the plan carries
Docker-specific fields. Drop the 'Docker' prefix and re-export from
claude_bottle.bottles so callers see it as cross-platform.

claude_bottle/bottles/__init__.py

@@ -25,7 +25,9 @@ from dataclasses import dataclass
 from typing import Callable, Protocol
 
 from ..log import die
-from .docker import launch_docker_bottle, prepare_docker_bottle
+from .docker import BottleSpec, launch_docker_bottle, prepare_docker_bottle
+
+__all__ = ["Bottle", "BottlePlatform", "BottleSpec", "get_bottle_platform"]
 
 
 class Bottle(Protocol):

claude_bottle/bottles/docker.py

@@ -55,10 +55,11 @@ def runsc_available() -> bool:
 
 
 @dataclass(frozen=True)
-class DockerBottleSpec:
-    """CLI-supplied inputs to the Docker factory. Small and intent-only;
-    everything else (image names, container name, scratch file paths,
-    runsc availability) is resolved by prepare_docker_bottle."""
+class BottleSpec:
+    """CLI-supplied intent. Platform-agnostic — each platform's prepare
+    step consumes it and produces its own platform-specific plan.
+    Resolved values (image names, container name, scratch paths, runsc
+    availability) live on the plan, not the spec."""
 
     manifest: Manifest
     agent_name: str
@@ -72,7 +73,7 @@ class DockerBottlePlan:
     """Output of prepare_docker_bottle. Frozen; the launch step consumes
     it without further resolution. show_plan reads from it directly."""
 
-    spec: DockerBottleSpec
+    spec: BottleSpec
     slug: str
     container_name: str
     container_name_pinned: bool
@@ -130,7 +131,7 @@ class _DockerBottle:
 # --- Prepare ---------------------------------------------------------------
 
 
-def prepare_docker_bottle(spec: DockerBottleSpec, *, stage_dir: Path) -> DockerBottlePlan:
+def prepare_docker_bottle(spec: BottleSpec, *, stage_dir: Path) -> DockerBottlePlan:
     """Resolve names, validate, write scratch files. No Docker resources
     are created; the only side effects are host-side files under
     stage_dir and a probe of `docker info`."""

claude_bottle/cli/start.py

@@ -11,8 +11,8 @@ import sys
 import tempfile
 from pathlib import Path
 
-from ..bottles import get_bottle_platform
-from ..bottles.docker import DockerBottlePlan, DockerBottleSpec
+from ..bottles import BottleSpec, get_bottle_platform
+from ..bottles.docker import DockerBottlePlan
 from ..log import info
 from ..manifest import Manifest
 from ._common import PROG, USER_CWD, read_tty_line
@@ -72,7 +72,7 @@ def cmd_start(argv: list[str]) -> int:
     dry_run = args.dry_run or os.environ.get("CLAUDE_BOTTLE_DRY_RUN") == "1"
 
     manifest = Manifest.resolve(USER_CWD)
-    spec = DockerBottleSpec(
+    spec = BottleSpec(
         manifest=manifest,
         agent_name=args.name,
         copy_cwd=args.cwd,