refactor(backend): extract shared bottle preparation planner

bot_bottle/backend/base.py

@@ -23,14 +23,14 @@ from dataclasses import dataclass
 from pathlib import Path
 from typing import Generator, Generic, Sequence, TypeVar
 
-from ..agent_provider import AgentProvisionPlan, get_provider, build_agent_provision_plan
+from ..agent_provider import AgentProvisionPlan, get_provider
 from ..egress import EgressPlan
 from ..git_gate import GitGatePlan
 from ..log import die, info
 from ..util import expand_tilde
 from ..manifest import Manifest, ManifestIndex
 from ..supervisor.plan import SupervisePlan
-from ..env import resolve_env, ResolvedEnv
+from ..env import ResolvedEnv
 from ..workspace import WorkspacePlan, workspace_plan
 from .print_util import print_multi, visible_agent_env_names
 from .util import host_skill_dir
@@ -296,82 +296,18 @@ class BottleBackend(ABC, Generic[PlanT, CleanupT]):
         backend-specific resolution (names, scratch files, etc.). The
         validation step is enforced here so a future backend cannot
         accidentally skip it. No remote/runtime resources are created."""
-        from .resolve_common import (
+        from .preparation import BottlePreparationPlanner
-            merge_provision_env_vars,
+        prepared = BottlePreparationPlanner(self).prepare(spec)
-            mint_slug,
-            prepare_agent_state_dir,
-            prepare_egress,
-            prepare_git_gate,
-            prepare_supervise,
-            reject_nested_containers,
-            resolve_manifest_dockerfile,
-            write_launch_metadata,
-        )
-
-        manifest = self._validate(spec)
-
-        if not self.supports_nested_containers:
-            reject_nested_containers(self.name, manifest)
-
-        self._preflight()
-
-        from ..git_gate import GitGate
-        manifest = GitGate().preflight_host_keys(
-            manifest,
-            headless=spec.headless,
-            home_md=spec.manifest.home_md,
-        )
-
-        manifest_bottle = manifest.bottle
-        manifest_agent_provider = manifest_bottle.agent_provider
-        agent_provider = get_provider(manifest_agent_provider.template)
-        resolved_env = resolve_env(manifest)
-        workspace = workspace_plan(spec, guest_home=agent_provider.guest_home)
-
-        slug = mint_slug(spec)
-        write_launch_metadata(slug, spec, compose_project="", backend=self.name)
-
-        # Manifest may override the Dockerfile per-bottle; otherwise fall
-        # back to the provider plugin's bundled Dockerfile (next to its
-        # agent_provider.py module).
-        if manifest_agent_provider.dockerfile:
-            agent_dockerfile_path = resolve_manifest_dockerfile(
-                manifest_agent_provider.dockerfile, spec,
-            )
-        else:
-            agent_dockerfile_path = str(agent_provider.dockerfile)
-
-        agent_dir, prompt_file = prepare_agent_state_dir(slug, manifest)
-
-        agent_provision_plan = build_agent_provision_plan(
-            template=manifest_agent_provider.template,
-            dockerfile=agent_dockerfile_path,
-            state_dir=agent_dir,
-            instance_name=f"bot-bottle-{slug}",
-            prompt_file=prompt_file,
-            guest_env=self._build_guest_env(resolved_env),
-            forward_host_credentials=manifest_agent_provider.forward_host_credentials,
-            auth_token=manifest_agent_provider.auth_token,
-            host_env=dict(os.environ),
-            trusted_project_path=workspace.workdir,
-            label=spec.label,
-            color=spec.color,
-            provider_settings=manifest_agent_provider.settings,
-        )
-        agent_provision_plan = merge_provision_env_vars(agent_provision_plan)
-        egress_plan = prepare_egress(manifest_bottle, slug, agent_provision_plan)
-        supervise_plan = prepare_supervise(manifest_bottle, slug)
-        git_gate_plan = prepare_git_gate(manifest_bottle, slug)
 
         return self._resolve_plan(
             spec,
-            manifest=manifest,
+            manifest=prepared.manifest,
-            slug=slug,
+            slug=prepared.slug,
-            resolved_env=resolved_env,
+            resolved_env=prepared.resolved_env,
-            agent_provision_plan=agent_provision_plan,
+            agent_provision_plan=prepared.agent_provision_plan,
-            egress_plan=egress_plan,
+            egress_plan=prepared.egress_plan,
-            supervise_plan=supervise_plan,
+            supervise_plan=prepared.supervise_plan,
-            git_gate_plan=git_gate_plan,
+            git_gate_plan=prepared.git_gate_plan,
             stage_dir=stage_dir,
         )
 

bot_bottle/backend/preparation.py

@@ -0,0 +1,119 @@
+"""Backend-neutral preparation planner.
+
+This module owns the shared transformation from a CLI ``BottleSpec`` to the
+typed inputs consumed by a concrete backend's ``_resolve_plan``. Backend
+classes retain only their validation/preflight/env hooks and their
+backend-specific final resolution.
+"""
+
+from __future__ import annotations
+
+import os
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, Protocol
+
+from ..agent_provider import AgentProvisionPlan, build_agent_provision_plan, get_provider
+from ..egress import EgressPlan
+from ..env import ResolvedEnv, resolve_env
+from ..git_gate import GitGate, GitGatePlan
+from ..manifest import Manifest
+from ..supervisor.plan import SupervisePlan
+from ..workspace import workspace_plan
+from .resolve_common import (
+    merge_provision_env_vars,
+    mint_slug,
+    prepare_agent_state_dir,
+    prepare_egress,
+    prepare_git_gate,
+    prepare_supervise,
+    reject_nested_containers,
+    resolve_manifest_dockerfile,
+    write_launch_metadata,
+)
+
+if TYPE_CHECKING:
+    from .base import BottleSpec
+
+
+class PreparationBackend(Protocol):
+    """Backend hooks needed by the shared planner."""
+
+    name: str
+    supports_nested_containers: bool
+
+    def _validate(self, spec: BottleSpec) -> Manifest: ...
+    def _preflight(self) -> None: ...
+    def _build_guest_env(self, resolved_env: ResolvedEnv) -> dict[str, str]: ...
+
+
+@dataclass(frozen=True)
+class PreparedBottle:
+    """Typed, backend-neutral result of shared launch preparation."""
+
+    manifest: Manifest
+    slug: str
+    resolved_env: ResolvedEnv
+    agent_provision_plan: AgentProvisionPlan
+    egress_plan: EgressPlan
+    git_gate_plan: GitGatePlan
+    supervise_plan: SupervisePlan | None
+
+
+class BottlePreparationPlanner:
+    """Run the common, side-effect-limited part of bottle preparation."""
+
+    def __init__(self, backend: PreparationBackend) -> None:
+        self._backend = backend
+
+    def prepare(self, spec: BottleSpec) -> PreparedBottle:
+        backend = self._backend
+        manifest = backend._validate(spec)
+        if not backend.supports_nested_containers:
+            reject_nested_containers(backend.name, manifest)
+
+        backend._preflight()
+        manifest = GitGate().preflight_host_keys(
+            manifest,
+            headless=spec.headless,
+            home_md=spec.manifest.home_md,
+        )
+
+        bottle = manifest.bottle
+        provider_config = bottle.agent_provider
+        provider = get_provider(provider_config.template)
+        resolved_env = resolve_env(manifest)
+        workspace = workspace_plan(spec, guest_home=provider.guest_home)
+        slug = mint_slug(spec)
+        write_launch_metadata(slug, spec, compose_project="", backend=backend.name)
+
+        dockerfile = (
+            resolve_manifest_dockerfile(provider_config.dockerfile, spec)
+            if provider_config.dockerfile
+            else str(provider.dockerfile)
+        )
+        agent_dir, prompt_file = prepare_agent_state_dir(slug, manifest)
+        provision = build_agent_provision_plan(
+            template=provider_config.template,
+            dockerfile=dockerfile,
+            state_dir=agent_dir,
+            instance_name=f"bot-bottle-{slug}",
+            prompt_file=prompt_file,
+            guest_env=backend._build_guest_env(resolved_env),
+            forward_host_credentials=provider_config.forward_host_credentials,
+            auth_token=provider_config.auth_token,
+            host_env=dict(os.environ),
+            trusted_project_path=workspace.workdir,
+            label=spec.label,
+            color=spec.color,
+            provider_settings=provider_config.settings,
+        )
+        provision = merge_provision_env_vars(provision)
+        return PreparedBottle(
+            manifest=manifest,
+            slug=slug,
+            resolved_env=resolved_env,
+            agent_provision_plan=provision,
+            egress_plan=prepare_egress(bottle, slug, provision),
+            git_gate_plan=prepare_git_gate(bottle, slug),
+            supervise_plan=prepare_supervise(bottle, slug),
+        )

tests/unit/test_architecture_guardrails.py

@@ -64,3 +64,16 @@ class TestRuntimeModuleSizes(unittest.TestCase):
                     ".addon_core import" in text:
                 violations.append(str(path.relative_to(ROOT)))
         self.assertEqual([], violations)
+
+    def test_backend_contract_does_not_absorb_preparation_logic(self) -> None:
+        caps = {
+            ROOT / "bot_bottle" / "backend" / "base.py": 580,
+            ROOT / "bot_bottle" / "backend" / "preparation.py": 160,
+        }
+        oversized = [
+            f"{path.relative_to(ROOT)} "
+            f"({len(path.read_text().splitlines())}>{cap})"
+            for path, cap in caps.items()
+            if len(path.read_text().splitlines()) > cap
+        ]
+        self.assertEqual([], oversized)