refactor: rename platform abstraction to backend

Across the package:
  - claude_bottle/platform/         -> claude_bottle/backend/
  - platform/docker/platform.py     -> backend/docker/backend.py
  - class BottlePlatform            -> BottleBackend
  - class DockerBottlePlatform      -> DockerBottleBackend
  - get_bottle_platform()           -> get_bottle_backend()
  - env var CLAUDE_BOTTLE_PLATFORM  -> CLAUDE_BOTTLE_BACKEND
  - dict _PLATFORMS                 -> _BACKENDS

"Backend" is shorter and more established as the term for a
pluggable strategy-pattern implementation. "Platform" was vague
(could mean OS, hardware, cloud) and mildly redundant — Docker is
itself a platform.

The previous PRD section claiming "the Backend protocol was
rejected" referred to a low-level run/exec/cp/network_connect
protocol; the name was never the reason. The PRD is updated to
describe that rejected design by shape rather than by name.

The bottle/agent concepts and the manifest schema are unchanged.

claude_bottle/backend/__init__.py

@@ -1,7 +1,7 @@
-"""Per-platform bottle factories.
+"""Per-backend bottle factories.
 
 A bottle is a running, isolated environment with claude inside. Each
-platform exposes four methods:
+backend exposes five methods:
 
   prepare(spec, stage_dir=...) -> BottlePlan
       Resolves names, validates host-side prerequisites, and writes
@@ -19,8 +19,11 @@ platform exposes four methods:
   cleanup(plan) -> None
       Actually removes everything described by the cleanup plan.
 
-Selection is driven by CLAUDE_BOTTLE_PLATFORM (default "docker"). Per
-PRD 0003 the manifest does not carry a platform field; the host
+  list_active() -> None
+      Print every currently-running bottle on this backend to stderr.
+
+Selection is driven by CLAUDE_BOTTLE_BACKEND (default "docker"). Per
+PRD 0003 the manifest does not carry a backend field; the host
 environment picks.
 """
 
@@ -38,8 +41,8 @@ from ..manifest import Manifest
 
 @dataclass(frozen=True)
 class BottleSpec:
-    """CLI-supplied intent. Platform-agnostic — each platform's prepare
-    step consumes it and produces its own platform-specific plan.
+    """CLI-supplied intent. Backend-agnostic — each backend's prepare
+    step consumes it and produces its own backend-specific plan.
     Resolved values (image names, container name, scratch paths, runsc
     availability) live on the plan, not the spec."""
 
@@ -52,8 +55,8 @@ class BottleSpec:
 
 @dataclass(frozen=True)
 class BottlePlan(ABC):
-    """Base output of a platform's prepare step. Concrete subclasses
-    (e.g. DockerBottlePlan) add platform-specific resolved fields and
+    """Base output of a backend's prepare step. Concrete subclasses
+    (e.g. DockerBottlePlan) add backend-specific resolved fields and
     implement `print`."""
 
     spec: BottleSpec
@@ -66,8 +69,8 @@ class BottlePlan(ABC):
 
 @dataclass(frozen=True)
 class BottleCleanupPlan(ABC):
-    """Base output of a platform's prepare_cleanup step. Concrete
-    subclasses (e.g. DockerBottleCleanupPlan) carry platform-specific
+    """Base output of a backend's prepare_cleanup step. Concrete
+    subclasses (e.g. DockerBottleCleanupPlan) carry backend-specific
     lists of resources to be removed and implement `print` + `empty`."""
 
     @abstractmethod
@@ -82,7 +85,7 @@ class BottleCleanupPlan(ABC):
 
 
 class Bottle(ABC):
-    """Handle to a running bottle. Yielded by a platform's launch step.
+    """Handle to a running bottle. Yielded by a backend's launch step.
 
     `exec_claude` runs `claude` inside the bottle and blocks until the
     session ends. `cp_in` copies a host path into the bottle. `close`
@@ -101,9 +104,9 @@ class Bottle(ABC):
     def close(self) -> None: ...
 
 
-class BottlePlatform(ABC):
-    """Abstract base for selectable bottle platforms. Concrete subclasses
-    (e.g. DockerBottlePlatform) own their own prepare/launch impls.
+class BottleBackend(ABC):
+    """Abstract base for selectable bottle backends. Concrete subclasses
+    (e.g. DockerBottleBackend) own their own prepare/launch impls.
     Symmetric with the BottlePlan → DockerBottlePlan hierarchy."""
 
     name: str
@@ -128,37 +131,37 @@ class BottlePlatform(ABC):
 
     @abstractmethod
     def list_active(self) -> None:
-        """Print every currently-running bottle on this platform to
+        """Print every currently-running bottle on this backend to
         stderr (name + status)."""
 
 
-# Import concrete platform classes AFTER the base types are defined, so
-# each platform module can pull BottleSpec / BottlePlan / BottlePlatform
+# Import concrete backend classes AFTER the base types are defined, so
+# each backend module can pull BottleSpec / BottlePlan / BottleBackend
 # via `from . import ...` without hitting a partially-initialized module.
-from .docker import DockerBottlePlatform  # noqa: E402
+from .docker import DockerBottleBackend  # noqa: E402
 
 
-_PLATFORMS: dict[str, BottlePlatform] = {
-    "docker": DockerBottlePlatform(),
+_BACKENDS: dict[str, BottleBackend] = {
+    "docker": DockerBottleBackend(),
 }
 
 
-def get_bottle_platform() -> BottlePlatform:
-    """Resolve the bottle platform for the active environment. Dies with
-    a pointer at the known platforms if CLAUDE_BOTTLE_PLATFORM names an
+def get_bottle_backend() -> BottleBackend:
+    """Resolve the bottle backend for the active environment. Dies with
+    a pointer at the known backends if CLAUDE_BOTTLE_BACKEND names an
     unimplemented one."""
-    name = os.environ.get("CLAUDE_BOTTLE_PLATFORM", "docker")
-    if name not in _PLATFORMS:
-        known = ", ".join(sorted(_PLATFORMS))
-        die(f"unknown CLAUDE_BOTTLE_PLATFORM={name!r}; known platforms: {known}")
-    return _PLATFORMS[name]
+    name = os.environ.get("CLAUDE_BOTTLE_BACKEND", "docker")
+    if name not in _BACKENDS:
+        known = ", ".join(sorted(_BACKENDS))
+        die(f"unknown CLAUDE_BOTTLE_BACKEND={name!r}; known backends: {known}")
+    return _BACKENDS[name]
 
 
 __all__ = [
     "Bottle",
+    "BottleBackend",
     "BottleCleanupPlan",
     "BottlePlan",
-    "BottlePlatform",
     "BottleSpec",
-    "get_bottle_platform",
+    "get_bottle_backend",
 ]

claude_bottle/backend/docker/__init__.py

@@ -1,28 +1,29 @@
-"""Docker bottle platform.
+"""Docker bottle backend.
 
 The bulk of the implementation lives in sibling modules:
 
   - util:                 thin Docker subprocess wrappers
+  - network:              Docker network plumbing
   - bottle_plan:          DockerBottlePlan
   - bottle_cleanup_plan:  DockerBottleCleanupPlan
   - bottle:               DockerBottle handle
-  - platform:             DockerBottlePlatform
+  - backend:              DockerBottleBackend
 
 This file only re-exports the public names so
-`from claude_bottle.platform.docker import DockerBottlePlatform` keeps
+`from claude_bottle.backend.docker import DockerBottleBackend` keeps
 working.
 """
 
 from __future__ import annotations
 
+from .backend import DockerBottleBackend
 from .bottle import DockerBottle
 from .bottle_cleanup_plan import DockerBottleCleanupPlan
 from .bottle_plan import DockerBottlePlan
-from .platform import DockerBottlePlatform
 
 __all__ = [
     "DockerBottle",
+    "DockerBottleBackend",
     "DockerBottleCleanupPlan",
     "DockerBottlePlan",
-    "DockerBottlePlatform",
 ]

claude_bottle/backend/docker/backend.py

@@ -1,4 +1,4 @@
-"""DockerBottlePlatform — the Docker implementation of BottlePlatform.
+"""DockerBottleBackend — the Docker implementation of BottleBackend.
 
 Methods:
   .prepare(spec, stage_dir=...) -> DockerBottlePlan
@@ -22,7 +22,7 @@ from ... import skills as skills_mod
 from ... import ssh as ssh_mod
 from ...env_resolve import env_resolve
 from ...log import die, info
-from .. import BottleCleanupPlan, BottlePlan, BottlePlatform, BottleSpec
+from .. import BottleBackend, BottleCleanupPlan, BottlePlan, BottleSpec
 from . import network as network_mod
 from . import util as docker_mod
 from .bottle import DockerBottle
@@ -34,8 +34,8 @@ from .bottle_plan import DockerBottlePlan
 _REPO_DIR = str(Path(__file__).resolve().parent.parent.parent.parent)
 
 
-class DockerBottlePlatform(BottlePlatform):
-    """Docker platform implementation. Selected by CLAUDE_BOTTLE_PLATFORM
+class DockerBottleBackend(BottleBackend):
+    """Docker backend implementation. Selected by CLAUDE_BOTTLE_BACKEND
     (default)."""
 
     name = "docker"
@@ -131,7 +131,7 @@ class DockerBottlePlatform(BottlePlatform):
     def launch(self, plan: BottlePlan) -> Iterator[DockerBottle]:
         """Build, launch, and provision a Docker bottle. Teardown on exit."""
         assert isinstance(plan, DockerBottlePlan), (
-            f"DockerBottlePlatform.launch expects DockerBottlePlan, "
+            f"DockerBottleBackend.launch expects DockerBottlePlan, "
             f"got {type(plan).__name__}"
         )
 
@@ -358,7 +358,7 @@ class DockerBottlePlatform(BottlePlatform):
         Containers first; networks would refuse to delete while
         containers are still attached."""
         assert isinstance(plan, DockerBottleCleanupPlan), (
-            f"DockerBottlePlatform.cleanup expects DockerBottleCleanupPlan, "
+            f"DockerBottleBackend.cleanup expects DockerBottleCleanupPlan, "
             f"got {type(plan).__name__}"
         )
         for name in plan.containers:

claude_bottle/backend/docker/bottle.py

@@ -1,5 +1,5 @@
 """DockerBottle — concrete Bottle handle yielded by
-DockerBottlePlatform.launch.
+DockerBottleBackend.launch.
 
 Holds the container name plus the in-container prompt path so
 exec_claude can transparently add --append-system-prompt-file when a

claude_bottle/backend/docker/bottle_cleanup_plan.py

@@ -1,7 +1,7 @@
 """DockerBottleCleanupPlan — concrete subclass of BottleCleanupPlan.
 
 Holds the tuples of container and network names that
-DockerBottlePlatform.cleanup will remove. The y/N preflight reads
+DockerBottleBackend.cleanup will remove. The y/N preflight reads
 these via `print`; the CLI short-circuits via `empty`.
 """
 
@@ -16,7 +16,7 @@ from .. import BottleCleanupPlan
 
 @dataclass(frozen=True)
 class DockerBottleCleanupPlan(BottleCleanupPlan):
-    """Resources DockerBottlePlatform.cleanup will remove. Produced by
+    """Resources DockerBottleBackend.cleanup will remove. Produced by
     `prepare_cleanup` from a snapshot of `docker ps -a` + `docker
     network ls`; sorted so the y/N output is stable."""
 

claude_bottle/backend/docker/bottle_plan.py

@@ -1,7 +1,7 @@
 """DockerBottlePlan — concrete subclass of BottlePlan.
 
 Carries the Docker-specific resolved fields produced by
-DockerBottlePlatform.prepare. The launch step consumes it without
+DockerBottleBackend.prepare. The launch step consumes it without
 further resolution; show_plan-style rendering is the `print` method.
 """
 
@@ -18,7 +18,7 @@ from .. import BottlePlan
 @dataclass(frozen=True)
 class DockerBottlePlan(BottlePlan):
     """Docker-specific resolved fields produced by
-    DockerBottlePlatform.prepare. Inherits `spec` and `stage_dir` from
+    DockerBottleBackend.prepare. Inherits `spec` and `stage_dir` from
     BottlePlan."""
 
     slug: str

claude_bottle/backend/docker/util.py

@@ -1,4 +1,4 @@
-"""Docker host-side primitives used by DockerBottlePlatform: probing
+"""Docker host-side primitives used by DockerBottleBackend: probing
 for docker on PATH, slugifying agent names, checking image/container
 existence, and building images."""
 

claude_bottle/cli/cleanup.py

@@ -5,14 +5,14 @@ from __future__ import annotations
 
 import sys
 
-from ..platform import get_bottle_platform
+from ..backend import get_bottle_backend
 from ..log import info
 from ._common import read_tty_line
 
 
 def cmd_cleanup(_argv: list[str]) -> int:
-    platform = get_bottle_platform()
-    plan = platform.prepare_cleanup()
+    backend = get_bottle_backend()
+    plan = backend.prepare_cleanup()
 
     if plan.empty:
         info("no claude-bottle resources to clean up")
@@ -26,6 +26,6 @@ def cmd_cleanup(_argv: list[str]) -> int:
         info("aborted")
         return 0
 
-    platform.cleanup(plan)
+    backend.cleanup(plan)
     info("done")
     return 0

claude_bottle/cli/list.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 import argparse
 
-from ..platform import get_bottle_platform
+from ..backend import get_bottle_backend
 from ..manifest import Manifest
 from ._common import PROG, USER_CWD
 
@@ -20,5 +20,5 @@ def cmd_list(argv: list[str]) -> int:
             print(name)
         return 0
 
-    get_bottle_platform().list_active()
+    get_bottle_backend().list_active()
     return 0

claude_bottle/cli/start.py

@@ -11,7 +11,7 @@ import sys
 import tempfile
 from pathlib import Path
 
-from ..platform import BottleSpec, get_bottle_platform
+from ..backend import BottleSpec, get_bottle_backend
 from ..log import info
 from ..manifest import Manifest
 from ._common import PROG, USER_CWD, read_tty_line
@@ -38,8 +38,8 @@ def cmd_start(argv: list[str]) -> int:
 
     stage_dir = Path(tempfile.mkdtemp(prefix="claude-bottle-stage."))
     try:
-        platform = get_bottle_platform()
-        plan = platform.prepare(spec, stage_dir=stage_dir)
+        backend = get_bottle_backend()
+        plan = backend.prepare(spec, stage_dir=stage_dir)
         plan.print(remote_control=args.remote_control)
 
         if dry_run:
@@ -53,7 +53,7 @@ def cmd_start(argv: list[str]) -> int:
             info("aborted by user")
             return 0
 
-        with platform.launch(plan) as bottle:
+        with backend.launch(plan) as bottle:
             info(
                 "attaching interactive claude session "
                 "(Ctrl-D or 'exit' to leave; container will be removed)"

docs/prds/0003-bottle-factory-abstraction.md

@@ -6,10 +6,10 @@
 
 ## Summary
 
-Introduce a per-platform factory function that owns the end-to-end
+Introduce a per-backend factory function that owns the end-to-end
 lifecycle of a "bottle" (a running, isolated environment with claude
 inside). The first and only implementation lands as
-`create_docker_bottle`. No second platform ships in this PRD.
+`create_docker_bottle`. No second backend ships in this PRD.
 
 ## Problem
 
@@ -33,11 +33,11 @@ Today, "how to launch a bottle" is spread across roughly six modules
   and exists only because the current code can't decide on its own.
 
 The shape that fits the project's actual goals (isolated agent runs
-across multiple platforms) is "one factory per platform," not "one
+across multiple backends) is "one factory per backend," not "one
 container-runtime SDK with N drivers." A previous draft of this PRD
-considered a low-level `Backend` protocol (`run`, `exec`, `cp`,
-`network_connect`, ...) and rejected it as the wrong layer — it would
-have forced fly.io to pretend it's Docker.
+considered a low-level runtime-primitive protocol (`run`, `exec`,
+`cp`, `network_connect`, ...) and rejected it as the wrong layer —
+it would have forced fly.io to pretend it's Docker.
 
 ## Goals / Success Criteria
 
@@ -57,7 +57,7 @@ The feature works when all of the following are observable:
 
 The feature is **done** when all of the following ship:
 
-- A new `claude_bottle/bottles/` package exists with
+- A new `claude_bottle/backend/` package exists with
   `__init__.py` (factory selection) and `docker.py`
   (`create_docker_bottle`).
 - `create_docker_bottle` returns a context manager yielding a `Bottle`
@@ -65,23 +65,23 @@ The feature is **done** when all of the following ship:
   and teardown on context exit.
 - Every existing `subprocess.run(["docker", ...])` call in
   `cli/start.py`, `pipelock.py`, `network.py`, `ssh.py`, and
-  `skills.py` either moves into `bottles/docker.py` or is called from
+  `skills.py` either moves into `backend/docker.py` or is called from
   it. No top-level CLI code references `docker` directly.
 - `bottles[].runtime` is removed from the manifest schema, the
   dataclass in `manifest.py`, the example manifest, and any README /
   docs references. `require_runsc()` in `claude_bottle/docker.py` is
   deleted.
-- A single env var, `CLAUDE_BOTTLE_PLATFORM` (default `"docker"`),
+- A single env var, `CLAUDE_BOTTLE_BACKEND` (default `"docker"`),
   selects the factory. Unknown values die at startup with a list of
-  known platforms.
+  known backends.
 - The y/N preflight in `cli.py` includes the resolved Docker runtime
   alongside the allowlist summary.
 
 ## Non-goals
 
-- No second platform implementation. `create_container_bottle` and
+- No second backend implementation. `create_container_bottle` and
   `create_flyio_bottle` are not in this PRD. The factory dict in
-  `bottles/__init__.py` ships with one entry.
+  `backend/__init__.py` ships with one entry.
 - No retries, async, or streaming exec. The current code is
   synchronous `subprocess.run`; the `Bottle` handle matches.
 - No behavior change beyond the runsc auto-detect. Pipelock topology,
@@ -89,14 +89,14 @@ The feature is **done** when all of the following ship:
   provisioning all stay byte-identical.
 - No `--require-runsc` CLI escape hatch. If a user later wants "fail
   rather than silently downgrade," that's a follow-up.
-- No `bottles[].platform` manifest field. Platform is a property of
+- No `bottles[].backend` manifest field. Backend is a property of
   the host environment, not the bottle definition (at least for now).
 
 ## Scope
 
 ### In scope
 
-- New `claude_bottle/bottles/` package containing `__init__.py` and
+- New `claude_bottle/backend/` package containing `__init__.py` and
   `docker.py`.
 - The `Bottle` Protocol definition and `create_docker_bottle` factory.
 - Moving Docker-specific subprocess calls into the factory.
@@ -113,9 +113,9 @@ The feature is **done** when all of the following ship:
 
 - Apple `container` and fly.io factories (separate PRDs, deferred
   until the Docker factory is the only thing shipping).
-- Generalizing the pipelock sidecar to other platforms. Pipelock
+- Generalizing the pipelock sidecar to other backends. Pipelock
   topology is, after this PRD, an implementation detail private to
-  `bottles/docker.py`.
+  `backend/docker.py`.
 - Rewriting `pipelock.py`'s YAML generation. The allowlist→YAML
   translation stays where it is and is called by the Docker factory.
 - Changes to `env_resolve.py`, `manifest.py` (beyond the `runtime`
@@ -126,13 +126,13 @@ The feature is **done** when all of the following ship:
 
 ### New services / components
 
-A new package, `claude_bottle/bottles/`:
+A new package, `claude_bottle/backend/`:
 
-- **`claude_bottle/bottles/__init__.py`** — Defines the `Bottle`
+- **`claude_bottle/backend/__init__.py`** — Defines the `Bottle`
   Protocol and `get_bottle_factory()`. The factory registry is a
-  module-level dict mapping platform name → factory function.
-  Selection reads `CLAUDE_BOTTLE_PLATFORM` (default `"docker"`).
-  Unknown values call `die()` with the list of known platforms.
+  module-level dict mapping backend name → factory function.
+  Selection reads `CLAUDE_BOTTLE_BACKEND` (default `"docker"`).
+  Unknown values call `die()` with the list of known backends.
 
   ```python
   class Bottle(Protocol):
@@ -145,7 +145,7 @@ A new package, `claude_bottle/bottles/`:
       ...
   ```
 
-- **`claude_bottle/bottles/docker.py`** — `create_docker_bottle(...)`,
+- **`claude_bottle/backend/docker.py`** — `create_docker_bottle(...)`,
   the only factory implementation in this PRD. Owns:
   - probing for `runsc` availability (`docker info --format
     '{{json .Runtimes}}'`),
@@ -178,19 +178,19 @@ A new package, `claude_bottle/bottles/`:
   consumes.
 - **`claude_bottle/pipelock.py`** — keep all the allowlist resolution
   and YAML generation. Remove `pipelock_start` / `pipelock_stop` (or
-  inline them into `bottles/docker.py` — decide during
+  inline them into `backend/docker.py` — decide during
   implementation). Pipelock-the-sidecar becomes a Docker-factory
   internal concept.
 - **`claude_bottle/network.py`** — same call-sites moved into
-  `bottles/docker.py`. The module either becomes a thin set of pure
+  `backend/docker.py`. The module either becomes a thin set of pure
   name-derivation helpers (`network_name_for_slug`, etc.) or folds
-  entirely into `bottles/docker.py`. Decide during implementation.
+  entirely into `backend/docker.py`. Decide during implementation.
 - **`claude_bottle/ssh.py`** and **`claude_bottle/skills.py`** — the
   `docker cp` and `docker exec` calls move into / are called from
-  `bottles/docker.py`. The host-side file-tree generation stays put.
+  `backend/docker.py`. The host-side file-tree generation stays put.
 - **`claude-bottle.example.json`** — remove the `runtime` field from
   any example bottle.
-- **`README.md`** — note `CLAUDE_BOTTLE_PLATFORM` and the runsc
+- **`README.md`** — note `CLAUDE_BOTTLE_BACKEND` and the runsc
   auto-detect; remove any mention of `runtime: "runsc"` as a manifest
   field.
 
@@ -241,9 +241,9 @@ they're about to run under before approving.
 
 - **Where the pipelock sidecar lifecycle lives.** Two reasonable
   splits: (a) `pipelock.py` keeps `pipelock_start` / `pipelock_stop`
-  and `bottles/docker.py` calls them; (b) the sidecar
+  and `backend/docker.py` calls them; (b) the sidecar
   `docker create/cp/network connect/start` sequence moves entirely
-  into `bottles/docker.py` and `pipelock.py` shrinks to the YAML +
+  into `backend/docker.py` and `pipelock.py` shrinks to the YAML +
   allowlist helpers. (a) keeps git blame intact and is the smaller
   diff; (b) makes pipelock-as-an-implementation-detail more obvious.
   Decide during implementation.

tests/test_orphan_cleanup.py

@@ -7,7 +7,7 @@ import os
 import subprocess
 import unittest
 
-from claude_bottle.platform.docker.network import (
+from claude_bottle.backend.docker.network import (
     network_create_egress,
     network_create_internal,
     network_remove,