refactor(git-gate): make GitGate a service class in a git_gate package

Turn the git_gate module into a package with GitGate as a concrete service class
(dropping the ABC), mirroring the Supervisor shape. The host-side git-gate
operations are now methods the backend drives:

  git_gate/
    __init__.py  — thin __getattr__ facade (keeps `from bot_bottle.git_gate
                   import …` working; render/hook names lazily forwarded to
                   gateway.git_gate_render)
    plan.py      — GitGatePlan (the launch DTO the backend contract references)
    service.py   — GitGate: prepare / provision_dynamic_keys /
                   revoke_provisioned_keys / preflight_host_keys
    provision.py — deploy-key lifecycle (was git_gate_provision.py)
    host_key.py  — host-key preflight (was git_gate_host_key.py)

The backend launch + base.py preflight now call GitGate() methods instead of the
free functions. The runtime rendering / in-gateway hook execution stay in
gateway/git_gate_render.py (data plane) — only the host-side service moved.

Because the facade forwards names lazily, the ~25 `from bot_bottle.git_gate
import GitGatePlan` call-sites are unchanged, and importing git_gate.plan (the
contract's dependency) no longer drags in the provisioning / forge-API code.

Full unit suite green (2243).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot_bottle/git_gate/provision.py

@@ -0,0 +1,149 @@
+"""git-gate deploy-key lifecycle for `gitea` upstreams (PRD 0047/0048).
+
+Provisions a fresh ed25519 deploy key via the forge API at prepare time
+and revokes it at teardown, so the agent never holds an upstream
+credential. Split out of `git_gate.py`; the forge HTTP client is lazily
+imported (`deploy_key_provisioner`) to keep its cost off the host path.
+`git_gate` re-exports these names for API stability."""
+
+from __future__ import annotations
+
+import os
+import dataclasses
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+from ..bottle_state import globalize_slug
+from ..errors import MissingEnvVarError
+from ..log import info
+from ..manifest import ManifestBottle, ManifestGitEntry
+from ..gateway.git_gate_render import GitGateUpstream
+
+if TYPE_CHECKING:
+    from .plan import GitGatePlan
+
+def _provision_dynamic_key(
+    entry: ManifestGitEntry,
+    slug: str,
+    stage_dir: Path,
+) -> str:
+    """Generate a fresh ed25519 keypair, register the public half with
+    the forge, and persist the private key + key ID under `stage_dir`.
+
+    Returns the host-side path to the private key file so the caller
+    can inject it into the GitGateUpstream as `identity_file`."""
+    from ..deploy_key_provisioner import get_provisioner
+    pk = entry.Key
+    token = os.environ.get(pk.forge_token_env)
+    if token is None:
+        raise MissingEnvVarError(
+            pk.forge_token_env,
+            f"git-gate.repos[{entry.Name!r}] key.forge_token_env"
+            f" = {pk.forge_token_env!r}: env var is not set",
+        )
+    api_url = pk.api_url or f"https://{entry.UpstreamHost}"
+    provisioner = get_provisioner(pk.provider, token, api_url)
+
+    owner_repo = entry.UpstreamPath
+    if owner_repo.endswith(".git"):
+        owner_repo = owner_repo[:-4]
+    title = f"bot-bottle:{globalize_slug(slug)}:{entry.Name}"
+
+    info(f"provisioning deploy key for git-gate.repos[{entry.Name!r}]")
+    key_id, private_key_bytes = provisioner.create(owner_repo, title)
+
+    key_file = stage_dir / f"{entry.Name}-key"
+    key_file.write_bytes(private_key_bytes)
+    key_file.chmod(0o600)
+
+    id_file = stage_dir / f"{entry.Name}-deploy-key-id"
+    id_file.write_text(key_id)
+    id_file.chmod(0o600)
+
+    info(f"provisioned deploy key {key_id} for git-gate.repos[{entry.Name!r}]")
+    return str(key_file)
+
+
+def revoke_git_gate_provisioned_keys(bottle: ManifestBottle, stage_dir: Path) -> None:
+    """Revoke all deploy keys provisioned for `bottle` during prepare.
+
+    Called at teardown after containers stop. Raises if any revocation
+    fails — a stranded key is a security concern that the operator must
+    address manually."""
+    from ..deploy_key_provisioner import get_provisioner
+    for entry in bottle.git:
+        if entry.Key.provider != "gitea":
+            continue
+        pk = entry.Key
+        id_file = stage_dir / f"{entry.Name}-deploy-key-id"
+        if not id_file.exists():
+            continue
+        key_id = id_file.read_text().strip()
+        token = os.environ.get(pk.forge_token_env)
+        if token is None:
+            raise MissingEnvVarError(
+                pk.forge_token_env,
+                f"git-gate.repos[{entry.Name!r}] key.forge_token_env"
+                f" = {pk.forge_token_env!r}: env var is not set;"
+                f" cannot revoke deploy key {key_id}",
+            )
+        api_url = pk.api_url or f"https://{entry.UpstreamHost}"
+        provisioner = get_provisioner(pk.provider, token, api_url)
+        owner_repo = entry.UpstreamPath
+        if owner_repo.endswith(".git"):
+            owner_repo = owner_repo[:-4]
+        info(f"revoking deploy key {key_id} for git-gate.repos[{entry.Name!r}]")
+        provisioner.delete(owner_repo, key_id)
+        info(f"revoked deploy key {key_id} for git-gate.repos[{entry.Name!r}]")
+
+
+def _resolve_identity_file(entry: ManifestGitEntry, slug: str, stage_dir: Path) -> str:
+    """Return the host-side SSH identity file path for this entry.
+    For gitea entries, provisions a fresh deploy key first."""
+    if entry.Key.provider == "gitea":
+        return _provision_dynamic_key(entry, slug, stage_dir)
+    return entry.IdentityFile
+
+
+def provision_git_gate_dynamic_keys(
+    bottle: ManifestBottle,
+    plan: "GitGatePlan",
+    stage_dir: Path,
+) -> "GitGatePlan":
+    """Provision dynamic git-gate keys and return an updated plan.
+
+    This runs during backend launch, after the operator confirms the
+    preflight. Plan preparation intentionally stays side-effect-light:
+    dry-runs and aborted launches must not create remote deploy keys.
+    """
+    if not plan.upstreams:
+        return plan
+
+    upstreams_by_name: dict[str, GitGateUpstream] = {
+        upstream.name: upstream for upstream in plan.upstreams
+    }
+    updated: list[GitGateUpstream] = []
+    for entry in bottle.git:
+        upstream = upstreams_by_name.get(entry.Name)
+        if upstream is None:
+            continue
+        if entry.Key.provider == "gitea":
+            identity_file = _provision_dynamic_key(entry, plan.slug, stage_dir)
+            upstream = dataclasses.replace(upstream, identity_file=identity_file)
+        updated.append(upstream)
+
+    if len(updated) != len(plan.upstreams):
+        updated_names = {u.name for u in updated}
+        for upstream in plan.upstreams:
+            if upstream.name not in updated_names:
+                updated.append(upstream)
+
+    return dataclasses.replace(plan, upstreams=tuple(updated))
+
+
+__all__ = [
+    "revoke_git_gate_provisioned_keys",
+    "provision_git_gate_dynamic_keys",
+    "_provision_dynamic_key",
+    "_resolve_identity_file",
+]