refactor(git-gate): split git_gate.py into render / provision / control

git_gate.py (699 LOC) mixed three responsibilities. Split into:

- git_gate_render.py — pure host-side rendering: the gate constants,
  GitGateUpstream, gitconfig/known-hosts rendering, and the entrypoint /
  pre-receive / access-hook script builders.
- git_gate_provision.py — the gitea deploy-key lifecycle
  (_provision_dynamic_key / revoke / _resolve_identity_file).
- git_gate.py — the GitGate ABC + GitGatePlan, now 169 LOC, re-exporting
  all moved names (see __all__) so the 19 importers are unchanged.

Host-side only (not flat-bundled), so no sidecar import shim. The one
test that patched the internal `_provision_dynamic_key` lookup is
repointed to its new module (public API unchanged). The two new modules
are added to scripts/critical-modules.txt so the decompose doesn't move
security code out of the measured core — critical aggregate stays 95%
(git_gate 100%, render 100%, provision 97%).

Closes #303

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NkwFXLFff9PYPy4wgVBJp9

bot_bottle/git_gate_provision.py

@@ -0,0 +1,102 @@
+"""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
+from pathlib import Path
+
+from .log import info
+from .manifest import ManifestBottle, ManifestGitEntry
+
+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 RuntimeError(
+            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:{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 RuntimeError(
+                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
+
+
+__all__ = [
+    "revoke_git_gate_provisioned_keys",
+    "_provision_dynamic_key",
+    "_resolve_identity_file",
+]