feat(agent-provider): user plugin discovery, Dockerfile cascade, and provider-owned ca/git provisioning

- Add _load_user_plugin: loads AgentProvider subclass from
  ~/.bot-bottle/contrib/<name>/agent_provider.py; get_provider()
  checks there first before falling back to built-ins
- Add Dockerfile cascade to docker prepare: per-bottle override →
  manifest dockerfile → user plugin Dockerfile → provider default
- Move provision_ca and provision_git from backend-specific
  provision/ modules to AgentProvider ABC as overridable defaults;
  delete docker/provision/ca.py, docker/provision/git.py,
  smolmachines/provision/ca.py, smolmachines/provision/git.py
- Add git_gate_insteadof_host/scheme properties to BottlePlan base;
  SmolmachinesBottlePlan overrides them to return agent_git_gate_host
  and "http" so provision_git works correctly on both backends
- Move SIGKILL retry from smolmachines provision/ca.py into
  SmolmachinesBottle.exec via _exec_raw helper — all exec calls
  on smolmachines now transparently retry once on exit 137
- Relax manifest_agent template validation to allow user-defined
  template names; keep auth_token/forward_host_credentials guards
  for built-in-only features
- Update tests: rewrite test_docker_provision_git_user and
  test_smolmachines_provision to call provider methods directly;
  add TestSmolmachinesBottleExec for SIGKILL retry coverage

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bot_bottle/backend/docker/provision/__init__.py

@@ -2,10 +2,11 @@
 
 Per PRD 0050 the per-provider provisioning steps (prompt, skills,
 declarative provision-plan apply, supervise MCP registration) live on
-the `AgentProvider` plugin under `bot_bottle/contrib/`. The modules
-left in this subpackage handle only the steps that are
-backend-specific:
+the `AgentProvider` plugin under `bot_bottle/contrib/`. CA and git
+provisioning also moved to the AgentProvider ABC (with Debian/node
+defaults); user plugins override them for non-standard images.
 
-  - ca.py   — install per-bottle CA bundle into the guest trust store
-  - git.py  — copy host cwd `.git` into the guest when --cwd is used
+No modules remain in this subpackage — the directory is kept so that
+existing imports of `from .provision import ...` don't need updating
+if new backend-specific provisioners are added later.
 """

bot_bottle/backend/docker/provision/ca.py

@@ -1,40 +0,0 @@
-"""Install the per-bottle egress MITM CA into the agent container's
-trust store.
-
-By the time this provisioner runs, `egress_tls_init` has generated
-the egress CA and the path is re-bound into `plan.egress_plan`.
-
-Cert lands on Debian's standard source path
-(`/usr/local/share/ca-certificates/`); `update-ca-certificates`
-rebuilds `/etc/ssl/certs/ca-certificates.crt`, which is what curl,
-Python `ssl`, and OpenSSL-based tools all read by default. The env
-trio set on the agent's `docker run` covers Node
-(`NODE_EXTRA_CA_CERTS`) and Python `requests` /
-`SSL_CERT_FILE`-honoring libraries that don't load the system
-bundle.
-
-The fingerprint is computed via stdlib (`ssl.PEM_cert_to_DER_cert`
-+ `hashlib.sha256`) and logged once to stderr. The private key
-stays on the host (under `stage_dir`) until teardown wipes the
-stage dir; nothing in the agent ever sees it."""
-
-from __future__ import annotations
-
-from ... import Bottle
-from ...util import AGENT_CA_PATH, log_ca_fingerprint, select_ca_cert
-from ..bottle_plan import DockerBottlePlan
-
-
-def provision_ca(plan: DockerBottlePlan, bottle: Bottle) -> None:
-    """Copy the agent-facing CA cert into the agent, rebuild the
-    trust bundle, emit a one-line fingerprint log. Called from
-    `BottleBackend.provision` after the agent container is up."""
-    cert_host_path, label = select_ca_cert(plan.egress_plan)
-
-    bottle.cp_in(str(cert_host_path), AGENT_CA_PATH)
-    bottle.exec(
-        f"chmod 644 {AGENT_CA_PATH} && update-ca-certificates",
-        user="root",
-    )
-
-    log_ca_fingerprint(cert_host_path, label)

bot_bottle/backend/docker/provision/git.py

@@ -1,106 +0,0 @@
-"""Git provisioning inside a running Docker bottle.
-
-Three concerns, all about git in the agent:
-
-  1. If --cwd was passed AND the host cwd has a .git, copy that .git
-     into the planned guest workspace so the agent operates on the
-     user's repo.
-  2. If the bottle declares `git` entries (PRD 0008), write a
-     ~/.gitconfig with insteadOf rules so every git operation
-     against a declared upstream (push, fetch, clone, pull,
-     ls-remote) transparently hits the per-agent git-gate. The
-     gate mirrors the upstream in both directions, so URL
-     rewriting is symmetric.
-  3. If the bottle declares `git.user` (issue #86), set
-     `git config --global user.{name,email}` inside the bottle so
-     the agent's commits are attributed to that identity.
-"""
-
-from __future__ import annotations
-
-import shlex
-
-from ....git_gate import GIT_GATE_HOSTNAME, git_gate_render_gitconfig
-from ....log import info
-from ... import Bottle
-from ..bottle_plan import DockerBottlePlan
-
-
-def provision_git(plan: DockerBottlePlan, bottle: Bottle) -> None:
-    """Set up git inside the bottle. Runs all three subcases; each
-    no-ops when its condition isn't met."""
-    _provision_cwd_git(plan, bottle)
-    _provision_git_gate_config(plan, bottle)
-    _provision_git_user(plan, bottle)
-
-
-def _provision_cwd_git(plan: DockerBottlePlan, bottle: Bottle) -> None:
-    """If --cwd was set and the host cwd has a .git directory, copy
-    it into /home/node/workspace/.git and fix ownership. No-op
-    otherwise."""
-    workspace = plan.workspace_plan
-    if not (workspace.enabled and workspace.copy_git and workspace.has_host_git_dir):
-        return
-    guest_workspace_git = f"{workspace.guest_path}/.git"
-    host_git = str(workspace.host_path / ".git")
-    info(f"copying {host_git} -> {bottle.name}:{guest_workspace_git}")
-    bottle.cp_in(host_git, guest_workspace_git)
-    bottle.exec(
-        f"chown -R {shlex.quote(workspace.owner)} {shlex.quote(guest_workspace_git)}",
-        user="root",
-    )
-
-
-def _provision_git_gate_config(plan: DockerBottlePlan, bottle: Bottle) -> None:
-    """Write ~/.gitconfig in the bottle with the git-gate
-    insteadOf rules. No-op when the bottle has no `git` entries."""
-    manifest_bottle = plan.spec.manifest.bottle_for(plan.spec.agent_name)
-    if not manifest_bottle.git:
-        return
-    container_gitconfig = f"{plan.guest_home}/.gitconfig"
-
-    content = git_gate_render_gitconfig(manifest_bottle.git, GIT_GATE_HOSTNAME)
-    config_file = plan.stage_dir / "agent_gitconfig"
-    config_file.write_text(content)
-    config_file.chmod(0o600)
-
-    info(f"writing {container_gitconfig} with {len(manifest_bottle.git)} insteadOf rule(s)")
-    bottle.cp_in(str(config_file), container_gitconfig)
-    bottle.exec(
-        f"chown node:node {shlex.quote(container_gitconfig)} && "
-        f"chmod 644 {shlex.quote(container_gitconfig)}",
-        user="root",
-    )
-
-
-def _provision_git_user(plan: DockerBottlePlan, bottle: Bottle) -> None:
-    """Apply `git config --global user.{name,email}` inside the
-    bottle so the agent's commits are attributed to the operator-
-    chosen identity instead of the agent image's default
-    (which is no user — git would refuse to commit at all
-    until the agent ran its own `git config`).
-
-    Runs as the `node` user so `--global` lands in
-    `/home/node/.gitconfig` (matching the existing
-    `_provision_git_gate_config` write location). No-op when the
-    bottle didn't declare `git.user`.
-
-    Each field set independently — name-only or email-only
-    configs only run the `git config` line for the field
-    present."""
-    manifest_bottle = plan.spec.manifest.bottle_for(plan.spec.agent_name)
-    gu = manifest_bottle.git_user
-    if gu.is_empty():
-        return
-    if gu.name:
-        info(f"git config --global user.name = {gu.name!r}")
-        bottle.exec(
-            f"git config --global user.name {shlex.quote(gu.name)}",
-            user="node",
-        )
-    if gu.email:
-        info(f"git config --global user.email = {gu.email!r}")
-        bottle.exec(
-            f"git config --global user.email {shlex.quote(gu.email)}",
-            user="node",
-        )