feat(prd-0081): reprovision CA, git-gate, and egress tokens on gateway bring-up

On a Firecracker gateway cold boot, reconcile every live agent VM against
the fresh gateway: push the new mitmproxy CA into each agent's trust store,
re-provision git-gate repos/creds from the persisted upstreams snapshot,
and restore egress tokens. Per-bottle failures are logged and skipped so
one unreachable VM does not block the rest.

New modules / changes:
- backend/firecracker/reconcile.py: attach_bottled_agents_to_gateway,
  _push_ca, _reprovision_git_gate, _guest_ip_from_config
- git_gate/provision.py: write upstreams.json after key provisioning so
  the bring-up reconcile can reconstruct the upstream table without the
  manifest
- backend/firecracker/infra.py: call attach_bottled_agents_to_gateway in
  the cold-boot branch of ensure_running()
- backend/base.py: no-op default on BottleBackend
- backend/firecracker/consolidated_launch.py: remove superseded
  _reprovision_running_bottles / _guest_ip_from_config
- orchestrator: OrchestratorCore.update_agent_secret + POST
  /bottles/<id>/secret + client.update_agent_secret (single-secret
  in-place update, the reusable primitive from the 2026-07-26 hotfix)
- tests: 15 new tests in test_firecracker_reconcile.py; updated
  test_firecracker_infra.py cold-boot cases; stale FC reprovision tests
  removed from test_backend_secret_reprovision.py

Closes #516.

bot_bottle/backend/firecracker/consolidated_launch.py

@@ -26,22 +26,19 @@ The TAP slot allocation, rootfs build, and VM boot are the caller's job.
 
 from __future__ import annotations
 
-import json
 import subprocess
 from dataclasses import dataclass
 from pathlib import Path
 
 from ...egress import EgressPlan
 from ...git_gate import GitGatePlan
-from ...log import info
-from ...orchestrator.client import OrchestratorClient, OrchestratorClientError
+from ...orchestrator.client import OrchestratorClient
 from ...orchestrator.lifecycle import (
     OrchestratorStartError,  # re-exported so callers can catch it
 )
-from ...orchestrator.reprovision import reprovision_bottles
 from ...orchestrator.store.secret_store import ENV_VAR_SECRET_NAME
 from ..provision_bottle import deprovision_bottle, provision_bottle
-from . import cleanup, util
+from . import util
 from .gateway import FirecrackerGateway
 from .infra import FirecrackerInfraService
 
@@ -64,17 +61,6 @@ class LaunchContext:
     env_var_secret: str = ""  # encryption key injected into the agent's env
 
 
-def _guest_ip_from_config(config_path: Path) -> str:
-    """Read the kernel's configured guest IP from a Firecracker config."""
-    try:
-        config = json.loads(config_path.read_text())
-        args = config["boot-source"]["boot_args"]
-        ip_arg = next(part for part in args.split() if part.startswith("ip="))
-        return ip_arg.removeprefix("ip=").split(":", 1)[0]
-    except (OSError, ValueError, KeyError, TypeError, StopIteration):
-        return ""
-
-
 def persist_env_var_secret(private_key: Path, guest_ip: str, secret: str) -> None:
     """Mirror the exec-time key into guest tmpfs for restart recovery."""
     proc = subprocess.run(
@@ -89,29 +75,6 @@ def persist_env_var_secret(private_key: Path, guest_ip: str, secret: str) -> Non
         )
 
 
-def _reprovision_running_bottles(client: OrchestratorClient) -> None:
-    """Read keys from live agent VMs and restore the restarted gateway."""
-    try:
-        secrets_by_ip: dict[str, str] = {}
-        for run_dir in cleanup.live_run_dirs():
-            guest_ip = _guest_ip_from_config(run_dir / "config.json")
-            private_key = run_dir / "bottle_id_ed25519"
-            if not guest_ip or not private_key.is_file():
-                continue
-            proc = subprocess.run(
-                util.ssh_base_argv(private_key, guest_ip)
-                + [f"cat {_ENV_VAR_SECRET_PATH}"],
-                capture_output=True, text=True, check=False,
-            )
-            if proc.returncode == 0 and proc.stdout.strip():
-                secrets_by_ip[guest_ip] = proc.stdout.strip()
-        count = reprovision_bottles(client, secrets_by_ip)
-        if count:
-            info(f"reprovisioned egress tokens for {count} Firecracker bottle(s)")
-    except (OSError, OrchestratorClientError) as exc:
-        info(f"egress token reprovision skipped: {exc}")
-
-
 def launch_consolidated(
     egress_plan: EgressPlan,
     git_gate_plan: GitGatePlan,
@@ -126,7 +89,6 @@ def launch_consolidated(
     service = FirecrackerInfraService()
     url = service.ensure_running()
     client = OrchestratorClient(url)
-    _reprovision_running_bottles(client)
 
     # Read the gateway's provisioning transport + CA off the Gateway service.
     gateway = service.gateway()