fix(onboarding): identity read that survives a rewrite, disk refused before the pull — 0.1.8

Three faults from one agent-managed onboarding (env-dev-08, 2026-09-09), each of which pointed
the diagnosis away from the actual fault.

1. install.sh granted the agent's read on the ziti identity with a POSIX ACL. ziti-edge-tunnel
   rewrites that file on a controller config update and the rewrite drops the ACL: the agent
   applied cleanly at 01:21 and was failing every tick by 01:32. Group membership survives the
   rewrite (the file stays ziti:ziti 0640), so install.sh and the package postinstall now add
   monky-deployd to the `ziti` group, and a default ACL on the identity directory carries the
   grant onto a newly created file. The explicit ACLs stay for the boxes that need them.

2. openziti.load() accepts an unreadable or malformed identity: the C SDK logs "configuration is
   invalid" and returns a context that only fails at dial, as a bare TypeError, which the
   transport reported as a missing intercept or a policy gap. The SDK transport now reads and
   parses the identity itself and names the real fault first.

3. The disk pre-flight ran only when the bundle declared disk_need_bytes, so a bundle without one
   died mid-pull with containerd's "no space left on device" — which reads as a registry fault.
   A bundle that declares no size now has to clear the headroom floor, and the pre-flight measures
   containerd's root as well as the docker data-root: docker 29 keeps image layers in the
   containerd image store, and on env-dev-08 those sat on different filesystems (93 GiB free where
   the agent looked, 2.8 GiB where the pull wrote).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KLB7jieMNRkTsJ2epr4Ds1

monky_deployd/transport.py

@@ -16,6 +16,7 @@ from __future__ import annotations
 import http.client
 import json
 import logging
+import os
 import socket
 import ssl
 from dataclasses import dataclass
@@ -35,6 +36,27 @@ class TransportError(Exception):
 class Transport:
     name = "base"
 
+    def _check_identity_readable(self) -> None:
+        path = self.identity_path
+        try:
+            with open(path, "rb") as fh:
+                raw = fh.read()
+        except FileNotFoundError as exc:
+            raise TransportError(f"transport sdk: identity {path} does not exist") from exc
+        except PermissionError as exc:
+            raise TransportError(
+                f"transport sdk: identity {path} is not readable by this user "
+                f"(uid {os.geteuid()}) — the file is owned by the tunneller and rewritten on every "
+                "config refresh, which drops POSIX ACLs; add the agent's user to the file's group "
+                "(usually `ziti`) so the grant survives"
+            ) from exc
+        except OSError as exc:
+            raise TransportError(f"transport sdk: identity {path} is unreadable: {exc}") from exc
+        try:
+            json.loads(raw)
+        except ValueError as exc:
+            raise TransportError(f"transport sdk: identity {path} is not valid JSON: {exc}") from exc
+
     def connect(self, host: str, port: int, timeout: float) -> socket.socket:  # pragma: no cover
         raise NotImplementedError
 
@@ -87,6 +109,13 @@ class SdkTransport(Transport):
                 "transport sdk: the openziti module is not installed in this venv; "
                 "use transport: proxy (monky-deployd-proxy.service) or system"
             ) from exc
+        # openziti.load() does NOT raise on an unreadable or malformed identity: the C SDK logs
+        # "Failed to load Ziti Identity ...: configuration is invalid" and hands back a context
+        # that fails LATER, at dial, as a bare TypeError — which reads as a missing intercept or
+        # a policy gap and sends you hunting the mesh instead of the file (env-dev-08,
+        # 2026-09-09: ziti-edge-tunnel rewrote the identity and dropped the agent's ACL).
+        # So check the file ourselves first and name the real fault.
+        self._check_identity_readable()
         try:
             self._ctx = openziti.load(self.identity_path)
         except Exception as exc: