Keep future Coulomb release evidence directories private

Assistant: codex
Assistant-Model: gpt-6-astra
Assistant-Session: 01a18e2d-f513-7742-b8e7-12af0b744ff3

tools/coulomb_image_release_node.py

@@ -16,6 +16,7 @@ import subprocess
 import tempfile
 import time
 import urllib.request
+from contextlib import ExitStack
 from datetime import UTC, datetime
 from pathlib import Path
 
@@ -35,6 +36,33 @@ class Refused(RuntimeError):
     pass
 
 
+def private_directories(root, relative):
+    """Create every component privately; never repair existing unsafe state."""
+    if not root.is_absolute() or relative.is_absolute() or ".." in relative.parts:
+        raise Refused("private_directory_path_required")
+    with ExitStack() as stack:
+        def opened(name, parent=None):
+            fd = os.open(name, os.O_RDONLY | os.O_DIRECTORY | os.O_NOFOLLOW, dir_fd=parent)
+            stack.callback(os.close, fd)
+            return fd
+
+        fd = opened("/")
+        for component in root.parts[1:]:
+            fd = opened(component, fd)
+        for component in (*relative.parts, None):
+            info = os.fstat(fd)
+            if info.st_uid != os.getuid() or stat.S_IMODE(info.st_mode) != 0o700:
+                raise Refused("private_owned_directory_required")
+            if component is None:
+                break
+            try:
+                os.mkdir(component, mode=0o700, dir_fd=fd)
+                os.fsync(fd)
+            except FileExistsError:
+                pass
+            fd = opened(component, fd)
+
+
 class Release:
     def __init__(self, capsule, expected, read_only=False):
         self.root = capsule
@@ -73,12 +101,13 @@ class Release:
             return
         if self.journal.exists():
             raise Refused("prior_execution_requires_review")
-        self.journal.mkdir(parents=True, mode=0o700)
+        private_directories(JOURNAL_ROOT.parent, Path(JOURNAL_ROOT.name))
+        self.journal.mkdir(mode=0o700)
         self.root = self.journal / "capsule"
         self.root.mkdir(mode=0o700)
         for name, data in frozen.items():
             target = self.root / name
-            target.parent.mkdir(mode=0o700, parents=True, exist_ok=True)
+            private_directories(self.root, Path(name).parent)
             fd = os.open(target, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600)
             with os.fdopen(fd, "wb") as stream:
                 stream.write(data)