fix(ntn-files): propagate NOTION_API_KEY into ntn subprocesses

Force ntn to authenticate as the same integration that writes the page by
injecting NOTION_API_TOKEN=$NOTION_API_KEY into every ntn subprocess env.
Notion scopes file uploads to the creating integration, so a mismatch caused
"Could not find file_upload with ID …" when attaching uploaded images.

Added test_upload_passes_token_env (9 total in test_ntn_files.py) and updated
code/CLAUDE.md to reflect that a separate ntn login is no longer required.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

custom-skills/32-notion-writer/code/scripts/ntn_files.py

@@ -8,6 +8,7 @@ lifecycle (create -> send bytes -> complete) and prints the upload ID.
 from __future__ import annotations
 
 import json
+import os
 import shutil
 import subprocess
 import sys
@@ -17,6 +18,19 @@ from typing import Dict, List, Optional, Callable, Any
 _WORKSPACE: Optional[Dict[str, str]] = None
 
 
+def _ntn_env():
+    """Env for ntn subprocesses: force ntn to authenticate as the SAME
+    integration the script uses (NOTION_API_KEY/NOTION_TOKEN), so an uploaded
+    file and the page that references it share one identity. Notion scopes
+    file uploads to the creating integration, so a mismatch makes the upload
+    un-attachable."""
+    env = dict(os.environ)
+    token = os.environ.get("NOTION_API_KEY") or os.environ.get("NOTION_TOKEN")
+    if token:
+        env["NOTION_API_TOKEN"] = token
+    return env
+
+
 class NtnUploadError(Exception):
     """Raised when `ntn` is unavailable or a file upload fails."""
 
@@ -45,7 +59,7 @@ def preflight() -> Dict[str, str]:
 
     result = subprocess.run(
         ["ntn", "api", "v1/users/me"],
-        capture_output=True, text=True,
+        capture_output=True, text=True, env=_ntn_env(),
     )
     if result.returncode != 0:
         raise NtnUploadError(
@@ -73,7 +87,7 @@ def upload(path: Path) -> str:
     with open(path, "rb") as fh:
         result = subprocess.run(
             ["ntn", "files", "create", "--plain"],
-            stdin=fh, capture_output=True, text=True,
+            stdin=fh, capture_output=True, text=True, env=_ntn_env(),
         )
     if result.returncode != 0:
         raise NtnUploadError(