Fix ETag format to prevent WsgiDAV crashes on PUT requests

[TheZupZup]

Summary

This PR fixes a regression where WsgiDAV would crash with a 500 error when handling PUT requests to WebDAV resources (note.json and page_1.ink files) due to improperly formatted ETags. The issue occurred because ETags were being returned as quoted ISO timestamps, which violated WsgiDAV's checked_etag validator.

Key Changes

• Replaced ISO timestamp-based ETags with hash-based ETags: Changed _safe_etag() to generate SHA256 hex digests from resource identity components (resource type, ID, page number, and last-modified timestamp) instead of returning raw ISO timestamps. Hex digests are guaranteed to be quote-free and satisfy WsgiDAV's validation rules.

• Updated ETag generation for NoteMetaFile: Modified get_etag() to include the note ID and type identifier in the hash, ensuring the ETag changes only when the note's content actually changes.

• Updated ETag generation for InkFile: Modified get_etag() to include the page's note ID, page number, and type identifier in the hash for proper cache invalidation.

• Added comprehensive test coverage:

  • Unit tests verifying ETags pass WsgiDAV's checked_etag validator
  • Tests confirming ETags are never quoted, never weak, and properly formatted
  • Tests verifying ETags change when content changes
  • Integration tests reproducing the original crash scenario and confirming PUT requests now succeed end-to-end

Implementation Details

• The _safe_etag() function now accepts variable arguments representing resource identity components
• Each component is converted to a string (with special handling for datetime objects to ensure consistent ISO format)
• Components are separated by a null byte (0x1f) before hashing to prevent collisions
• The function returns only the hex digest, never pre-quoted, allowing WsgiDAV to add quotes when emitting the ETag header
• This approach ensures deterministic, collision-resistant ETags that properly reflect resource state changes

https://claude.ai/code/session_01UCTNs51gDsbdzVXExMUDAg