Fix: Detect files modified directly on GitHub

[TheOutdoorProgrammer]

Problem

Fixes #45

When files are edited directly on GitHub (via web UI or other means outside the plugin), the plugin fails to detect these changes during sync. The user sees "Nothing to sync" even though files have been modified remotely.

Root Cause

The plugin uses a manifest file (github-sync-metadata.json) to track file SHAs. The manifest only updates when syncing through this plugin. When someone edits a file directly on GitHub:

1. The file's SHA in the git tree changes
2. The manifest file's SHA remains the same (old value)
3. The sync logic only compares manifest-to-manifest
4. Result: Remote changes are invisible to the plugin

Solution

After fetching the remote manifest, we now compare:

• Actual remote file SHAs (from the git tree via getRepoContent())
• Manifest-recorded SHAs (from the manifest blob)

If they differ, we update the manifest entry to reflect the actual state. This allows determineSyncActions() to detect the change and trigger a download.

Changes Made

// New logic in syncImpl() after loading remote metadata:
Object.keys(files).forEach((filePath: string) => {
  const actualRemoteSHA = files[filePath].sha;
  const manifestEntry = remoteMetadata.files[filePath];
  
  if (manifestEntry && manifestEntry.sha !== actualRemoteSHA) {
    // File was modified externally - update manifest
    manifestEntry.sha = actualRemoteSHA;
    manifestEntry.lastModified = Date.now();
  } else if (!manifestEntry) {
    // New file added externally - add to manifest
    remoteMetadata.files[filePath] = { ... };
  }
});

Testing

✅ Tested and verified working:

1. Synced a note to GitHub via the plugin
2. Edited the note directly on GitHub web UI
3. Triggered sync in Obsidian (mobile)
4. Result: Updated content downloaded successfully

Before fix: "Nothing to sync"
After fix: File detected and downloaded

Test Environment

• Obsidian Mobile (iOS/Android)
• Plugin version: 1.0.8-beta.1
• Original reporter (@tohizma) and @TheOutdoorProgrammer confirmed fix works

Impact

• No breaking changes - only adds detection logic
• Minimal code change - ~30 lines in sync-manager.ts
• Preserves existing behavior - all existing sync scenarios still work
• Fixes edge case - now handles external modifications correctly

Additional Notes

This fix handles two scenarios:

1. Modified files: SHA mismatch triggers update
2. New files: Missing manifest entry triggers addition

The manifest comment documents why this comparison is necessary - without it, future maintainers wouldn't understand the limitation of the manifest-based approach.