Markdown file links with spaces or umlauts in the path are not clickable (file not found)

Environment: Claude Code desktop app on macOS (Darwin 25.4.0)

Repro:

1. Have the assistant reference a local file whose path contains spaces and non-ASCII characters (e.g. a German umlaut), as a markdown link relative or absolute, e.g.:

[Übersicht Plan 2026.pdf](/Users/x/Documents/Some Folder/Übersicht Plan 2026.pdf)

1. Click the rendered link in the app.

Actual: The internal viewer/browser cannot resolve the path — reports the file as not found. Links to ASCII-only paths without spaces work fine.

Expected: The link opens the file.

Notes: Looks like the link handler neither URL-encodes spaces nor handles non-ASCII characters; on macOS there may additionally be a Unicode NFC/NFD normalization mismatch (HFS+/APFS store decomposed umlauts, ä = a + U+0308). The file definitely exists at the linked path.

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