[2.1.114] Cmd+C / right-click copies entire message block, not the selected text

Summary

In assistant messages, standard macOS partial-copy is broken:

• Cmd+C with text selected → copies the ENTIRE message block
• Right-click on selection → only "メッセージをコピー" is offered (no standard "Copy" item for the selection)

Drag-and-drop of the selected text still works, but that's not a practical substitute for Cmd+C during normal reading/quoting.

Repro

1. Highlight a span of text inside an assistant message
2. Press Cmd+C → clipboard receives the whole message, not the span
3. Right-click on the selection → menu shows only "メッセージをコピー"

Expected

• Cmd+C on a selection copies only the selected text (macOS standard)
• Right-click menu on a selection includes a "Copy" item alongside "メッセージをコピー"

Impact

Partial quoting from assistant messages is effectively blocked in normal workflow. The only workarounds are:

• Dragging the selection to another app (impractical for routine use)
• Using DevTools to read window.getSelection()
• Asking the assistant to re-emit the fragment

This is a major workflow regression from prior versions.

Environment

• Claude Code desktop 2.1.114
• macOS