Bug: "Attach selection as context" duplicates selection into the message input

Question

**What happened:**
Right-clicking a portion of a previous assistant message and choosing "Attach selection as context" inserts the selected text into the message input (as quoted lines), instead of (or in addition to) attaching it as a separate context block.

**Expected:**
The selection should be attached as a discrete context block, not pasted into the message input.

**Actual:**
The selected text appears as duplicated `>` quoted lines in the input area.

**Environment:**
- Claude Code (deskto