[Bug] Slash command menu not triggering mid-input in terminal mode

Bug Description
Bug: Slash command menu no longer triggers mid-input in terminal mode

Description
Previously, typing / anywhere in the input (including mid-sentence) would trigger the slash command menu in the terminal version of Claude Code. This behavior no longer works — the menu only appears when / is typed at the very beginning of an empty input.

Steps to Reproduce

1. Open Claude Code in terminal (not the desktop app)
2. Type any text in the input field
3. Type / after the text
4. Expected: slash command menu appears
5. Actual: no menu appears; / is treated as a literal character

Expected Behavior
Slash command menu should trigger when / is typed mid-input, consistent with:

• Previous terminal behavior (changelog references "Fixed ghost text flickering when typing slash commands mid-input", confirming this was once supported)
• Current desktop app behavior, where mid-input / still correctly triggers the menu

Environment

• Claude Code version: 2.1.92
• macOS: 26.3.1 (Apple M1)
• Terminal: Ghostty 1.3.1
• Interface: Terminal (not desktop app)

Additional Notes
The desktop app still supports mid-input slash command triggering. This appears to be a regression specific to the terminal version.

Environment Info

• Platform: darwin
• Terminal: ghostty
• Version: 2.1.92
• Feedback ID: 3670b006-47b1-4d32-ba39-b2bbef5160ed

Additional Evidence

Found two sources confirming this was an intentionally implemented feature:

1. From the official changelog (https://code.claude.com/docs/en/changelog#2-1-0):

> "Ghost text fix - Fixed flickering when typing slash commands mid-input"

1. From a GitHub commit (https://github.com/anthropics/claude-code/commit/870624fc1581a70590e382f263e2972b3f1e56f5):

> "Added slash command autocomplete support when / appears anywhere in input, not just at the beginning"

This confirms the mid-input / trigger was deliberately added at some point. The current behavior (only triggering at the start of an empty input in terminal mode) is a regression.

<img width="510" height="231" alt="Image" src="https://github.com/user-attachments/assets/e830e6af-a4d2-4a35-a0e1-5bd04032938f" />

<img width="552" height="289" alt="Image" src="https://github.com/user-attachments/assets/598a6280-67b4-475b-af00-826b734f351a" />