Session exports use Windows-reserved filenames

Description

Session export filenames are sanitized for punctuation but not for Windows reserved device basenames. A session titled CON, PRN, AUX, NUL, COM1 through COM9, or LPT1 through LPT9 receives a download name such as con.json, which Windows cannot represent reliably. Reserved sanitized basenames should receive a safe suffix while ordinary export names remain unchanged.

Plugins

None

OpenCode version

1.18.30

Steps to reproduce

1. Create or rename a session to CON.
2. Export the session from the app.
3. Observe that the suggested download filename is con.json.
4. Repeat with PRN, AUX, NUL, COM1, or LPT9.

Expected: the app suggests a portable filename such as con-session.json.

Actual: it suggests a Windows-reserved device filename.

Screenshot and/or share link

Not applicable; the filename helper reproduces the issue directly.

Operating System

Windows

Terminal

All