Long session titles produce unsavable export filenames

Description

Session export filenames have no length limit after title sanitization. A 300-character ASCII title produces a 305-byte filename including .json, exceeding the common 255-byte filename-component limit and causing saves to fail with ENAMETOOLONG on affected filesystems. The sanitized basename should be capped while preserving the .json extension.

Plugins

None

OpenCode version

1.18.30

Steps to reproduce

1. Create a session whose title contains 300 ASCII letters.
2. Generate its session-export filename.
3. Observe that the result is 305 bytes long.
4. Try to create a file with that name on a filesystem with a 255-byte component limit.

Expected: the suggested filename fits within the filesystem limit and retains .json.

Actual: saving fails because the generated filename is too long.

Screenshot and/or share link

Not applicable; the filename length and filesystem error reproduce the issue directly.

Operating System

All

Terminal

All