[V2 compat] All legacy v1 session avatars render as "/" (sessions bound to project_id "global") #57067

Summary

After migrating from v1 (1.18.23) to V2 (Desktop 2.0.29 / CLI 2.0.27), every session
in the Desktop home/sidebar shows the same "/" avatar, regardless of project.

Environment

• Linux x64 (Ubuntu 24.04), Desktop 2.0.29, CLI 2.0.27
• Migrated per https://opencode.ai/v2/docs/migrate-v1/ (sessions/config preserved)

Root cause (verified against my database)

• All 48 v1-created sessions have project_id = 'global'; the global project row
  has worktree = '/' and name = NULL.
• Verified via backup comparison that v1 data already looked like this before
  migration — so this is not migration data loss, but a V2 rendering regression
  for legacy data.
• ProjectAvatar fallback chain displayName = name || basename(worktree) || worktree
  followed by first(...) yields '/' for this project, so every session avatar
  becomes /.
• session.directory is correct for all 48 sessions (e.g. /home/user/myproject),
  so grouping/display could still be derived correctly.

Expected

Session avatars fall back to the session's directory basename (or the project matched
by worktree) instead of /.

Actual

All session avatars show /.

Notes

• Project.resolve still assigns ID.global for directories without a git/hg root,
  so new sessions in non-git directories appear to hit the same path.
• User-side workaround I applied offline: remap session.project_id /
  session_v2.project_id by exact directory → project.worktree match
  (fixed 43/48; 5 sessions whose directory has no project row remain on global).

Happy to provide more diagnostics if needed.