migrate-v1: non-git sessions in "global" project hidden after V1→V2 upgrade

Summary

After upgrading from V1.18.31 to V2.0.8, sessions that V1 stored in the global project (sessions created in non-git directories) become invisible in the TUI session picker, because V2 creates a per-directory project and the picker filters to the current project. The history is still in the database, so users perceive all recent conversations as lost.

Environment

• opencode version: 2.0.8 (upgraded from 1.18.31)
• OS: Linux 6.18.33.2-microsoft-standard-WSL2 (WSL2), x86_64
• Terminal: xterm-256color
• Shell: /bin/bash
• Install/channel: latest (curl installer replaced the V1 binary)
• Active plugins: @wallbreakerno4/opencode-commandcode

Reproduction

1. On V1.18.31, run opencode in a non-git directory (e.g. /home/wjf) and create several sessions. They are stored with project_id = 'global'.
2. Upgrade to V2.0.8 so the installer replaces the V1 binary.
3. Start V2 in the same directory (/home/wjf).
4. V2 creates a new project keyed to /home/wjf. The session picker defaults to filtering by the current project and directory, so only sessions created after the upgrade are listed; all prior sessions are hidden.

Expected Behavior

Sessions created for the same working directory should remain visible after upgrading. V1's global sessions in a non-git directory should be migrated to that directory's V2 project (or otherwise kept visible), per the migration guide's statement that supported non-API V1 behavior stays compatible.

Actual Behavior

The sessions remain in ~/.local/share/opencode/opencode.db but are not shown in the default session list. GET /api/session returns them (they carry projectID: "global"), while the TUI picker filters client-side to projectID === current project.id && location.directory === current directory. The Ctrl+O dialog reports No matches · search all sessions with <leader>l.

Additional Context

• Database: ~/.local/share/opencode/opencode.db, table session_v2. Before repair: 104 sessions total, 93 with project_id = 'global' (81 in /home/wjf, 8 in /tmp/opencode, 3 in /home/wjf/novel, 1 in /home/wjf/videos).
• Sessions in a git repository were unaffected: /home/wjf/fadebreak kept a stable project id across the upgrade and stayed visible.
• Relevant log timing: migrations ran at 2026-09-18T17:52:20Z; the new /home/wjf project row was created at 2026-09-18T17:52:21Z.
• Workaround: Ctrl+X then L ("List all sessions") shows everything, including the global project. Inside Ctrl+O, pressing <leader>l switches to searching all sessions.
• Repair performed locally: POST /api/session/{sessionID}/move with {"directory": "<the session's directory>"} re-bound each of the 93 global sessions to its directory project, after which they appear normally. This worked, but required knowing the sessions were hidden.
• Likely cause: V1 used a single global project for non-git directories, while V2 derives a per-directory project id (SHA-1 of the path). No data migration re-keys V1 global sessions.

Start by tracing the TUI session picker’s project and directory filter, then inspect the session_v2 records returned by GET /api/session and the existing POST /api/session/{sessionID}/move behavior. Reproduce the V1-to-V2 upgrade with non-git sessions and ensure sessions stored under the global project remain visible for their working directory after migration, while preserving the existing all-sessions workaround.