bug(core): empty git repos share the same "global" project ID, causing sessions to leak across unrelated directories

Description

When opencode runs inside a Git repository that has no commits and no remote, project resolution falls back to project_id = "global" for ALL such repos. This causes session.list to return sessions from completely unrelated directories.

For example, repos at:
/home/user/testing (empty repo)
/home/user/projeto-a (empty repo)
/home/user/Área de trabalho/teste_Engram (empty repo)

all get project_id = "global". When you open /sessions in any of them, you see sessions from all of them mixed together because listByProject filters only by project_id, not by directory.

Expected: each directory/repo should have its own project identity (or at least sessions should be scoped by directory when project_id is global).

Plugins

No response

OpenCode version

1.18.10

Steps to reproduce

1. mkdir -p /tmp/repo-a /tmp/repo-b
2. cd /tmp/repo-a && git init && opencode # starts TUI
3. In another terminal: cd /tmp/repo-b && git init && opencode
4. Create a session in repo-a (e.g. "session from A")
5. Create a session in repo-b (e.g. "session from B")
6. In either TUI, type /sessions
   → Both "session from A" and "session from B" appear

Screenshot and/or share link

No response

Operating System

Fedora Linux 44 (KDE Plasma Desktop Edition) x86_64

Terminal

Konsole