Oracle flagged the previous commit: "omo-agents" was a shared constant,
so when two plugin instances ran in the same tmux server they wrote into
the same session. One instance's cleanup would then kill-session on the
shared name and tear down the other instance's live attached panes.
Replace the const ISOLATED_SESSION_NAME with getIsolatedSessionName(pid)
which defaults to process.pid, so every opencode process owns its own
"omo-agents-<pid>" session. spawnTmuxSession and cleanup both resolve
the name through this helper. Discovery is straightforward from the
host tmux via 'tmux list-sessions | grep omo-agents-'.
Manager test covers two concurrent managers and asserts each kills a
per-pid session name, proving they no longer collide on a global name.
Adds killTmuxSessionIfExists(sessionName), a best-effort no-op when the
named session is absent. Drains both stdio streams so it does not leak
pipe buffers the way closeTmuxPane historically did.
Also exports ISOLATED_SESSION_NAME ("omo-agents") from session-spawn so
callers can tear down the shared isolated session without hard-coding
the name in multiple places.
YeonGyu-Kim