opencode emits one trailing session.idle/error for a turn cancelled via client.session.abort(), carrying only a sessionID (no turn id). The warm-server backend settled activeTurn on that event, so after Stop + an immediate new message the orphan idle settled the NEXT turn early as success (one-click reachable since v2.6.5's Send->Stop composer).
Adds a pure per-session guard (backends/turn-guard.ts: armAbortGuard / noteTurnActivity / consumeTerminal over swallowNextTerminal) wired into opencode-server.ts: abort arms it, the next terminal is swallowed once, and a new turn's first delta self-heals so a never-arriving orphan can't strand a real turn. Test-first; 3 regression tests in turn-guard.test.ts. Paseo parallel: 1d38aac.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
