observePullRequest used to reveal and focus the explorer pane, and the persisted focus leak then made ambient tab opens (sidebar agent clicks, reconcile auto-open) insert agent tabs into the explorer pane while the main pane sat empty.
PR detection now only background-adds the PR tab to the explorer pane, with no reveal and no focus change, so a tab the user already opened elsewhere stays where it is.
Placement policy is centralized in workspace-layout-actions.ts (resolvePlacementPane / insertNewTabIntoPane): explicit paneId wins, and ambient entity opens (agent, provider_subagent, terminal, draft, browser) reroute from the explorer pane to the primary pane. explorerPaneId is a required input so callers cannot silently fail open.
Pane-rail + affordances thread explicit paneId instead of focus-then-open.
Mohamed Boudra
b638f7d3ee