feat(next): route agent beside opens through right pane

TE
6d ago
+99-6

Stacked on #26582 (A1). This routes real agent beside callers through the shared right-column decision path.

Leo said: "leo view changes is still bad / it should open to the right" and clarified that documents should use the top-right area while the first session gets a bottom split, with later sessions staying in the matching area.

Changes:

  • wires AgentTabStore with a workspace-local right-pane lookup backed by LinkOpener;
  • makes header and Session Info document opens reuse the existing right pane and its active-tab order;
  • makes subagent opens use the right pane for the first session, split below it once, then reuse the bottom session area for later subagents;
  • keeps the existing new-right-column path when no right pane exists and never crosses workspace/window boundaries.

Validation: git diff --check. Swift compilation is delegated to the managed PR CI route (Swift is unavailable on this Linux host). Real-app before/after capture remains part of the parent capture pass.

Related: #26093, #25721

agent-identity footer --repo manaflow-ai/cmux