[BUG] claude agents: back (←) navigation is shared across two open agent views — leaving a session in one window yanks every window on that same session back to the list

Bug description

When two claude agents views are open at the same time (two separate terminal windows, each running the interactive agent view), navigation state appears to be shared globally between them instead of being per-window.

Steps that trigger it:

1. Open claude agents in two terminal windows simultaneously (Window A and Window B), both pointing at the same machine/sessions.
2. In both windows, select (enter) the same session — so A and B are both attached to / viewing that one session.
3. In one window (say A), press the ← (left arrow) back-navigation to leave the session and return to the agent view.

Expected: only Window A navigates back to the agent view; Window B stays inside the session it was viewing.

Actual: both windows navigate back to the agent view. The back action in A is mirrored into B, even though B never received the keystroke.

This makes the navigation/view state behave as if it were a single shared global ("which screen am I on") rather than per-window, so a navigation action in one window yanks every other window that happens to be on the same session back to the list.

Why this looks like a real bug

• The in-session ← back navigation to the agent view is the documented/expected gesture (cf. #64463, which discusses ← returning to the agent view).
• The two windows are independent UI surfaces and should each own their own navigation stack; a ← in one should not affect the other.
• The trigger condition is specifically both windows on the same session — which strongly suggests the view/navigation pointer is keyed only by session (or stored in a single shared on-disk/global state) and is re-read/written by all attached views.

Environment

• Claude Code: 2.1.173
• Surface: terminal claude agents view (two terminal windows). (If this also reproduces in the desktop FleetView with two app windows, the title/labels should be adjusted — reporter's host is a headless Linux box, so this was observed with the terminal agent view.)
• OS: Linux aarch64 (NVIDIA Jetson / Tegra, kernel 5.10.216-tegra)
• Node: v20.20.2

Notes

• Reproduction requires two agent views open concurrently and both entering the same session before pressing ← in one of them.
• I searched open and closed issues (terms: multi-window navigation, two windows same session, back button both windows, FleetView navigation sync, shared view state) and found no existing report. Related but distinct: #61553 (groups not synced across new windows), #63016 (detached "Open in → New Window" session), #64463 (← agent-view scoping feature request).