---
id: "c739c130-a204-4a3b-a2c0-40cd45bdaf09"
name: "Switch Tab Session Binding"
micro_summary: "Captures the session_id from switch_tab() for CDP mouse events and reuses it, avoiding events being sent to another tab."
status: "resolved"
see_also: []
scope: "How switch_tab() returns a CDP session_id that must be used for Input.dispatchMouseEvent. Without the explicit session_id, mouse events go to the wrong tab."
warnings: "Always capture and reuse the session_id from switch_tab(). Don't call switch_tab multiple times or attach separately — each creates a new session."
---
## How It Works

`switch_tab(targetId)` returns a CDP session_id. This session must be passed explicitly to every `cdp("Input.dispatchMouseEvent", ...)` call:

```python
sid = switch_tab("340ABBFAEC9A82B9FD65ECD77020B23C")
# later...
cdp("Input.dispatchMouseEvent", type="mousePressed", x=380, y=400, button="left", clickCount=1, session_id=sid)
```

## Why This Matters

After `switch_tab()`, `js()` runs correctly on the Gmail tab (it uses the default session). But `cdp("Input.dispatchMouseEvent", ...)` and `click_at_xy()` send events to whichever CDP session is active — which may NOT be Gmail's if a subsequent `js(target_id=...)` call attached to a different target.

## Key Findings

- Each `switch_tab()` call creates a NEW session. Reuse the returned `sid`.
- Don't call `Target.attachToTarget` again — that creates a separate session and splits the context.
- `click_at_xy()` does NOT use the session from `switch_tab()`. It uses the default cdp() path.
- Verified: events sent without session_id are received by a different tab (confirmed by mousedown listener not firing on Gmail).