[BUG] macOS: opening the embedded Browser pane freezes it and leaves orphaned renderer processes spinning at ~125% CPU each

Summary

Opening the embedded Browser pane in Claude Desktop (macOS) leaves behind orphaned Claude Helper (Renderer) processes that spin a busy loop at ~100–125% CPU each, indefinitely. The Browser pane itself freezes/becomes unresponsive at the same time. Killing the rogue renderers with kill -9 has zero visible effect on the app — all windows and sessions keep working — confirming the processes were already detached/abandoned by the app but never reaped.

This appears to connect two symptoms currently reported separately:

• #76965 — frozen/blank Browser pane on macOS (same freeze symptom; that report doesn't cover the CPU angle)
• #81130 — orphaned renderer processes on Windows (same leak shape; not tied to the Browser pane trigger)

Proposed causal story: the pane's renderer enters a busy loop → pane freezes → app detaches/abandons the renderer without terminating it → renderer keeps spinning at a full core until manually killed.

Steps to reproduce

1. Use Claude Desktop with a session that opens the in-app Browser pane (mcp__Claude_Browser__* / preview feature).
2. Observe the Browser pane freeze.
3. Check Activity Monitor / ps aux -r: a Claude Helper (Renderer) process is pinned at ~100–125% CPU and stays there indefinitely, even after the pane/session it belonged to is closed.

Reproduced 3 times in one afternoon (one rogue renderer per Browser-pane use).

Evidence (from the affected machine, 2026-07-31)

Three rogue renderers observed simultaneously, each pinning a full core:

USER    PID    %CPU  STARTED  TIME       COMMAND
dimitar 78324  124.8 2:14PM   30:53.63   Claude Helper (Renderer) --type=renderer ... renderer-client-id=16
dimitar 78569  123.7 2:16PM   17:12.77   Claude Helper (Renderer) --type=renderer ... renderer-client-id=18
dimitar 85370  124.7 2:36PM    5:14.47   Claude Helper (Renderer) --type=renderer ... renderer-client-id=19

• One accumulated 31+ CPU-minutes; system load average 4.5, fans at full speed.
• kill -9 on all three: no visible change in the app whatsoever — no window reload, no crashed pane, all sessions kept functioning. Load average dropped to 0.8.
• The processes did not respawn after being killed.

Environment

• Claude Desktop 1.24012.9 (claude-code engine 2.1.219)
• macOS, Darwin 25.4.0, Apple Silicon (arm64)
• Renderer flags observed: --enable-sandbox --lang=en-GB ... --renderer-client-id=16/18/19

Expected behavior

• The Browser pane should not freeze on open.
• When a renderer is detached/replaced, the app should terminate and reap it rather than leaving it spinning at 100%+ CPU.

Workaround

ps aux -r | grep "Claude Helper (Renderer)" and kill -9 any renderer pinned at ~100%+ — safe in practice, since the app has already abandoned them.