False 'Blocked by endpoint security' popup: SIGKILLs correlate exactly with session-switching (WarmLifecycle) — desktop 1.17377.2

Summary

The misleading "Blocked by endpoint security" popup (previously #58626, closed stale; #59292, closed duplicate) still reproduces on current versions — and I have new evidence: the SIGKILLs correlate exactly with switching between sessions in the desktop app UI.

Environment

• Claude desktop 1.17377.2, claude-code runtime 2.1.197
• macOS 26.5.2, MacBook Air M5, 24 GB RAM
• Clean personal Mac: no MDM/EDR/security software; codesign --verify passes on app + CLI; no quarantine attrs; memory healthy at kill times (swap 0 MB in early repros, 35% RAM free in later ones — jetsam ruled out; zero jetsam/crash reports)

Evidence — kills land on session-switch, within ~1 second

~/Library/Logs/Claude/main.log, 2026-07-02:

17:17:36 [error] Session local_6c9c... query error: Claude Code process terminated by signal SIGKILL
17:17:37 [info]  [WarmLifecycle:session] Warming up session local_6c9c...       <- session switched TO
17:17:37 [info]  [WarmLifecycle:session] Starting idle timeout for local_4674...: 900s
17:17:38 [error] Session local_4674... query error: Claude Code process terminated by signal SIGKILL
                 ^ session switched AWAY FROM - killed immediately, not after the 900s idle timeout

Same pattern at 16:52:13-14 and 16:54:17 (both open sessions killed simultaneously). Stack in every case:

Error: Claude Code process terminated by signal SIGKILL
    at getProcessExitError (app.asar/.vite/build/index.js:890:8436)
    at ChildProcess.<anonymous> (app.asar/.vite/build/index.js:890:8178)

claude.ai-web.log shows [AutoSyncConnectorsToSession] replaceRemoteMcpServers failing with the same SIGKILL at the same timestamps.

Impact

• Switching sessions kills the backgrounded session's in-flight turn (session auto-resumes, but running work is lost) — cross-session workflows are effectively unusable
• One false "endpoint security / ask your IT team / allowlist Q6L2SF6YDW" popup per kill on a personal Mac with no IT team

Expected

1. Backgrounded sessions should not be SIGKILLed on switch while a turn is in flight (or should be stopped gracefully)
2. Per #58626's suggestion: don't map every child SIGKILL to the endpoint-security UI — gate that message on actual EndpointSecurity/MDM evidence

Updating the app and reinstalling do not help. Happy to provide full logs.