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Fixed PreToolUse and Stop hook HTTP 502 errors (regression in claude-code 2.1.118) - #87
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…code 2.1.118) Two root causes: 1. Hook servlet blocked a Jetty thread per pending request (user had not yet clicked Accept/Reject in the diff dialog). When multiple diffs were open simultaneously the thread pool was exhausted and subsequent requests returned 502. Fixed by converting HookServlet to async Jetty API (startAsync / whenComplete) so threads are released immediately after reading the request. Added MCPSseServerPerSessionTest TC-5/TC-6 and test_hook_concurrent.py to reproduce and guard against regression. 2. Hook and MCP SSE URLs used "localhost" which on systems where localhost resolves to ::1 (IPv6) first causes claude-code's Bun HTTP client to connect to ::1:PORT. Jetty's ServerConnector binds to 0.0.0.0 (IPv4 only) and refuses the connection; claude-code reports the failure as "HTTP 502". Fixed by using 127.0.0.1 instead of localhost in all hook and SSE URLs written to settings.local.json. Added test_hook_ipv6_localhost.py to verify. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Backport of #86 to release/0.21.
Summary
Two root causes for HTTP 502 on PreToolUse/Stop hooks:
HookServletblocked a Jetty thread per pending request. With multiple diff dialogs open simultaneously the thread pool was exhausted. Fixed by convertingHookServletto async Jetty API (startAsync/whenComplete).localhostwhich on systems wherelocalhostresolves to::1(IPv6) first causes claude-code's Bun HTTP client to connect to::1:PORT. Jetty'sServerConnectorbinds to0.0.0.0(IPv4 only) and refuses the connection; claude-code reports this as "HTTP 502". Fixed by using127.0.0.1instead oflocalhostin all URLs written tosettings.local.json.🤖 Generated with Claude Code