refactor: extract hook_bus collaborator from webserver_impl

Move the server-wide lifecycle hook state and behaviour out of the
webserver_impl god-object into a cohesive detail::hook_bus collaborator
(the server-scope sibling of detail::resource_hook_table). The bus owns
the eleven per-phase vectors, the shared registration mutex, the advisory
any_hooks_ gate array, and the handler_exception / log_access alias slots;
it exposes add / remove / fire_* / has_hooks_for / phase_hook_count and
takes a per-call error logger so it needs no back-pointer to the server.

webserver_impl now holds one hook_bus by value and keeps thin fire_* /
has_hooks_for / phase_hook_count forwarders (binding log_dispatch_error as
the logger), so every dispatch call site and the webserver_test_access
bridge stay source-compatible. Registration (webserver_add_hook.cpp),
removal (hook_handle.cpp), firing (hook_phase_dispatch.cpp), and the v1
setter aliases (webserver_aliases.cpp) all delegate into the bus.

This is the third of six planned webserver_impl decompositions (after
ip_access_control and ws_registry). No behaviour change: the five
independent mutexes still never nest; the hook mutex is now internal to
the bus. White-box hook tests are re-pointed at impl->hooks_.

Build green; 109/109 tests pass; file-size gate PASS.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: etr

src/Makefile.am

@@ -25,11 +25,11 @@ lib_LTLIBRARIES = libhttpserver.la
 # builds. The WS-off branch in websocket_handler.cpp provides stub
 # definitions (every member throws feature_unavailable except is_valid()
 # which returns false).
-libhttpserver_la_SOURCES = string_utilities.cpp webserver.cpp webserver_add_hook.cpp http_utils.cpp file_info.cpp http_request.cpp http_request_auth.cpp http_response.cpp http_response_factories.cpp http_resource.cpp create_webserver.cpp create_test_request.cpp websocket_handler.cpp hook_handle.cpp peer_address.cpp resource_hook_table.cpp cookie.cpp detail/http_endpoint.cpp detail/body.cpp detail/ip_representation.cpp detail/ip_access_control.cpp detail/ws_registry.cpp detail/http_request_impl.cpp detail/http_request_impl_args.cpp detail/http_request_impl_tls.cpp detail/webserver_lifecycle.cpp detail/webserver_register.cpp detail/webserver_routes.cpp detail/webserver_routes_upsert.cpp detail/webserver_callbacks.cpp detail/webserver_callbacks_lifecycle.cpp detail/webserver_websocket.cpp detail/webserver_dispatch.cpp detail/webserver_request.cpp detail/webserver_response_queue.cpp detail/webserver_body_pipeline.cpp detail/webserver_error_pages.cpp detail/webserver_aliases.cpp detail/webserver_hook_firing.cpp detail/hook_phase_dispatch.cpp
+libhttpserver_la_SOURCES = string_utilities.cpp webserver.cpp webserver_add_hook.cpp http_utils.cpp file_info.cpp http_request.cpp http_request_auth.cpp http_response.cpp http_response_factories.cpp http_resource.cpp create_webserver.cpp create_test_request.cpp websocket_handler.cpp hook_handle.cpp peer_address.cpp resource_hook_table.cpp cookie.cpp detail/http_endpoint.cpp detail/body.cpp detail/ip_representation.cpp detail/ip_access_control.cpp detail/ws_registry.cpp detail/hook_bus.cpp detail/http_request_impl.cpp detail/http_request_impl_args.cpp detail/http_request_impl_tls.cpp detail/webserver_lifecycle.cpp detail/webserver_register.cpp detail/webserver_routes.cpp detail/webserver_routes_upsert.cpp detail/webserver_callbacks.cpp detail/webserver_callbacks_lifecycle.cpp detail/webserver_websocket.cpp detail/webserver_dispatch.cpp detail/webserver_request.cpp detail/webserver_response_queue.cpp detail/webserver_body_pipeline.cpp detail/webserver_error_pages.cpp detail/webserver_aliases.cpp detail/webserver_hook_firing.cpp detail/hook_phase_dispatch.cpp
 # noinst_HEADERS: shipped in the tarball but NEVER installed under $prefix/include.
 # Detail headers (httpserver/detail/*.hpp) live here so they cannot leak to
 # downstream consumers — the public surface comes in through <httpserver.hpp>.
-noinst_HEADERS = httpserver/string_utilities.hpp httpserver/detail/modded_request.hpp httpserver/detail/http_endpoint.hpp httpserver/detail/body.hpp httpserver/detail/webserver_impl.hpp httpserver/detail/webserver_impl_dispatch.hpp httpserver/detail/connection_state.hpp httpserver/detail/ip_access_control.hpp httpserver/detail/ws_registry.hpp httpserver/detail/secure_zero.hpp httpserver/detail/http_request_impl.hpp httpserver/detail/resource_hook_table.hpp httpserver/detail/route_entry.hpp httpserver/detail/lambda_resource.hpp httpserver/detail/segment_trie.hpp httpserver/detail/route_cache.hpp httpserver/detail/route_tier.hpp httpserver/detail/unescape_helpers.hpp gettext.h
+noinst_HEADERS = httpserver/string_utilities.hpp httpserver/detail/modded_request.hpp httpserver/detail/http_endpoint.hpp httpserver/detail/body.hpp httpserver/detail/webserver_impl.hpp httpserver/detail/webserver_impl_dispatch.hpp httpserver/detail/connection_state.hpp httpserver/detail/ip_access_control.hpp httpserver/detail/ws_registry.hpp httpserver/detail/hook_bus.hpp httpserver/detail/secure_zero.hpp httpserver/detail/http_request_impl.hpp httpserver/detail/resource_hook_table.hpp httpserver/detail/route_entry.hpp httpserver/detail/lambda_resource.hpp httpserver/detail/segment_trie.hpp httpserver/detail/route_cache.hpp httpserver/detail/route_tier.hpp httpserver/detail/unescape_helpers.hpp gettext.h
 nobase_include_HEADERS = httpserver.hpp httpserver/body_kind.hpp httpserver/cookie.hpp httpserver/constants.hpp httpserver/create_webserver.hpp httpserver/create_webserver_setters.hpp httpserver/create_test_request.hpp httpserver/webserver.hpp httpserver/webserver_routes.hpp httpserver/webserver_runtime.hpp httpserver/webserver_websocket.hpp httpserver/webserver_hooks.hpp httpserver/websocket_handler.hpp httpserver/http_utils.hpp httpserver/http_utils_helpers.hpp httpserver/ip_representation.hpp httpserver/file_info.hpp httpserver/http_request.hpp httpserver/http_response.hpp httpserver/http_resource.hpp httpserver/feature_unavailable.hpp httpserver/iovec_entry.hpp httpserver/http_arg_value.hpp httpserver/http_method.hpp httpserver/hook_phase.hpp httpserver/hook_action.hpp httpserver/hook_handle.hpp httpserver/hook_context.hpp
 
 AM_CXXFLAGS += -fPIC -Wall