W17: extract ai_common shared module + fix anthropic data race + brace bugs

- New plugins_upper/ai_common/ static library: shared PluginConfig, ToolCallAccum,
  StreamContext, secure_zero, extract_host_port, serialize_tool_calls, free_chat_result
- Refactored openai/anthropic plugins to use dstalk_ai:: namespace from ai_common
- Fixed anthropic g_config raw pointer → std::atomic (data race)
- Added SSE parse error counter with threshold abort (kMaxSseParseErrors=5)
- Fixed missing closing brace in both plugins' error-body catch block
- Updated test targets: ai_common include path + link, using namespace dstalk_ai
- plugin_loader_test: added stub_unreg + service_registry.cpp for unregister_service
- Includes pre-existing uncommitted changes from prior waves

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins_middle/network/CMakeLists.txt

@@ -1,15 +1,15 @@
 find_package(Boost REQUIRED CONFIG)
 find_package(OpenSSL REQUIRED CONFIG)
 
-add_library(plugin-network SHARED src/network_plugin.cpp)
+add_library(plugin_network SHARED src/network_plugin.cpp)
 
-target_link_libraries(plugin-network PRIVATE
+target_link_libraries(plugin_network PRIVATE
     dstalk
     boost::boost
     openssl::openssl
 )
 
-set_target_properties(plugin-network PROPERTIES
+set_target_properties(plugin_network PROPERTIES
     PREFIX ""
     LIBRARY_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/plugins"
     RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/plugins"

plugins_middle/network/src/network_plugin.cpp

@@ -278,7 +278,13 @@ static int do_post_stream(
                 beast::get_lowest_layer(stream).expires_after(
                     std::chrono::seconds(ctx.request_timeout));
                 http::read_some(stream, buffer, parser, ec);
-                if (ec) break;
+                if (ec) {
+                    if (ec != http::error::end_of_stream && ec != asio::error::eof) {
+                        if (g_host) g_host->log(DSTALK_LOG_WARN,
+                            "[http] stream read error: %s", ec.message().c_str());
+                    }
+                    break;
+                }
 
                 const std::string& full_body = parser.get().body();
                 if (full_body.size() > processed) {
@@ -301,7 +307,13 @@ static int do_post_stream(
                 beast::get_lowest_layer(stream).expires_after(
                     std::chrono::seconds(ctx.request_timeout));
                 http::read_some(stream, buffer, parser, ec);
-                if (ec) break;
+                if (ec) {
+                    if (ec != http::error::end_of_stream && ec != asio::error::eof) {
+                        if (g_host) g_host->log(DSTALK_LOG_WARN,
+                            "[http] stream read error: %s", ec.message().c_str());
+                    }
+                    break;
+                }
             }
         }