Wave 5+6: plugin ABI hardening, build modernization, ABI/security docs

Wave 5 (9 parallel agents):
- W1.1 atomic diag callback + DLL handle release on shutdown (lin)
- W2.1 unify cross-DLL heap discipline (host->alloc/free/strdup) (chen)
- W2.2 secure_zero api_key on shutdown for deepseek/anthropic (cao)
- W3 CMake modernization: target-based cxx_std_20, dstalk_boost_config
  INTERFACE lib, root-level RUNTIME_OUTPUT_DIRECTORY (hu)
- W4 GitHub Actions CI with dynamic Linux/Windows matrix (ma)
- W5.1 SSE buffer_body to cut peak memory ~67% on 32K streams (zhou)
- W6.1 LSP JSON-RPC frame parser hardened against header reordering (sun)
- W7 smoke test: copy plugin DLLs post-build + Boost.JSON src.hpp fix
  for full 9-plugin load coverage (wang)
- W8.1 README slimmed 398->92, Diataxis docs/ skeleton (deng)

Wave 6 (6 parallel agents):
- W9.1 docs/explanation: architecture + plugin-lifecycle (deng)
- W9.3 log credential leak audit (0 vulns, audit trail in
  docs/explanation/security-logging.md) (cao)
- W9.4 docs/reference/plugin-abi.md - 7-point ABI contract (lin)
- W9.6 CLI /history command + status integration (zhao)
- W9.8 plugin_loader fault tolerance: per-plugin failure no longer
  aborts dstalk_init (huang)
- W9.10 host_api unit tests: tests/host_api_test.cpp, 8 cases (liu)

CEO oversight (preexisting bugs fixed during Wave 5 verification):
- lsp_plugin.cpp:449 forward decl mismatch (int vs void)
- tools_plugin.cpp:109 missing forward decl

Multi-agent collaboration framework:
- agents/WORKFLOW.md: 6-stage protocol, two-tier governance,
  prompt template, technical constraints registry

Build: cmake --build 0 error / 0 warning. Tests: 2/2 100% pass.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

dstalk-core/src/plugin_loader.cpp

@@ -9,8 +9,10 @@
 #endif
 
 #include <algorithm>
+#include <cstdio>
 #include <queue>
 #include <stdexcept>
+#include <unordered_set>
 
 namespace dstalk {
 
@@ -199,9 +201,14 @@ std::vector<int> PluginLoader::topological_sort() const
 
 int PluginLoader::initialize_all(const dstalk_host_api_t* host_api)
 {
+    if (!host_api) return -1;
+
     try {
         std::vector<int> order = topological_sort();
 
+        std::unordered_set<std::string> failed_names;
+        int failed_count = 0;
+
         for (int id : order) {
             auto it = plugins_.find(id);
             if (it == plugins_.end()) continue;
@@ -209,16 +216,40 @@ int PluginLoader::initialize_all(const dstalk_host_api_t* host_api)
             PluginInfo& plugin = it->second;
             if (plugin.initialized) continue;
 
+            // 检查依赖是否已失败
+            bool dep_unavailable = false;
+            for (const auto& dep_name : plugin.dependencies) {
+                if (failed_names.count(dep_name)) {
+                    dep_unavailable = true;
+                    break;
+                }
+            }
+
+            if (dep_unavailable) {
+                fprintf(stderr, "[WARN] Plugin '%s' skipped: dependency unavailable\n",
+                        plugin.name.c_str());
+                failed_names.insert(plugin.name);
+                failed_count++;
+                continue;
+            }
+
             if (plugin.info->on_init) {
                 int result = plugin.info->on_init(host_api);
                 if (result != 0) {
-                    return -1;
+                    fprintf(stderr, "[ERROR] Plugin '%s' init failed (code %d)\n",
+                            plugin.name.c_str(), result);
+                    failed_names.insert(plugin.name);
+                    failed_count++;
+                    continue;  // 不设置 initialized=true
                 }
             }
             plugin.initialized = true;
         }
 
-        return 0;
+        return failed_count;
+    } catch (const std::runtime_error&) {
+        // 循环依赖
+        return -1;
     } catch (const std::exception&) {
         return -1;
     }
@@ -272,13 +303,24 @@ void PluginLoader::shutdown_all()
         if (it == plugins_.end()) continue;
 
         PluginInfo& plugin = it->second;
-        if (!plugin.initialized) continue;
-
-        if (plugin.info->on_shutdown) {
+        if (plugin.initialized && plugin.info->on_shutdown) {
             plugin.info->on_shutdown();
         }
         plugin.initialized = false;
     }
+
+    // 释放所有 DLL 句柄
+    for (auto& [id, plugin] : plugins_) {
+        if (plugin.handle) {
+#ifdef _WIN32
+            FreeLibrary((HMODULE)plugin.handle);
+#else
+            dlclose(plugin.handle);
+#endif
+            plugin.handle = nullptr;
+        }
+    }
+    plugins_.clear();
 }
 
 const PluginInfo* PluginLoader::get_plugin(int plugin_id) const