Sprint 277: LSP Advanced Orchestration (steps 1913-1917)

- LSPWorkspaceIndex: track open docs, URI→{languageId,content,version}
- LSPDiagnosticsAggregator: merge diagnostics from multiple LSP sources per URI
- LSPCompletionMerger: merge+deduplicate completion items from multiple sources
- LSPOrchestrator: top-level coordinator composing all three + proxy + cross-lang resolver
- Sprint277IntegrationSummary: poly-api (Go+TypeScript) end-to-end integration

26/26 tests passing (5+5+5+5+6). All new headers ≤600 lines.
LoRA recorded: sprint277-2026-03-01 (1 call, 569 tokens).

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

editor/src/LSPWorkspaceIndex.h

@@ -0,0 +1,72 @@
+#pragma once
+#include <algorithm>
+#include <map>
+#include <set>
+#include <string>
+#include <vector>
+
+namespace whetstone {
+
+struct DocumentInfo {
+    std::string uri;
+    std::string languageId;
+    std::string content;
+    int         version = 0;
+};
+
+class LSPWorkspaceIndex {
+public:
+    void open(const std::string& uri, const std::string& languageId,
+              const std::string& content, int version) {
+        docs_[uri] = DocumentInfo{uri, languageId, content, version};
+    }
+
+    void update(const std::string& uri, const std::string& content, int version) {
+        auto it = docs_.find(uri);
+        if (it == docs_.end()) return;
+        it->second.content = content;
+        it->second.version = version;
+    }
+
+    void close(const std::string& uri) {
+        docs_.erase(uri);
+    }
+
+    bool contains(const std::string& uri) const {
+        return docs_.count(uri) > 0;
+    }
+
+    std::string getLanguage(const std::string& uri) const {
+        auto it = docs_.find(uri);
+        if (it == docs_.end()) return "";
+        return it->second.languageId;
+    }
+
+    DocumentInfo getDocument(const std::string& uri) const {
+        auto it = docs_.find(uri);
+        if (it == docs_.end()) return {};
+        return it->second;
+    }
+
+    std::vector<std::string> listUris(const std::string& languageId) const {
+        std::vector<std::string> result;
+        for (const auto& [uri, info] : docs_)
+            if (info.languageId == languageId)
+                result.push_back(uri);
+        return result;
+    }
+
+    std::vector<std::string> allLanguages() const {
+        std::set<std::string> langs;
+        for (const auto& [uri, info] : docs_)
+            langs.insert(info.languageId);
+        return {langs.begin(), langs.end()};
+    }
+
+    int size() const { return static_cast<int>(docs_.size()); }
+
+private:
+    std::map<std::string, DocumentInfo> docs_;
+};
+
+} // namespace whetstone