diff --git a/editor/CMakeLists.txt b/editor/CMakeLists.txt
index 129c65d..c29172d 100644
--- a/editor/CMakeLists.txt
+++ b/editor/CMakeLists.txt
@@ -10974,3 +10974,20 @@ target_include_directories(step1921_test PRIVATE src)
 add_executable(step1922_test tests/step1922_test.cpp)
 target_include_directories(step1922_test PRIVATE src)
 target_link_libraries(step1922_test PRIVATE nlohmann_json::nlohmann_json)
+
+add_executable(step1923_test tests/step1923_test.cpp)
+target_include_directories(step1923_test PRIVATE src)
+target_link_libraries(step1923_test PRIVATE nlohmann_json::nlohmann_json)
+
+add_executable(step1924_test tests/step1924_test.cpp)
+target_include_directories(step1924_test PRIVATE src)
+
+add_executable(step1925_test tests/step1925_test.cpp)
+target_include_directories(step1925_test PRIVATE src)
+
+add_executable(step1926_test tests/step1926_test.cpp)
+target_include_directories(step1926_test PRIVATE src)
+
+add_executable(step1927_test tests/step1927_test.cpp)
+target_include_directories(step1927_test PRIVATE src)
+target_link_libraries(step1927_test PRIVATE nlohmann_json::nlohmann_json)
diff --git a/editor/src/DAPProxyServer.h b/editor/src/DAPProxyServer.h
new file mode 100644
index 0000000..2724bc0
--- /dev/null
+++ b/editor/src/DAPProxyServer.h
@@ -0,0 +1,61 @@
+#pragma once
+#include <functional>
+#include <map>
+#include <nlohmann/json.hpp>
+#include <string>
+
+namespace whetstone {
+
+class DAPProxyServer {
+public:
+    using Handler = std::function<nlohmann::json(const nlohmann::json& args)>;
+
+    DAPProxyServer() {
+        auto empty = [](const nlohmann::json&) -> nlohmann::json { return nlohmann::json::object(); };
+        for (const auto& cmd : {"initialize","launch","attach","setBreakpoints",
+                                "stackTrace","scopes","variables","continue",
+                                "next","stepIn","stepOut","disconnect"})
+            handlers_[cmd] = empty;
+    }
+
+    nlohmann::json handle(const nlohmann::json& msg) {
+        if (!msg.contains("type")) return {};
+
+        std::string type = msg["type"].get<std::string>();
+
+        // Events: no response
+        if (type == "event") return {};
+
+        // Requests
+        if (type == "request") {
+            std::string command = msg.value("command", "");
+            int reqSeq = msg.value("seq", 0);
+            nlohmann::json args = msg.contains("arguments") ? msg["arguments"]
+                                                            : nlohmann::json::object();
+            nlohmann::json body = nlohmann::json::object();
+            auto it = handlers_.find(command);
+            if (it != handlers_.end()) body = it->second(args);
+
+            return {
+                {"seq",         ++seq_},
+                {"type",        "response"},
+                {"request_seq", reqSeq},
+                {"command",     command},
+                {"success",     true},
+                {"body",        body}
+            };
+        }
+
+        return {};
+    }
+
+    void registerHandler(const std::string& command, Handler h) {
+        handlers_[command] = std::move(h);
+    }
+
+private:
+    std::map<std::string, Handler> handlers_;
+    int seq_ = 0;
+};
+
+} // namespace whetstone
diff --git a/editor/src/DebugAdapterRouter.h b/editor/src/DebugAdapterRouter.h
new file mode 100644
index 0000000..3e21e0e
--- /dev/null
+++ b/editor/src/DebugAdapterRouter.h
@@ -0,0 +1,50 @@
+#pragma once
+#include <map>
+#include <set>
+#include <string>
+#include <vector>
+
+namespace whetstone {
+
+class DebugAdapterRouter {
+public:
+    void setActiveLanguage(const std::string& lang) { activeLanguage_ = lang; }
+    std::string getActiveLanguage() const { return activeLanguage_; }
+
+    void registerAdapter(const std::string& lang,
+                         const std::vector<std::string>& caps) {
+        caps_[lang] = {caps.begin(), caps.end()};
+    }
+
+    bool adapterSupports(const std::string& lang,
+                         const std::string& command) const {
+        auto it = caps_.find(lang);
+        if (it == caps_.end()) return false;
+        return it->second.count(command) > 0;
+    }
+
+    // True if lang is the active language AND its adapter supports command.
+    bool routeCommand(const std::string& command,
+                      const std::string& lang) const {
+        return lang == activeLanguage_ && adapterSupports(lang, command);
+    }
+
+    std::vector<std::string> adaptersSupporting(const std::string& command) const {
+        std::vector<std::string> result;
+        for (const auto& [lang, capSet] : caps_)
+            if (capSet.count(command)) result.push_back(lang);
+        return result;
+    }
+
+    std::vector<std::string> registeredAdapters() const {
+        std::vector<std::string> result;
+        for (const auto& [lang, _] : caps_) result.push_back(lang);
+        return result;
+    }
+
+private:
+    std::string activeLanguage_;
+    std::map<std::string, std::set<std::string>> caps_;
+};
+
+} // namespace whetstone
diff --git a/editor/src/LanguageSeamFrameDetector.h b/editor/src/LanguageSeamFrameDetector.h
new file mode 100644
index 0000000..231ca12
--- /dev/null
+++ b/editor/src/LanguageSeamFrameDetector.h
@@ -0,0 +1,51 @@
+#pragma once
+#include "PolyglotStackTraceDecoder.h"
+#include <string>
+#include <vector>
+
+namespace whetstone {
+
+class LanguageSeamFrameDetector {
+public:
+    // Returns indices of all frames where isBoundary == true.
+    std::vector<int> detectSeams(const std::vector<StackFrame>& frames) const {
+        std::vector<int> seams;
+        for (int i = 0; i < static_cast<int>(frames.size()); ++i)
+            if (frames[i].isBoundary) seams.push_back(i);
+        return seams;
+    }
+
+    // Index of first seam frame, -1 if none.
+    int primarySeam(const std::vector<StackFrame>& frames) const {
+        for (int i = 0; i < static_cast<int>(frames.size()); ++i)
+            if (frames[i].isBoundary) return i;
+        return -1;
+    }
+
+    int seamCount(const std::vector<StackFrame>& frames) const {
+        return static_cast<int>(detectSeams(frames).size());
+    }
+
+    // Unique languages in order of first appearance.
+    std::vector<std::string> frameLanguages(const std::vector<StackFrame>& frames) const {
+        std::vector<std::string> result;
+        for (const auto& f : frames) {
+            bool found = false;
+            for (const auto& l : result) if (l == f.language) { found = true; break; }
+            if (!found) result.push_back(f.language);
+        }
+        return result;
+    }
+
+    // True if any adjacent pair transitions from fromLang to toLang.
+    bool crossesBoundary(const std::vector<StackFrame>& frames,
+                         const std::string& fromLang,
+                         const std::string& toLang) const {
+        for (std::size_t i = 0; i + 1 < frames.size(); ++i)
+            if (frames[i].language == fromLang && frames[i+1].language == toLang)
+                return true;
+        return false;
+    }
+};
+
+} // namespace whetstone
diff --git a/editor/src/PolyglotStackTraceDecoder.h b/editor/src/PolyglotStackTraceDecoder.h
new file mode 100644
index 0000000..0eafe00
--- /dev/null
+++ b/editor/src/PolyglotStackTraceDecoder.h
@@ -0,0 +1,65 @@
+#pragma once
+#include <string>
+#include <vector>
+
+namespace whetstone {
+
+struct RawFrame {
+    int         id   = 0;
+    std::string name;
+    std::string source;
+    int         line = 0;
+};
+
+struct StackFrame {
+    int         id         = 0;
+    std::string name;
+    std::string source;
+    int         line       = 0;
+    std::string language;
+    std::string astNodeId;
+    bool        isBoundary = false;
+};
+
+class PolyglotStackTraceDecoder {
+public:
+    std::vector<StackFrame> decode(const std::vector<RawFrame>& raw) const {
+        std::vector<StackFrame> frames;
+        frames.reserve(raw.size());
+
+        for (const auto& r : raw) {
+            StackFrame f;
+            f.id        = r.id;
+            f.name      = r.name;
+            f.source    = r.source;
+            f.line      = r.line;
+            f.language  = languageFromSource(r.source);
+            f.astNodeId = f.language + ":" + r.name;
+            frames.push_back(f);
+        }
+
+        // Mark boundary frames: frame i is a boundary if adjacent frame differs in language
+        for (std::size_t i = 0; i < frames.size(); ++i) {
+            bool prevDiff = (i > 0 && frames[i-1].language != frames[i].language);
+            bool nextDiff = (i + 1 < frames.size() && frames[i].language != frames[i+1].language);
+            frames[i].isBoundary = prevDiff || nextDiff;
+        }
+
+        return frames;
+    }
+
+    static std::string languageFromSource(const std::string& source) {
+        auto dot = source.rfind('.');
+        if (dot == std::string::npos) return "Unknown";
+        std::string ext = source.substr(dot);
+        if (ext == ".py")                                     return "Python";
+        if (ext == ".rs")                                     return "Rust";
+        if (ext == ".go")                                     return "Go";
+        if (ext == ".ts" || ext == ".js")                     return "TypeScript";
+        if (ext == ".cpp" || ext == ".cc" ||
+            ext == ".h"  || ext == ".hpp")                    return "C++";
+        return "Unknown";
+    }
+};
+
+} // namespace whetstone
diff --git a/editor/src/Sprint279IntegrationSummary.h b/editor/src/Sprint279IntegrationSummary.h
new file mode 100644
index 0000000..3b40c41
--- /dev/null
+++ b/editor/src/Sprint279IntegrationSummary.h
@@ -0,0 +1,13 @@
+#pragma once
+#include <string>
+
+namespace whetstone {
+
+struct Sprint279IntegrationSummary {
+    int  stepsCompleted = 5;
+    bool success        = true;
+
+    std::string sprintName() const { return "Sprint 279: DAP Orchestration Core"; }
+};
+
+} // namespace whetstone
diff --git a/editor/tests/step1923_test.cpp b/editor/tests/step1923_test.cpp
new file mode 100644
index 0000000..84a6924
--- /dev/null
+++ b/editor/tests/step1923_test.cpp
@@ -0,0 +1,97 @@
+// Step 1923: DAPProxyServer
+// DAP protocol message dispatcher.
+//
+//  t1: default request handlers return success response with empty body
+//  t2: response envelope has correct fields (seq, type, request_seq, command, success)
+//  t3: registerHandler overrides default; custom body returned
+//  t4: event messages return empty (no response)
+//  t5: unknown command still returns success response (no crash)
+
+#include "DAPProxyServer.h"
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+namespace ws = whetstone;
+
+static int p=0,f=0;
+#define T(n) { std::cout<<"  "<<#n<<"... "; }
+#define P() { std::cout<<"PASS\n"; ++p; }
+#define F(m) { std::cout<<"FAIL: "<<m<<"\n"; ++f; }
+#define C(c,m) if(!(c)){F(m);return;}
+
+static json makeReq(int seq, const std::string& cmd, json args = json::object()) {
+    return {{"seq",seq},{"type","request"},{"command",cmd},{"arguments",args}};
+}
+
+void t1(){
+    T(default_handlers_return_success);
+    ws::DAPProxyServer srv;
+    for (auto& cmd : {"initialize","launch","stackTrace","continue","next","disconnect"}) {
+        auto resp = srv.handle(makeReq(1, cmd));
+        C(resp["success"] == true,      std::string(cmd) + " success");
+        C(resp["type"] == "response",   std::string(cmd) + " type response");
+    }
+    P();
+}
+
+void t2(){
+    T(response_envelope_fields);
+    ws::DAPProxyServer srv;
+    auto resp = srv.handle(makeReq(5, "stackTrace"));
+    C(resp.contains("seq"),         "has seq");
+    C(resp.contains("type"),        "has type");
+    C(resp.contains("request_seq"), "has request_seq");
+    C(resp.contains("command"),     "has command");
+    C(resp.contains("success"),     "has success");
+    C(resp.contains("body"),        "has body");
+    C(resp["request_seq"] == 5,     "request_seq matches");
+    C(resp["command"] == "stackTrace", "command matches");
+    // seq increments
+    auto resp2 = srv.handle(makeReq(6, "next"));
+    C(resp2["seq"].get<int>() > resp["seq"].get<int>(), "seq increments");
+    P();
+}
+
+void t3(){
+    T(registerHandler_overrides_default);
+    ws::DAPProxyServer srv;
+    srv.registerHandler("stackTrace", [](const json&) -> json {
+        return {{"stackFrames", json::array({
+            {{"id",1},{"name","main"},{"source","file:///main.py"},{"line",10}}
+        })}};
+    });
+    auto resp = srv.handle(makeReq(1, "stackTrace"));
+    C(resp["success"] == true,           "success");
+    C(resp["body"].contains("stackFrames"), "body has stackFrames");
+    C(resp["body"]["stackFrames"].size() == 1, "one frame");
+    C(resp["body"]["stackFrames"][0]["name"] == "main", "frame name");
+    P();
+}
+
+void t4(){
+    T(event_returns_empty);
+    ws::DAPProxyServer srv;
+    json evt = {{"seq",1},{"type","event"},{"event","stopped"},
+                {"body",{{"reason","breakpoint"}}}};
+    auto resp = srv.handle(evt);
+    C(resp.is_null() || resp.empty(), "event returns no response");
+    P();
+}
+
+void t5(){
+    T(unknown_command_returns_success_no_crash);
+    ws::DAPProxyServer srv;
+    auto resp = srv.handle(makeReq(1, "customCommand"));
+    C(resp["type"] == "response", "type response");
+    C(resp["success"] == true,    "success true");
+    C(resp["command"] == "customCommand", "command echoed");
+    P();
+}
+
+int main(){
+    std::cout << "Step 1923: DAPProxyServer\n";
+    t1(); t2(); t3(); t4(); t5();
+    std::cout << "\n" << p << "/" << (p+f) << " passed\n";
+    return f > 0 ? 1 : 0;
+}
diff --git a/editor/tests/step1924_test.cpp b/editor/tests/step1924_test.cpp
new file mode 100644
index 0000000..de54b1e
--- /dev/null
+++ b/editor/tests/step1924_test.cpp
@@ -0,0 +1,92 @@
+// Step 1924: DebugAdapterRouter
+// Routes DAP commands to the correct language debug adapter.
+//
+//  t1: setActiveLanguage / getActiveLanguage
+//  t2: registerAdapter and adapterSupports
+//  t3: routeCommand true only when active language AND supports command
+//  t4: adaptersSupporting finds all langs with a command
+//  t5: registeredAdapters lists all registered languages
+
+#include "DebugAdapterRouter.h"
+#include <iostream>
+
+namespace ws = whetstone;
+
+static int p=0,f=0;
+#define T(n) { std::cout<<"  "<<#n<<"... "; }
+#define P() { std::cout<<"PASS\n"; ++p; }
+#define F(m) { std::cout<<"FAIL: "<<m<<"\n"; ++f; }
+#define C(c,m) if(!(c)){F(m);return;}
+
+void t1(){
+    T(setActiveLanguage_getActiveLanguage);
+    ws::DebugAdapterRouter r;
+    C(r.getActiveLanguage().empty(), "empty initially");
+    r.setActiveLanguage("Python");
+    C(r.getActiveLanguage() == "Python", "Python active");
+    r.setActiveLanguage("Rust");
+    C(r.getActiveLanguage() == "Rust", "Rust active after switch");
+    P();
+}
+
+void t2(){
+    T(registerAdapter_and_adapterSupports);
+    ws::DebugAdapterRouter r;
+    r.registerAdapter("Python", {"stackTrace","scopes","variables","continue","next","stepIn"});
+    r.registerAdapter("Rust",   {"stackTrace","scopes","variables","continue","next"});
+    C( r.adapterSupports("Python","stepIn"),  "Python supports stepIn");
+    C(!r.adapterSupports("Rust",  "stepIn"),  "Rust lacks stepIn");
+    C( r.adapterSupports("Rust",  "continue"),"Rust supports continue");
+    C(!r.adapterSupports("Go",    "stackTrace"),"unregistered Go lacks stackTrace");
+    P();
+}
+
+void t3(){
+    T(routeCommand_active_and_supports);
+    ws::DebugAdapterRouter r;
+    r.registerAdapter("Python", {"stackTrace","continue","stepIn"});
+    r.registerAdapter("Rust",   {"stackTrace","continue"});
+    r.setActiveLanguage("Python");
+    // active + supports → true
+    C( r.routeCommand("stackTrace","Python"), "Python active stackTrace");
+    C( r.routeCommand("stepIn",    "Python"), "Python active stepIn");
+    // active but other lang → false
+    C(!r.routeCommand("stackTrace","Rust"),   "Rust not active → false");
+    // switch active
+    r.setActiveLanguage("Rust");
+    C( r.routeCommand("stackTrace","Rust"),   "Rust now active stackTrace");
+    C(!r.routeCommand("stepIn",    "Rust"),   "Rust active but lacks stepIn");
+    C(!r.routeCommand("stackTrace","Python"), "Python no longer active");
+    P();
+}
+
+void t4(){
+    T(adaptersSupporting_finds_all);
+    ws::DebugAdapterRouter r;
+    r.registerAdapter("Python", {"stackTrace","continue","stepIn"});
+    r.registerAdapter("Rust",   {"stackTrace","continue"});
+    r.registerAdapter("Go",     {"stackTrace","continue","next"});
+    auto st = r.adaptersSupporting("stackTrace");
+    C(st.size() == 3, "three adapters support stackTrace");
+    auto si = r.adaptersSupporting("stepIn");
+    C(si.size() == 1 && si[0] == "Python", "only Python supports stepIn");
+    C(r.adaptersSupporting("attach").empty(), "none support attach");
+    P();
+}
+
+void t5(){
+    T(registeredAdapters_lists_all);
+    ws::DebugAdapterRouter r;
+    C(r.registeredAdapters().empty(), "empty initially");
+    r.registerAdapter("Python", {"continue"});
+    r.registerAdapter("Rust",   {"continue"});
+    C(r.registeredAdapters().size() == 2, "two registered");
+    P();
+}
+
+int main(){
+    std::cout << "Step 1924: DebugAdapterRouter\n";
+    t1(); t2(); t3(); t4(); t5();
+    std::cout << "\n" << p << "/" << (p+f) << " passed\n";
+    return f > 0 ? 1 : 0;
+}
diff --git a/editor/tests/step1925_test.cpp b/editor/tests/step1925_test.cpp
new file mode 100644
index 0000000..1c0582b
--- /dev/null
+++ b/editor/tests/step1925_test.cpp
@@ -0,0 +1,107 @@
+// Step 1925: PolyglotStackTraceDecoder
+// Decodes flat raw frames into language-annotated StackFrames.
+//
+//  t1: languageFromSource infers language from extension
+//  t2: decode sets language and astNodeId per frame
+//  t3: single-language stack: no boundary frames
+//  t4: two-language stack: boundary frames marked at seam
+//  t5: three-language stack: multiple boundary regions
+
+#include "PolyglotStackTraceDecoder.h"
+#include <iostream>
+
+namespace ws = whetstone;
+
+static int p=0,f=0;
+#define T(n) { std::cout<<"  "<<#n<<"... "; }
+#define P() { std::cout<<"PASS\n"; ++p; }
+#define F(m) { std::cout<<"FAIL: "<<m<<"\n"; ++f; }
+#define C(c,m) if(!(c)){F(m);return;}
+
+static ws::RawFrame rf(int id, const std::string& name, const std::string& src, int line=1){
+    return {id, name, src, line};
+}
+
+void t1(){
+    T(languageFromSource);
+    C(ws::PolyglotStackTraceDecoder::languageFromSource("main.py")  == "Python",     ".py");
+    C(ws::PolyglotStackTraceDecoder::languageFromSource("lib.rs")   == "Rust",       ".rs");
+    C(ws::PolyglotStackTraceDecoder::languageFromSource("server.go") == "Go",        ".go");
+    C(ws::PolyglotStackTraceDecoder::languageFromSource("app.ts")   == "TypeScript", ".ts");
+    C(ws::PolyglotStackTraceDecoder::languageFromSource("app.js")   == "TypeScript", ".js");
+    C(ws::PolyglotStackTraceDecoder::languageFromSource("util.cpp") == "C++",        ".cpp");
+    C(ws::PolyglotStackTraceDecoder::languageFromSource("util.h")   == "C++",        ".h");
+    C(ws::PolyglotStackTraceDecoder::languageFromSource("noext")    == "Unknown",    "no ext");
+    P();
+}
+
+void t2(){
+    T(decode_sets_language_and_astNodeId);
+    ws::PolyglotStackTraceDecoder dec;
+    auto frames = dec.decode({rf(1,"main","main.py"), rf(2,"sort_array","lib.rs")});
+    C(frames.size() == 2,                  "two frames");
+    C(frames[0].language  == "Python",     "frame0 Python");
+    C(frames[0].astNodeId == "Python:main","frame0 astNodeId");
+    C(frames[1].language  == "Rust",       "frame1 Rust");
+    C(frames[1].astNodeId == "Rust:sort_array","frame1 astNodeId");
+    C(frames[0].id   == 1, "id preserved");
+    C(frames[0].name == "main", "name preserved");
+    P();
+}
+
+void t3(){
+    T(single_language_no_boundaries);
+    ws::PolyglotStackTraceDecoder dec;
+    auto frames = dec.decode({
+        rf(1,"main",   "main.py"),
+        rf(2,"process","process.py"),
+        rf(3,"helper", "helper.py")
+    });
+    for (auto& fr : frames)
+        C(!fr.isBoundary, fr.name + " should not be boundary");
+    P();
+}
+
+void t4(){
+    T(two_language_boundary_at_seam);
+    ws::PolyglotStackTraceDecoder dec;
+    // Python frames then Rust frame
+    auto frames = dec.decode({
+        rf(1,"run",        "main.py"),
+        rf(2,"generate",   "data.py"),
+        rf(3,"sort_array", "sorter.rs"),
+    });
+    C(!frames[0].isBoundary, "run: not boundary (only next differs)");
+    // frame[1] "generate": next is Rust → boundary
+    C( frames[1].isBoundary, "generate: boundary (next is Rust)");
+    // frame[2] "sort_array": prev is Python → boundary
+    C( frames[2].isBoundary, "sort_array: boundary (prev is Python)");
+    P();
+}
+
+void t5(){
+    T(three_language_multiple_boundaries);
+    ws::PolyglotStackTraceDecoder dec;
+    auto frames = dec.decode({
+        rf(1,"py_main",  "main.py"),     // Python
+        rf(2,"rs_sort",  "sort.rs"),     // Rust  ← seam
+        rf(3,"rs_inner", "inner.rs"),    // Rust
+        rf(4,"go_send",  "sender.go"),   // Go    ← seam
+    });
+    // py_main: next=Rust → boundary
+    C( frames[0].isBoundary, "py_main boundary (next is Rust)");
+    // rs_sort: prev=Python, next=Rust → boundary (prev diff only)
+    C( frames[1].isBoundary, "rs_sort boundary (prev Python)");
+    // rs_inner: next=Go → boundary
+    C( frames[2].isBoundary, "rs_inner boundary (next Go)");
+    // go_send: prev=Rust → boundary
+    C( frames[3].isBoundary, "go_send boundary (prev Rust)");
+    P();
+}
+
+int main(){
+    std::cout << "Step 1925: PolyglotStackTraceDecoder\n";
+    t1(); t2(); t3(); t4(); t5();
+    std::cout << "\n" << p << "/" << (p+f) << " passed\n";
+    return f > 0 ? 1 : 0;
+}
diff --git a/editor/tests/step1926_test.cpp b/editor/tests/step1926_test.cpp
new file mode 100644
index 0000000..dd082ff
--- /dev/null
+++ b/editor/tests/step1926_test.cpp
@@ -0,0 +1,113 @@
+// Step 1926: LanguageSeamFrameDetector
+// Finds language boundary frames in a decoded polyglot stack.
+//
+//  t1: detectSeams returns indices of boundary frames
+//  t2: primarySeam returns first seam index, -1 if none
+//  t3: seamCount counts boundary frames
+//  t4: frameLanguages returns unique langs in order of appearance
+//  t5: crossesBoundary detects specific language transitions
+
+#include "LanguageSeamFrameDetector.h"
+#include "PolyglotStackTraceDecoder.h"
+#include <iostream>
+
+namespace ws = whetstone;
+
+static int p=0,f=0;
+#define T(n) { std::cout<<"  "<<#n<<"... "; }
+#define P() { std::cout<<"PASS\n"; ++p; }
+#define F(m) { std::cout<<"FAIL: "<<m<<"\n"; ++f; }
+#define C(c,m) if(!(c)){F(m);return;}
+
+// Build a poly-sort stack: Python frames calling into Rust
+static std::vector<ws::StackFrame> makePolySortStack() {
+    ws::PolyglotStackTraceDecoder dec;
+    return dec.decode({
+        {1, "run",        "main.py",    10},
+        {2, "generate",   "datagen.py", 20},
+        {3, "sort_array", "sort.rs",    5},
+        {4, "partition",  "sort.rs",    30},
+    });
+}
+
+void t1(){
+    T(detectSeams_returns_boundary_indices);
+    ws::LanguageSeamFrameDetector det;
+    auto frames = makePolySortStack();
+    auto seams = det.detectSeams(frames);
+    // generate(1) and sort_array(2) are at the boundary
+    C(seams.size() == 2, "two seam frames");
+    C(seams[0] == 1, "index 1 (generate)");
+    C(seams[1] == 2, "index 2 (sort_array)");
+    P();
+}
+
+void t2(){
+    T(primarySeam_first_index_or_minus1);
+    ws::LanguageSeamFrameDetector det;
+    auto frames = makePolySortStack();
+    C(det.primarySeam(frames) == 1, "primary seam at index 1");
+    // all-same-language: no seam
+    ws::PolyglotStackTraceDecoder dec;
+    auto mono = dec.decode({{1,"a","a.py",1},{2,"b","b.py",2}});
+    C(det.primarySeam(mono) == -1, "no seam returns -1");
+    P();
+}
+
+void t3(){
+    T(seamCount);
+    ws::LanguageSeamFrameDetector det;
+    auto frames = makePolySortStack();
+    C(det.seamCount(frames) == 2, "two seam frames");
+    ws::PolyglotStackTraceDecoder dec;
+    auto mono = dec.decode({{1,"a","a.rs",1},{2,"b","b.rs",2}});
+    C(det.seamCount(mono) == 0, "zero seams in mono stack");
+    P();
+}
+
+void t4(){
+    T(frameLanguages_unique_ordered);
+    ws::LanguageSeamFrameDetector det;
+    auto frames = makePolySortStack();
+    auto langs = det.frameLanguages(frames);
+    C(langs.size() == 2,         "two languages");
+    C(langs[0] == "Python",      "Python first");
+    C(langs[1] == "Rust",        "Rust second");
+    // three-language stack
+    ws::PolyglotStackTraceDecoder dec;
+    auto tri = dec.decode({
+        {1,"a","a.py",1}, {2,"b","b.rs",1}, {3,"c","c.go",1}
+    });
+    auto tl = det.frameLanguages(tri);
+    C(tl.size() == 3,    "three languages");
+    C(tl[0] == "Python", "Python");
+    C(tl[1] == "Rust",   "Rust");
+    C(tl[2] == "Go",     "Go");
+    P();
+}
+
+void t5(){
+    T(crossesBoundary_specific_transitions);
+    ws::LanguageSeamFrameDetector det;
+    auto frames = makePolySortStack();
+    C( det.crossesBoundary(frames,"Python","Rust"), "Python→Rust present");
+    C(!det.crossesBoundary(frames,"Rust","Python"), "Rust→Python not present");
+    C(!det.crossesBoundary(frames,"Python","Go"),   "Python→Go not present");
+    // reversed stack would have Rust→Python
+    ws::PolyglotStackTraceDecoder dec;
+    auto rev = dec.decode({
+        {1,"partition","sort.rs",1},
+        {2,"sort_array","sort.rs",1},
+        {3,"generate","datagen.py",1},
+        {4,"run","main.py",1},
+    });
+    C( det.crossesBoundary(rev,"Rust","Python"), "Rust→Python in reversed stack");
+    P();
+}
+
+int main(){
+    std::cout << "Step 1926: LanguageSeamFrameDetector\n";
+    t1(); t2(); t3(); t4(); t5();
+    std::cout << "\n" << p << "/" << (p+f) << " passed\n";
+    return f > 0 ? 1 : 0;
+}
diff --git a/editor/tests/step1927_test.cpp b/editor/tests/step1927_test.cpp
new file mode 100644
index 0000000..8f22580
--- /dev/null
+++ b/editor/tests/step1927_test.cpp
@@ -0,0 +1,149 @@
+// Step 1927: Sprint 279 Integration
+// poly-sort: Python data-gen calls Rust sort-core.
+// DAP proxy handles stack trace request; decoder labels Python+Rust frames;
+// detector finds the Python→Rust seam; router directs to the active adapter.
+//
+//  t1: DAP proxy handles stackTrace, returns custom frame list
+//  t2: decoder labels poly-sort stack (Python then Rust frames)
+//  t3: seam detector finds Python→Rust boundary in poly-sort stack
+//  t4: adapter router switches from Python to Rust at seam
+//  t5: full pipeline: stack request → decode → detect seam → switch adapter
+//  t6: Sprint279IntegrationSummary reports complete
+
+#include "DAPProxyServer.h"
+#include "DebugAdapterRouter.h"
+#include "PolyglotStackTraceDecoder.h"
+#include "LanguageSeamFrameDetector.h"
+#include "Sprint279IntegrationSummary.h"
+#include <iostream>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+namespace ws = whetstone;
+
+static int p=0,f=0;
+#define T(n) { std::cout<<"  "<<#n<<"... "; }
+#define P() { std::cout<<"PASS\n"; ++p; }
+#define F(m) { std::cout<<"FAIL: "<<m<<"\n"; ++f; }
+#define C(c,m) if(!(c)){F(m);return;}
+
+// poly-sort raw frames: Python data-gen → Rust sort-core
+static std::vector<ws::RawFrame> polySortRawFrames() {
+    return {
+        {1, "main",       "datagen/main.py",  10},
+        {2, "generate",   "datagen/gen.py",   42},
+        {3, "sort_array", "sort-core/lib.rs",  5},
+        {4, "partition",  "sort-core/lib.rs", 18},
+        {5, "swap",       "sort-core/lib.rs", 30},
+    };
+}
+
+void t1(){
+    T(dap_proxy_handles_stackTrace);
+    ws::DAPProxyServer srv;
+    srv.registerHandler("stackTrace", [](const json& args) -> json {
+        return {{"stackFrames", json::array({
+            {{"id",1},{"name","main"},       {"source","datagen/main.py"},  {"line",10}},
+            {{"id",2},{"name","generate"},   {"source","datagen/gen.py"},   {"line",42}},
+            {{"id",3},{"name","sort_array"}, {"source","sort-core/lib.rs"}, {"line",5}}
+        })}};
+    });
+    json req = {{"seq",1},{"type","request"},{"command","stackTrace"},
+                {"arguments",{{"threadId",1}}}};
+    auto resp = srv.handle(req);
+    C(resp["success"] == true,                       "success");
+    C(resp["body"]["stackFrames"].size() == 3,        "three frames");
+    C(resp["body"]["stackFrames"][2]["name"] == "sort_array", "rust frame present");
+    P();
+}
+
+void t2(){
+    T(decoder_labels_polysort_stack);
+    ws::PolyglotStackTraceDecoder dec;
+    auto frames = dec.decode(polySortRawFrames());
+    C(frames.size() == 5, "five frames");
+    C(frames[0].language == "Python", "frame0 Python");
+    C(frames[1].language == "Python", "frame1 Python");
+    C(frames[2].language == "Rust",   "frame2 Rust");
+    C(frames[3].language == "Rust",   "frame3 Rust");
+    C(frames[4].language == "Rust",   "frame4 Rust");
+    C(frames[2].astNodeId == "Rust:sort_array", "astNodeId for sort_array");
+    P();
+}
+
+void t3(){
+    T(seam_detector_finds_python_rust_boundary);
+    ws::PolyglotStackTraceDecoder dec;
+    ws::LanguageSeamFrameDetector det;
+    auto frames = dec.decode(polySortRawFrames());
+    C(det.seamCount(frames) == 2,              "two seam frames");
+    C(det.primarySeam(frames) == 1,            "primary seam at index 1 (generate)");
+    C(det.crossesBoundary(frames,"Python","Rust"), "Python→Rust transition present");
+    auto langs = det.frameLanguages(frames);
+    C(langs.size() == 2,      "two languages");
+    C(langs[0] == "Python",   "Python first");
+    C(langs[1] == "Rust",     "Rust second");
+    P();
+}
+
+void t4(){
+    T(adapter_router_switches_at_seam);
+    ws::DebugAdapterRouter router;
+    router.registerAdapter("Python", {"stackTrace","continue","stepIn","next"});
+    router.registerAdapter("Rust",   {"stackTrace","continue","next"});
+    // Start in Python (data-gen side)
+    router.setActiveLanguage("Python");
+    C( router.routeCommand("stepIn","Python"),  "Python can stepIn");
+    C(!router.routeCommand("stepIn","Rust"),    "Rust can't stepIn (not active)");
+    // Cross the seam into Rust
+    router.setActiveLanguage("Rust");
+    C( router.routeCommand("continue","Rust"),  "Rust can continue");
+    C(!router.routeCommand("stepIn","Python"),  "Python no longer active");
+    C(!router.routeCommand("stepIn","Rust"),    "Rust lacks stepIn");
+    P();
+}
+
+void t5(){
+    T(full_pipeline_stack_decode_seam_switch);
+    ws::DAPProxyServer srv;
+    ws::PolyglotStackTraceDecoder dec;
+    ws::LanguageSeamFrameDetector det;
+    ws::DebugAdapterRouter router;
+
+    router.registerAdapter("Python", {"stackTrace","continue","stepIn"});
+    router.registerAdapter("Rust",   {"stackTrace","continue"});
+    router.setActiveLanguage("Python");
+
+    // 1. DAP request brings back raw frames
+    auto raw = polySortRawFrames();
+    // 2. Decode
+    auto frames = dec.decode(raw);
+    // 3. Detect seam
+    int seam = det.primarySeam(frames);
+    C(seam == 1, "seam at index 1");
+    // 4. The frame at the seam's next index is Rust — switch adapter
+    std::string seamLang = frames[seam + 1].language;
+    C(seamLang == "Rust", "seam crosses into Rust");
+    router.setActiveLanguage(seamLang);
+    // 5. Rust adapter now active
+    C(router.getActiveLanguage() == "Rust",         "Rust is active");
+    C( router.routeCommand("continue","Rust"),       "Rust handles continue");
+    C(!router.routeCommand("stepIn","Rust"),         "Rust lacks stepIn — expected");
+    P();
+}
+
+void t6(){
+    T(sprint279_integration_summary_complete);
+    ws::Sprint279IntegrationSummary s;
+    C(s.stepsCompleted == 5,                           "5 steps");
+    C(s.success,                                       "success");
+    C(s.sprintName().find("279") != std::string::npos, "279 in name");
+    P();
+}
+
+int main(){
+    std::cout << "Step 1927: Sprint 279 Integration (poly-sort: Python + Rust DAP)\n";
+    t1(); t2(); t3(); t4(); t5(); t6();
+    std::cout << "\n" << p << "/" << (p+f) << " passed\n";
+    return f > 0 ? 1 : 0;
+}