diff --git a/editor/CMakeLists.txt b/editor/CMakeLists.txt
index d486add..b84a2ef 100644
--- a/editor/CMakeLists.txt
+++ b/editor/CMakeLists.txt
@@ -2281,4 +2281,13 @@ target_link_libraries(step377_test PRIVATE
     tree_sitter_javascript tree_sitter_typescript
     tree_sitter_java tree_sitter_rust tree_sitter_go)
 
+add_executable(step378_test tests/step378_test.cpp)
+target_include_directories(step378_test PRIVATE src)
+target_link_libraries(step378_test PRIVATE
+    nlohmann_json::nlohmann_json
+    unofficial::tree-sitter::tree-sitter
+    tree_sitter_python tree_sitter_cpp tree_sitter_elisp
+    tree_sitter_javascript tree_sitter_typescript
+    tree_sitter_java tree_sitter_rust tree_sitter_go)
+
 # Step 12: Dear ImGui shell scaffolding created (main.cpp exists but not built due to dependencies)
diff --git a/editor/src/WorkflowOrchestrator.h b/editor/src/WorkflowOrchestrator.h
new file mode 100644
index 0000000..49d7d2e
--- /dev/null
+++ b/editor/src/WorkflowOrchestrator.h
@@ -0,0 +1,231 @@
+#pragma once
+
+#include "WorkflowState.h"
+#include "RoutingEngine.h"
+#include "WorkerRegistry.h"
+#include "ContextAssembler.h"
+#include "ReviewGate.h"
+#include <functional>
+#include <string>
+#include <vector>
+
+struct OrchestratorEvent {
+    std::string type;
+    std::string itemId;
+    json detail;
+    std::string timestamp;
+};
+
+struct BlockerInfo {
+    std::string type;
+    std::vector<std::string> itemIds;
+    std::string description;
+};
+
+class WorkflowOrchestrator {
+public:
+    WorkflowOrchestrator(WorkflowState& workflowState,
+                         RoutingEngine& routingEngine,
+                         WorkerRegistry& workerRegistry,
+                         ContextAssembler& contextAssembler,
+                         ReviewGate& reviewGate)
+        : state_(&workflowState), routing_(&routingEngine), workers_(&workerRegistry),
+          context_(&contextAssembler), review_(&reviewGate) {}
+
+    void setBuffers(const std::map<std::string, BufferInfo>& buffers) {
+        buffers_ = buffers;
+    }
+
+    void setReviewPolicy(const ReviewPolicy& policy) {
+        reviewPolicy_ = policy;
+    }
+
+    OrchestratorEvent step() {
+        auto ready = state_->queue.getReady();
+        if (ready.empty()) {
+            return blockedEvent();
+        }
+        return advanceItem(ready.front()).back();
+    }
+
+    std::vector<OrchestratorEvent> advance() {
+        std::vector<OrchestratorEvent> all;
+        auto ready = state_->queue.getReady();
+        for (const auto& item : ready) {
+            auto events = advanceItem(item);
+            all.insert(all.end(), events.begin(), events.end());
+        }
+        return all;
+    }
+
+    WorkflowStats runToCompletion() {
+        while (true) {
+            auto events = advance();
+            if (events.empty()) break;
+            bool anyProgress = false;
+            for (const auto& ev : events) {
+                if (ev.type != "blocked") {
+                    anyProgress = true;
+                    break;
+                }
+            }
+            if (!anyProgress) break;
+        }
+        return state_->getStats();
+    }
+
+    WorkflowStats runUntil(const std::function<bool(const WorkflowState&)>& predicate) {
+        while (!predicate(*state_)) {
+            auto events = advance();
+            if (events.empty()) break;
+            bool anyProgress = false;
+            for (const auto& ev : events) {
+                if (ev.type != "blocked") {
+                    anyProgress = true;
+                    break;
+                }
+            }
+            if (!anyProgress) break;
+        }
+        return state_->getStats();
+    }
+
+    std::vector<BlockerInfo> getBlockers() {
+        std::vector<BlockerInfo> out;
+
+        auto reviewItems = state_->queue.getByStatus(WI_REVIEW);
+        if (!reviewItems.empty()) {
+            BlockerInfo b;
+            b.type = "needs-review";
+            b.description = "Items are waiting in review.";
+            for (const auto& i : reviewItems) b.itemIds.push_back(i.id);
+            out.push_back(b);
+        }
+
+        BlockerInfo human;
+        human.type = "needs-human";
+        human.description = "Items are routed to human execution.";
+
+        BlockerInfo external;
+        external.type = "needs-external-model";
+        external.description = "Items are prepared for SLM/LLM external execution.";
+
+        for (const auto& status : {WI_ASSIGNED, WI_IN_PROGRESS}) {
+            for (const auto& item : state_->queue.getByStatus(status)) {
+                if (item.workerType == "human") {
+                    human.itemIds.push_back(item.id);
+                } else if (item.workerType == "slm" || item.workerType == "llm") {
+                    external.itemIds.push_back(item.id);
+                }
+            }
+        }
+
+        if (!human.itemIds.empty()) out.push_back(human);
+        if (!external.itemIds.empty()) out.push_back(external);
+        return out;
+    }
+
+private:
+    WorkflowState* state_ = nullptr;
+    RoutingEngine* routing_ = nullptr;
+    WorkerRegistry* workers_ = nullptr;
+    ContextAssembler* context_ = nullptr;
+    ReviewGate* review_ = nullptr;
+    ReviewPolicy reviewPolicy_ = ReviewPolicy::getDefault();
+    std::map<std::string, BufferInfo> buffers_;
+
+    static OrchestratorEvent makeEvent(const std::string& type,
+                                       const std::string& itemId,
+                                       const json& detail = json::object()) {
+        OrchestratorEvent ev;
+        ev.type = type;
+        ev.itemId = itemId;
+        ev.detail = detail;
+        ev.timestamp = workItemTimestamp();
+        return ev;
+    }
+
+    OrchestratorEvent blockedEvent() {
+        auto blockers = getBlockers();
+        if (blockers.empty()) {
+            return makeEvent("blocked", "", json{{"reason", "no-ready-items"}});
+        }
+        return makeEvent("blocked", "", json{{"blockers", toJsonBlockers(blockers)}});
+    }
+
+    static json toJsonBlockers(const std::vector<BlockerInfo>& blockers) {
+        json arr = json::array();
+        for (const auto& b : blockers) {
+            arr.push_back({{"type", b.type},
+                           {"itemIds", b.itemIds},
+                           {"description", b.description}});
+        }
+        return arr;
+    }
+
+    std::vector<OrchestratorEvent> advanceItem(const WorkItem& readyItem) {
+        std::vector<OrchestratorEvent> events;
+
+        auto maybeItem = state_->queue.getItem(readyItem.id);
+        if (!maybeItem.has_value()) return events;
+        WorkItem item = maybeItem.value();
+
+        RoutingDecision decision = routing_->route(item);
+        item.workerType = decision.workerType;
+        item.contextWidth = decision.contextWidth;
+        item.reviewRequired = decision.reviewRequired;
+
+        transitionWorkItem(item, WI_ASSIGNED);
+        transitionWorkItem(item, WI_IN_PROGRESS);
+        state_->queue.updateItem(item.id, item);
+
+        events.push_back(makeEvent("routed", item.id, decision.toJson()));
+
+        WorkerContext ctx = context_->assembleContext(item, buffers_, item.contextWidth,
+                                                      decision.contextBudgetTokens);
+        events.push_back(makeEvent("context-assembled", item.id,
+                                   json{{"contextWidth", item.contextWidth},
+                                        {"tokensBudget", decision.contextBudgetTokens}}));
+
+        WorkerInterface* worker = workers_->getWorker(item.workerType);
+        if (!worker) {
+            events.push_back(makeEvent("blocked", item.id,
+                                       json{{"reason", "worker-not-registered"},
+                                            {"workerType", item.workerType}}));
+            return events;
+        }
+
+        item.result = worker->execute(item, ctx);
+        state_->queue.updateItem(item.id, item);
+        events.push_back(makeEvent("executed", item.id,
+                                   json{{"workerType", item.workerType},
+                                        {"confidence", item.result.confidence}}));
+
+        if (item.workerType == "human") {
+            events.push_back(makeEvent("blocked", item.id,
+                                       json{{"reason", "needs-human"}}));
+            return events;
+        }
+        if (item.workerType == "slm" || item.workerType == "llm") {
+            events.push_back(makeEvent("blocked", item.id,
+                                       json{{"reason", "needs-external-model"}}));
+            return events;
+        }
+
+        ReviewDecision reviewDecision = review_->shouldAutoApprove(item, item.result, reviewPolicy_);
+        if (reviewDecision.approved) {
+            state_->queue.updateItem(item.id, item);
+            state_->queue.complete(item.id);
+            events.push_back(makeEvent("auto-approved", item.id,
+                                       json{{"rule", reviewDecision.ruleMatched}}));
+            events.push_back(makeEvent("completed", item.id));
+        } else {
+            transitionWorkItem(item, WI_REVIEW);
+            state_->queue.updateItem(item.id, item);
+            events.push_back(makeEvent("sent-to-review", item.id,
+                                       json{{"reason", reviewDecision.reasoning}}));
+        }
+
+        return events;
+    }
+};
diff --git a/editor/tests/step378_test.cpp b/editor/tests/step378_test.cpp
new file mode 100644
index 0000000..70329e8
--- /dev/null
+++ b/editor/tests/step378_test.cpp
@@ -0,0 +1,249 @@
+// Step 378: WorkflowOrchestrator main loop (12 tests)
+
+#include <cassert>
+#include <iostream>
+#include <string>
+#include "WorkflowOrchestrator.h"
+
+static WorkItem makeItem(const std::string& id,
+                         const std::string& name,
+                         const std::string& workerType,
+                         bool reviewRequired = false) {
+    WorkItem w;
+    w.id = id;
+    w.nodeId = id + "_node";
+    w.nodeName = name;
+    w.nodeType = "Function";
+    w.bufferId = "buf";
+    w.contextWidth = "local";
+    w.workerType = workerType;
+    w.reviewRequired = reviewRequired;
+    w.priority = "medium";
+    w.status = WI_PENDING;
+    w.createdAt = workItemTimestamp();
+    return w;
+}
+
+int main() {
+    int passed = 0;
+
+    // Test 1: single deterministic/template task completes in one step
+    {
+        WorkflowState ws("p1");
+        ws.queue.enqueue(makeItem("wi1", "getName", "template"));
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+
+        OrchestratorEvent ev = orch.step();
+        assert(ev.type == "completed");
+        assert(ws.queue.getByStatus(WI_COMPLETE).size() == 1);
+        std::cout << "Test 1 PASSED: single template task completes in one step\n";
+        passed++;
+    }
+
+    // Test 2: dependency cascade after completion
+    {
+        WorkflowState ws("p2");
+        WorkItem a = makeItem("a", "getA", "template");
+        WorkItem b = makeItem("b", "getB", "template");
+        b.dependencies.push_back("a");
+        ws.queue.enqueue(a);
+        ws.queue.enqueue(b);
+
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+        orch.step();
+        assert(ws.queue.getByStatus(WI_COMPLETE).size() == 1);
+        assert(ws.queue.getByStatus(WI_READY).size() == 1); // b promoted
+        std::cout << "Test 2 PASSED: dependency cascade promotion\n";
+        passed++;
+    }
+
+    // Test 3: human task blocks as needs-human
+    {
+        WorkflowState ws("p3");
+        ws.queue.enqueue(makeItem("wi3", "hardTask", "human"));
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+        orch.step();
+        auto blockers = orch.getBlockers();
+        bool hasHuman = false;
+        for (const auto& b : blockers) if (b.type == "needs-human") hasHuman = true;
+        assert(hasHuman);
+        std::cout << "Test 3 PASSED: human task blocks\n";
+        passed++;
+    }
+
+    // Test 4: SLM task blocks as needs-external-model
+    {
+        WorkflowState ws("p4");
+        ws.queue.enqueue(makeItem("wi4", "fileTask", "slm"));
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+        orch.step();
+        auto blockers = orch.getBlockers();
+        bool hasExternal = false;
+        for (const auto& b : blockers) if (b.type == "needs-external-model") hasExternal = true;
+        assert(hasExternal);
+        std::cout << "Test 4 PASSED: agent task blocks for external model\n";
+        passed++;
+    }
+
+    // Test 5: runToCompletion processes deterministic tasks
+    {
+        WorkflowState ws("p5");
+        ws.queue.enqueue(makeItem("w1", "getOne", "template"));
+        ws.queue.enqueue(makeItem("w2", "getTwo", "template"));
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+        auto stats = orch.runToCompletion();
+        assert(stats.complete == 2);
+        std::cout << "Test 5 PASSED: runToCompletion completes deterministic tasks\n";
+        passed++;
+    }
+
+    // Test 6: advance emits stage events
+    {
+        WorkflowState ws("p6");
+        ws.queue.enqueue(makeItem("wi6", "getX", "template"));
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+        auto events = orch.advance();
+        bool routed = false, context = false, executed = false, completed = false;
+        for (const auto& e : events) {
+            if (e.type == "routed") routed = true;
+            if (e.type == "context-assembled") context = true;
+            if (e.type == "executed") executed = true;
+            if (e.type == "completed") completed = true;
+        }
+        assert(routed && context && executed && completed);
+        std::cout << "Test 6 PASSED: stage events emitted\n";
+        passed++;
+    }
+
+    // Test 7: blockers report review items
+    {
+        WorkflowState ws("p7");
+        ws.queue.enqueue(makeItem("wi7", "getY", "template", true)); // force review
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+        orch.step();
+        auto blockers = orch.getBlockers();
+        bool hasReview = false;
+        for (const auto& b : blockers) if (b.type == "needs-review") hasReview = true;
+        assert(hasReview);
+        std::cout << "Test 7 PASSED: review blockers reported\n";
+        passed++;
+    }
+
+    // Test 8: empty workflow returns immediately
+    {
+        WorkflowState ws("p8");
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+        auto stats = orch.runToCompletion();
+        assert(stats.total == 0);
+        auto ev = orch.step();
+        assert(ev.type == "blocked");
+        std::cout << "Test 8 PASSED: empty workflow no-op\n";
+        passed++;
+    }
+
+    // Test 9: mixed workflow advances what it can
+    {
+        WorkflowState ws("p9");
+        ws.queue.enqueue(makeItem("d1", "getFast", "template"));
+        ws.queue.enqueue(makeItem("h1", "manual", "human"));
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+        auto stats = orch.runToCompletion();
+        assert(stats.complete == 1);
+        assert(!orch.getBlockers().empty());
+        std::cout << "Test 9 PASSED: mixed workflow partially advances\n";
+        passed++;
+    }
+
+    // Test 10: runUntil predicate can stop early
+    {
+        WorkflowState ws("p10");
+        ws.queue.enqueue(makeItem("a1", "getA", "template"));
+        ws.queue.enqueue(makeItem("a2", "getB", "template"));
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+        auto stats = orch.runUntil([](const WorkflowState& s) {
+            return s.getStats().complete >= 1;
+        });
+        assert(stats.complete >= 1);
+        std::cout << "Test 10 PASSED: runUntil predicate stop\n";
+        passed++;
+    }
+
+    // Test 11: blocked event includes blocker detail when applicable
+    {
+        WorkflowState ws("p11");
+        ws.queue.enqueue(makeItem("h2", "manual2", "human"));
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+        orch.step(); // process human task first
+        OrchestratorEvent ev = orch.step(); // now no ready, returns blocked
+        assert(ev.type == "blocked");
+        assert(ev.detail.contains("blockers"));
+        std::cout << "Test 11 PASSED: blocked event includes blocker detail\n";
+        passed++;
+    }
+
+    // Test 12: agent task stores context payload in result
+    {
+        WorkflowState ws("p12");
+        ws.queue.enqueue(makeItem("ll1", "llTask", "llm"));
+        RoutingEngine routing;
+        auto workers = WorkerRegistry::getDefaultRegistry();
+        ContextAssembler assembler;
+        ReviewGate review;
+        WorkflowOrchestrator orch(ws, routing, workers, assembler, review);
+        orch.step();
+        auto item = ws.queue.getItem("ll1");
+        assert(item.has_value());
+        assert(item->result.astJson.is_object());
+        assert(item->result.astJson.contains("workerType"));
+        std::cout << "Test 12 PASSED: agent context payload preserved\n";
+        passed++;
+    }
+
+    std::cout << "\nResults: " << passed << "/12\n";
+    assert(passed == 12);
+    return 0;
+}
diff --git a/progress.md b/progress.md
index bd4379c..ae2e02a 100644
--- a/progress.md
+++ b/progress.md
@@ -2744,6 +2744,51 @@ Scheme.
 - `editor/tests/step377_test.cpp` remains within project file-size guidance
   for test artifacts (`188` lines)
 
+### Step 378: Orchestrator Core Main Loop
+**Status:** PASS (12/12 tests)
+
+Implemented Sprint 15 orchestration-loop core as a dedicated workflow engine
+that advances ready work items through routing, context assembly, execution,
+review, completion, and blocker reporting.
+
+**Files created:**
+- `editor/src/WorkflowOrchestrator.h` — orchestration core:
+  - `step()` (advance one ready item one stage-set)
+  - `advance()` (advance all currently ready items)
+  - `runToCompletion()` (progress until no further non-blocked progress)
+  - `runUntil(predicate)` (predicate-controlled progression)
+  - `getBlockers()` with typed blockers:
+    `needs-human`, `needs-review`, `needs-external-model`
+  - event stream via `OrchestratorEvent` (`routed`, `context-assembled`,
+    `executed`, `auto-approved`, `sent-to-review`, `completed`, `blocked`)
+- `editor/tests/step378_test.cpp` — 12 tests covering:
+  1. single deterministic/template completion in one step
+  2. dependency cascade promotion
+  3. human-task blocker classification
+  4. agent-task external-model blocker classification
+  5. `runToCompletion()` deterministic completion behavior
+  6. stage event emission coverage
+  7. review blocker reporting
+  8. empty-workflow no-op behavior
+  9. mixed workflow partial progress behavior
+  10. `runUntil(...)` predicate stop behavior
+  11. blocked-event detail payload includes blockers
+  12. agent context payload preservation
+
+**Files modified:**
+- `editor/CMakeLists.txt` — `step378_test` target
+
+**Verification run:**
+- `step378_test` — PASS (12/12) new step coverage
+- `step377_test` — PASS (8/8) regression coverage
+- `step376_test` — PASS (12/12) regression coverage
+- `step375_test` — PASS (12/12) regression coverage
+- `step331_test` — PASS (8/8) orchestration-foundation regression
+
+**Architecture gate check:**
+- `editor/src/WorkflowOrchestrator.h` is within header size limit
+  (`231` lines <= `600`)
+
 # Roadmap Planning — Sprints 12-25+
 
 ## Status: Planning Complete (Sprints 12-19 detailed, 20-25 in roadmap.md)