diff --git a/editor/CMakeLists.txt b/editor/CMakeLists.txt
index 84651b3..69f31d6 100644
--- a/editor/CMakeLists.txt
+++ b/editor/CMakeLists.txt
@@ -2533,4 +2533,13 @@ target_link_libraries(step405_test PRIVATE
     tree_sitter_javascript tree_sitter_typescript
     tree_sitter_java tree_sitter_rust tree_sitter_go)
 
+add_executable(step406_test tests/step406_test.cpp)
+target_include_directories(step406_test PRIVATE src)
+target_link_libraries(step406_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/Pipeline.h b/editor/src/Pipeline.h
index 3c5ae9a..13a8138 100644
--- a/editor/src/Pipeline.h
+++ b/editor/src/Pipeline.h
@@ -176,6 +176,9 @@ public:
         } else if (language == "csharp") {
             CSharpGenerator gen;
             return gen.generate(ast);
+        } else if (language == "fsharp" || language == "f#" || language == "fs") {
+            FSharpGenerator gen;
+            return gen.generate(ast);
         } else if (language == "c") {
             CGenerator gen;
             return gen.generate(ast);
diff --git a/editor/src/ast/FSharpGenerator.h b/editor/src/ast/FSharpGenerator.h
new file mode 100644
index 0000000..256abaf
--- /dev/null
+++ b/editor/src/ast/FSharpGenerator.h
@@ -0,0 +1,348 @@
+#pragma once
+
+#include "ProjectionGenerator.h"
+#include "ClassDeclaration.h"
+#include "AsyncNodes.h"
+#include "EnumNamespaceNodes.h"
+#include "../SemannoAnnotationImpl.h"
+
+class FSharpGenerator : public ProjectionGenerator, public SemannoAnnotationImpl<FSharpGenerator> {
+public:
+    std::string commentPrefix() const { return "// "; }
+
+    std::string generate(const ASTNode* node) override {
+        return dispatchGenerate(this, node, "// Unknown concept: ");
+    }
+
+    std::string visitModule(const Module* module) override {
+        std::ostringstream oss;
+        oss << "// Module: " << module->name << "\n\n";
+
+        for (const auto* stmt : module->getChildren("statements")) {
+            oss << generate(stmt) << "\n";
+        }
+        if (!module->getChildren("statements").empty()) oss << "\n";
+
+        for (const auto* var : module->getChildren("variables")) {
+            oss << generate(var) << "\n";
+        }
+        if (!module->getChildren("variables").empty()) oss << "\n";
+
+        for (const auto* fn : module->getChildren("functions")) {
+            oss << generate(fn) << "\n";
+        }
+
+        return oss.str();
+    }
+
+    std::string visitFunction(const Function* function) override {
+        std::ostringstream oss;
+        for (const auto* anno : function->getChildren("annotations")) {
+            oss << generate(anno) << "\n";
+        }
+
+        oss << "let " << function->name;
+        auto params = function->getChildren("parameters");
+        for (const auto* p : params) {
+            oss << " " << static_cast<const Parameter*>(p)->name;
+        }
+        oss << " =";
+
+        auto body = function->getChildren("body");
+        if (body.empty()) {
+            oss << " ()";
+            return oss.str();
+        }
+
+        if (body.size() == 1) {
+            oss << " " << generate(body[0]);
+            return oss.str();
+        }
+
+        oss << "\n";
+        for (const auto* stmt : body) {
+            oss << "    " << generate(stmt) << "\n";
+        }
+        return trimTrailingNewline(oss.str());
+    }
+
+    std::string visitAsyncFunction(const ASTNode* node) override {
+        auto* fn = static_cast<const AsyncFunction*>(node);
+        std::ostringstream oss;
+        for (const auto* anno : fn->getChildren("annotations")) {
+            oss << generate(anno) << "\n";
+        }
+        oss << "let " << fn->name;
+        auto params = fn->getChildren("parameters");
+        for (const auto* p : params) {
+            oss << " " << static_cast<const Parameter*>(p)->name;
+        }
+        oss << " = async {\n";
+        auto body = fn->getChildren("body");
+        for (const auto* stmt : body) {
+            oss << "    " << generate(stmt) << "\n";
+        }
+        oss << "}";
+        return oss.str();
+    }
+
+    std::string visitVariable(const Variable* variable) override {
+        bool isMutable = false;
+        for (const auto* anno : variable->getChildren("annotations")) {
+            if (anno->conceptType == "MutAnnotation") {
+                isMutable = true;
+                break;
+            }
+        }
+
+        std::ostringstream oss;
+        oss << "let ";
+        if (isMutable) oss << "mutable ";
+        oss << variable->name;
+        auto init = variable->getChild("initializer");
+        if (init) oss << " = " << generate(init);
+        return oss.str();
+    }
+
+    std::string visitParameter(const Parameter* parameter) override {
+        return parameter->name;
+    }
+
+    std::string visitReturn(const Return* r) override {
+        auto value = r->getChild("value");
+        return value ? generate(value) : "()";
+    }
+
+    std::string visitAssignment(const Assignment* a) override {
+        auto target = a->getChild("target");
+        auto value = a->getChild("value");
+        return (target ? generate(target) : "_") + " <- " + (value ? generate(value) : "()");
+    }
+
+    std::string visitIfStatement(const IfStatement* s) override {
+        std::ostringstream oss;
+        auto cond = s->getChild("condition");
+        oss << "if " << (cond ? generate(cond) : "true") << " then";
+        auto thenBranch = s->getChildren("thenBranch");
+        auto elseBranch = s->getChildren("elseBranch");
+        if (!thenBranch.empty()) oss << " " << generate(thenBranch.front());
+        else oss << " ()";
+        if (!elseBranch.empty()) oss << " else " << generate(elseBranch.front());
+        return oss.str();
+    }
+
+    std::string visitExpressionStatement(const ExpressionStatement* s) override {
+        auto expr = s->getChild("expression");
+        return expr ? generate(expr) : "()";
+    }
+
+    std::string visitBinaryOperation(const BinaryOperation* b) override {
+        auto left = b->getChild("left");
+        auto right = b->getChild("right");
+        return (left ? generate(left) : "") + " " + b->op + " " + (right ? generate(right) : "");
+    }
+
+    std::string visitUnaryOperation(const UnaryOperation* u) override {
+        auto operand = u->getChild("operand");
+        return u->op + (operand ? generate(operand) : "");
+    }
+
+    std::string visitFunctionCall(const FunctionCall* c) override {
+        // Parser uses this marker for F# pipe chains.
+        if (c->functionName == "pipeline") return "|> pipeline";
+
+        std::ostringstream oss;
+        oss << c->functionName;
+        auto args = c->getChildren("arguments");
+        for (const auto* arg : args) oss << " " << generate(arg);
+        return oss.str();
+    }
+
+    std::string visitWhileLoop(const WhileLoop* l) override {
+        std::ostringstream oss;
+        auto cond = l->getChild("condition");
+        oss << "while " << (cond ? generate(cond) : "true") << " do";
+        auto body = l->getChildren("body");
+        if (body.empty()) return oss.str() + " ()";
+        oss << "\n";
+        for (const auto* s : body) oss << "    " << generate(s) << "\n";
+        return trimTrailingNewline(oss.str());
+    }
+
+    std::string visitForLoop(const ForLoop* l) override {
+        std::ostringstream oss;
+        auto iter = l->getChild("iterable");
+        oss << "for " << (l->iteratorName.empty() ? "item" : l->iteratorName)
+            << " in " << (iter ? generate(iter) : "[]") << " do";
+        auto body = l->getChildren("body");
+        if (body.empty()) return oss.str() + " ()";
+        oss << "\n";
+        for (const auto* s : body) oss << "    " << generate(s) << "\n";
+        return trimTrailingNewline(oss.str());
+    }
+
+    std::string visitBlock(const Block* b) override {
+        std::ostringstream oss;
+        for (const auto* s : b->getChildren("statements")) {
+            oss << generate(s) << "\n";
+        }
+        return trimTrailingNewline(oss.str());
+    }
+
+    std::string visitListLiteral(const ListLiteral* l) override {
+        std::ostringstream oss;
+        oss << "[";
+        auto elems = l->getChildren("elements");
+        for (size_t i = 0; i < elems.size(); ++i) {
+            if (i > 0) oss << "; ";
+            oss << generate(elems[i]);
+        }
+        oss << "]";
+        return oss.str();
+    }
+
+    std::string visitIndexAccess(const IndexAccess* a) override {
+        auto* target = a->getChild("target");
+        auto* idx = a->getChild("index");
+        return (target ? generate(target) : "") + "[" + (idx ? generate(idx) : "") + "]";
+    }
+
+    std::string visitMemberAccess(const MemberAccess* a) override {
+        auto* target = a->getChild("target");
+        return (target ? generate(target) : "") + "." + a->memberName;
+    }
+
+    std::string visitVariableReference(const VariableReference* v) override {
+        return v->variableName;
+    }
+    std::string visitIntegerLiteral(const IntegerLiteral* l) override { return std::to_string(l->value); }
+    std::string visitFloatLiteral(const FloatLiteral* l) override { return l->value; }
+    std::string visitStringLiteral(const StringLiteral* l) override { return "\"" + l->value + "\""; }
+    std::string visitBooleanLiteral(const BooleanLiteral* l) override { return l->value ? "true" : "false"; }
+    std::string visitNullLiteral(const NullLiteral*) override { return "null"; }
+
+    std::string visitPrimitiveType(const PrimitiveType* t) override {
+        if (t->kind == "int") return "int";
+        if (t->kind == "float" || t->kind == "double") return "float";
+        if (t->kind == "string") return "string";
+        if (t->kind == "bool") return "bool";
+        if (t->kind == "void") return "unit";
+        return t->kind;
+    }
+    std::string visitListType(const ListType* t) override {
+        auto* e = t->getChild("elementType");
+        return (e ? generate(e) : "obj") + " list";
+    }
+    std::string visitSetType(const SetType* t) override {
+        auto* e = t->getChild("elementType");
+        return (e ? generate(e) : "obj") + " seq";
+    }
+    std::string visitMapType(const MapType* t) override {
+        auto* k = t->getChild("keyType");
+        auto* v = t->getChild("valueType");
+        return "(" + std::string(k ? generate(k) : "obj") + " * " +
+               std::string(v ? generate(v) : "obj") + ") list";
+    }
+    std::string visitTupleType(const TupleType* t) override {
+        std::ostringstream oss;
+        auto elems = t->getChildren("elementTypes");
+        for (size_t i = 0; i < elems.size(); ++i) {
+            if (i > 0) oss << " * ";
+            oss << generate(elems[i]);
+        }
+        return oss.str();
+    }
+    std::string visitArrayType(const ArrayType* t) override {
+        auto* e = t->getChild("elementType");
+        return (e ? generate(e) : "obj") + " array";
+    }
+    std::string visitOptionalType(const OptionalType* t) override {
+        auto* inner = t->getChild("innerType");
+        return (inner ? generate(inner) : "obj") + " option";
+    }
+    std::string visitCustomType(const CustomType* t) override {
+        if (t->typeName == "result") return "result";
+        return t->typeName;
+    }
+
+    // Subject 1 annotations not covered by SemannoAnnotationImpl.
+    std::string visitDerefStrategy(const DerefStrategy* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+    std::string visitOptimizationLock(const OptimizationLock* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+    std::string visitLangSpecific(const LangSpecific* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+    std::string visitDeallocateAnnotation(const DeallocateAnnotation* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+    std::string visitLifetimeAnnotation(const LifetimeAnnotation* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+    std::string visitReclaimAnnotation(const ReclaimAnnotation* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+    std::string visitOwnerAnnotation(const OwnerAnnotation* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+    std::string visitAllocateAnnotation(const AllocateAnnotation* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+    std::string visitHotColdAnnotation(const HotColdAnnotation* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+    std::string visitInlineAnnotation(const InlineAnnotation* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+    std::string visitPureAnnotation(const PureAnnotation* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+    std::string visitConstExprAnnotation(const ConstExprAnnotation* a) override {
+        return commentPrefix() + SemannoEmitter::emit(a);
+    }
+
+    std::string visitNamespaceDeclaration(const ASTNode* node) override {
+        auto* ns = static_cast<const NamespaceDeclaration*>(node);
+        return "module " + ns->name;
+    }
+
+    std::string visitEnumDeclaration(const ASTNode* node) override {
+        auto* en = static_cast<const EnumDeclaration*>(node);
+        std::ostringstream oss;
+        oss << "type " << en->name << " =";
+        auto members = en->getChildren("members");
+        if (members.empty()) {
+            oss << " | Unknown";
+            return oss.str();
+        }
+        for (const auto* m : members) {
+            auto* em = static_cast<const EnumMember*>(m);
+            oss << "\n    | " << em->name;
+        }
+        return oss.str();
+    }
+
+    std::string visitClassDeclaration(const ASTNode* node) override {
+        auto* cls = static_cast<const ClassDeclaration*>(node);
+        std::ostringstream oss;
+        oss << "type " << cls->name << " = {";
+        auto fields = cls->getChildren("fields");
+        if (!fields.empty()) oss << " ";
+        for (size_t i = 0; i < fields.size(); ++i) {
+            auto* v = static_cast<const Variable*>(fields[i]);
+            if (i > 0) oss << "; ";
+            oss << v->name << ": obj";
+        }
+        if (!fields.empty()) oss << " ";
+        oss << "}";
+        return oss.str();
+    }
+
+private:
+    static std::string trimTrailingNewline(std::string s) {
+        while (!s.empty() && (s.back() == '\n' || s.back() == '\r')) s.pop_back();
+        return s;
+    }
+};
diff --git a/editor/src/ast/Generator.h b/editor/src/ast/Generator.h
index ba0748f..afad958 100644
--- a/editor/src/ast/Generator.h
+++ b/editor/src/ast/Generator.h
@@ -11,6 +11,7 @@
 #include "GoGenerator.h"
 #include "KotlinGenerator.h"
 #include "CSharpGenerator.h"
+#include "FSharpGenerator.h"
 #include "CGenerator.h"
 #include "WatGenerator.h"
 #include "CommonLispGenerator.h"
diff --git a/editor/tests/step406_test.cpp b/editor/tests/step406_test.cpp
new file mode 100644
index 0000000..9cf9c1e
--- /dev/null
+++ b/editor/tests/step406_test.cpp
@@ -0,0 +1,205 @@
+// Step 406: F# Generator Tests (12 tests)
+
+#include "ast/FSharpGenerator.h"
+#include "ast/Module.h"
+#include "ast/Function.h"
+#include "ast/Variable.h"
+#include "ast/Parameter.h"
+#include "ast/Expression.h"
+#include "ast/Statement.h"
+#include "ast/EnumNamespaceNodes.h"
+#include "ast/ClassDeclaration.h"
+#include "ast/Type.h"
+#include "ast/Annotation.h"
+#include "ast/AsyncNodes.h"
+#include "Pipeline.h"
+
+#include <iostream>
+#include <string>
+
+static int passed = 0, failed = 0;
+#define TEST(name) { std::cout << "  " << #name << "... "; }
+#define PASS() { std::cout << "PASS\n"; ++passed; }
+#define FAIL(msg) { std::cout << "FAIL: " << msg << "\n"; ++failed; }
+#define CHECK(cond, msg) if (!(cond)) { FAIL(msg); return; } else {}
+
+void test_generate_let_function() {
+    TEST(generate_let_function);
+    Function fn("fn1", "add");
+    fn.addChild("parameters", new Parameter("p1", "x"));
+    fn.addChild("parameters", new Parameter("p2", "y"));
+    auto* ret = new Return();
+    ret->id = "ret1";
+    ret->setChild("value", new BinaryOperation("b1", "+"));
+    fn.addChild("body", ret);
+
+    FSharpGenerator gen;
+    std::string out = gen.generate(&fn);
+    CHECK(out.find("let add x y =") != std::string::npos, "expected let function signature");
+    PASS();
+}
+
+void test_generate_mutable_variable() {
+    TEST(generate_mutable_variable);
+    Variable v("v1", "counter");
+    auto* mut = new MutAnnotation();
+    mut->id = "m1";
+    v.addChild("annotations", mut);
+
+    FSharpGenerator gen;
+    std::string out = gen.generate(&v);
+    CHECK(out.find("let mutable counter") != std::string::npos, "expected mutable variable");
+    PASS();
+}
+
+void test_generate_discriminated_union() {
+    TEST(generate_discriminated_union);
+    EnumDeclaration en("e1", "Shape");
+    en.addChild("members", new EnumMember("c1", "Circle"));
+    en.addChild("members", new EnumMember("c2", "Rectangle"));
+
+    FSharpGenerator gen;
+    std::string out = gen.generate(&en);
+    CHECK(out.find("type Shape =") != std::string::npos, "expected type declaration");
+    CHECK(out.find("| Circle") != std::string::npos, "expected Circle case");
+    CHECK(out.find("| Rectangle") != std::string::npos, "expected Rectangle case");
+    PASS();
+}
+
+void test_generate_record_class() {
+    TEST(generate_record_class);
+    ClassDeclaration cls("c1", "Person");
+    cls.addChild("fields", new Variable("f1", "name"));
+    cls.addChild("fields", new Variable("f2", "age"));
+
+    FSharpGenerator gen;
+    std::string out = gen.generate(&cls);
+    CHECK(out.find("type Person = {") != std::string::npos, "expected record type");
+    CHECK(out.find("name: obj") != std::string::npos, "expected name field");
+    CHECK(out.find("age: obj") != std::string::npos, "expected age field");
+    PASS();
+}
+
+void test_generate_async_function() {
+    TEST(generate_async_function);
+    AsyncFunction fn("a1", "fetchData");
+    fn.addChild("body", new Return());
+
+    FSharpGenerator gen;
+    std::string out = gen.generate(&fn);
+    CHECK(out.find("let fetchData = async {") != std::string::npos, "expected async function form");
+    PASS();
+}
+
+void test_generate_module_namespace() {
+    TEST(generate_module_namespace);
+    NamespaceDeclaration ns("n1", "MyApp.Core");
+    FSharpGenerator gen;
+    std::string out = gen.generate(&ns);
+    CHECK(out == "module MyApp.Core", "expected module declaration");
+    PASS();
+}
+
+void test_generate_if_statement() {
+    TEST(generate_if_statement);
+    IfStatement ifs;
+    ifs.id = "if1";
+    ifs.setChild("condition", new BooleanLiteral("b1", true));
+    auto* thenRet = new Return();
+    thenRet->id = "ret1";
+    thenRet->setChild("value", new StringLiteral("s1", "yes"));
+    ifs.addChild("thenBranch", thenRet);
+
+    FSharpGenerator gen;
+    std::string out = gen.generate(&ifs);
+    CHECK(out.find("if true then") != std::string::npos, "expected if then");
+    PASS();
+}
+
+void test_generate_pipeline_call_marker() {
+    TEST(generate_pipeline_call_marker);
+    FunctionCall call;
+    call.id = "call1";
+    call.functionName = "pipeline";
+    FSharpGenerator gen;
+    std::string out = gen.generate(&call);
+    CHECK(out.find("|>") != std::string::npos, "expected pipeline operator");
+    PASS();
+}
+
+void test_type_mapping() {
+    TEST(type_mapping);
+    PrimitiveType i("t1", "int");
+    PrimitiveType s("t2", "string");
+    PrimitiveType v("t3", "void");
+    OptionalType opt;
+    opt.id = "opt1";
+    opt.setChild("innerType", new CustomType("ct1", "result"));
+
+    FSharpGenerator gen;
+    CHECK(gen.generate(&i) == "int", "int mapping");
+    CHECK(gen.generate(&s) == "string", "string mapping");
+    CHECK(gen.generate(&v) == "unit", "void->unit mapping");
+    CHECK(gen.generate(&opt) == "result option", "optional mapping");
+    PASS();
+}
+
+void test_comment_prefix() {
+    TEST(comment_prefix);
+    FSharpGenerator gen;
+    CHECK(gen.commentPrefix() == "// ", "expected // comment prefix");
+    PASS();
+}
+
+void test_semanno_annotation_output() {
+    TEST(semanno_annotation_output);
+    Function fn("f1", "compute");
+    auto* c = new ComplexityAnnotation();
+    c->id = "a1";
+    c->timeComplexity = "O(n)";
+    fn.addChild("annotations", c);
+
+    FSharpGenerator gen;
+    std::string out = gen.generate(&fn);
+    CHECK(out.find("@semanno:complexity") != std::string::npos, "expected semanno complexity output");
+    PASS();
+}
+
+void test_pipeline_generate_routing() {
+    TEST(pipeline_generate_routing);
+    Module mod;
+    mod.id = "m1";
+    mod.name = "demo";
+    auto* fn = new Function("f1", "run");
+    mod.addChild("functions", fn);
+
+    Pipeline p;
+    std::string o1 = p.generate(&mod, "fsharp");
+    std::string o2 = p.generate(&mod, "f#");
+    std::string o3 = p.generate(&mod, "fs");
+    CHECK(o1.find("let run") != std::string::npos, "fsharp route");
+    CHECK(o2.find("let run") != std::string::npos, "f# route");
+    CHECK(o3.find("let run") != std::string::npos, "fs route");
+    PASS();
+}
+
+int main() {
+    std::cout << "Step 406: F# Generator Tests\n";
+
+    test_generate_let_function();      // 1
+    test_generate_mutable_variable();  // 2
+    test_generate_discriminated_union();// 3
+    test_generate_record_class();      // 4
+    test_generate_async_function();    // 5
+    test_generate_module_namespace();  // 6
+    test_generate_if_statement();      // 7
+    test_generate_pipeline_call_marker();// 8
+    test_type_mapping();               // 9
+    test_comment_prefix();             // 10
+    test_semanno_annotation_output();  // 11
+    test_pipeline_generate_routing();  // 12
+
+    std::cout << "\nResults: " << passed << "/" << (passed + failed)
+              << " passed\n";
+    return failed == 0 ? 0 : 1;
+}
diff --git a/progress.md b/progress.md
index 8434691..c379e23 100644
--- a/progress.md
+++ b/progress.md
@@ -3674,6 +3674,57 @@ and pipe-operator chains.
   - `editor/src/MCPServer.h` (`1679` > `600`)
   - `editor/src/HeadlessAgentRPCHandler.h` (`2623` > `600`)
 
+### Step 406: F# Generator
+**Status:** PASS (12/12 tests)
+
+Added a dedicated F# generator with Semanno annotation emission support and
+pipeline generate-route aliases (`fsharp`, `f#`, `fs`). Outputs functional
+`let` forms, async computation expressions, discriminated-union style enum
+output, record-style class output, and F#-style type mappings.
+
+**Files created:**
+- `editor/src/ast/FSharpGenerator.h` — F# generation support:
+  - module/function/variable generation using `let`
+  - mutable variable output from `MutAnnotation`
+  - async output: `let name = async { ... }`
+  - namespace/module output (`module Name`)
+  - union output (`type Name = | Case...`)
+  - record output (`type Name = { field: obj; ... }`)
+  - pipeline marker generation (`|> pipeline`)
+  - type mapping for `int`, `float`, `string`, `bool`, `unit`, `option`, `result`
+  - Semanno output for subject 1 and extended annotation families
+- `editor/tests/step406_test.cpp` — 12 tests covering:
+  1. `let` function generation
+  2. mutable variable generation
+  3. discriminated union generation
+  4. record/class generation
+  5. async function generation
+  6. module namespace generation
+  7. if-statement generation
+  8. pipeline marker generation
+  9. type mapping behavior
+  10. comment prefix (`// `)
+  11. Semanno annotation output
+  12. pipeline generate routing for `fsharp` / `f#` / `fs`
+
+**Files modified:**
+- `editor/src/ast/Generator.h` — include `FSharpGenerator.h`
+- `editor/src/Pipeline.h` — generate routing for `fsharp`, `f#`, `fs`
+- `editor/CMakeLists.txt` — `step406_test` target
+
+**Verification run:**
+- `step406_test` — PASS (12/12) new step coverage
+- `step405_test` — PASS (12/12) regression coverage
+- `step404_test` — PASS (8/8) regression coverage
+
+**Architecture gate check:**
+- `editor/src/ast/FSharpGenerator.h` within header-size limit (`348` <= `600`)
+- `editor/tests/step406_test.cpp` within test-file size guidance (`205` lines)
+- `editor/src/Pipeline.h` within header-size limit (`240` <= `600`)
+- Legacy oversized headers persist:
+  - `editor/src/MCPServer.h` (`1679` > `600`)
+  - `editor/src/HeadlessAgentRPCHandler.h` (`2623` > `600`)
+
 # Roadmap Planning — Sprints 12-25+
 
 ## Status: Planning Complete (Sprints 12-19 detailed, 20-25 in roadmap.md)