refactor: split MDLParser.g4 into domain-specific files (#515)

Reduces merge conflicts: PRs that add syntax to different domains now
touch separate domain files instead of the same monolithic grammar.

MDLParser.g4 shrinks from 4082 → 400 lines (master dispatch rules only).
Nine domain files created in mdl/grammar/domains/:

  MDLDomainModel.g4  — entities, associations, enums, constants, mappings
  MDLMicroflow.g4    — microflows, nanoflows, Java actions, REST calls, list ops
  MDLPage.g4         — pages, snippets, xpath, page V3 widgets, notebooks
  MDLSecurity.g4     — roles, grants, revokes, project security, demo users
  MDLAgent.g4        — agent editor: models, knowledge bases, MCP services, agents
  MDLWorkflow.g4     — CREATE/ALTER WORKFLOW
  MDLService.g4      — database connections, REST/OData clients+services, BES
  MDLCatalog.g4      — SHOW/DESCRIBE statements, SELECT CATALOG, OQL query
  MDLSettings.g4     — ALTER SETTINGS, utility statements, expressions, common rules

ANTLR4 merges all rules at generation time — the generated Go parser is
unchanged and all listener/visitor code continues to work without modification.

Updated mdl/grammar/Makefile and generate.sh to pass -lib domains so ANTLR4
can resolve imported grammars. Updated keyword_coverage_test.go to search
all domain files since the keyword rule moved to MDLSettings.g4.

Applied main's grammar changes to domain files:
- addToListStatement: ADD expression TO VARIABLE (MDLMicroflow.g4)
- sessionSetStatement already present from original grammar

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

Author: ako

mdl/grammar/MDLParser.g4

@@ -15,6 +15,18 @@ PARSER = MDLParser.g4
 OUTPUT_DIR = parser
 PACKAGE = parser
 
+# Domain grammar files (imported by MDLParser.g4 via the `import` directive)
+DOMAIN_FILES = \
+    domains/MDLDomainModel.g4 \
+    domains/MDLMicroflow.g4 \
+    domains/MDLPage.g4 \
+    domains/MDLSecurity.g4 \
+    domains/MDLAgent.g4 \
+    domains/MDLWorkflow.g4 \
+    domains/MDLService.g4 \
+    domains/MDLCatalog.g4 \
+    domains/MDLSettings.g4
+
 # Find antlr4 command (try common locations)
 ANTLR4 := $(shell which antlr4 2>/dev/null || which antlr 2>/dev/null)
 
@@ -25,9 +37,9 @@ ifndef ANTLR4
 	$(error ANTLR4 not found. Install with: brew install antlr4 (macOS) or pip install antlr4-tools)
 endif
 
-generate: check-antlr $(LEXER) $(PARSER)
+generate: check-antlr $(LEXER) $(PARSER) $(DOMAIN_FILES)
 	@mkdir -p $(OUTPUT_DIR)
-	$(ANTLR4) -Dlanguage=Go -no-visitor -package $(PACKAGE) -o $(OUTPUT_DIR) $(LEXER) $(PARSER)
+	$(ANTLR4) -Dlanguage=Go -no-visitor -package $(PACKAGE) -lib domains -o $(OUTPUT_DIR) $(LEXER) $(PARSER)
 	@echo "Generated Go parser in $(OUTPUT_DIR)/"
 
 clean:

mdl/grammar/Makefile

@@ -0,0 +1,91 @@
+/**
+ * MDL Agent Grammar — agent editor: models, knowledge bases,
+ * consumed MCP services, agents.
+ */
+parser grammar MDLAgent;
+
+options { tokenVocab = MDLLexer; }
+
+// =============================================================================
+// AGENT-EDITOR MODEL CREATION
+// =============================================================================
+// CREATE MODEL Module.Name (
+//   Provider: MxCloudGenAI,
+//   Key: Module.SomeConstant
+//   [, DisplayName: '...', KeyName: '...', etc. — Portal-populated metadata]
+// );
+createModelStatement
+    : MODEL qualifiedName
+      LPAREN modelProperty (COMMA modelProperty)* RPAREN
+    ;
+
+modelProperty
+    : identifierOrKeyword COLON identifierOrKeyword       // Provider: MxCloudGenAI
+    | identifierOrKeyword COLON qualifiedName             // Key: Module.Constant
+    | identifierOrKeyword COLON STRING_LITERAL            // DisplayName: 'GPT-4 Turbo' etc.
+    | identifierOrKeyword COLON NUMBER_LITERAL            // ConnectionTimeoutSeconds: 30
+    | identifierOrKeyword COLON booleanLiteral            // Enabled: true
+    | identifierOrKeyword COLON DOLLAR_STRING              // SystemPrompt: $$multi-line...$$
+    | identifierOrKeyword COLON LPAREN variableDefList RPAREN  // Variables: ("Key": EntityAttribute, ...)
+    ;
+
+variableDefList
+    : variableDef (COMMA variableDef)*
+    ;
+
+variableDef
+    : (STRING_LITERAL | QUOTED_IDENTIFIER) COLON identifierOrKeyword  // "Key": EntityAttribute
+    ;
+
+// =============================================================================
+// AGENT-EDITOR CONSUMED MCP SERVICE CREATION
+// =============================================================================
+// CREATE CONSUMED MCP SERVICE Module.Name (
+//   ProtocolVersion: v2025_03_26,
+//   Version: '0.0.1',
+//   ConnectionTimeoutSeconds: 30,
+//   Documentation: '...'
+// );
+createConsumedMCPServiceStatement
+    : CONSUMED MCP SERVICE qualifiedName
+      LPAREN modelProperty (COMMA modelProperty)* RPAREN
+    ;
+
+// =============================================================================
+// AGENT-EDITOR KNOWLEDGE BASE CREATION
+// =============================================================================
+// CREATE KNOWLEDGE BASE Module.Name (
+//   Provider: MxCloudGenAI,
+//   Key: Module.SomeConstant
+// );
+createKnowledgeBaseStatement
+    : KNOWLEDGE BASE qualifiedName
+      LPAREN modelProperty (COMMA modelProperty)* RPAREN
+    ;
+
+// =============================================================================
+// AGENT-EDITOR AGENT CREATION
+// =============================================================================
+// CREATE AGENT Module.Name (
+//   UsageType: Task,
+//   Model: Module.MyModel,
+//   SystemPrompt: '...',
+//   ...
+// )
+// [ { TOOL ... | MCP SERVICE ... | KNOWLEDGE BASE ... } ]
+// ;
+createAgentStatement
+    : AGENT qualifiedName
+      LPAREN modelProperty (COMMA modelProperty)* RPAREN
+      agentBody?
+    ;
+
+agentBody
+    : LBRACE agentBodyBlock* RBRACE
+    ;
+
+agentBodyBlock
+    : MCP SERVICE qualifiedName LBRACE modelProperty (COMMA modelProperty)* RBRACE       // MCP SERVICE Mod.Name { ... }
+    | KNOWLEDGE BASE identifierOrKeyword LBRACE modelProperty (COMMA modelProperty)* RBRACE // KNOWLEDGE BASE MyKB { ... }
+    | TOOL identifierOrKeyword LBRACE modelProperty (COMMA modelProperty)* RBRACE        // TOOL ToolName { ... }
+    ;