feat: sdk subagent support

packages/core/src/config/config.ts

@@ -613,6 +613,12 @@ export class Config {
     }
     this.promptRegistry = new PromptRegistry();
     this.subagentManager = new SubagentManager(this);
+
+    // Load session subagents if they were provided before initialization
+    if (this.sessionSubagents.length > 0) {
+      this.subagentManager.loadSessionSubagents(this.sessionSubagents);
+    }
+
     this.toolRegistry = await this.createToolRegistry();
 
     await this.geminiClient.initialize();
@@ -874,13 +880,6 @@ export class Config {
     this.sessionSubagents = subagents;
   }
 
-  addSessionSubagents(subagents: SubagentConfig[]): void {
-    if (this.initialized) {
-      throw new Error('Cannot modify sessionSubagents after initialization');
-    }
-    this.sessionSubagents = [...this.sessionSubagents, ...subagents];
-  }
-
   getSdkMode(): boolean {
     return this.sdkMode;
   }

packages/core/src/subagents/subagent-manager.test.ts

@@ -182,7 +182,7 @@ You are a helpful assistant.
     it('should parse valid markdown content', () => {
       const config = manager.parseSubagentContent(
         validMarkdown,
-        validConfig.filePath,
+        validConfig.filePath!,
         'project',
       );
 
@@ -207,7 +207,7 @@ You are a helpful assistant.
 
       const config = manager.parseSubagentContent(
         markdownWithTools,
-        validConfig.filePath,
+        validConfig.filePath!,
         'project',
       );
 
@@ -228,7 +228,7 @@ You are a helpful assistant.
 
       const config = manager.parseSubagentContent(
         markdownWithModel,
-        validConfig.filePath,
+        validConfig.filePath!,
         'project',
       );
 
@@ -249,7 +249,7 @@ You are a helpful assistant.
 
       const config = manager.parseSubagentContent(
         markdownWithRun,
-        validConfig.filePath,
+        validConfig.filePath!,
         'project',
       );
 
@@ -267,7 +267,7 @@ You are a helpful assistant.
 
       const config = manager.parseSubagentContent(
         markdownWithNumeric,
-        validConfig.filePath,
+        validConfig.filePath!,
         'project',
       );
 
@@ -288,7 +288,7 @@ You are a helpful assistant.
 
       const config = manager.parseSubagentContent(
         markdownWithBoolean,
-        validConfig.filePath,
+        validConfig.filePath!,
         'project',
       );
 
@@ -324,7 +324,7 @@ Just content`;
       expect(() =>
         manager.parseSubagentContent(
           invalidMarkdown,
-          validConfig.filePath,
+          validConfig.filePath!,
           'project',
         ),
       ).toThrow(SubagentError);
@@ -341,7 +341,7 @@ You are a helpful assistant.
       expect(() =>
         manager.parseSubagentContent(
           markdownWithoutName,
-          validConfig.filePath,
+          validConfig.filePath!,
           'project',
         ),
       ).toThrow(SubagentError);
@@ -358,7 +358,7 @@ You are a helpful assistant.
       expect(() =>
         manager.parseSubagentContent(
           markdownWithoutDescription,
-          validConfig.filePath,
+          validConfig.filePath!,
           'project',
         ),
       ).toThrow(SubagentError);
@@ -438,7 +438,7 @@ You are a helpful assistant.
       await manager.createSubagent(validConfig, { level: 'project' });
 
       expect(fs.mkdir).toHaveBeenCalledWith(
-        path.normalize(path.dirname(validConfig.filePath)),
+        path.normalize(path.dirname(validConfig.filePath!)),
         { recursive: true },
       );
       expect(fs.writeFile).toHaveBeenCalledWith(

packages/core/src/subagents/subagent-manager.ts

@@ -159,7 +159,14 @@ export class SubagentManager {
       return this.findSubagentByNameAtLevel(name, level);
     }
 
-    // Try project level first
+    // Try session level first (highest priority for runtime)
+    const sessionSubagents = this.subagentsCache?.get('session') || [];
+    const sessionConfig = sessionSubagents.find((agent) => agent.name === name);
+    if (sessionConfig) {
+      return sessionConfig;
+    }
+
+    // Try project level
     const projectConfig = await this.findSubagentByNameAtLevel(name, 'project');
     if (projectConfig) {
       return projectConfig;
@@ -220,6 +227,15 @@ export class SubagentManager {
     // Validate the updated configuration
     this.validator.validateOrThrow(updatedConfig);
 
+    // Ensure filePath exists for file-based agents
+    if (!existing.filePath) {
+      throw new SubagentError(
+        `Cannot update subagent "${name}": no file path available`,
+        SubagentErrorCode.FILE_ERROR,
+        name,
+      );
+    }
+
     // Write the updated configuration
     const content = this.serializeSubagent(updatedConfig);
 
@@ -302,11 +318,6 @@ export class SubagentManager {
 
     // In SDK mode, only load session-level subagents
     if (this.config.getSdkMode()) {
-      const sessionSubagents = this.config.getSessionSubagents();
-      if (sessionSubagents && sessionSubagents.length > 0) {
-        this.loadSessionSubagents(sessionSubagents);
-      }
-
       const levelsToCheck: SubagentLevel[] = options.level
         ? [options.level]
         : ['session'];

packages/core/src/subagents/types.ts

@@ -42,8 +42,8 @@ export interface SubagentConfig {
   /** Storage level - determines where the configuration file is stored */
   level: SubagentLevel;
 
-  /** Absolute path to the configuration file */
-  filePath: string;
+  /** Absolute path to the configuration file. Optional for session subagents. */
+  filePath?: string;
 
   /**
    * Optional model configuration. If not provided, uses defaults.