feat(agent): Introduce Foundational Subagent Architecture (#1805)

Co-authored-by: Colt McAnlis <colton@google.com>

packages/core/src/utils/environmentContext.ts

@@ -0,0 +1,109 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { Part } from '@google/genai';
+import { Config } from '../config/config.js';
+import { getFolderStructure } from './getFolderStructure.js';
+
+/**
+ * Generates a string describing the current workspace directories and their structures.
+ * @param {Config} config - The runtime configuration and services.
+ * @returns {Promise<string>} A promise that resolves to the directory context string.
+ */
+export async function getDirectoryContextString(
+  config: Config,
+): Promise<string> {
+  const workspaceContext = config.getWorkspaceContext();
+  const workspaceDirectories = workspaceContext.getDirectories();
+
+  const folderStructures = await Promise.all(
+    workspaceDirectories.map((dir) =>
+      getFolderStructure(dir, {
+        fileService: config.getFileService(),
+      }),
+    ),
+  );
+
+  const folderStructure = folderStructures.join('\n');
+
+  let workingDirPreamble: string;
+  if (workspaceDirectories.length === 1) {
+    workingDirPreamble = `I'm currently working in the directory: ${workspaceDirectories[0]}`;
+  } else {
+    const dirList = workspaceDirectories.map((dir) => `  - ${dir}`).join('\n');
+    workingDirPreamble = `I'm currently working in the following directories:\n${dirList}`;
+  }
+
+  return `${workingDirPreamble}
+Here is the folder structure of the current working directories:
+
+${folderStructure}`;
+}
+
+/**
+ * Retrieves environment-related information to be included in the chat context.
+ * This includes the current working directory, date, operating system, and folder structure.
+ * Optionally, it can also include the full file context if enabled.
+ * @param {Config} config - The runtime configuration and services.
+ * @returns A promise that resolves to an array of `Part` objects containing environment information.
+ */
+export async function getEnvironmentContext(config: Config): Promise<Part[]> {
+  const today = new Date().toLocaleDateString(undefined, {
+    weekday: 'long',
+    year: 'numeric',
+    month: 'long',
+    day: 'numeric',
+  });
+  const platform = process.platform;
+  const directoryContext = await getDirectoryContextString(config);
+
+  const context = `
+This is the Gemini CLI. We are setting up the context for our chat.
+Today's date is ${today}.
+My operating system is: ${platform}
+${directoryContext}
+        `.trim();
+
+  const initialParts: Part[] = [{ text: context }];
+  const toolRegistry = await config.getToolRegistry();
+
+  // Add full file context if the flag is set
+  if (config.getFullContext()) {
+    try {
+      const readManyFilesTool = toolRegistry.getTool('read_many_files');
+      if (readManyFilesTool) {
+        const invocation = readManyFilesTool.build({
+          paths: ['**/*'], // Read everything recursively
+          useDefaultExcludes: true, // Use default excludes
+        });
+
+        // Read all files in the target directory
+        const result = await invocation.execute(AbortSignal.timeout(30000));
+        if (result.llmContent) {
+          initialParts.push({
+            text: `\n--- Full File Context ---\n${result.llmContent}`,
+          });
+        } else {
+          console.warn(
+            'Full context requested, but read_many_files returned no content.',
+          );
+        }
+      } else {
+        console.warn(
+          'Full context requested, but read_many_files tool not found.',
+        );
+      }
+    } catch (error) {
+      // Not using reportError here as it's a startup/config phase, not a chat/generation phase error.
+      console.error('Error reading full file context:', error);
+      initialParts.push({
+        text: '\n--- Error reading full file context ---',
+      });
+    }
+  }
+
+  return initialParts;
+}