🖼️ refactor: Enhance Env Extraction & Agent Image Handling (#6131)

* refactor: use new image output format for agents using DALL-E tools

* refactor: Enhance image fetching with proxy support and adjust logging placement in DALL-E 3 integration

* refactor: Enhance StableDiffusionAPI to support agent-specific return values and display message for generated images

* refactor: Add unit test execution for librechat-mcp in backend review workflow

* refactor: Update environment variable extraction logic, export from serpate module to avoid circular refs, and remove deprecated tests

* refactor: Add unit tests for environment variable extraction and enhance StdioOptionsSchema to process env variables

packages/data-provider/src/utils.ts

@@ -0,0 +1,44 @@
+export const envVarRegex = /^\${(.+)}$/;
+
+/** Extracts the value of an environment variable from a string. */
+export function extractEnvVariable(value: string) {
+  if (!value) {
+    return value;
+  }
+
+  // Trim the input
+  const trimmed = value.trim();
+
+  // Special case: if it's just a single environment variable
+  const singleMatch = trimmed.match(envVarRegex);
+  if (singleMatch) {
+    const varName = singleMatch[1];
+    return process.env[varName] || trimmed;
+  }
+
+  // For multiple variables, process them using a regex loop
+  const regex = /\${([^}]+)}/g;
+  let result = trimmed;
+
+  // First collect all matches and their positions
+  const matches = [];
+  let match;
+  while ((match = regex.exec(trimmed)) !== null) {
+    matches.push({
+      fullMatch: match[0],
+      varName: match[1],
+      index: match.index,
+    });
+  }
+
+  // Process matches in reverse order to avoid position shifts
+  for (let i = matches.length - 1; i >= 0; i--) {
+    const { fullMatch, varName, index } = matches[i];
+    const envValue = process.env[varName] || fullMatch;
+
+    // Replace at exact position
+    result = result.substring(0, index) + envValue + result.substring(index + fullMatch.length);
+  }
+
+  return result;
+}