Merge PR #565: fix/553-edge-prompt-empty (#553)

packages/cli-workflow/src/moderator/__tests__/evaluate.test.ts

@@ -1,6 +1,97 @@
 import { describe, expect, test } from "vitest";
 import { evaluate } from "../evaluate.js";
 
+describe("Edge prompt template variable resolution", () => {
+  test("returns error when rendered prompt is empty string", () => {
+    const graph = {
+      $START: {
+        _: { role: "classifier", prompt: "{{{userPrompt}}}", location: null },
+      },
+    };
+
+    const result = evaluate(graph, "$START", {});
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error.message).toContain("prompt");
+      expect(result.error.message).toContain("empty");
+    }
+  });
+
+  test("returns error when rendered prompt is whitespace-only", () => {
+    const graph = {
+      $START: {
+        _: { role: "classifier", prompt: "  {{{userPrompt}}}  ", location: null },
+      },
+    };
+
+    const result = evaluate(graph, "$START", {});
+
+    expect(result.ok).toBe(false);
+    if (!result.ok) {
+      expect(result.error.message).toContain("prompt");
+      expect(result.error.message).toContain("empty");
+    }
+  });
+
+  test("succeeds when all template variables resolve to non-empty values", () => {
+    const graph = {
+      $START: {
+        _: { role: "classifier", prompt: "{{{userPrompt}}}", location: null },
+      },
+    };
+
+    const result = evaluate(graph, "$START", { userPrompt: "Fix the bug" });
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.prompt).toBe("Fix the bug");
+    }
+  });
+
+  test("succeeds with static (no-variable) prompt", () => {
+    const graph = {
+      $START: {
+        _: { role: "classifier", prompt: "Classify this input", location: null },
+      },
+    };
+
+    const result = evaluate(graph, "$START", {});
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.prompt).toBe("Classify this input");
+    }
+  });
+
+  test("succeeds when prompt has mix of static text and unresolved variables", () => {
+    const graph = {
+      $START: {
+        _: { role: "classifier", prompt: "Please handle: {{{userPrompt}}}", location: null },
+      },
+    };
+
+    const result = evaluate(graph, "$START", {});
+
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.prompt).toBe("Please handle: ");
+    }
+  });
+
+  test("returns error when ALL variables missing and no static text remains", () => {
+    const graph = {
+      $START: {
+        _: { role: "classifier", prompt: "{{{a}}}{{{b}}}", location: null },
+      },
+    };
+
+    const result = evaluate(graph, "$START", {});
+
+    expect(result.ok).toBe(false);
+  });
+});
+
 describe("Moderator location resolution", () => {
   test("returns null location when edge has no location field", () => {
     const graph = {

packages/cli-workflow/src/moderator/evaluate.ts

@@ -43,6 +43,14 @@ export function evaluate(
 
   try {
     const prompt = mustache.render(target.prompt, lastOutput);
+    if (prompt.trim() === "") {
+      return {
+        ok: false,
+        error: new Error(
+          `edge prompt resolved to empty string for role "${target.role}" (template: "${target.prompt}"). Check that upstream output includes required variables.`,
+        ),
+      };
+    }
     const location = target.location !== null ? mustache.render(target.location, lastOutput) : null;
     return { ok: true, value: { role: target.role, prompt, location } };
   } catch (error) {