diff --git a/src/cli/commands.ts b/src/cli/commands.ts
index 3bf8d8b..4fdba79 100644
--- a/src/cli/commands.ts
+++ b/src/cli/commands.ts
@@ -169,6 +169,7 @@ export function createRunCommand(): Command {
     .option("--all", "Execute all remaining phases sequentially")
     .option("--phase <number>", "Phase number", "1")
     .option("--backend <provider>", "Override intelligence backend for this run")
+    .option("--ideate", "Insert ideation stage between research and plan")
     .action(async (phase, options) => {
       const projectPath = process.cwd();
 
@@ -177,6 +178,49 @@ export function createRunCommand(): Command {
         process.exit(1);
       }
 
+      if (options.ideate) {
+        console.log("─── CIAgent Ideate (pipeline mode) ───\n");
+
+        const ciFiles = new CIAgentFiles(projectPath);
+        const slug = ciFiles.getProjectSlug() || ciFiles.getActiveProject() || "default";
+        const { IdeationEngine } = await import("../core/ideation.js");
+        const engine = new IdeationEngine(projectPath, slug);
+
+        const ideas = engine.runMechanical();
+
+        const ideaCategory: IdeationCategory[] = options.category
+          ? options.category.split(",").map((c: string) => c.trim() as IdeationCategory)
+          : [];
+
+        if (ideaCategory.length > 0) {
+          const filtered = engine.runMechanical(ideaCategory);
+          ideas.push(...filtered);
+        }
+
+        const seen = new Set<string>();
+        const uniqueIdeas = ideas.filter((idea: Idea) => {
+          if (seen.has(idea.title)) return false;
+          seen.add(idea.title);
+          return true;
+        });
+
+        uniqueIdeas.sort((a: Idea, b: Idea) => b.confidence - a.confidence);
+
+        console.log(`Found ${uniqueIdeas.length} improvement ${uniqueIdeas.length === 1 ? "idea" : "ideas"} from ideation stage.\n`);
+
+        if (uniqueIdeas.length > 0) {
+          const { accepted: savedIdeas, results } = engine.acceptIdeas(uniqueIdeas);
+          const savedCount = results.filter((r: { addedToRequirements: boolean; addedToRoadmap: boolean }) => r.addedToRequirements || r.addedToRoadmap).length;
+
+          if (savedCount > 0) {
+            console.log(`${savedCount} idea${savedCount === 1 ? "" : "s"} added to REQUIREMENTS.md and ROADMAP.md.`);
+          }
+
+          const commitMsg = `decision(P${options.phase || 1}): ideation results — ${uniqueIdeas.length} total, ${savedCount} accepted`;
+          console.log(`\nCommit suggestion: ${commitMsg}`);
+        }
+      }
+
       const config = loadConfig(projectPath);
       const { backend, error: backendError } = await resolveBackendForCommand(config, options.backend);
 
diff --git a/src/core/ideation.test.ts b/src/core/ideation.test.ts
index a43c9ce..a73248a 100644
--- a/src/core/ideation.test.ts
+++ b/src/core/ideation.test.ts
@@ -327,4 +327,60 @@ describe("IdeationEngine", () => {
       expect(titles.some((t) => t.includes("coverage"))).toBe(true);
     });
   });
+
+  describe("Phase 3: External signals and cascade impact", () => {
+    let tempDir: string;
+
+    beforeEach(() => {
+      resetIdeaCounter();
+      tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "ciagent-p3-test-"));
+    });
+
+    afterEach(() => {
+      fs.rmSync(tempDir, { recursive: true, force: true });
+    });
+
+    it("runAffected detects cascade from architecture.md", () => {
+      const ciagentDir = path.join(tempDir, ".ciagent");
+      fs.mkdirSync(ciagentDir, { recursive: true });
+      fs.writeFileSync(
+        path.join(ciagentDir, "config.json"),
+        JSON.stringify({ projects: [], active_project: "default" })
+      );
+      fs.writeFileSync(
+        path.join(ciagentDir, "ARCHITECTURE.md"),
+        "# Architecture\n\n## Overview\n\nTest.\n\n## Components\n\n### CLI\n\n- **Description**: Command line interface\n- **Boundaries**: User-facing only\n- **Depends on**: Core\n\n### Core\n\n- **Description**: Core engine\n- **Boundaries**: Internal only\n- **Depends on**: None\n\n## Data Flow\n\nSimple.\n\n## Build Order\n\n1. CLI\n2. Core\n"
+      );
+
+      const engine = new IdeationEngine(tempDir);
+      const ideas = engine.runAffected();
+      expect(Array.isArray(ideas)).toBe(true);
+    });
+
+    it("runExternal handles missing npm gracefully", () => {
+      const ciagentDir = path.join(tempDir, ".ciagent");
+      fs.mkdirSync(ciagentDir, { recursive: true });
+      fs.writeFileSync(
+        path.join(ciagentDir, "config.json"),
+        JSON.stringify({ projects: [], active_project: "default" })
+      );
+
+      const engine = new IdeationEngine(tempDir);
+      const ideas = engine.runExternal();
+      expect(Array.isArray(ideas)).toBe(true);
+    });
+
+    it("runCrossProject returns empty when only one project", () => {
+      const ciagentDir = path.join(tempDir, ".ciagent");
+      fs.mkdirSync(ciagentDir, { recursive: true });
+      fs.writeFileSync(
+        path.join(ciagentDir, "config.json"),
+        JSON.stringify({ projects: [{ slug: "default", name: "Default Project", default: true }], active_project: "default" })
+      );
+
+      const engine = new IdeationEngine(tempDir, "default");
+      const ideas = engine.runCrossProject();
+      expect(ideas).toEqual([]);
+    });
+  });
 });
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