feat(FN-837): add workflow step phase support with pre-merge and post-merge execution

- Add phase field to workflow step definitions (pre-merge vs post-merge) with persistence and API
- Execute pre-merge steps in executor before merge; post-merge steps in merger after successful merge
- Pre-merge failures block merge and keep task in in-review; post-merge failures are logged only
- Expose phase controls and phase-aware results in the dashboard UI
- Add changeset for the published @gsxdsm/fusion package

packages/dashboard/src/routes.test.ts

@@ -6262,6 +6262,7 @@ describe("POST /workflow-steps", () => {
       name: "Docs",
       description: "Check docs",
       mode: "prompt",
+      phase: undefined,
       prompt: undefined,
       scriptName: undefined,
       enabled: undefined,
@@ -6316,6 +6317,7 @@ describe("POST /workflow-steps", () => {
       name: "Security",
       description: "Security audit",
       mode: "prompt",
+      phase: undefined,
       prompt: undefined,
       scriptName: undefined,
       enabled: undefined,
@@ -6362,6 +6364,7 @@ describe("POST /workflow-steps", () => {
       name: "Docs",
       description: "Check docs",
       mode: "prompt",
+      phase: undefined,
       prompt: undefined,
       scriptName: undefined,
       enabled: undefined,
@@ -6389,6 +6392,7 @@ describe("POST /workflow-steps", () => {
       name: "Run Tests",
       description: "Execute tests",
       mode: "script",
+      phase: undefined,
       prompt: undefined,
       scriptName: "test",
       enabled: undefined,
@@ -6432,6 +6436,39 @@ describe("POST /workflow-steps", () => {
     expect(res.status).toBe(400);
     expect(res.body.error).toContain("mode must be");
   });
+
+  it("creates a workflow step with 'post-merge' phase", async () => {
+    const created = { id: "WS-001", name: "Post Merge", description: "After merge", mode: "prompt", phase: "post-merge", prompt: "", enabled: true, createdAt: "2026-01-01", updatedAt: "2026-01-01" };
+    (store.createWorkflowStep as ReturnType<typeof vi.fn>).mockResolvedValueOnce(created);
+
+    const res = await REQUEST(buildApp(), "POST", "/api/workflow-steps", JSON.stringify({
+      name: "Post Merge",
+      description: "After merge",
+      phase: "post-merge",
+    }), { "Content-Type": "application/json" });
+
+    expect(res.status).toBe(201);
+    expect(store.createWorkflowStep).toHaveBeenCalledWith({
+      name: "Post Merge",
+      description: "After merge",
+      mode: "prompt",
+      phase: "post-merge",
+      prompt: undefined,
+      scriptName: undefined,
+      enabled: undefined,
+    });
+  });
+
+  it("returns 400 for invalid phase value", async () => {
+    const res = await REQUEST(buildApp(), "POST", "/api/workflow-steps", JSON.stringify({
+      name: "Test",
+      description: "Test",
+      phase: "during-merge",
+    }), { "Content-Type": "application/json" });
+
+    expect(res.status).toBe(400);
+    expect(res.body.error).toContain("phase must be");
+  });
 });
 
 describe("PATCH /workflow-steps/:id", () => {
@@ -6554,6 +6591,36 @@ describe("PATCH /workflow-steps/:id", () => {
     expect(res.status).toBe(400);
     expect(res.body.error).toContain("scriptName is required when mode is 'script'");
   });
+
+  it("updates a workflow step phase", async () => {
+    const updated = { id: "WS-001", name: "Post Merge", description: "After merge", phase: "post-merge", createdAt: "2026-01-01", updatedAt: "2026-01-02" };
+    (store.updateWorkflowStep as ReturnType<typeof vi.fn>).mockResolvedValueOnce(updated);
+    (store.getWorkflowStep as ReturnType<typeof vi.fn>).mockResolvedValueOnce({
+      id: "WS-001", name: "Pre Merge", description: "Before merge", mode: "prompt", prompt: "", enabled: true, createdAt: "2026-01-01", updatedAt: "2026-01-01",
+    });
+
+    const res = await REQUEST(buildApp(), "PATCH", "/api/workflow-steps/WS-001", JSON.stringify({
+      phase: "post-merge",
+    }), { "Content-Type": "application/json" });
+
+    expect(res.status).toBe(200);
+    expect(store.updateWorkflowStep).toHaveBeenCalledWith("WS-001", expect.objectContaining({
+      phase: "post-merge",
+    }));
+  });
+
+  it("returns 400 for invalid phase value on update", async () => {
+    (store.getWorkflowStep as ReturnType<typeof vi.fn>).mockResolvedValueOnce({
+      id: "WS-001", name: "Test", description: "Test", mode: "prompt", prompt: "", enabled: true, createdAt: "2026-01-01", updatedAt: "2026-01-01",
+    });
+
+    const res = await REQUEST(buildApp(), "PATCH", "/api/workflow-steps/WS-001", JSON.stringify({
+      phase: "during-merge",
+    }), { "Content-Type": "application/json" });
+
+    expect(res.status).toBe(400);
+    expect(res.body.error).toContain("phase must be");
+  });
 });
 
 describe("DELETE /workflow-steps/:id", () => {

packages/dashboard/src/routes.ts

@@ -5988,7 +5988,7 @@ export function createApiRoutes(store: TaskStore, options?: ServerOptions): Rout
   router.post("/workflow-steps", async (req, res) => {
     try {
       const scopedStore = await getScopedStore(req);
-      const { name, description, mode, prompt, scriptName, enabled, modelProvider, modelId } = req.body;
+      const { name, description, mode, phase, prompt, scriptName, enabled, modelProvider, modelId } = req.body;
 
       if (!name || typeof name !== "string" || !name.trim()) {
         res.status(400).json({ error: "name is required" });
@@ -6006,6 +6006,12 @@ export function createApiRoutes(store: TaskStore, options?: ServerOptions): Rout
         return;
       }
 
+      // Validate phase
+      if (phase !== undefined && phase !== "pre-merge" && phase !== "post-merge") {
+        res.status(400).json({ error: "phase must be 'pre-merge' or 'post-merge'" });
+        return;
+      }
+
       if (prompt !== undefined && typeof prompt !== "string") {
         res.status(400).json({ error: "prompt must be a string" });
         return;
@@ -6047,6 +6053,7 @@ export function createApiRoutes(store: TaskStore, options?: ServerOptions): Rout
         name: name.trim(),
         description: description.trim(),
         mode: resolvedMode,
+        phase,
         prompt: prompt?.trim(),
         scriptName: scriptName?.trim(),
         enabled,
@@ -6069,7 +6076,7 @@ export function createApiRoutes(store: TaskStore, options?: ServerOptions): Rout
   router.patch("/workflow-steps/:id", async (req, res) => {
     try {
       const scopedStore = await getScopedStore(req);
-      const { name, description, mode, prompt, scriptName, enabled, modelProvider, modelId } = req.body;
+      const { name, description, mode, phase, prompt, scriptName, enabled, modelProvider, modelId } = req.body;
 
       const updates: Record<string, unknown> = {};
       if (name !== undefined) {
@@ -6093,6 +6100,13 @@ export function createApiRoutes(store: TaskStore, options?: ServerOptions): Rout
         }
         updates.mode = mode;
       }
+      if (phase !== undefined) {
+        if (phase !== "pre-merge" && phase !== "post-merge") {
+          res.status(400).json({ error: "phase must be 'pre-merge' or 'post-merge'" });
+          return;
+        }
+        updates.phase = phase;
+      }
       if (prompt !== undefined) {
         if (typeof prompt !== "string") {
           res.status(400).json({ error: "prompt must be a string" });