feat(goose2): add useActiveProjectTint hook

Pure selector: active session → project → color (or null). Route gating
lives at the application point in AppShell, not here. Unit-tested
against four cases: no active session, no project on session, in-
project, deleted project.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/goose2/src/features/chat/hooks/__tests__/useActiveProjectTint.test.ts

@@ -0,0 +1,124 @@
+import { renderHook } from "@testing-library/react";
+import { beforeEach, describe, expect, it } from "vitest";
+
+import { useChatSessionStore } from "@/features/chat/stores/chatSessionStore";
+import { useProjectStore } from "@/features/projects/stores/projectStore";
+
+import { useActiveProjectTint } from "../useActiveProjectTint";
+
+const baseSessionState = {
+  sessions: [],
+  activeSessionId: null,
+  isLoading: false,
+  hasHydratedSessions: true,
+  contextPanelOpenBySession: {},
+  activeWorkspaceBySession: {},
+};
+
+const baseProjectState = {
+  projects: [],
+  loading: false,
+  activeProjectId: null,
+};
+
+describe("useActiveProjectTint", () => {
+  beforeEach(() => {
+    useChatSessionStore.setState(baseSessionState);
+    useProjectStore.setState(baseProjectState);
+  });
+
+  it("returns null when there is no active session", () => {
+    const { result } = renderHook(() => useActiveProjectTint());
+    expect(result.current).toBeNull();
+  });
+
+  it("returns null when the active session has no projectId", () => {
+    useChatSessionStore.setState({
+      ...baseSessionState,
+      sessions: [
+        {
+          id: "s1",
+          title: "Chat",
+          providerId: "openai",
+          modelId: "gpt-4o",
+          modelName: "GPT-4o",
+          createdAt: "2026-04-28T00:00:00.000Z",
+          updatedAt: "2026-04-28T00:00:00.000Z",
+          messageCount: 0,
+        },
+      ],
+      activeSessionId: "s1",
+    });
+
+    const { result } = renderHook(() => useActiveProjectTint());
+    expect(result.current).toBeNull();
+  });
+
+  it("returns the project's color when the active session is in-project", () => {
+    useProjectStore.setState({
+      ...baseProjectState,
+      projects: [
+        {
+          id: "p1",
+          name: "Blue project",
+          color: "#3b82f6",
+          description: "",
+          prompt: "",
+          icon: "",
+          preferredProvider: null,
+          preferredModel: null,
+          workingDirs: [],
+          useWorktrees: false,
+          order: 0,
+          archivedAt: null,
+          createdAt: "2026-04-28T00:00:00.000Z",
+          updatedAt: "2026-04-28T00:00:00.000Z",
+          artifactsDir: "",
+        },
+      ],
+    });
+    useChatSessionStore.setState({
+      ...baseSessionState,
+      sessions: [
+        {
+          id: "s1",
+          title: "Chat",
+          providerId: "openai",
+          modelId: "gpt-4o",
+          modelName: "GPT-4o",
+          createdAt: "2026-04-28T00:00:00.000Z",
+          updatedAt: "2026-04-28T00:00:00.000Z",
+          messageCount: 0,
+          projectId: "p1",
+        },
+      ],
+      activeSessionId: "s1",
+    });
+
+    const { result } = renderHook(() => useActiveProjectTint());
+    expect(result.current).toBe("#3b82f6");
+  });
+
+  it("returns null when the active session references a deleted project", () => {
+    useChatSessionStore.setState({
+      ...baseSessionState,
+      sessions: [
+        {
+          id: "s1",
+          title: "Chat",
+          providerId: "openai",
+          modelId: "gpt-4o",
+          modelName: "GPT-4o",
+          createdAt: "2026-04-28T00:00:00.000Z",
+          updatedAt: "2026-04-28T00:00:00.000Z",
+          messageCount: 0,
+          projectId: "ghost-project",
+        },
+      ],
+      activeSessionId: "s1",
+    });
+
+    const { result } = renderHook(() => useActiveProjectTint());
+    expect(result.current).toBeNull();
+  });
+});

ui/goose2/src/features/chat/hooks/useActiveProjectTint.ts

@@ -0,0 +1,21 @@
+import { useChatSessionStore } from "@/features/chat/stores/chatSessionStore";
+import { useProjectStore } from "@/features/projects/stores/projectStore";
+
+/**
+ * Resolves the active chat session's project color. Returns the hex string
+ * if the active session is bound to a known project, otherwise null. The
+ * route gate (only-tint-when-on-chat-view) lives at the application point
+ * in AppShell, not here — this hook stays a pure session→project→color
+ * selector so it has one named place to test.
+ */
+export function useActiveProjectTint(): string | null {
+  const activeSessionId = useChatSessionStore((s) => s.activeSessionId);
+  const sessions = useChatSessionStore((s) => s.sessions);
+  const projects = useProjectStore((s) => s.projects);
+
+  if (!activeSessionId) return null;
+  const session = sessions.find((s) => s.id === activeSessionId);
+  if (!session?.projectId) return null;
+  const project = projects.find((p) => p.id === session.projectId);
+  return project?.color ?? null;
+}