feat: add scratchpad chat sessions

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/shared/contracts/sidecar.ts

@@ -27,6 +27,7 @@ export interface RunTurnCommand {
   requestId: string;
   sessionId: string;
   projectPath: string;
+  workspaceKind?: 'project' | 'scratchpad';
   pattern: PatternDefinition;
   messages: ChatMessageRecord[];
 }

src/shared/domain/project.ts

@@ -1,6 +1,44 @@
+import { nowIso } from '@shared/utils/ids';
+
 export interface ProjectRecord {
   id: string;
   name: string;
   path: string;
   addedAt: string;
 }
+
+export const SCRATCHPAD_PROJECT_ID = 'project-scratchpad';
+export const SCRATCHPAD_PROJECT_NAME = 'Scratchpad';
+
+export function createScratchpadProject(path: string, addedAt = nowIso()): ProjectRecord {
+  return {
+    id: SCRATCHPAD_PROJECT_ID,
+    name: SCRATCHPAD_PROJECT_NAME,
+    path,
+    addedAt,
+  };
+}
+
+export function isScratchpadProject(projectIdOrProject?: string | Pick<ProjectRecord, 'id'>): boolean {
+  if (!projectIdOrProject) {
+    return false;
+  }
+
+  return (
+    (typeof projectIdOrProject === 'string' ? projectIdOrProject : projectIdOrProject.id)
+    === SCRATCHPAD_PROJECT_ID
+  );
+}
+
+export function mergeScratchpadProject(existingProjects: ProjectRecord[], scratchpadPath: string): ProjectRecord[] {
+  const existingScratchpad = existingProjects.find((project) => isScratchpadProject(project));
+  const scratchpadProject = createScratchpadProject(
+    scratchpadPath,
+    existingScratchpad?.addedAt ?? nowIso(),
+  );
+
+  return [
+    scratchpadProject,
+    ...existingProjects.filter((project) => !isScratchpadProject(project.id)),
+  ];
+}