diff --git a/src/extensions/shared/workspace/index.ts b/src/extensions/shared/workspace/index.ts
new file mode 100644
index 0000000..a21a9fb
--- /dev/null
+++ b/src/extensions/shared/workspace/index.ts
@@ -0,0 +1,97 @@
+import { createHash } from "node:crypto";
+import { appendFile, mkdir, readFile, writeFile } from "node:fs/promises";
+import { homedir } from "node:os";
+import { join, resolve } from "node:path";
+
+import type { Extension } from "../../../kernel";
+import { ExtensionId, Hook } from "../../catalog";
+
+export type MessageRole = "system" | "user" | "assistant";
+
+export interface ChatMessage {
+  role: MessageRole;
+  content: string;
+  createdAt: string;
+}
+
+export interface WorkspaceService {
+  home: string;
+  projectPath: string;
+  workspaceId: string;
+  conversationId: string;
+  messages(): Promise<ChatMessage[]>;
+  append(role: MessageRole, content: string): Promise<ChatMessage>;
+}
+
+export interface WorkspaceOptions {
+  home?: string;
+  projectPath?: string;
+  conversationId?: string;
+}
+
+export function createWorkspaceExtension(options: WorkspaceOptions = {}): Extension {
+  const home = resolve(
+    options.home ?? process.env.LLM_TO_AGENT_HOME ?? join(homedir(), ".llm-to-agent"),
+  );
+  const projectPath = resolve(options.projectPath ?? process.cwd());
+  const workspaceId = createHash("sha256").update(projectPath).digest("hex").slice(0, 16);
+  const conversationId = options.conversationId ?? "default";
+  const workspaceDirectory = join(home, "workspaces", workspaceId);
+  const conversationDirectory = join(workspaceDirectory, "conversations", conversationId);
+  const messagesFile = join(conversationDirectory, "messages.jsonl");
+
+  const workspace: WorkspaceService = {
+    home,
+    projectPath,
+    workspaceId,
+    conversationId,
+
+    async messages() {
+      try {
+        const content = await readFile(messagesFile, "utf8");
+        return content
+          .split("\n")
+          .filter(Boolean)
+          .map((line) => JSON.parse(line) as ChatMessage);
+      } catch (error) {
+        if ((error as NodeJS.ErrnoException).code === "ENOENT") return [];
+        throw error;
+      }
+    },
+
+    async append(role, content) {
+      const message = {
+        role,
+        content,
+        createdAt: new Date().toISOString(),
+      };
+
+      await appendFile(messagesFile, `${JSON.stringify(message)}\n`, "utf8");
+      return message;
+    },
+  };
+
+  return {
+    id: ExtensionId.Workspace,
+
+    async setup(context) {
+      await mkdir(conversationDirectory, { recursive: true });
+      await writeFile(
+        join(workspaceDirectory, "workspace.json"),
+        `${JSON.stringify(
+          {
+            id: workspaceId,
+            kind: "linked",
+            projectPath,
+            activeConversationId: conversationId,
+          },
+          null,
+          2,
+        )}\n`,
+        "utf8",
+      );
+
+      context.add(Hook.Workspace, workspace);
+    },
+  };
+}