docs: add ROADMAP.md with package layering refactor plan

- Add focused ROADMAP with TOC and clear priorities
- Pin package layering refactor as #1 urgent work
- Add multi-harness agent OS notice to all language READMEs
- Add ROADMAP section to root README with contributor guidance
- All ROADMAP-related PRs should use the ROADMAP label

README.md

@@ -1,3 +1,8 @@
+> [!NOTE]
+> **Multi-Harness Agent OS Refactor in Progress**
+>
+> We are restructuring the codebase to support multiple agent harnesses (OpenCode, Codex, Pi, and others). If you are interested in contributing, please read the [ROADMAP](./ROADMAP.md) first. PRs related to roadmap work should use the `ROADMAP` label.
+
 > [!TIP]
 > **Building in Public**
 >
@@ -127,6 +132,12 @@ Read this and tell me why it's not just another boilerplate: https://raw.githubu
 ```
 
 
+## ROADMAP
+
+We are restructuring the codebase to support multiple agent harnesses (OpenCode, Codex, Pi, Claude Code, and others). The most urgent work is the package layering refactor: separating pure TypeScript core logic, MCP servers, skills, and adapter shims into distinct layers so the same logic can be reused across harnesses without duplication.
+
+If you want to contribute, read the [ROADMAP](./ROADMAP.md) first. PRs related to this refactor should use the `ROADMAP` label so we can track them.
+
 ## Highlights
 
 ### 🪄 `ultrawork`