docs(rfc): RFC-003 — adapter packages + dynamic prompts

- Adapter packages: each adapter in own package (@nerve/adapter-cursor, etc.)
- AgentRegistry accepts adapter factories at construction (plugin model)
- Migration path: move spawn logic from workflow-utils to adapter packages
- Dynamic prompts: RoleSpec.prompt supports string | async function
- Workspace only installs adapters it uses

Ref: #234

docs/rfc-003-agent-config-layer.md

@@ -103,6 +103,73 @@ nerve.yaml#extract →  ExtractFn(string, schema) → T (typed meta)
 
 `AgentRegistry` reads config, instantiates adapters, and returns `AgentFn` by name. Role assembly is handled by the runtime — users never call Role factories directly.
 
+### Adapter Packages
+
+Each agent adapter lives in its own package to avoid pulling unnecessary dependencies:
+
+```
+packages/
+  adapter-cursor/     # @nerve/adapter-cursor — cursor-agent CLI
+  adapter-hermes/     # @nerve/adapter-hermes — hermes CLI subagent
+  adapter-claude/     # @nerve/adapter-claude — claude-code CLI (future)
+  adapter-codex/      # @nerve/adapter-codex — codex CLI (future)
+```
+
+Each adapter exports a single factory function:
+
+```ts
+// @nerve/adapter-cursor
+import type { AgentConfig, AgentFn } from "@nerve/core";
+
+export function createCursorAdapter(config: AgentConfig): AgentFn;
+```
+
+The factory receives the full `AgentConfig` (type, model, timeout) and returns an `AgentFn` that spawns the CLI tool, passes the prompt, and returns raw output.
+
+**Registration** — `AgentRegistry` accepts adapter factories at construction:
+
+```ts
+import { createCursorAdapter } from "@nerve/adapter-cursor";
+import { createHermesAdapter } from "@nerve/adapter-hermes";
+
+const registry = createAgentRegistry(config.agents, {
+  cursor: createCursorAdapter,
+  hermes: createHermesAdapter,
+});
+```
+
+The daemon's entry point wires installed adapters; adapters not installed are not imported. `nerve validate` checks that referenced adapter types have a registered factory.
+
+**Workspace `package.json`** only lists the adapters it actually uses:
+
+```json
+{
+  "dependencies": {
+    "@nerve/adapter-cursor": "workspace:*",
+    "@nerve/adapter-hermes": "workspace:*"
+  }
+}
+```
+
+**Migration from `workflow-utils`** — the existing `role-cursor.ts` / `shared/cursor-agent.ts` spawn logic moves to `@nerve/adapter-cursor`. `role-hermes.ts` / `shared/hermes-agent.ts` moves to `@nerve/adapter-hermes`. `workflow-utils` retains only extract, prompt utilities, and shared spawn infrastructure.
+
+### Dynamic Prompts
+
+`RoleSpec.prompt` supports both static strings and async functions:
+
+```ts
+type PromptInput = string | ((start: StartStep, messages: WorkflowMessage[]) => Promise<string>);
+
+type RoleSpec<M> = {
+  agent: string;
+  prompt: PromptInput;
+  meta: Schema<M>;
+  timeout: string | null;
+};
+```
+
+Static prompts cover simple cases. Dynamic prompts (functions) are needed when the prompt depends on thread context — e.g. reading issue content, injecting prior step results, or resolving repo paths at runtime.
+
 ### Timeout Resolution
 
 Two-layer with role override: