review: the persona becomes the system-prompt plugin's deployment config

Review round 2 (tianyicui inline comments):

- dsh-system-prompt itself registers the harness:identity (-100) and
  deployment:persona (0) sections — they must survive a swapped loop
  plugin, so they leave dsh-agent-loop; the persona text is the plugin's
  own validated 'persona' config. The model/cwd variables STAY on the
  loop: runtime facts of the agents it drives.
- AgentOptions.systemPrompt is deleted with all its forwarding plumbing:
  the app configs' systemPrompt keys become 'persona' routed through
  dsh-agent-core (schema = z.intersect of the owners'), the ACP bridge
  and tool-subagent stop carrying persona configuration, and subagent
  children now render the deployment persona like every other agent.
- Example personas drop transport/interface trivia (ACP, CLI) — facts
  irrelevant to the model.
- Root CONTEXT.md removed (not idiomatic); its persona definition was
  wrong under the new ownership anyway.
- Docs, READMEs, the prompt-variables RFC, and generated catalogs
  updated; new loop test pins the assemble-waterfall escape valve
  (an emptied assembly sends NO system field).

packages/ui/stdio-agent/tests/stdio-agent.spec.ts

@@ -8,8 +8,9 @@ import * as stdioAgent from '../src/index.ts'
  * Unit coverage for the @deepseek-ai/dsh-stdio-agent app plugin: mounting it
  * composes the console logger, the agent-core spine (pre-creating the `main`
  * agent from the app config), the JSONL backend, and the readline UI in one
- * `ctx.plugin`. The forwarded `model`/`systemPrompt` reach the pre-created
- * agent; `persistenceRoot`/`welcome`/`resumeSessionId` route to their backends.
+ * `ctx.plugin`. The forwarded `model` reaches the pre-created agent and
+ * `persona` the system-prompt plugin; `persistenceRoot`/`welcome`/
+ * `resumeSessionId` route to their backends.
  *
  * `hmr` is NOT part of this plugin (it is a leaf entry — a Loader-only dev
  * plugin the in-process tier cannot import); the keyless echo smoke in
@@ -30,7 +31,7 @@ async function mount(config: stdioAgent.Config): Promise<Context> {
 
 describe('dsh-stdio-agent app', () => {
   it('composes the spine + front-door cluster and pre-creates the main agent', async () => {
-    const ctx = await mount({ model: 'mock', systemPrompt: 'hi', persistenceRoot: '/tmp/dsh-stdio-agent-spec' })
+    const ctx = await mount({ model: 'mock', persona: 'hi', persistenceRoot: '/tmp/dsh-stdio-agent-spec' })
     // The spine services (brought up by the agent-core bundle) are all present.
     expect(ctx.get('agents')).toBeDefined()
     expect(ctx.get('agentLoop')).toBeDefined()
@@ -46,7 +47,8 @@ describe('dsh-stdio-agent app', () => {
     // apply()'s last two lines are the ones that fire — covering a
     // schema-bypassing direct-mount caller.
     const ctx = new Context()
-    stdioAgent.apply(ctx, { model: 'mock', systemPrompt: 'hi' })
+    // No persona: covers the omitted-persona forwarding branch too.
+    stdioAgent.apply(ctx, { model: 'mock' })
     await new Promise(resolve => setTimeout(resolve, 80))
     expect(ctx.get('sessionPersistence')).toBeDefined()
     expect(ctx.get('agents')?.get(AgentId('main'))).toBeDefined()
@@ -59,7 +61,7 @@ describe('dsh-stdio-agent app', () => {
     // the branch that maps resumeSessionId through is what this covers.
     const ctx = await mount({
       model: 'mock',
-      systemPrompt: 'hi',
+      persona: 'hi',
       persistenceRoot: '/tmp/dsh-stdio-agent-spec-resume',
       resumeSessionId: 'no-such-session',
     })