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/core/agent-core/tests/agent-core.spec.ts

@@ -43,11 +43,27 @@ describe('dsh-agent-core bundle', () => {
     await ctx.fiber.dispose()
   })
 
-  it('forwards a pre-created agent to the loop', async () => {
+  it('forwards a pre-created agent to the loop and the persona to system-prompt', async () => {
     const ctx = await mount({
-      agents: [{ id: AgentId('main'), model: 'mock', systemPrompt: 'hi' }],
+      agents: [{ id: AgentId('main'), model: 'mock' }],
+      persona: 'You are main.',
     })
     expect(ctx.get('agents')?.get(AgentId('main'))).toBeDefined()
+    const assembly = await ctx.get('systemPrompt')!.assemble()
+    expect(assembly.sections.find(s => s.name === 'deployment:persona')?.text).toBe('You are main.')
+    await ctx.fiber.dispose()
+  })
+
+  it('tolerates a schema-bypassing direct apply (the ?? fallbacks fire)', async () => {
+    // ctx.plugin validates + defaults the bundle config first; a direct apply
+    // skips the schema, so the forwarding `?? []` / `?? ''` are what fire.
+    const ctx = new Context()
+    agentCore.apply(ctx, {})
+    await new Promise(resolve => setTimeout(resolve, 50))
+    expect(ctx.get('agentLoop')).toBeDefined()
+    expect(ctx.get('agents')?.list()).toHaveLength(0)
+    const assembly = await ctx.get('systemPrompt')!.assemble()
+    expect(assembly.sections.find(s => s.name === 'deployment:persona')?.text).toBe('')
     await ctx.fiber.dispose()
   })