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feat(system-prompt): prompt variables, persona-as-section, tool-guidance ownership

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One principle: every fact in the assembled prompt has exactly one owner.

- dsh-system-prompt: merge-extensible AssembleContext on assemble();
  a variable(name, provider) registry; {{name}} interpolation in
  renderPrompt, strict (unknown/valueless/malformed references throw);
  duplicate section and variable names rejected; assembly carries
  resolved section text + variables through the assemble waterfall.
- dsh-agent declares AssembleContext.agent; dsh-agent-loop registers
  the agent:persona section (order 0 - identity renders before tool
  guidance) and the model/cwd variables, and drops its string join:
  renderPrompt(assembly) IS the full prompt.
- Tool guidance moves to its owners: descriptions carry per-tool
  semantics; sections only cross-call habits (tool:bash exit-code
  habit at order 105; read's not-shell nudge). todo/subagent need no
  section - their descriptions already carry the contract.
- SubagentProvider.inheritsParentContext (spawn/acp false, fork true);
  dsh-tool-subagent derives truthful per-provider wording and resolves
  the provider at load (backend must be listed first).
- Example personas shrink to identity + behavior with {{model}} (and
  {{cwd}} in the ACP tree); the welcome banner stops enumerating tools.

RFC: docs/rfc/implemented/architecture/2026-07-05-prompt-variables-and-tool-guidance-ownership.md
This commit is contained in:
Tianyi Cui
2026-07-05 01:54:46 +08:00
parent 1e2efc861e
commit f256f3961d
41 changed files with 746 additions and 177 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
packages/core/agent-loop/README.md
View File

@@ -28,12 +28,12 @@ interface Config {
agents: Array<{
id: string // required
model?: string
systemPrompt?: string
systemPrompt?: string // the agent's persona TEMPLATE (may reference {{model}}/{{cwd}})
}>
}
```
Agents listed in config are auto-created at startup.
Agents listed in config are auto-created at startup. The plugin also registers the per-agent prompt pieces on `ctx.systemPrompt`: the `agent:persona` section (order 0 — `AgentOptions.systemPrompt` renders before all tool guidance) and the built-in `model`/`cwd` prompt variables, each resolved per step from the `assemble({ agent })` context.
### Classes
@@ -55,7 +55,7 @@ forever:
if every prompt blocked: 'turn/end'(rejected), no step ⟵ zero-step turn
STEP loop:
drain steering
assembly = systemPrompt.assemble()
assembly = systemPrompt.assemble({agent}) ⟵ renderPrompt(assembly) IS the full prompt
await serial agent/pre-step ⟵ surface mutation (compaction) outside the step
session('step/start')
request = waterfall agent/request

14
packages/core/agent-loop/src/index.ts
View File

@@ -82,6 +82,20 @@ export class AgentLoop extends Service implements AgentFactory {
// Provide the agent-creation factory to the registry (effect-scoped: the
// slot is cleared on dispose).
ctx.effect(() => this.ctx.agents.setFactory(this), 'agentLoop.setFactory()')
// The per-agent prompt pieces, registered once and resolved per assembly
// from the AssembleContext the loop passes (loop.ts assembles with
// `{ agent }` each step). The persona is the order-0 section — identity
// renders before all tool guidance; `{{model}}`/`{{cwd}}` are the built-in
// prompt variables projecting the agent's configured model and its
// session workspace. A provider returns undefined when the fact is absent
// (renderPrompt then rejects a persona that claims it — fail loud).
ctx.systemPrompt.section({
name: 'agent:persona',
order: 0,
text: context => context.agent?.options.systemPrompt ?? '',
})
ctx.systemPrompt.variable('model', context => context.agent?.options.model)
ctx.systemPrompt.variable('cwd', context => context.agent?.session.header.cwd)
for (const { id, resumeSessionId, ...options } of config.agents) {
if (resumeSessionId !== undefined && resumeSessionId !== '') {
// Resume a prior session instead of starting fresh. resume() needs

13
packages/core/agent-loop/src/loop.ts
View File

@@ -152,7 +152,8 @@ export interface LoopHandle {
* every prompt blocked → 'turn/end'(rejected), 0 steps
* STEP loop:
* drain steering → session('steering/message') ⟵ catches late steering
* assembly = ctx.systemPrompt.assemble() ⟵ waterfall system-prompt/assemble
* assembly = ctx.systemPrompt.assemble({agent}) ⟵ waterfall system-prompt/assemble; renderPrompt
* (persona section + {{variables}}) IS the full prompt
* await ctx.serial('agent/pre-step') ⟵ surface mutation (compaction) OUTSIDE the step
* session('step/start') ⟵ durable step boundary (no agent/* mirror)
* req = {model, system, tools, messages: session.deriveMessages(), signal}
@@ -434,11 +435,11 @@ async function runTurn(ctx: Context, agent: ReactLoopAgent, handle: LoopHandle,
// because the pre-step seam needs it: compaction measures token pressure
// against the system prompt (it counts toward the budget). runStep reuses
// this same assembly for the request, so the prompt is assembled once per
// step.
const assembly = await ctx.systemPrompt.assemble()
const fullSystemPrompt = [renderPrompt(assembly), agent.options.systemPrompt ?? '']
.filter(text => text.length > 0)
.join('\n\n')
// step. renderPrompt IS the full prompt — the persona is the order-0
// section (registered by the AgentLoop plugin) and `{{variable}}`
// interpolation happens in the render, so there is no separate join.
const assembly = await ctx.systemPrompt.assemble({ agent })
const fullSystemPrompt = renderPrompt(assembly)
// Interruption landing after assembly: dispose() or cancel() in a
// turn-start listener (or a listener whose promise resolved before the

47
packages/core/agent-loop/tests/loop.spec.ts
View File

@@ -141,10 +141,10 @@ describe('agent loop', () => {
.toEqual({ diffs: [{ path: 'a.txt', oldText: null, newText: 'x' }] })
})
it('passes assembled system prompt and tool schemas into the request', async () => {
it('renders the persona as the order-0 section — before tool guidance — with {{variables}} resolved', async () => {
const adapter = new MockAdapter([textResponse('ok')])
const ctx = await harness(adapter)
ctx.systemPrompt.section({ name: 'persona', order: 0, text: 'You are a test agent.' })
ctx.systemPrompt.section({ name: 'tool:noop', order: 100, text: 'Use the noop tool wisely.' })
ctx.tools.register(defineTool({
name: 'noop',
description: 'does nothing',
@@ -153,16 +153,55 @@ describe('agent loop', () => {
return []
},
}))
const agent = ctx.agentLoop.create(AgentId('a1'), { model: 'mock', systemPrompt: 'Agent-specific suffix.' })
// The persona is a TEMPLATE: {{model}} is the loop-registered variable
// projecting this agent's configured model, so the model knows its own name.
const agent = ctx.agentLoop.create(AgentId('a1'), { model: 'mock', systemPrompt: 'You are a test agent on {{model}}.' })
send(agent, 'hi')
await waitForIdle(ctx, agent)
const request = adapter.requests[0]
expect(request!.system).toBe('You are a test agent.\n\nAgent-specific suffix.')
expect(request!.system).toBe('You are a test agent on mock.\n\nUse the noop tool wisely.')
expect(request!.tools?.map(t => t.name)).toEqual(['noop'])
})
it('resolves {{cwd}} from the agent session workspace (factory create with meta.cwd)', async () => {
const adapter = new MockAdapter([textResponse('ok')])
const ctx = await harness(adapter)
const handle = ctx.agents.create({
agentId: AgentId('a-cwd'),
sessionId: SessionId('s-cwd'),
meta: { cwd: '/work/space' },
agentOptions: { model: 'mock', systemPrompt: 'Working in {{cwd}}.' },
})
const agent = handle.agent as ReactLoopAgent
send(agent, 'hi')
await waitForIdle(ctx, agent)
expect(adapter.requests[0]!.system).toBe('Working in /work/space.')
})
it('contains a strict-variable render failure: the turn errors, the loop survives', async () => {
// A persona claiming {{cwd}} on a session with NO cwd is a deployment
// authoring error — renderPrompt throws, the turn ends with an error, and
// the agent (and loop) stay alive for the next prompt.
const adapter = new MockAdapter([textResponse('never reached'), textResponse('ok')])
const ctx = await harness(adapter)
const errors: Error[] = []
ctx.on('agent/error', (_agent, _turn, _step, error) => void errors.push(error))
const agent = ctx.agentLoop.create(AgentId('a1'), { model: 'mock', systemPrompt: 'In {{cwd}}.' })
send(agent, 'hi')
await waitForIdle(ctx, agent)
expect(adapter.requests).toHaveLength(0) // the request was never sent
expect(errors.some(e => e.message.includes('no value for this assembly'))).toBe(true)
const turnEnd = agent.session.events.find(e => e.type === 'turn/end')
expect(turnEnd?.type === 'turn/end' && turnEnd.data.reason.kind).toBe('error')
expect(agent.status).toBe('idle') // contained: the loop is still serving
})
it('records raw chunks for replay as assistant/chunk session events', async () => {
const adapter = new MockAdapter([textResponse('abc')])
const ctx = await harness(adapter)

6
packages/core/agent-loop/tests/review-fixes.spec.ts
View File

@@ -1016,7 +1016,7 @@ describe('disposal/cancel honored during pre-step assembly (P1-1)', () => {
ctx.llm.registerAdapter(['mock'], adapter)
// Blocking listener on the parent context (survives fiber disposal).
const unlisten = ctx.on('system-prompt/assemble', async function (_assembly, next) {
const unlisten = ctx.on('system-prompt/assemble', async function (_assembly, _context, next) {
await blocked
return next()
})
@@ -1072,7 +1072,7 @@ describe('disposal/cancel honored during pre-step assembly (P1-1)', () => {
await ctx.plugin(Invariants, { freeze: false })
ctx.llm.registerAdapter(['mock'], adapter)
const unlisten = ctx.on('system-prompt/assemble', async function (_assembly, next) {
const unlisten = ctx.on('system-prompt/assemble', async function (_assembly, _context, next) {
await blocker
return next()
})
@@ -1229,7 +1229,7 @@ describe('disposal/cancel honored during pre-step assembly (P1-1)', () => {
await ctx.plugin(Invariants, { freeze: false })
ctx.llm.registerAdapter(['mock'], adapter)
ctx.on('system-prompt/assemble', async function (_assembly, next) {
ctx.on('system-prompt/assemble', async function (_assembly, _context, next) {
await blocker
return next()
})