preset data-agent fails on DSH core 0.2.1-rc.1: unknown prompt variable "{{cwd}}"

Summary

preset/data-agent/agent.cordis.yml renders its persona through
@deepseek-ai/dsh-persona with an active {{cwd}} placeholder:

- id: persona
  name: '@deepseek-ai/dsh-persona'
  config:
    prefix: &data_agent_persona >-
      你是数据工程师 Agent。工作目录 {{cwd}}。可用工具：sql-query（只读 SQL，返回结构化

DSH core 0.2.1-rc.1 registers only three prompt variables — provider,
model, vision_router_mode_sync — and
@deepseek-ai/dsh-system-prompt/lib/index.js:174-177 throws on any other
name:

unknown prompt variable "{{cwd}}" in section "deployment:persona-suffix";
registered variables: provider, model, vision_router_mode_sync

Because this happens inside renderPrompt() on agent/pre-step, every session
using the data-agent preset dies at turn 1, step 1, before a single request
reaches a model and before any tool call. The session is not slow or degraded —
it never starts.

Impact (measured 2026-10-17, Windows, DSH desktop profile)

Eight sessions were killed inside a three-minute window, all at step: 1,
repeatably across retries:

09:28:03  session-9be5d66d…  turn 1  unknown prompt variable "{{cwd}}"
09:28:21  session-9be5d66d…  turn 2  (same, retry)
09:29:11  session-9be5d66d…  turn 3  (same, retry)
09:30:22  session-9be5d66d…  turn 4  (same, retry)

Knock-on damage: an automated archiver that spawns an extractor session with
this preset received turn/end {kind:'error'} at step 1 and reported the
extractor as "crashed before writing its verdict" — a false signal that sent a
repair agent to chase a nonexistent content bug.

Cause

{{cwd}} was a valid prompt variable in an older core and is no longer
registered. Nothing warns at preset load time: the preset mounts fine and fails
only when a turn actually renders the prompt.

Suggested fix

Either

1. register cwd in the core's prompt-variable registry so presets keep
   working (and document the full variable list), or
2. drop the placeholder from this preset — the working directory already
   reaches the prompt through the runtime context section, so nothing is lost:

    prefix: &data_agent_persona >-
      你是数据工程师 Agent。可用工具：sql-query（只读 SQL，返回结构化

Option 2 is a one-line change and is what I applied locally to unblock.

Suggested hardening

A preset that references an unregistered prompt variable should be reported at
mount time (or by a validation pass over preset/**/agent.cordis.yml), not on
the first turn of every session. An interpolate: false escape hatch or a
startup lint would turn a silent prod outage into a visible warning.

Verification after the local fix

• No active {{cwd}} remains in any preset under ~/.dsh/.agent-presets or in
  packaged preset/ directories.
• A guard script scanning both roots exits 0; with the placeholder
  reintroduced it exits 1 and names the exact file and line.
• dsh-errors.jsonl shows no unknown prompt variable … cwd entries after the
  fix.

Version: @yejiming/dsh-data-agent 0.2.2, DSH core 0.2.1-rc.1.