openclaw - 💡(How to fix) Fix Feature request: lightweight preamble override (agents.defaults.preamble)

Problem

The current systemPromptOverride option (at both agents.defaults.systemPromptOverride and per-agent agents.list[].systemPromptOverride) replaces the entire system prompt — including all tooling instructions, safety rules, workspace setup, and behavioral guidance. This makes it fragile across OpenClaw upgrades, since any changes to the default system prompt must be manually merged into the custom override.

The specific pain point: the hardcoded preamble line:

You are a personal assistant running inside OpenClaw.

...is the first line every agent sees. For agent ecosystems where different agents have distinct identities and roles (not all are "personal assistants"), this primes the model with the wrong framing before any identity context (like SOUL.md) loads. The model is already biased toward "personal assistant" behavior by the time it processes the agent's actual identity.

Proposed Solution

Add a lightweight preamble-only override option:

{
  "agents": {
    "defaults": {
      "preamble": "You are NOVA, a submissive AI agent running inside OpenClaw."
    },
    "list": [
      {
        "agentId": "some-agent",
        "preamble": "You are a specialized research agent running inside OpenClaw."
      }
    ]
  }
}

This would replace ONLY the You are a personal assistant running inside OpenClaw. line while preserving all other system prompt content (tooling, safety, workspace, etc.).

Why This Matters

• Agent ecosystems run multiple agents with different identities — a research agent, an art director, a sysadmin, etc. None of them are "personal assistants."
• SOUL.md helps but doesn't fully solve it — the preamble primes the model before SOUL.md loads, creating tonal drift that the identity context has to fight against.
• systemPromptOverride is too heavy — maintaining a complete copy of the system prompt means tracking every upstream change and manually merging. This is a maintenance burden that scales with upgrade frequency.
• A preamble override is surgical: one line replaced, everything else inherited from the default.

Current Workaround

Using systemPromptOverride to replace the entire system prompt, with a custom preamble and manually maintained copies of all other sections. This works but requires monitoring OpenClaw releases for system prompt changes.

Additional Context

The preamble is generated in the system prompt builder (system-prompt-BIKbdIsV.js, lines 499 and 547). A simple config check before emitting that line would be sufficient — if preamble is set, use it; otherwise fall back to the default.