[MCP-001] SYSTEM_PROMPT — align with chatbot Writer/Planner rules

[github-actions]

MCP-001 — Sync data360://system-prompt with chatbot prompts

Goal

Reduce drift between MCP-only LLM clients and the Data AI Chatbot: update SYSTEM_PROMPT in src/data360/mcp_server/prompts.py so tool-loop behavior and final answer structure / link expectations stay consistent with vercel-ai-chatbot backend/app/ai/prompts.py after BE-001.

Context

• Resource registration: src/data360/mcp_server/resources.py exposes data360://system-prompt.
• Do not duplicate entire Writer prompt if inappropriate for MCP; align non-conflicting bullets: section order hints, link discipline, when to call data360_get_viz_spec.

Implementation hints

• Entry point: src/data360/mcp_server/prompts.py — SYSTEM_PROMPT string literal lines 11–56.
• Current structure: 4 sections — ### Non-negotiable rule (line 15), ### Operating loop (line 19, 5-step workflow: search → codelist → availability → get data → visualize), ### Defaults (line 47, 20-year range hardcoded in text), ### Output behavior (line 52).
• Exposed via: src/data360/mcp_server/resources.py line 159–162 as MCP resource data360://system-prompt.
• Desired behavior: After BE-001 finalises section order and link discipline in the chatbot Writer prompt, mirror the non-conflicting bullets here — specifically: section order hints for final answer, link discipline for API/indicator URLs, when to call data360_get_viz_spec. Do NOT duplicate the full Writer prompt.
• Test file: No tests for SYSTEM_PROMPT content. After update, manually verify that data360://system-prompt resource returns the updated string via MCP inspector or a quick test script.
• Gotchas: SYSTEM_PROMPT is a plain string — preserve existing markdown formatting exactly. The 20-year default is hardcoded in text (line 48–49), not a config variable. Sync changes in prompts.py to README.md and docs/overview.md if they quote the resource content.

Acceptance criteria

• SYSTEM_PROMPT updated to reflect agreed structure and link/viz nudges (scoped to MCP tool use).
• README/docs that quote the resource updated if needed (README.md, docs/overview.md).
• No contradiction with existing mandatory tool-call rules in the same file.

Dependencies

• BE-001 (vercel-ai-chatbot) — source of truth for product wording; complete or sync in pair review.

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Task file: TODO/MCP-001-system-prompt-sync.md
Depends on: BE-001