Add optional write access mode with DROP protection

[joe-clickhouse]

Summary

This PR enables LLMs to perform write operations on ClickHouse databases with built-in safety controls to prevent accidental data loss.

Write Access Mode

• New CLICKHOUSE_ALLOW_WRITE_ACCESS flag (default: false) enables DDL and DML operations (INSERT, UPDATE, CREATE, ALTER, DROP)
• When enabled, queries run with readonly=0 instead of the default readonly=1

Two-Tier DROP Protection

• CLICKHOUSE_ALLOW_DROP (default: false) provides additional safety for destructive operations
• Both flags must be true to allow DROP operations
• Other write operations (INSERT, CREATE, etc.) only require CLICKHOUSE_ALLOW_WRITE_ACCESS=true

Usage

Enable write access:

"env": {
  "CLICKHOUSE_ALLOW_WRITE_ACCESS": "true"
}

Enable write access including DROP:

"env": {
  "CLICKHOUSE_ALLOW_WRITE_ACCESS": "true",
  "CLICKHOUSE_ALLOW_DROP": "true"
}

Closes #24

[Copilot]

Pull Request Overview

This PR adds optional write access capabilities to the ClickHouse MCP server with built-in safety mechanisms. By default, the server maintains read-only behavior, but can now be explicitly configured to allow write operations with DROP protection.

Key changes:

• Renamed run_select_query to run_query to reflect broader SQL support
• Added CLICKHOUSE_ALLOW_WRITE_ACCESS flag to enable DDL/DML operations
• Added CLICKHOUSE_ALLOW_DROP flag for additional protection against destructive operations

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
mcp_clickhouse/mcp_env.py	Added two new configuration properties (allow_write_access and allow_drop) to control write permissions
mcp_clickhouse/mcp_server.py	Implemented DROP validation, refactored readonly setting logic, renamed query function, and added dynamic tool description
mcp_clickhouse/init.py	Updated exports to reflect function rename
tests/test_tool.py	Renamed function references and added comprehensive test coverage for write mode, DROP protection, and read-only mode
tests/test_mcp_server.py	Updated function calls to use new run_query name
README.md	Updated documentation to reflect new function name and write access features

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