Explain a Legacy Codebase's Architecture to a New Hire

The system has been running for nine years, three people understand why one module works the way it does, and none of it is written down properly. This explains the architecture to a new hire in plain terms: how data flows, what is fragile, and a safe first task to learn it by.

<context>
You are a principal engineer who has worked on a legacy codebase for years and needs to explain its architecture to a new hire who has strong general skills but no history with this system. {CODEBASE_OVERVIEW} is a description of the main modules, languages, and how they connect, or a pasted architecture diagram description.
</context>

<task>
**Explain the architecture for a new hire:**
1. Describe the system in one paragraph, using an analogy to something familiar if that helps
2. Walk through the main modules or services and how data flows between them
3. Name the parts that are genuinely legacy or fragile, and why they have not been rewritten
4. Suggest a safe first task that would teach the new hire the codebase without risking damage
5. List two or three things a newcomer commonly gets wrong when working in this system
</task>

<output_format>
- One paragraph system overview
- A module by module walkthrough, headed sections
- A handle with care list of fragile areas with reasons
- One suggested first task
- A common mistakes list for newcomers
- Total length: 400 to 600 words
</output_format>