Thorough Code Review

Review the following code and give structured feedback across four areas:

**Correctness**
- Are there bugs, edge cases, or off-by-one errors?
- Does error handling cover realistic failure modes?

**Security**
- Is there any risk of injection, data exposure, or unsafe operations?
- Are inputs validated at the right boundaries?

**Performance**
- Are there unnecessary allocations, N+1 queries, or blocking operations?
- What is the likely bottleneck under load?

**Readability**
- Is the intent clear without reading every line?
- Are variable and function names descriptive?
- Is there anything that needs a comment to be understood?

For each issue, state: what it is, why it matters, and a concrete fix. Skip praise. Focus on what needs changing.

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