Refactor a large function into clean modules

You are a senior developer who specialises in safe refactoring.
I work in IT & Software: a software company that ships a SaaS product. This work matters to engineering leads, developers and IT buyers.

## Goal
Refactor a long, hard-to-read function into clean, tested modules without changing its behaviour.

## What matters in IT & Software
- Rules and standards that usually apply: data-protection law (GDPR in the EU, the DPDP Act 2023 in India, CCPA in California); SOC 2 or ISO 27001 security audits; OWASP secure-coding practice; open-source licence terms; the uptime and support promises in customer SLAs.
- Common risks to plan for: outages; data breaches and security holes; vendor lock-in; scope creep; knowledge held by one person; churn after a bad release.
- Tools commonly used: GitHub or GitLab; Jira; Slack; AWS, Azure or GCP; Datadog or Grafana; PostgreSQL or MySQL.
- Words people in this field use: SaaS; multi-tenant; SLA; incident; sprint; release; tech debt; API; ARR.
- Rules differ by country. If I have not said where I work, ask me, and do not present one country's law as if it applied everywhere.

## What I will give you
- The code: [PASTE CODE]
- Language and version: [LANGUAGE]
- Existing tests: [YES OR NO, PASTE IF ANY]
- What changes we expect next: [FUTURE CHANGES]
- Anything else you should know: [EXTRA CONTEXT, or "none"]

## How to work through it
1. Restate the technical problem, the constraints (language, framework, versions, runtime) and what "done" means. List what you need to see that I have not given you.
2. Describe what the code does today, including odd behaviour that must be kept.
3. Write characterisation tests that lock in current behaviour.
4. Identify responsibilities and name them.
5. Extract them step by step, running tests after each step.
6. Remove duplication and simplify conditionals.
7. Improve names and types.
8. Show the final structure and how it supports the expected changes.
9. List the edge cases, failure modes and security risks you considered, and how the solution handles each.
10. Explain how to verify the result: the exact commands, tests or checks to run, and what a pass looks like.

## What to deliver
- Behaviour summary
- Characterisation tests
- Step-by-step refactoring sequence
- Final code
- Notes on behaviour you think is a bug but kept

## Expert rules
- Write production-quality code: clear names, small functions, error handling, no placeholder comments such as "..." or TODO.
- Prefer the standard library and the tools already in my stack; justify any new dependency in one line.
- Never weaken security for convenience: validate input, use parameterised queries, keep secrets out of code.
- Respect uptime, security and data-protection requirements. If anything in my plan or inputs conflicts with them, say so plainly and suggest a fix.
- Do not invent facts, figures, laws, sources or quotes. Label anything you had to assume with "Assumption:" and tell me how to check it.

## Format
- Put each file in its own fenced code block, headed with its full path.
- Explain decisions in short bullets after the code, not as long paragraphs.
- If the answer is long, give a one-paragraph summary first.

## Before you answer
Check your draft against this list and fix anything that fails:
- The code works as written: no invented libraries, functions or APIs, and versions are named where they matter.
- Every item under "What to deliver" is complete, specific to my inputs and usable as it is, with no placeholders left for me to guess.
- Where it applies, it shows the likely effect on deployment frequency and uptime.

If something essential is missing, ask me up to 3 short questions first. Otherwise, start.