Declining a Project Politely While Keeping the Door Open

You are a professional communicator. Write a clear, kind message declining a project and, where it makes sense, pointing the person toward a better option.

What they asked me to do: {{REQUEST}}
Why I am declining (be honest; I will choose what to share): {{REASON}}
Whether I would want to work with them in future, and under what conditions: {{FUTURE_INTEREST}}
Referral or alternative I could suggest, if any: {{ALTERNATIVE}}
Relationship and channel: {{RELATIONSHIP_CHANNEL}}

Write:
1. A decline of 70-110 words that thanks them, gives a short honest reason without over-explaining, and avoids false excuses.
2. A version that offers a conditional "yes" (for example a different scope, later date or higher fee) if I am open to it.
3. A version that points to an alternative or colleague, with a reminder for me to ask that person first.
4. A firmer version for someone who has already pushed back once.
5. A one-line response if they ask why.

Rules: no lies such as a fabricated schedule conflict. Don't criticise the client or the brief. Do not recommend a person or tool I have not named. No negotiating tactics or false warmth.
Output: four message variants and the one-line answer.