Feature Request: Support for multiple prebuilt block templates (template cache)

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Motivation

Currently, the DATUM Gateway only works with a single active block template at a time.
For miners, especially on slower hardware or with higher latency, it would be useful to prebuild and cache multiple templates ahead of time.

This would reduce delays when:

• A new block is found
• Transactions are added to the mempool
• Work needs to be regenerated quickly

Proposed Feature

• Add a configuration option prebuild_templates
• Allow specifying how many templates to keep in cache (e.g. 5–10)
• Support different strategies, such as:
  • empty (no txns, fastest propagation)
  • mempool (full/minimal txns, higher fees)
• When a new block arrives, rotate the templates, drop stale ones, and generate new ones in the background.

Benefits

• Miners can switch instantly to fresh work without waiting for GBT roundtrips
• Reduces the risk of idle ASICs between block updates
• Aligns with the decentralization goals of DATUM by giving miners more flexibility in block construction

References

• Similar caching ideas exist in mining software (e.g., Stratum job queues, extranonce handling)
• Bitcoin Knots already supports fine-grained block template policies, which could complement this feature

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Additional Context / Use Case

I’m running a solo-mining setup with smaller ASICs (NerdQaxe, Bitaxe Gamma, Avalon Nano, Avalon Q).
For this kind of hardware, it would be very helpful if DATUM Gateway could:
• Cache multiple prebuilt templates (e.g., 5–10) of different types (empty, minimal, full mempool)
• Support Vardiff handling directly in Gateway, so that even slow devices can stay connected without frequent disconnects when they don’t submit shares quickly enough.

Right now, I notice my miners sometimes idle or drop connection if:
• the template update comes too late
• the difficulty is too high compared to their hashrate

Having template caching + Vardiff support inside DATUM Gateway would make these smaller miners much more stable, and help decentralize mining further by keeping them online longer.

[luke-jr]

DATUM Gateway already does both of these things...?