Durable long-running jobs: consider Temporal (or org standard) for multi-day stream windows

[greatest0fallt1me]

Spike: Temporal/Step Functions for long-lived streaming schedules and child workflows

    ## Description

    **Spike** whether **durable** workflow engines (**Temporal**, AWS SFW, or org standard) fit

multi-day or monthly stream accrual with Soroban settlement, better than
pure cron+queue. Output is an ADR with build vs not-build recommendation, not
production roll-out in 96h unless trivially adopted.

    ## Requirements and context

    - **Prototype** 2 flows: `sleep-until` next tick, **child** workflow per stream.

• Cost and operational comparison vs current BullMQ (from existing issues) + cron.

• Security of worker identity and secrets; network egress controls.

• ADRs in docs/adr/.

• If rejected, document risks of staying on cron (missed tick, idempotency).

    ## Suggested execution
  
    1. `git checkout -b spike/temporal-streams`
  

2. Timebox 3 days; do not block release train on the spike.

3. PR with ADR, no need for 95% test coverage (spike) but include tests for any code merged.

4. Guidelines on timeframe: 96h to ADR+prototype branch; mark issue done when merged.

5. Child issue for production if approved.

    ## Test and commit
   

• Run the full test suite; add or update tests until the agreed coverage bar is met.
• Cover edge cases listed in this issue; document any intentional exclusions with brief rationale in the PR.
• Include relevant test output (e.g. test runner summary) or a link to a passing CI run in the pull request.
• Add security notes for auth, keys, PII, chain settlement, or money movement (assumptions verified, out-of-scope items).

Example commit message

docs(adr): spike Temporal (or org equivalent) for long-lived stream and Soroban workflows

Guidelines

• Target: at least 95% coverage on new or meaningfully changed code (per the repo’s standard tooling).
• Documentation: update contributor-facing or API documentation where a reviewer would be blocked without it.
• Timeframe: 96 hours to ready-for-review (surface blockers early).