mock-db.ts's transactions array grows unbounded for the lifetime of the process with no eviction

[ndii-dev]

saveTransaction does this.transactions.unshift(tx) with no cap. In a long-lived dev server or any deployment that keeps a Node process warm across many requests, this array grows without bound — this is exactly the kind of latent bug that's invisible in fixture-scale testing (MOCK_TRANSACTIONS_COMPACT seeds a small fixed set) and only surfaces under load. Not urgent to fix in mock-db.ts itself (it should be replaced by real persistence per the auth/custody issues above) but worth a guard rail plus an explicit test proving the growth-without-bound behavior, so whoever replaces this with a real DB has a written spec for pagination/retention.

Definition of done:

• Test demonstrating unbounded growth under repeated saveTransaction calls (documents the bug concretely)
• A written retention/pagination policy for the real datastore that replaces this

---

Before opening a PR for this issue, read CONTRIBUTING.md.

This is not a starter-issue. The Definition of done above is the full
acceptance criteria, not a subset to sample from — a PR that addresses part
of it is an unfinished issue, not a smaller one. Your PR must include, in
the PR description itself:

• Root cause / design-decision rationale in your own words — not a restatement of this issue
• Every Definition of done bullet above addressed explicitly, with a one-line note on how
• Evidence the code actually runs: pasted test/build output, a screen recording or before/after screenshots for UI changes, or real (non-mocked) logs for network/contract-facing work
• New or updated tests included and shown passing (paste the output)
• Any adjacent/related behavior this issue calls out re-verified, not assumed unaffected

PRs missing these will be sent back before review, not reviewed and rejected — please do this up front.

[iamb8t0-oss]

Hi i would like to work on this issue

[grantfox-oss]

🦊 GrantFox — @iamb8t0-oss has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #80)
2. Your PR will be reviewed by the Orbit-Wal maintainers

Good luck! Track your progress on GrantFox.