Add a pluggable persistence adapter so the pair registry survives restarts

[1nonlypiece]

Add a pluggable persistence adapter for in-memory stores

Description

Every store in src/index.ts — pairRegistry, pairMeta, apiKeyStore, webhookStore, and eventLog — lives only in process memory. The code comments even acknowledge this ("Process restart resets the map; persistence lands with the database adapter"). A restart wipes all registered pairs, keys, and webhooks. This issue introduces a small persistence abstraction with a default file-backed (JSON) adapter so state survives restarts, without committing to a specific database yet.

Requirements and context

• Repository scope: StableRoute-Org/Stableroute-backend only.
• Create src/persistence.ts (create file) exporting a StoreAdapter interface (load(), save(snapshot)) and two implementations: an in-memory no-op adapter (preserving current behavior under tests) and a JSON-file adapter selected by a PERSIST_PATH env var.
• On startup, hydrate the stores from the adapter; on each mutation (or on a debounced interval) persist a snapshot.
• Default to the in-memory adapter when PERSIST_PATH is unset and under NODE_ENV=test, so the existing suite is unaffected.
• Keep all current route behavior and response shapes identical; this adds durability, not new endpoints.
• Persist atomically (write-temp-then-rename) so a crash mid-write cannot corrupt the snapshot.

Suggested execution

• Fork the repo and create a branch
• git checkout -b feature/persistence-27-store-adapter
• Implement changes
  • Write code in: create src/persistence.ts; wire hydration and snapshotting from src/index.ts.
  • Write comprehensive tests in: create src/__tests__/persistence.test.ts — save a snapshot, reload into a fresh store, assert pairs/keys/webhooks restored; assert atomic write via temp file.
  • Add documentation: document PERSIST_PATH and the snapshot format in README.md.
  • Add TSDoc on the StoreAdapter interface and both implementations.
  • Validate security: never persist raw API keys in plaintext if hashing has been adopted; restrict snapshot file permissions.
• Test and commit

Test and commit

• Run npm run build, npm run lint, and npm test.
• Cover edge cases: missing snapshot file, corrupt snapshot, round-trip restore.
• Paste the full npm test output in the PR.

Example commit message

feat(persistence): add pluggable store adapter with JSON-file backend

Guidelines

• Minimum 95 percent test coverage for impacted code.
• Clear, reviewer-focused documentation.
• Timeframe: 96 hours.

Community & contribution rewards

• 💬 Join the StableRoute community on Discord for questions, reviews, and faster merges: https://discord.gg/37aCpusvx
• ⭐ This is a GrantFox OSS / Official Campaign task and may be rewarded. When your PR is merged you'll be prompted to rate the project — if this issue and the maintainers helped you ship, we'd be grateful for a 5-star rating. Clear questions in Discord and tidy, well-tested PRs are the fastest path to a merge and a reward.

[ekwe7]

I would love to work on this issue. I have experience building production ready applications and collaborating through GitHub workflows. I'll carefully analyze the current implementation, propose a reliable solution, and submit a well-tested PR. My focus is on clean code, maintainability, and timely delivery

[brain-marchine]

Picking up GrantFox #70.

Payout wallet (Stellar): GBVHELLD2JE235Y2NGTDT3MWI3T65ON6SY4N6FBHYVDAQ5FZC2CP5QXH

[brain-marchine]

Hi maintainers — CI shows action required for this fork PR (workflows need approval before they can run).

Local verification: relevant tests pass for the touched modules.

Could you please approve the workflow run when you have a moment? Thanks!

GrantFox OSS campaign — smart escrow payout on merge.
Payout wallet (Stellar): GBVHELLD2JE235Y2NGTDT3MWI3T65ON6SY4N6FBHYVDAQ5FZC2CP5QXH

[brain-marchine]

Hi maintainers — CI shows action required for this fork PR (workflows need approval before they can run).
Local verification: npm run check passes (53 tests + build without TS5101).
Could you please approve the workflow run when you have a moment? Thanks!