Add tests for the usage event payload and the new-total return contract of record_usage

[mikewheeleer]

Test the record_usage event and UsageRecord return semantics

Description

record_usage in contracts/escrow/src/lib.rs emits a usage(agent, service_id, requests, total) event and returns a UsageRecord carrying the new total (not the delta), per its doc comment. contracts/escrow/src/test.rs does not assert the emitted event payload nor that the returned requests field equals the accumulated total rather than the per-call delta. This issue verifies both the event and the documented return contract.

Requirements and context

• Repository scope: Agentpay-Org/Agentpay-contracts only.
• Cover: after record_usage(agent, svc, n), the returned UsageRecord.requests equals the accumulated total (e.g. two calls of 3 then 5 return 8, not 5); the event payload's requests field is the per-call delta while the total field is the running total.
• Cover: the usage event topic and tuple are emitted exactly once per call via env.events().all().
• Cover: lifetime counters (get_total_usage_by_agent, get_total_requests_all_time) advance by the delta on each call.
• Test-only change unless a genuine bug surfaces.

Suggested execution

• Fork the repo and create a branch
• git checkout -b test/contracts-record-usage-event-tests
• Implement changes
  • Write code in: contracts/escrow/src/lib.rs — no changes expected; only touch if a bug is found.
  • Write comprehensive tests in: contracts/escrow/src/test.rs — the return-value, event-payload, and lifetime-counter scenarios above.
  • Add documentation: note the covered contract in the test module header comment.
  • Include NatSpec-style doc comments (///) on any test helpers.
  • Validate security: the recorded total and emitted event agree, so off-chain loops cannot be misled.
• Test and commit

Test and commit

• Run cargo fmt --all -- --check, cargo build, and cargo test.
• Cover edge cases: first call, repeated calls accumulating, multi-service isolation, single large delta.
• Include the full cargo test output and a short security notes section in the PR description.

Example commit message

test: cover record_usage event payload and new-total return contract

Guidelines

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

Community & contribution rewards

• 💬 Join the AgentPay community on Discord for questions, reviews, and faster merges: https://discord.gg/eXvRKkgcv
• ⭐ 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.

[gloskull]

Hello, I have 4 years of experience delivering solutions for projects like this, covering backend, frontend, and smart contract development. After carefully reviewing your requirements, I have a clear understanding of the task and am confident in my ability to deliver a clean, efficient, and thoroughly tested solution on time. I prioritize code quality, maintainability, and industry best practices throughout the development process.
My PR will be submitted in under 10hours.

[yunus-dev-codecrafter]

Hi! I've carefully reviewed the entire task description and fully understand the requirements and expected outcome.
I have experience working on similar tasks and I'm confident I can complete this within about an hour. I'd be happy to take ownership of this issue and submit a clean, well-tested solution promptly.
If it's available, please assign it to me. Thank you!

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@yunus-dev-codecrafter's PR #141 was approved and merged by @mikewheeleer.

🏆 @yunus-dev-codecrafter: You earned 40 FoxPoints for this contribution! Your current tier: Builder (2,191 total points). Track your full progress on GrantFox.

👏 Great work, @yunus-dev-codecrafter! Keep contributing to Agentpay-Org.