fix: make computeTrend time-independent via injectable now (#7)

[four-bytes-robby]

fixes issue #7 — computeTrend gained an optional now param; trend tests now pass a fixed now so they are deterministic (full suite 146/146 green). Closes #7.

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Summary by cubic

Makes computeTrend deterministic by accepting an optional now parameter instead of calling new Date() internally, so trend calculations no longer depend on wall-clock time.

Bug Fixes

• computeTrend now takes an optional now argument; callers who don't pass it keep the previous behavior.
• Trend tests pass a fixed reference date, making the full suite deterministic and green (146/146).

^{Written for commit 7ae8383. Summary will update on new commits.}

Summary by CodeRabbit

• Bug Fixes

  • Trend calculations now use a consistent reference time, improving result stability across repeated evaluations.

• Tests

  • Trend behavior is now validated against a fixed reference date, making test outcomes more consistent and reliable.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Team

Run ID: ffdbe7d0-e206-4fc0-8a58-45d7d63be428

📥 Commits

Reviewing files that changed from the base of the PR and between 13965fa and 7ae8383.

📒 Files selected for processing (2)

• src/tools/trend.ts
• tests/trend.test.ts

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📝 Walkthrough

Walkthrough

computeTrend now accepts an optional reference date and uses it for both trend windows. Trend tests pass a fixed June 15, 2026 date to remove wall-clock dependence.

Changes

Trend calculation determinism

Layer / File(s)	Summary
Injectable trend reference time and deterministic tests src/tools/trend.ts, tests/trend.test.ts	computeTrend accepts an optional now date and derives both reference dates from it. All trend tests pass a fixed reference date.

Estimated code review effort: 1 (Trivial) | ~5 minutes

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/7-trend-time-dependence

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch fix/7-trend-time-dependence

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