Fix test_flow_run_lateness flake by tying tolerance to API request latency

[devin-ai-integration]

Overview

Fixes a flaky test (test_flow_run_lateness) that occasionally fails in CI due to timing sensitivity. The test compares client-side request_time against server-side sa.func.now() (evaluated during query execution), and the original tolerance calculation didn't properly account for this drift.

Root Cause

The test was calculating tolerance as (now - start_of_test), which included unrelated test setup time. When API calls took longer due to CI runner contention, the tolerance became insufficient. Additionally, since the test sums lateness for 2 scheduled runs, the request→DB "now" drift applies per run and must be multiplied by 2.

Changes

1. Changed tolerance basis: From (now - start_of_test) to (now - request_time) to measure actual API latency
2. Consolidated constant: Extracted 2.0 into fudge_seconds variable used in both tolerance calculation and expected value adjustment
3. Account for per-run drift: Multiply test_elapsed by 2 since the test sums lateness for 2 scheduled runs
4. Applied ruff formatting: Wrapped long line to comply with line length limits

Testing

• ✅ Test passes locally with the fix
• ⏳ Waiting for CI to verify fix works across all Python versions and databases

Review Focus

⚠️ Key assumption: The hardcoded 2 multiplier in tolerance = fudge_seconds + 2 * test_elapsed assumes this test always sums exactly 2 scheduled runs. If the test changes in the future, this will need updating. Consider whether this should be derived from interval["states"][2]["count_runs"] instead.

• Verify the logic that drift applies per-run is correct
• Confirm the fix is appropriate for both SQLite and PostgreSQL
• Check if the tolerance is now too loose or still appropriate

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Link to Devin run: https://app.devin.ai/sessions/bf389bc601d2448cbf9140fd612d43da
Requested by: Nate Nowack ([email protected]) / @zzstoatzz

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • Fixes flake from CI run: https://github.com/PrefectHQ/prefect/actions/runs/19238678536/job/54995454569
• If this pull request adds new functionality, it includes unit tests that cover the changes
  • N/A - This is a test fix, not new functionality
• If this pull request removes docs files, it includes redirect settings in mint.json.
  • N/A
• If this pull request adds functions or classes, it includes helpful docstrings.
  • N/A

[devin-ai-integration]

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