fix: truncate large test result samples to prevent oversized alert payloads (#2044)

[zerafachris]

Fixes #2044

Test result samples rendered in an alert are converted into a table block with no upper bound on row count. When a failing/warning test has many rows (e.g. 25+ rows across several columns), the resulting alert payload can exceed size limits enforced by downstream integrations such as Microsoft Teams, causing edr monitor to crash before any alert is sent.

This adds a maximum_rows_in_alert_samples config option to MessageBuilderConfig (default 25, mirroring the existing maximum_columns_in_alert_samples knob) and truncates the rendered sample to that limit in _get_result_blocks, appending a note indicating how many rows were omitted.

Added tests/unit/alerts/alert_messages/test_result_blocks_row_truncation.py:

• A 37-row sample with maximum_rows_in_alert_samples=10 is truncated to 10 rows with a "Showing 10 of 37 rows (27 omitted...)" note. Before this change: assert len(table_block.rows) == 10 fails (assert 37 == 10). After: passes.
• A 3-row sample under the limit renders unchanged, with no truncation note (regression guard).

Full unit suite (pytest tests/unit): 453 passed. black/isort/flake8/mypy all clean on the touched files and across the package.

Prepared with AI assistance (Claude, agent: claude-sonnet-5), reviewed for correctness before submission.

Summary by CodeRabbit

• New Features

  • Alert result tables now limit displayed rows to 25 by default.
  • Added configuration to customize the maximum number of rows shown.
  • Truncated tables include a note showing displayed and omitted row counts.

• Bug Fixes

  • Prevented large alert result samples from displaying unnecessarily many rows.

• Tests

  • Added coverage for both truncated and fully displayed result samples.

[github-actions]

👋 @zerafachris
Thank you for raising your pull request.
Please make sure to add tests and document all user-facing changes.
You can do this by editing the docs files in this pull request.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 2bd02c56-ee31-4765-aaa8-81480836e7a0

📥 Commits

Reviewing files that changed from the base of the PR and between 594b89d and d81b2d6.

📒 Files selected for processing (2)

• elementary/monitor/alerts/alert_messages/builder.py
• tests/unit/alerts/alert_messages/test_result_blocks_row_truncation.py

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📝 Walkthrough

Walkthrough

Changes

The alert message builder adds a configurable maximum of 25 rendered result-sample rows, truncates larger tables, and reports shown and omitted counts. Unit tests cover both truncated and untruncated samples.

Alert sample truncation

Layer / File(s)	Summary
Configure and render row limits elementary/monitor/alerts/alert_messages/builder.py	MessageBuilderConfig adds maximum_rows_in_alert_samples, and result sample tables apply the limit and append truncation details when rows are omitted.
Validate truncation behavior tests/unit/alerts/alert_messages/test_result_blocks_row_truncation.py	Tests verify that large samples are limited to the configured row count while smaller samples retain all rows without an omission note.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: truncating large test result samples to avoid oversized alert payloads.
Linked Issues check	✅ Passed	The PR reduces oversized alert payloads by truncating test samples, adding an omission note, and keeping small samples unchanged.
Out of Scope Changes check	✅ Passed	The changes stay focused on alert sample truncation and matching tests, with no unrelated functionality added.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

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