qa/1337: harden MSSQL PMDA test for mssql-tools18 and improve value parsing

[kurik]

Support mssql-tools18 path with -C flag, fall back to legacy mssql-tools.
Use _wait_for_port 1433 when sqlservr binary is absent.
SQL queries now select only cntr_value, and new helper functions (_sql_scalar_from_sqlcmd_out, _pm_value_from_pmprobe_out) robustly extract numeric values for comparison.
Cumulative metrics (Logins/sec, Logouts/sec) use a wider 20% tolerance.

Summary by CodeRabbit

• Chores
  • Improved QA tooling reliability: better detection/installation of SQL client and waiting for database readiness.
  • More robust and clearer metric extraction and validation, with explicit failures for invalid results.
  • Added configurable tolerance for metric comparisons (default 10%), with logins/logouts checks using a 20% tolerance.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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• qa/1337

🚧 Files skipped from review as they are similar to previous changes (1)

• qa/1337

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📝 Walkthrough

Walkthrough

The QA 1337 script improves SQLCMD discovery and TLS detection, waits for SQL Server readiness on port 1433, refactors SQL execution/output parsing into dedicated helpers that validate scalar and pmprobe outputs, and updates metric queries to fetch cntr_value with configurable tolerances (default 10%, 20% for logins/logouts).

Changes

SQL Server QA Script Refactor

Layer / File(s)	Summary
SQL Server Readiness and SQLCMD Discovery qa/1337	SQLCMD discovery prefers /opt/mssql-tools18/bin/sqlcmd with fallback to /opt/mssql-tools/bin/sqlcmd, detects TLS-capable sqlcmd (-C) when present, and waits for port 1433 to ensure SQL Server is reachable before running queries.
SQL Execution and Output Parsing Helpers qa/1337	_query standardizes sqlcmd output (trimmed, headerless). Added _sql_scalar_from_sqlcmd_out to extract the first numeric scalar and _pm_value_from_pmprobe_out to parse pmprobe output treating negative values as errors. _compare_values now accepts an optional tolerance (default 10%) and fails explicitly on parse/pmprobe errors.
Metric Validation Queries with Tolerances qa/1337	Metric checks now select cntr_value for specific counters (Active Temp Tables, Logins/sec, Logouts/sec). Comparison calls use 20% tolerance for Logins/sec and Logouts/sec; other checks use the default 10% tolerance.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Poem

🐰 A rabbit checks the server's door, waits on port one-four-three-three,

Parses numbers, flags the bad—no negatives allowed for me.
Tolerances set, comparisons sing, metrics tidy, outputs neat,
The QA script hops along the run, and lands the tests complete.

🚥 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 accurately describes the main changes: hardening the MSSQL PMDA test for mssql-tools18 compatibility and improving value parsing robustness.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@qa/1337`:
- Around line 135-136: The failure message hard-codes "10%" while the script
uses the caller-supplied $tolerance; update the call to _fail in the block that
calls _within_tolerance so it embeds the $tolerance variable (e.g. use
"$tolerance%") instead of "10%" and keep the same context variables ($metric,
$pcpvalue, $sqlvalue) so the message reads like: "$metric outside ${tolerance}%
tolerance (PCP $pcpvalue vs SQL $sqlvalue)".
- Around line 62-80: _sql_scalar_from_sqlcmd_out currently treats the first
numeric line as a scalar and exits immediately, which hides multi-row results;
update the function to scan all non-empty, non-header lines, collect numeric
matches instead of exiting on the first, and then: if exactly one numeric value
was found print it and exit 0, otherwise do not print a value and exit non‑zero
to signal an error (so callers detect multi-row results). Ensure changes are
made inside the _sql_scalar_from_sqlcmd_out awk program block referenced in the
diff so it counts numeric lines and enforces the single-row requirement.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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Reviewing files that changed from the base of the PR and between 509a6bb and a2c58a6.

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• qa/1337