Add adversarial testing for Dashboard and Installer

[erikdarlingdata]

Summary

The Lite analysis engine now has 24 adversarial/misery-path tests (FactCollectorMiseryTests) that probe division by zero, empty tables, reversed time ranges, DMV corruption, overflow, boundary conditions, and full-pipeline resilience. This uncovered a real scoring bug (PLE=0 scored as harmless).

The Dashboard and Installer projects would benefit from the same treatment — tests designed to break things, not just confirm happy paths.

Areas to cover

Dashboard

• Empty/null data from SQL Server (no rows in PerformanceMonitor tables)
• Connection failures mid-refresh (network drop, timeout)
• Corrupt or truncated query plan XML
• Charts with zero data points, single data points, or extreme outliers
• Very large result sets (memory pressure on the UI thread)
• Missing or renamed columns after a schema upgrade

Installer (CLI + GUI)

• Upgrade from a database with missing tables or columns (partial prior install)
• Upgrade scripts that encounter locked tables or active connections
• Fresh install on a server with restricted permissions
• Upgrade folder with out-of-order or duplicate scripts
• Database already at target version (idempotency)
• Installer run against an incompatible SQL Server version
• Disk full or path not found during file copy
• Interrupted upgrade (power failure simulation — partial script execution)

Context

This came out of the ErikAI work on feature/erikai where misery-path testing caught a real bug in the scorer. The same discipline should be applied more broadly.

[erikdarlingdata]

Phase 1 complete (PR #574)

Installer — done for release

34 tests (19 unit + 15 integration), all passing:

Adversarial scenarios covered:

• Upgrade from database with missing tables (partial prior install)
• Upgrade folder with out-of-order or duplicate scripts
• Database already at target version (idempotency — all scripts run twice)
• Interrupted upgrade (cancellation mid-script, version unchanged)
• Corrupt SQL content, empty files
• Critical vs non-critical file failure abort behavior
• Version detection fallback ([BUG] PerformanceMonitorInstaller-2.2.0 failed and deleted the existing PerformanceMonitor database #538 regression)

Remaining (Phase 2, post-release):

• Upgrade scripts encountering locked tables / active connections
• Fresh install with restricted permissions
• Installer against incompatible SQL Server version (add version check first)

Dashboard — not started (Phase 2)

• Empty/null data from SQL Server
• Connection failures mid-refresh
• Corrupt or truncated query plan XML
• Charts with zero/single/extreme data points
• Very large result sets (memory pressure)
• Missing or renamed columns after schema upgrade

[erikdarlingdata]

Phase 1 complete — Installer adversarial testing done

38 tests across 4 test files (PRs #574, #575, #579, #580), all passing.

Covered

• Upgrade failure doesn't drop database ([BUG] PerformanceMonitorInstaller-2.2.0 failed and deleted the existing PerformanceMonitor database #538 regression)
• Partial install recovery (only installation_history exists)
• Critical file failure (01-03) aborts remaining scripts
• Non-critical file failure (04+) continues
• Cancellation mid-upgrade leaves version unchanged
• Corrupt/empty SQL files handled gracefully
• Version detection fallback — empty history returns "1.0.0" ([BUG] PerformanceMonitorInstaller-2.2.0 failed and deleted the existing PerformanceMonitor database #538 regression)
• Restricted permissions fails clearly with permission error
• SQL Server version check — rejects 2014 and earlier, Azure MI always passes
• Idempotency — all install scripts run twice with zero failures
• Connection failure behavior documented
• File filtering — 00_/97_/99_ exclusion ([BUG] PerformanceMonitorInstaller-2.2.0 failed and deleted the existing PerformanceMonitor database #538 regression)
• Upgrade ordering — version ranges, normalization, malformed folders

Remaining (low priority)

• Locked tables during upgrade (transient in practice)

Closing — installer coverage is solid for the release.