Plan 04: Health Distribution Badge Counts on Dashboard

Goal

Add health status distribution counts (Healthy N, Warning N, Declining N, Critical N) to the dashboard stats section. The distribution is computed via a new query in StatsQuery and rendered as inline badge counts below the existing stats cards.

Task 1: Add health status distribution to StatsQuery

What: Extend StatsQuery#call to include a health_distribution hash with counts per health status.

Files to modify:

• lib/source_monitor/dashboard/queries/stats_query.rb

Implementation details:

• Add health_distribution key to the returned hash
• Query: SourceMonitor::Source.active.group(:health_status).count (returns { "healthy" => 42, "warning" => 3, ... })
• This is a single SQL query: SELECT health_status, COUNT(*) FROM sources WHERE active = true GROUP BY health_status
• Ensure all known statuses are present in the result (default to 0 for missing): %w[healthy warning declining critical].each_with_object({}) { |s, h| h[s] = raw_counts.fetch(s, 0) }
• Only count active sources (inactive sources don't have meaningful health status)

Acceptance criteria:

• stats[:health_distribution] returns { "healthy" => N, "warning" => N, "declining" => N, "critical" => N }
• Zero-count statuses still appear in the hash with value 0
• Single additional DB query (GROUP BY), not N+1

Task 2: Render health distribution badges on dashboard

What: Add a row of inline badge counts below the existing stats cards grid.

Files to modify:

• app/views/source_monitor/dashboard/_stats.html.erb

Implementation details:

• Below the existing grid of stat cards, add a <div> with inline flex badges
• Each badge shows the health status label + count, using the same color scheme from HealthBadgeHelper:
  • Healthy: bg-green-100 text-green-700
  • Warning: bg-amber-100 text-amber-700
  • Declining: bg-orange-100 text-orange-700
  • Critical: bg-rose-100 text-rose-700
• Badge format: <span class="inline-flex items-center gap-1 rounded-full px-3 py-1 text-xs font-semibold [color-classes]">Healthy <span class="font-bold">42</span></span>
• Only render badges for statuses with count > 0 (don't show "Critical 0" if no critical sources)
• If no active sources exist, don't render the badge row at all
• The badge row uses id="source_monitor_dashboard_health_distribution" for Turbo Stream targeting

Acceptance criteria:

• Badges appear below stats cards
• Only non-zero statuses show badges
• Colors match existing health status badge convention
• Visible above the fold on standard viewport

Task 3: Update Dashboard::Queries metrics recording for health distribution

What: Record health distribution metrics via the existing instrumentation pattern.

Files to modify:

• lib/source_monitor/dashboard/queries.rb

Implementation details:

• In record_stats_metrics, add gauges for each health status count:
  • SourceMonitor::Metrics.gauge(:dashboard_stats_health_healthy, stats[:health_distribution]["healthy"])
  • Same for warning, declining, critical
• This follows the existing pattern of recording stat values as gauges

Acceptance criteria:

• Health distribution metrics are recorded when stats are computed
• No new notification events needed (reuses existing stats instrumentation)

Task 4: Write tests for health distribution

What: Test the query and verify the badge rendering.

Files to create:

• test/lib/source_monitor/dashboard/stats_query_test.rb

Test cases:

• test "health_distribution counts active sources by health_status" -- Create sources with different health statuses, verify counts
• test "health_distribution excludes inactive sources" -- Create inactive source with "critical" status, verify it's not counted
• test "health_distribution includes zero for missing statuses" -- Only healthy sources exist, verify warning/declining/critical are 0
• test "health_distribution handles no active sources" -- No active sources, verify all counts are 0

Acceptance criteria:

• All tests pass
• Tests use create_source! factory with explicit health_status values
• Tests are isolated (scoped to test-created data)

File Disjointness (Wave 1)

This plan modifies:

• lib/source_monitor/dashboard/queries/stats_query.rb
• app/views/source_monitor/dashboard/_stats.html.erb
• lib/source_monitor/dashboard/queries.rb (metrics recording only -- different methods than Plan 02's upcoming_fetch_schedule method)
• test/lib/source_monitor/dashboard/stats_query_test.rb (NEW)

Conflict analysis with Plan 02: Both plans modify lib/source_monitor/dashboard/queries.rb. However:

• Plan 02 modifies the upcoming_fetch_schedule method signature and its cache key
• Plan 04 modifies the record_stats_metrics private method only
• These are disjoint code regions within the same file. To be safe, Plan 04 should modify record_stats_metrics by appending lines (not restructuring), making merge trivial.

No overlap with Plan 01 (paginator, shared partial, application_helper) or Plan 03 (sources controller/index).