monitoring: paper-roll lifecycle alerts (XL Track I)

Three new Prometheus alert rules for the print-services group, all routed
to thermal_print via alert_channel label (Grafana contact point ->
irc-notify -> Print.Web /api/print/alert):

- PrintPaperRollLow      (warning, 5-10% remaining, 5m for)
- PrintPaperRollCritical (critical, <=5% remaining, 2m for)
- PrintJobDeadLetter     (warning, any new dead-letter in 15m)

Source-of-truth gauge is print_paper_remaining_percent (Print.Web OTEL),
which is hydrated from the active PaperRoll row at process startup
(Print.Web@<TBD> HydrateMetricsAsync) so the gauge isn't blind for an
arbitrary window after every deploy.

Self-referential humor: low-roll alerts route to the printer that's
running out of paper, so it announces its own paper-out warning on its
remaining paper.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/monitoring/noc-monitoring.yaml

@@ -642,6 +642,42 @@ data:
               summary: "Print queue backlog on edge2 ({{ $value }} active jobs)"
               description: "CUPS has {{ $value }} active jobs queued. Possible printer jam, USB disconnect, or paper out."
 
+          # Paper roll lifecycle alerts (XL Track I, 2026-04-26).
+          # Source-of-truth gauge: print_paper_remaining_percent (Print.Web OTEL,
+          # hydrated on startup from the active PaperRoll row).
+          # alert_channel=thermal_print routes through irc-notify -> Print.Web
+          # /api/print/alert so the printer announces its own paper-out warning
+          # on its remaining paper. Self-referential humor + operator nudge.
+          - alert: PrintPaperRollLow
+            expr: print_paper_remaining_percent{job="printweb-otel"} < 10 and print_paper_remaining_percent{job="printweb-otel"} > 5
+            for: 5m
+            labels:
+              severity: warning
+              alert_channel: thermal_print
+            annotations:
+              summary: "Print roll low on edge2 ({{ $value | printf \"%.1f\" }}% remaining)"
+              description: "NuPrint 210 paper roll has {{ $value | printf \"%.1f\" }}% remaining. Operator should load a fresh roll soon. Run /api/paper/status for the precise mm + estimated jobs left."
+
+          - alert: PrintPaperRollCritical
+            expr: print_paper_remaining_percent{job="printweb-otel"} <= 5
+            for: 2m
+            labels:
+              severity: critical
+              alert_channel: thermal_print
+            annotations:
+              summary: "Print roll critical on edge2 ({{ $value | printf \"%.1f\" }}% remaining)"
+              description: "NuPrint 210 paper roll at {{ $value | printf \"%.1f\" }}% — load a new roll NOW. The 50ft roll has a ~12% red-stripe zone; once paper passes that, the printer can run dry mid-job."
+
+          - alert: PrintJobDeadLetter
+            expr: increase(print_jobs_dead_letter_total[15m]) > 0
+            for: 1m
+            labels:
+              severity: warning
+              alert_channel: thermal_print
+            annotations:
+              summary: "Print job(s) entered dead-letter on edge2 ({{ $value | printf \"%.0f\" }} in last 15m)"
+              description: "{{ $value | printf \"%.0f\" }} print job(s) exhausted MaxRetries and need operator action. Open /print-log, filter Status=DeadLetter, click 'Retry From Start' after fixing the underlying cause (paper jam, USB disconnect, printer power-cycle)."
+
           - alert: CUPSHighJobRate
             expr: rate(cups_job_total[5m]) * 60 > 30
             for: 5m