panic: Invalid name validation scheme requested: unset #6407

panic: Invalid name validation scheme requested: unset

goroutine 275 [running]:
github.com/prometheus/common/model.ValidationScheme.IsValidLabelName(0x8dd372f0dc0?, {0x8dd378b8c40?, 0xb?})
	github.com/prometheus/common@v0.67.5/model/metric.go:203 +0xc0
github.com/prometheus/prometheus/model/relabel.relabel(0x8dd374f40e0, 0x8dd3cea3ea0)
	github.com/prometheus/prometheus@v0.311.3/model/relabel/relabel.go:326 +0x3cc
github.com/prometheus/prometheus/model/relabel.ProcessBuilder(...)
	github.com/prometheus/prometheus@v0.311.3/model/relabel/relabel.go:276
github.com/parca-dev/parca/pkg/scrape.populateLabels(0x8dd3cea3ea0, 0x8dd3794a680)
	github.com/parca-dev/parca/pkg/scrape/target.go:285 +0x294
github.com/parca-dev/parca/pkg/scrape.targetsFromGroup(0x8dd3cef78c0, 0x8dd3794a680, {0x0?, 0x4f0b1d4?, 0x64a79c0?}, 0x8dd3cea3ea0)
	github.com/parca-dev/parca/pkg/scrape/target.go:380 +0x240
github.com/parca-dev/parca/pkg/scrape.(*scrapePool).Sync(0x8dd3d027320, {0x8dd3734fb00, 0x19, 0x4f0b240?})
	github.com/parca-dev/parca/pkg/scrape/scrape.go:237 +0x160
github.com/parca-dev/parca/pkg/scrape.(*Manager).reload.func1({0x8dd3d027320?, {0x8dd3734fb00?, 0x8dd379485b0?, 0x8dd370f4ecd?}})
	github.com/parca-dev/parca/pkg/scrape/manager.go:243 +0x4c
created by github.com/parca-dev/parca/pkg/scrape.(*Manager).reload in goroutine 9
	github.com/parca-dev/parca/pkg/scrape/manager.go:241 +0x650

 Root cause                                                                                                                                                                                 
                                                                                                                                                                                             
  This is not a config or Tilt issue — it's a fresh regression in Parca upstream, introduced today.                                                                                          
                                                                                                                                                                                             
  - Your manifest pins ghcr.io/parca-dev/parca:v0.29.0 (.tiltbuild/yaml/parca.observability.yaml:198).                                                                                       
  - v0.29.0 was published 2026-09-23T17:30:55Z — minutes before you hit this.                                                                                                                
  - It was cut right after PR #6405 merged into main (commit 4076831a, 17:15:53Z), which bumped github.com/prometheus/prometheus (and transitively prometheus/common to v0.67.5) while fixing
    a batch of Dependabot security alerts.                                                                                                                                                   
  - prometheus/common v0.66+ made a breaking change: model.NameValidationScheme now defaults to a zero value (UnsetValidation) instead of a usable default. Any caller of                    
    IsValidLabelName/relabeling must now explicitly set that scheme at startup — Prometheus's own main.go does this, but Parca's binary (pkg/scrape/target.go:285 → relabel.ProcessBuilder → 
    relabel()) never got that initialization added when the dependency was bumped.                                                                                                           
  - Result: the very first scrape-target relabel call panics with Invalid name validation scheme requested: unset.                                                                           
  - This exact breaking change has already bitten Thanos, Grafana Loki, Grafana Tempo, and Kubernetes CI over the past few months — all fixed the same way (explicitly setting               
    model.NameValidationScheme). Parca just hadn't hit it until today's dep bump landed in the v0.29.0 cut. No existing Parca issue for it yet.