feat: KEDA External Scaler for GitHub Issue-Driven Agent Autoscaling #516

Feature: KEDA External Scaler for GitHub-Based Agent Workloads

Problem

Running Squad on Kubernetes means agents sit idle when no work exists. KEDA (Kubernetes Event-Driven Autoscaler) solves this for queue-based workloads — but GitHub Issues isn't a native KEDA trigger.

Without autoscaling:

• Agent pods burn CPU/memory 24/7 even when there are 0 issues
• Manual scaling needed for burst work (10 issues labeled at once)
• No cost optimization — the cluster just runs

Proposed Solution: keda-copilot-scaler

A KEDA External Scaler (gRPC) that:

1. Polls GitHub API for issues matching squad:copilot label
2. Reports queue depth as a KEDA metric
3. Handles rate limits gracefully (Retry-After, exponential backoff)
4. Supports composite scaling (multi-metric decisions)

# ScaledObject example
apiVersion: keda.sh/v1alpha1
kind: ScaledObject
spec:
  scaleTargetRef:
    name: picard-agent
  triggers:
  - type: external
    metadata:
      scalerAddress: keda-copilot-scaler.squad-scaler:6000
      owner: bradygaster
      repo: squad
      labels: squad:copilot

Scaling behavior:

• 0 issues → scale to 0 (save money)
• 1-3 issues → scale to 1 pod
• 4-10 issues → scale to 2 pods
• 10+ issues → scale to ceiling

Implementation Available

Complete Go implementation: tamirdresher/keda-copilot-scaler

• gRPC external scaler (KEDA v2.19.0 compatible)
• 51 passing tests
• Helm chart + Kustomize manifests
• Rate limit aware (tracks X-RateLimit-Remaining)
• Running in production on AKS

The scaler is intentionally standalone (not embedded in Squad CLI) so it can run as a sidecar or separate deployment.

Integration Points

• Uses squad:copilot label convention from issue feat: persistent Ralph — wire squad watch + enable heartbeat cron #236
• Works with machine capability labels (feat: Machine Capability Discovery & Label-Based Issue Routing for Ralph #514 if accepted)
• Complements rate limiting coordination (feat: Cooperative Rate Limiting & Predictive Circuit Breaker for Multi-Agent Deployments #515)