diff --git a/cmd/sandbox_image.go b/cmd/sandbox_image.go
index b6dfe3a..4e89b23 100644
--- a/cmd/sandbox_image.go
+++ b/cmd/sandbox_image.go
@@ -2,12 +2,49 @@ package cmd
 
 import "os"
 
+var Version = "dev"
+
+// resolveSandboxImage determines which container image to use for sandbox execution.
+//
+// Image selection follows explicit precedence (highest to lowest):
+//   1. HARNESS_OS_IMAGE environment variable - operator override for all contexts
+//   2. agentImage parameter - workflow spec.sandbox.image explicit field
+//   3. versionedImage("sandbox") - versioned default base image
+//
+// This precedence enables:
+//   - Local development and debugging via environment variable
+//   - Explicit per-workflow image overrides
+//   - Consistent versioned defaults across contexts (local OpenShell, HyperShell)
+//
+// The resolved image must satisfy the Agent Runtime Contract (ARC):
+// - Run as unprivileged 'sandbox' user
+// - Provide writable Python virtualenv at /opt/agent/venv
+// - Maintain standard PATH conventions for agent tools
+// - Support multi-context execution (local, HyperShell personal, service-account)
 func resolveSandboxImage(agentImage string) string {
+	// 1. Environment override (highest priority)
 	if envImage := os.Getenv("HARNESS_OS_IMAGE"); envImage != "" {
 		return envImage
 	}
+	// 2. Explicit workflow image specification
 	if agentImage != "" {
 		return agentImage
 	}
+	// 3. Versioned default base image (fallback)
 	return versionedImage("sandbox")
 }
+
+// versionedImage returns a fully qualified image reference for the named component.
+// If Version is unset or "dev", returns the unversioned image (for local builds).
+// Otherwise, appends the version tag to enable stable release references.
+//
+// Example outputs:
+//   versionedImage("sandbox") with Version="dev" → quay.io/rcochran/openshell:sandbox
+//   versionedImage("sandbox") with Version="0.1.0" → quay.io/rcochran/openshell:sandbox-0.1.0
+func versionedImage(name string) string {
+	base := "quay.io/rcochran/openshell"
+	if Version == "" || Version == "dev" {
+		return base + ":" + name
+	}
+	return base + ":" + name + "-" + Version
+}