feat(amp): add per-client upstream API key mapping support

internal/watcher/diff/config_diff.go

@@ -185,6 +185,11 @@ func BuildConfigChangeDetails(oldCfg, newCfg *config.Config) []string {
 	if oldCfg.AmpCode.ForceModelMappings != newCfg.AmpCode.ForceModelMappings {
 		changes = append(changes, fmt.Sprintf("ampcode.force-model-mappings: %t -> %t", oldCfg.AmpCode.ForceModelMappings, newCfg.AmpCode.ForceModelMappings))
 	}
+	oldUpstreamAPIKeysCount := len(oldCfg.AmpCode.UpstreamAPIKeys)
+	newUpstreamAPIKeysCount := len(newCfg.AmpCode.UpstreamAPIKeys)
+	if !equalUpstreamAPIKeys(oldCfg.AmpCode.UpstreamAPIKeys, newCfg.AmpCode.UpstreamAPIKeys) {
+		changes = append(changes, fmt.Sprintf("ampcode.upstream-api-keys: updated (%d -> %d entries)", oldUpstreamAPIKeysCount, newUpstreamAPIKeysCount))
+	}
 
 	if entries, _ := DiffOAuthExcludedModelChanges(oldCfg.OAuthExcludedModels, newCfg.OAuthExcludedModels); len(entries) > 0 {
 		changes = append(changes, entries...)
@@ -301,3 +306,43 @@ func formatProxyURL(raw string) string {
 	}
 	return scheme + "://" + host
 }
+
+func equalStringSet(a, b []string) bool {
+	if len(a) == 0 && len(b) == 0 {
+		return true
+	}
+	aSet := make(map[string]struct{}, len(a))
+	for _, k := range a {
+		aSet[strings.TrimSpace(k)] = struct{}{}
+	}
+	bSet := make(map[string]struct{}, len(b))
+	for _, k := range b {
+		bSet[strings.TrimSpace(k)] = struct{}{}
+	}
+	if len(aSet) != len(bSet) {
+		return false
+	}
+	for k := range aSet {
+		if _, ok := bSet[k]; !ok {
+			return false
+		}
+	}
+	return true
+}
+
+// equalUpstreamAPIKeys compares two slices of AmpUpstreamAPIKeyEntry for equality.
+// Comparison is done by count and content (upstream key and client keys).
+func equalUpstreamAPIKeys(a, b []config.AmpUpstreamAPIKeyEntry) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if strings.TrimSpace(a[i].UpstreamAPIKey) != strings.TrimSpace(b[i].UpstreamAPIKey) {
+			return false
+		}
+		if !equalStringSet(a[i].APIKeys, b[i].APIKeys) {
+			return false
+		}
+	}
+	return true
+}