node-lookup: auto-qualify short node names to .main.unkin.net (#19)

Short `-n` node names silently returned nothing: `node-lookup -R -n ausyd1nxvm2120` found nothing while `-n ausyd1nxvm2120.main.unkin.net` worked, because the PuppetDB `certname` filter needs a FQDN. This auto-qualifies a dotless name before the lookup.

## Changes
- Add `qualifyNode()` pure helper: a dotless name gets `.<domain>` appended; a name already containing a dot (any domain, incl. `*.k8s.syd1.au.unkin.net`) is left unchanged; a single trailing dot is stripped first; empty input is preserved (same "no node" behavior as today).
- Apply normalization to the `-n` value and to stdin-sourced node names in `run()`, so both entry points behave consistently.
- Make the domain configurable: config key `domain`, `NODE_LOOKUP_DOMAIN` env var, and `--domain` flag, all defaulting to `main.unkin.net`.
- Surface `domain` in `config show` / `config init` output and document the new env var/flag/behavior in AGENTS.md.
- Add table-driven `qualifyNode` tests (short name appended, FQDN unchanged, multi-label other-domain FQDN unchanged, trailing-dot handling, empty input, custom domain) and a `NODE_LOOKUP_DOMAIN` env-override test.

Companion tools `pburl`/`pblastreport` take already-qualified hostnames (typically piped from `node-lookup`) via `puppet.ReadHosts` and do not share the `-n` code path, so they are intentionally left out to keep this PR atomic.

## Validation
- `gofmt -l .` clean, `go vet ./...` clean
- `go test -race ./...` pass
- `make build` builds all three binaries

Reviewed-on: #19
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

main.go

@@ -22,6 +22,7 @@ const (
 	defaultPuppetDBURL    = "http://puppetdbapi.service.consul:8080/pdb/query/v4/facts"
 	defaultRoleFact       = "enc_role"
 	defaultPuppetboardURL = "https://puppetboard.k8s.syd1.au.unkin.net"
+	defaultDomain         = "main.unkin.net"
 	configFileName        = "config.yaml"
 	appName               = "node-lookup"
 )
@@ -37,6 +38,8 @@ type config struct {
 	// the shared config file also configures the companion tools (pburl,
 	// pblastreport) that read this same file.
 	PuppetboardURL string `yaml:"puppetboard_url"`
+	// Domain is appended to a short (dotless) -n node name to form its FQDN.
+	Domain string `yaml:"domain"`
 }
 
 func defaultConfig() config {
@@ -44,6 +47,7 @@ func defaultConfig() config {
 		PuppetDBURL:    defaultPuppetDBURL,
 		RoleFact:       defaultRoleFact,
 		PuppetboardURL: defaultPuppetboardURL,
+		Domain:         defaultDomain,
 	}
 }
 
@@ -87,6 +91,9 @@ func loadConfig() (config, error) {
 	if v := os.Getenv("NODE_LOOKUP_PUPPETBOARD_URL"); v != "" {
 		cfg.PuppetboardURL = v
 	}
+	if v := os.Getenv("NODE_LOOKUP_DOMAIN"); v != "" {
+		cfg.Domain = v
+	}
 
 	return cfg, nil
 }
@@ -105,7 +112,7 @@ func writeDefaultConfig() error {
 
 	cfg := defaultConfig()
 	data, _ := yaml.Marshal(cfg)
-	header := []byte("# node-lookup configuration\n# Fields can be overridden with env vars: NODE_LOOKUP_URL, NODE_LOOKUP_ROLE_FACT, NODE_LOOKUP_PUPPETBOARD_URL\n# puppetboard_url is used by the companion tools (pburl, pblastreport).\n\n")
+	header := []byte("# node-lookup configuration\n# Fields can be overridden with env vars: NODE_LOOKUP_URL, NODE_LOOKUP_ROLE_FACT, NODE_LOOKUP_PUPPETBOARD_URL, NODE_LOOKUP_DOMAIN\n# puppetboard_url is used by the companion tools (pburl, pblastreport).\n# domain is appended to short (dotless) -n node names to form their FQDN.\n\n")
 	if err := os.WriteFile(path, append(header, data...), 0o644); err != nil {
 		return fmt.Errorf("writing config: %w", err)
 	}
@@ -144,6 +151,21 @@ func nameFilter(names []string) []interface{} {
 	return or
 }
 
+// qualifyNode auto-qualifies a short (dotless) node name by appending
+// ".<domain>", so `-n ausyd1nxvm2120` resolves the same as its FQDN. A name
+// that already contains a dot is treated as already-qualified (including names
+// in other domains like *.k8s.syd1.au.unkin.net) and returned unchanged. A
+// single trailing dot is stripped first, so a dotless name with a trailing dot
+// is still qualified. Empty input is returned unchanged to preserve the
+// existing "no node given" behavior.
+func qualifyNode(name, domain string) string {
+	name = strings.TrimSuffix(name, ".")
+	if name == "" || strings.Contains(name, ".") {
+		return name
+	}
+	return name + "." + domain
+}
+
 func buildQuery(node, factName, match, roleFact string, showRole, partial, inverse bool) string {
 	type filter = []interface{}
 	var filters []filter
@@ -318,6 +340,8 @@ func allFactsForNode(puppetDBURL, node string) ([]fact, error) {
 func run(cfg config, nodeName, factName, match string, showRole, partial, inverse, nodeOnly, valueOnly, count, ansible, jsonMode, allFacts bool) error {
 	signal.Ignore(syscall.SIGPIPE)
 
+	nodeName = qualifyNode(nodeName, cfg.Domain)
+
 	if allFacts {
 		if nodeName == "" {
 			return fmt.Errorf("-a requires -n")
@@ -365,7 +389,7 @@ func run(cfg config, nodeName, factName, match string, showRole, partial, invers
 				if len(fields) == 0 {
 					continue
 				}
-				if err := doQuery(fields[0]); err != nil {
+				if err := doQuery(qualifyNode(fields[0], cfg.Domain)); err != nil {
 					fmt.Fprintln(os.Stderr, "error:", err)
 				}
 			}
@@ -446,6 +470,7 @@ func main() {
 		jsonMode    bool
 		allFacts    bool
 		puppetDBURL string
+		domain      string
 	)
 
 	rootCmd := &cobra.Command{
@@ -461,6 +486,9 @@ func main() {
 			if cmd.Flags().Changed("url") {
 				cfg.PuppetDBURL = puppetDBURL
 			}
+			if cmd.Flags().Changed("domain") {
+				cfg.Domain = domain
+			}
 			return nil
 		},
 		RunE: func(cmd *cobra.Command, args []string) error {
@@ -482,6 +510,7 @@ func main() {
 	f.BoolVarP(&ansible, "ansible", "A", false, "Output as Ansible inventory")
 	f.BoolVarP(&jsonMode, "json", "j", false, "Emit valid JSON for all output")
 	f.BoolVarP(&allFacts, "all", "a", false, "Show all facts for a node (requires -n)")
+	f.StringVar(&domain, "domain", cfg.Domain, "Domain appended to short (dotless) -n node names (overrides config and NODE_LOOKUP_DOMAIN)")
 	rootCmd.PersistentFlags().StringVar(&puppetDBURL, "url", cfg.PuppetDBURL, "PuppetDB facts URL (overrides config and NODE_LOOKUP_URL)")
 
 	configCmd := &cobra.Command{
@@ -506,6 +535,7 @@ func main() {
 			fmt.Printf("puppetdb_url   : %s\n", cfg.PuppetDBURL)
 			fmt.Printf("role_fact      : %s\n", cfg.RoleFact)
 			fmt.Printf("puppetboard_url: %s\n", cfg.PuppetboardURL)
+			fmt.Printf("domain         : %s\n", cfg.Domain)
 			return nil
 		},
 		SilenceUsage: true,