kvm2: config block, constructor registration, IDs, state mapping and classify

The kvm2 block reuses KVMConfig; validateKVM gains a block-name variant so
messages say kvm2. The package skeleton has a non-dialing New, strict
providerID parsing, the state table and a 34-row classify test.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

internal/provider/config_kvm.go

@@ -114,20 +114,27 @@ var sha256Hex = regexp.MustCompile(`^[0-9a-fA-F]{64}$`)
 var kvmIdentifier = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9_.-]*$`)
 
 func validateKVM(prefix string, c *KVMConfig) error {
+	return validateKVMBlock(prefix, "kvm", c)
+}
+
+// validateKVMBlock checks a KVMConfig under the given block name, so the
+// kvm and kvm2 provider types share one validator and each reports its own
+// block in messages.
+func validateKVMBlock(prefix, block string, c *KVMConfig) error {
 	if c == nil {
-		return fmt.Errorf("%s: kvm block is required", prefix)
+		return fmt.Errorf("%s: %s block is required", prefix, block)
 	}
 	if c.SSHKeyFile == "" {
-		return fmt.Errorf("%s: kvm.sshKeyFile is required", prefix)
+		return fmt.Errorf("%s: %s.sshKeyFile is required", prefix, block)
 	}
 	if c.KnownHostsFile == "" && !c.InsecureIgnoreHostKey {
-		return fmt.Errorf("%s: kvm.knownHostsFile is required unless kvm.insecureIgnoreHostKey is true", prefix)
+		return fmt.Errorf("%s: %s.knownHostsFile is required unless %s.insecureIgnoreHostKey is true", prefix, block, block)
 	}
 	if c.DiskSizeGB < 0 {
-		return fmt.Errorf("%s: kvm.diskSizeGb must not be negative", prefix)
+		return fmt.Errorf("%s: %s.diskSizeGb must not be negative", prefix, block)
 	}
 	for name, img := range c.Images {
-		p := fmt.Sprintf("%s: kvm.images[%q]", prefix, name)
+		p := fmt.Sprintf("%s: %s.images[%q]", prefix, block, name)
 		if !kvmIdentifier.MatchString(name) {
 			return fmt.Errorf("%s: key must be letters, digits, dots, dashes or underscores"+
 				" — it becomes the cached volume name base-<key>.<format>", p)
@@ -146,19 +153,19 @@ func validateKVM(prefix string, c *KVMConfig) error {
 		}
 	}
 	if len(c.MachineTypes) == 0 {
-		return fmt.Errorf("%s: kvm.machineTypes must define at least one profile", prefix)
+		return fmt.Errorf("%s: %s.machineTypes must define at least one profile", prefix, block)
 	}
 	for name, mt := range c.MachineTypes {
 		if mt.VCPUs <= 0 || mt.MemoryMiB <= 0 {
-			return fmt.Errorf("%s: kvm.machineTypes[%q] needs vcpus > 0 and memoryMiB > 0", prefix, name)
+			return fmt.Errorf("%s: %s.machineTypes[%q] needs vcpus > 0 and memoryMiB > 0", prefix, block, name)
 		}
 	}
 	if len(c.Hosts) == 0 {
-		return fmt.Errorf("%s: kvm.hosts must list at least one host", prefix)
+		return fmt.Errorf("%s: %s.hosts must list at least one host", prefix, block)
 	}
 	seen := make(map[string]bool, len(c.Hosts))
 	for i, h := range c.Hosts {
-		p := fmt.Sprintf("%s: kvm.hosts[%d]", prefix, i)
+		p := fmt.Sprintf("%s: %s.hosts[%d]", prefix, block, i)
 		if h.Name == "" {
 			return fmt.Errorf("%s: name is required", p)
 		}