Name the provisioner client's account in the declaration, and share the apply's record

The local write of a filled file (ADR 0349 §4) accepts only the provisioner client's account, which the declaration names; the reader takes provisioner_account before any controller sends it (contract 10). The apply's record and its rule for what moved become helpers the write uses too. Issue 668.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/declaration/declaration.go

@@ -1645,6 +1645,25 @@ type Declaration struct {
 	// node-engine write only these. Absent is a controller that hands no file to the provisioner, and every
 	// file is written from the declaration as before.
 	Filled []string
+
+	// Provisioner is the account the provisioner's client runs as on this machine, by name (novox/hq ADR 0349 §4):
+	// the only account whose write of a filled file the node-engine's local write socket accepts. Absent is a
+	// controller that names none, and every such write is refused.
+	Provisioner string
+}
+
+// checkProvisioner refuses a provisioner client's account that is no account name, or is root: the account whose
+// writes the node-engine accepts must be one that could not write the file without it.
+func checkProvisioner(name string) []string {
+	switch {
+	case name == "":
+		return nil
+	case !accountName.MatchString(name):
+		return []string{fmt.Sprintf("provisioner_account %q is not an account name", name)}
+	case name == "root":
+		return []string{"provisioner_account is root; the provisioner's client runs as an account of its own"}
+	}
+	return nil
 }
 
 // Fills reports whether the provisioner fills the file at path on this machine.
@@ -2027,6 +2046,9 @@ type envelope struct {
 	// Filled is optional too (novox/hq ADR 0349 §5), as is a file's `owner-at-runtime`. **An older host refuses
 	// these keys**; a controller sends them only to a host whose health says link.OwnershipContract.
 	Filled []string `json:"filled_files,omitempty"`
+	// Provisioner is optional too (novox/hq ADR 0349 §4). **An older host refuses this key**; a controller sends it
+	// only to a host whose health says link.ProvisionerContract.
+	Provisioner string `json:"provisioner_account,omitempty"`
 }
 
 func parse(raw []byte, allowActions bool) (*Declaration, error) {
@@ -2045,8 +2067,10 @@ func parse(raw []byte, allowActions bool) (*Declaration, error) {
 
 	d := &Declaration{Version: env.Version, For: env.For, Adoption: env.Adoption, Sequence: env.Sequence,
 		Epoch: env.Epoch, LeftOut: env.LeftOut, Generation: env.Generation, PutBack: env.PutBack,
-		Identities: env.Identities, Groups: env.Groups, Libraries: env.Libraries, Filled: env.Filled}
+		Identities: env.Identities, Groups: env.Groups, Libraries: env.Libraries, Filled: env.Filled,
+		Provisioner: env.Provisioner}
 	problems := checkIdentities(env.Identities, env.Groups)
+	problems = append(problems, checkProvisioner(env.Provisioner)...)
 	problems = append(problems, checkLibraries(env.Groups, env.Libraries)...)
 	if env.Generation < 0 {
 		// Below zero would read as "none claimed" and pass every refusal of an older generation.