Name an ask's step key <node>.<ask id> and its watch, so the asker learns which node took it and refuses other keys (issue 1887 A1b, ADR 0525 §6)

go/delivery/stepasks.go

@@ -343,3 +343,33 @@ type KeptTaken struct {
 	Digest  string `json:"digest"`
 	Tests   int    `json:"tests"`
 }
+
+// AskStepKey is the key, in the build module's StepsBucket, of the step that runs an ask on node: `<node>.<ask id>`
+// (ADR 0525 §6). The node is the one that pulled the ask, which the asker learns from the key.
+func AskStepKey(node, askID string) (string, error) {
+	if err := checkAskID(askID); err != nil {
+		return "", err
+	}
+	return StepKey(node, askID)
+}
+
+// AskStepWatch is the pattern an asker watches its ask's step with, the node a wildcard: `*.<ask id>`.
+func AskStepWatch(askID string) (string, error) {
+	if err := checkAskID(askID); err != nil {
+		return "", err
+	}
+	return "*." + askID, nil
+}
+
+// ParseAskStepKey reads the node and the ask id from a step key of an ask; it refuses a key that is not `<node>.<ask
+// id>`, such as a have key `<node>.<module>` or a step key a direct tool call wrote under another id form.
+func ParseAskStepKey(key string) (node, askID string, err error) {
+	node, askID, err = ParseStepKey(key)
+	if err != nil {
+		return "", "", err
+	}
+	if err := checkAskID(askID); err != nil {
+		return "", "", fmt.Errorf("delivery: %q is not an ask's step key: %w", key, err)
+	}
+	return node, askID, nil
+}

go/delivery/stepasks_key_test.go

@@ -0,0 +1,38 @@
+package delivery_test
+
+import (
+	"testing"
+
+	"git.novox.be/novox/mesh-sdk/go/buildstep"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
+)
+
+// 1887/A1b: the ask's step key is <node>.<ask id>, watched with *.<ask id>, and its parser refuses another bucket's key.
+func TestAskStepKey(t *testing.T) {
+	id := buildstep.NewID() // an ask's id is a step id
+	key, err := delivery.AskStepKey("shanks", id)
+	if err != nil || key != "shanks."+id {
+		t.Fatalf("AskStepKey = %q, %v", key, err)
+	}
+	if w, err := delivery.AskStepWatch(id); err != nil || w != "*."+id {
+		t.Fatalf("AskStepWatch = %q, %v", w, err)
+	}
+	node, got, err := delivery.ParseAskStepKey(key)
+	if err != nil || node != "shanks" || got != id {
+		t.Fatalf("ParseAskStepKey = %q %q %v", node, got, err)
+	}
+	for _, other := range []string{
+		"shanks.mesh-delivery-view",      // a have key
+		"shanks.node",                    // a node's own have key
+		"shanks.postgres",                // a have key whose module is one token
+		"mesh-delivery-builder_builds.x", // a pulse key
+		"shanks",
+	} {
+		if _, _, err := delivery.ParseAskStepKey(other); err == nil {
+			t.Errorf("parsed %q", other)
+		}
+	}
+	if _, err := delivery.AskStepKey("shanks", "postgres"); err == nil {
+		t.Error("AskStepKey took a module's name for an ask id")
+	}
+}