Fold the retake test into the prefix test (issue 1748 review 1)

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

go/delivery/builder.go

@@ -150,6 +150,11 @@ const (
 	// WaitsFor: a fetch found the module's lock naming a package version the registry does not hold yet; the builder
 	// writes the key queued with Waits (novox/hq ADR 0500 clause 6), and it is built once the package is published.
 	WaitsFor = "waits for: "
+	// Retake: a failure that passes by itself (a name lookup that timed out, a refused connection): the builder takes
+	// the key again after a backoff, at most MaxRetakes times (issue 1748). A build module opens every such failure with it.
+	Retake = "retakeable: "
+	// MaxRetakes is how many times the builder takes a key again by itself for a retakeable failure.
+	MaxRetakes = 3
 )
 
 // FailedUntilChanged says whether a failed key's error is one that is not built again until the module's fingerprint
@@ -159,6 +164,12 @@ func FailedUntilChanged(err string) bool {
 	return strings.HasPrefix(err, NotPinned) || strings.HasPrefix(err, VersionTaken) || strings.HasPrefix(err, RefusedKind)
 }
 
+// Retakeable says whether a failed key's error opens with Retake: the builder takes it again by itself after a backoff,
+// until BuilderBuild.Retakes reaches MaxRetakes. An error that is FailedUntilChanged, or opens with no prefix, is not.
+func Retakeable(err string) bool {
+	return strings.HasPrefix(err, Retake) && !FailedUntilChanged(err)
+}
+
 // ToolchainUsed is what a build used for one language (ADR 0405 clauses 2 and 7): the installed toolchain's version and
 // the build module's recipe version.
 type ToolchainUsed struct {
@@ -180,6 +191,10 @@ type BuilderBuild struct {
 	Artifacts  []BuiltArtifact          `json:"artifacts,omitempty"`
 	Toolchains map[string]ToolchainUsed `json:"toolchains,omitempty"`
 	Error      string                   `json:"error,omitempty"`
+	// Retakes is how many times the builder took this key again by itself after a retakeable failure (Retake); it is kept
+	// on the key, so a builder that starts again reads it and the count survives a restart (issue 1748). A reader that
+	// does not know the field reads 0.
+	Retakes int `json:"retakes,omitempty"`
 	// Waits is, on a queued key only, the package version `<name>@<version>` the module's lock names and the registry
 	// does not yet hold: the key is not claimed until that package's trunk key is done and published (novox/hq ADR 0500
 	// clause 6). A reader that does not know the field reads the key as queued.

go/delivery/builder_reference_test.go

@@ -86,11 +86,38 @@ func TestOnlyAPushFailureIsBuiltAgainBeforeTheFingerprintChanges(t *testing.T) {
 		{VersionTaken + "@novox/mesh-sdk@0.1.15 holds another file", false},
 		{RefusedKind + "a package in go", false},
 		{"go test: 2 failed", true},
+		{Retake + "lookup git.novox.be: i/o timeout", true},
 	} {
 		if got := FailedUntilChanged(c.err); got == c.again {
 			t.Errorf("FailedUntilChanged(%q) = %v", c.err, got)
 		}
 	}
+	// A retakeable error opens with Retake and is not one that waits for the fingerprint; the count is on the key's value (issue 1748).
+	for _, c := range []struct {
+		err  string
+		want bool
+	}{
+		{Retake + "lookup git.novox.be: i/o timeout", true},
+		{NotPinned + "x", false},
+		{Retake[:4] + " not the prefix", false},
+		{"go test: 2 failed", false},
+		{"", false},
+		{VersionTaken + Retake, false},
+	} {
+		if got := Retakeable(c.err); got != c.want {
+			t.Errorf("Retakeable(%q) = %v", c.err, got)
+		}
+	}
+	data, err := EncodeBuilderBuild(BuilderBuild{State: BuildFailed, Error: Retake + "x", Retakes: 2})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if back, err := DecodeBuilderBuild(data); err != nil || back.Retakes != 2 {
+		t.Fatalf("decoded %+v, %v", back, err)
+	}
+	if Retake != "retakeable: " || MaxRetakes != 3 {
+		t.Fatal("the retake prefix or its bound changed")
+	}
 	if NotStored != "not stored: " || NotPinned != "not pinned: " || VersionTaken != "version taken: " || RefusedKind != "refused kind: " {
 		t.Fatal("a prefix changed its words")
 	}

go/delivery/history_records.go

@@ -175,6 +175,9 @@ type BuildLogEntry struct {
 	// sorted and each once, as the build module answered them (BuildAnswer.Imports; novox/hq ADR 0593 §2): the indexer
 	// keeps them on the module (KeptInputs2.Imports) when the build's fingerprint is the module's.
 	Imports []string `json:"imports,omitempty"`
+	// Retakes is, at a build's end, how many times the builder took the key again by itself after a retakeable failure
+	// (BuilderBuild.Retakes; issue 1748): builder_builds_since reads it.
+	Retakes int `json:"retakes,omitempty"`
 }
 
 // BuildsSince is the answer of BuildsSinceTool: every ended build since a time, oldest first, and whether the log held