disk_folders: bound the walk at 25 s, below the tool runner's 30 s, and say findings as lines (issue 1804)

modules/disk-load/cmd/disk-load/folders.go

@@ -13,7 +13,7 @@ import (
 )
 
 // FolderBudget is how long a folder walk may take before it answers what it has measured.
-const FolderBudget = 60 * time.Second
+const FolderBudget = 25 * time.Second
 
 // namedUnreadable is how many unreadable folders are named; the rest are only counted.
 const namedUnreadable = 50
@@ -130,7 +130,7 @@ func (m *Machine) Folders(path string, depth, limit int) (FolderReport, error) {
 	if len(r.Skipped) > 0 {
 		said = append(said, "other filesystems not entered: "+strings.Join(r.Skipped, ", "))
 	}
-	r.Said = strings.Join(said, "; ")
+	r.Said = said
 	return r, nil
 }
 

modules/disk-load/cmd/disk-load/folders_test.go

@@ -132,7 +132,7 @@ func TestUnreadableFoldersAreCountedAndNamed(t *testing.T) {
 	if r.Unreadable != 2 || strings.Join(r.UnreadableFolders, ",") != "/var/lib/docker/overlay2/b,/var/log" {
 		t.Errorf("%d: %v", r.Unreadable, r.UnreadableFolders)
 	}
-	if r.Partial || !strings.Contains(r.Said, "2 folders could not be read") {
+	if r.Partial || !strings.Contains(strings.Join(r.Said, "\n"), "2 folders could not be read") {
 		t.Errorf("%+v", r)
 	}
 }
@@ -144,7 +144,7 @@ func TestALongWalkAnswersPartialAndSaysWhereItStopped(t *testing.T) {
 	now := time.Unix(0, 0)
 	m.Clock = func() time.Time { now = now.Add(10 * time.Second); return now }
 	r := folders(t, m, nil)
-	if !r.Partial || r.StoppedAt == "" || !strings.Contains(r.Said, "PARTIAL") || !strings.Contains(r.Said, r.StoppedAt) {
+	if !r.Partial || r.StoppedAt == "" || len(r.Said) < 2 || !strings.HasPrefix(r.Said[0], "PARTIAL") || !strings.Contains(r.Said[0], r.StoppedAt) {
 		t.Errorf("%+v", r)
 	}
 }
@@ -161,3 +161,10 @@ func TestAHardLinkIsCountedOnce(t *testing.T) {
 		t.Errorf("counted twice: %d", r.Bytes)
 	}
 }
+
+// 1804/AC7: the bound sits below the 30 s the tool runner gives a call, so a partial answer reaches its caller.
+func TestTheWalkBoundIsBelowTheToolRunnersCallLimit(t *testing.T) {
+	if FolderBudget >= 30*time.Second {
+		t.Errorf("the budget %s is not below the 30 s a call gets", FolderBudget)
+	}
+}

modules/disk-load/cmd/disk-load/tools.go

@@ -141,7 +141,7 @@ func Tools(m *Machine) []stdio.Tool {
 			Description: "Which folders fill a disk, like du -x: the largest folders under a path, measured on disk (allocated bytes, a hard link " +
 				"once), staying on the path's one filesystem (a mount below it is named, never entered). path defaults to /, depth to 2 (at most 3), " +
 				"limit to 20 (at most 100). Sizes in bytes and GiB. It reads every folder the tool runner can read, none of the content; folders " +
-				"it cannot read are counted and named. It stops after 60 s and answers what it measured so far, marked partial, with where it stopped. " +
+				"it cannot read are counted and named. It stops after 25 s and answers what it measured so far, marked partial, with where it stopped. " +
 				"Replaces du. (r)",
 			Input: map[string]any{
 				"path":  map[string]any{"type": "string", "description": "the absolute folder to measure (default /)"},