Avoid retaining hidden simple deferred messages

docs/roadmap/remediation.md

@@ -1,6 +1,6 @@
 # Invocation reporting audit remediation
 
-Status: remediation in progress; 5 of 7 findings complete.
+Status: remediation in progress; 6 of 7 findings complete.
 
 ## Review scope
 
@@ -381,7 +381,13 @@ owners.
 
 ## 6. Avoid retaining deferred messages that need no presentation work
 
-Priority: P3. Status: for consideration.
+Priority: P3. Status: complete.
+
+- [x] Completed: renderer-free hidden deferred messages record suppression
+  without queue retention. Finalization detaches the queue without an array
+  copy and delivers captured callback lists without recopying them. Hidden rich
+  callbacks, FIFO order, no-content handling, capture, and closure remain covered.
+  Validation: root module suite and focused reporter race checks pass.
 
 ### Finding and complexity
 

reporter.go

@@ -249,6 +249,16 @@ func (r DeferredReporter) enqueue(category messageCategory, message string, deta
 	if state.closed {
 		return ErrReporterClosed
 	}
+	if !hasDetails(details) {
+		if message == "" {
+			return nil
+		}
+		if !state.visible(category) {
+			state.diagnostics.submitted = true
+			state.diagnostics.suppressed = true
+			return nil
+		}
+	}
 	state.deferred = append(state.deferred, deferredMessage{
 		category: category,
 		message:  message,
@@ -268,12 +278,16 @@ func (r *Reporter) finalize(outcome Outcome, completion func(*Reporter)) Outcome
 		state.mu.Unlock()
 		return normalizeOutcome(outcome)
 	}
-	deferred := append([]deferredMessage(nil), state.deferred...)
+	deferred := state.deferred
 	state.deferred = nil
 	state.mu.Unlock()
 
-	for _, message := range deferred {
-		_ = r.submitMessage(message.category, message.message, message.details)
+	for index := range deferred {
+		message := deferred[index]
+		deferred[index] = deferredMessage{}
+		state.mu.Lock()
+		_ = state.submitMessageLocked(message.category, message.message, message.details)
+		state.mu.Unlock()
 	}
 	if completion != nil {
 		completion(r)
@@ -339,10 +353,11 @@ func ensureFallbackExplanation(outcome Outcome) Outcome {
 }
 
 func hasExplanation(explanation Explanation) bool {
-	if explanation.Message != "" {
-		return true
-	}
-	for _, detail := range explanation.Details {
+	return explanation.Message != "" || hasDetails(explanation.Details)
+}
+
+func hasDetails(details []Detail) bool {
+	for _, detail := range details {
 		if detail != nil {
 			return true
 		}
@@ -405,16 +420,16 @@ func (r *Reporter) submitMessage(category messageCategory, message string, detai
 	if state.closed {
 		return ErrReporterClosed
 	}
+	return state.submitMessageLocked(category, message, append([]Detail(nil), details...))
+}
 
-	details = append([]Detail(nil), details...)
-	hasDetails := false
-	for _, detail := range details {
-		if detail != nil {
-			hasDetails = true
-			break
-		}
+// Queued detail lists have already been captured; delivery need not copy them.
+func (state *reportingState) submitMessageLocked(category messageCategory, message string, details []Detail) error {
+	if state.closed {
+		return ErrReporterClosed
 	}
-	if message == "" && !hasDetails {
+	rich := hasDetails(details)
+	if message == "" && !rich {
 		return nil
 	}
 
@@ -423,7 +438,7 @@ func (r *Reporter) submitMessage(category messageCategory, message string, detai
 	destination.submitted = true
 	if !visible {
 		destination.suppressed = true
-		if !hasDetails {
+		if !rich {
 			return nil
 		}
 	}

reporter_deferred_test.go

@@ -0,0 +1,69 @@
+package commandkit
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestHiddenSimpleDeferredMessagesDoNotAccumulate(t *testing.T) {
+	for _, mode := range []reportingMode{modeOrdinary, modeQuiet} {
+		t.Run(fmt.Sprint(mode), func(t *testing.T) {
+			reporter := newReporter(Streams{})
+			reporter.setVisibility(mode, false, false)
+			for index := 0; index < 256; index++ {
+				if err := reporter.AtEnd().Debug(fmt.Sprintf("hidden %d", index), nil); err != nil {
+					t.Fatal(err)
+				}
+				if err := reporter.AtEnd().Warn("hidden warning"); err != nil {
+					t.Fatal(err)
+				}
+			}
+			// This assertion owns the storage optimization, not a public queue API.
+			if len(reporter.state.deferred) != 0 {
+				t.Fatalf("retained %d renderer-free hidden messages", len(reporter.state.deferred))
+			}
+			got := reporter.finalize(Success(), nil)
+			if got.Status != 0 || got.Presentation.Diagnostics.State != DeliverySuppressed {
+				t.Fatalf("outcome=%#v", got)
+			}
+			if err := reporter.AtEnd().Debug("late"); !errors.Is(err, ErrReporterClosed) {
+				t.Fatalf("closed hidden submission=%v", err)
+			}
+		})
+	}
+	noContent := newReporter(Streams{})
+	_ = noContent.AtEnd().Warn("", nil)
+	if got := noContent.finalize(Success(), nil); got.Presentation.Diagnostics.State != DeliveryNone {
+		t.Fatalf("empty deferred submission became content: %#v", got)
+	}
+}
+
+func TestHiddenDeferredDetailsRemainDeferredAndCaptured(t *testing.T) {
+	var diagnostics bytes.Buffer
+	reporter := newReporter(Streams{Err: &diagnostics})
+	reporter.setVisibility(modeQuiet, false, false)
+	failure := errors.New("hidden rendering failed")
+	var order []string
+	details := []Detail{func(w io.Writer) error {
+		order = append(order, "first")
+		_, _ = io.WriteString(w, "hidden detail")
+		return failure
+	}}
+	_ = reporter.AtEnd().Warn("hidden", details...)
+	details[0] = func(io.Writer) error { t.Error("caller changed captured callback"); return nil }
+	_ = reporter.AtEnd().Info("", func(io.Writer) error { order = append(order, "second"); return nil })
+	if len(order) != 0 {
+		t.Fatal("details ran at submission")
+	}
+	got := reporter.finalize(Success(), nil)
+	if strings.Join(order, ",") != "first,second" || !errors.Is(got.Presentation.Diagnostics.RenderError, failure) || got.Status != 1 {
+		t.Fatalf("order=%v outcome=%#v", order, got)
+	}
+	if strings.Contains(diagnostics.String(), "hidden") || len(reporter.state.deferred) != 0 {
+		t.Fatalf("hidden content leaked or queue retained: %q", diagnostics.String())
+	}
+}