Release unused file buffers for empty artifacts

docs/internal/sources.md

@@ -131,9 +131,10 @@ fallback.
 Regular files are read synchronously in bounded chunks. The opened file's size
 is only an initial-capacity hint, capped at 1 MiB; reads continue to EOF, and
 the returned body determines artifact size and hash. If an overreported hint
-leaves more than twice the actual body length unused, the completed body is
+leaves unused capacity greater than the actual body length, the completed body
-copied to release the excess backing storage. Cancellation is checked before
+is copied to release the excess backing storage, including when the body is
-opening, before and after every read, and before publishing the artifact, so a
+empty. Cancellation is checked before opening, before and after every read,
+and before publishing the artifact, so a
 canceled read never publishes partial content. The ordinary reader does not
 detach file reads into background goroutines.
 

docs/roadmap/remediation.md

@@ -1,7 +1,6 @@
 # Implementation Review Remediation
 
-Status: One computational-efficiency finding awaits remediation. Earlier
+Status: All recorded findings have been resolved in separate remediation units.
-findings below remain resolved.
 
 ## Computational Efficiency Review
 
@@ -10,7 +9,16 @@ Review baseline: `8a5c0de`, compared with planning commit `3fde1f6`, the
 
 ### Finding 1 — Release A Stale File Reservation For An Empty Body (P3)
 
-**Status: Open.**
+**Status: Resolved.** Completed empty bodies now release stale file-size
+reservations using the existing compaction path. The stale-size table covers
+empty content, metadata, and hashes; the retained-artifact benchmark includes
+an empty-body fixture without enforcing capacity or allocation thresholds.
+Three offline, one-iteration samples for four retained empty artifacts changed
+from 4,194,928–4,194,976 retained bytes to 624–640 bytes. Initial reservation
+allocations still occur; this fix reduces retained storage, not cumulative
+allocation. The nonempty benchmark remains near 1 MiB for four 256 KiB bodies.
+Artifact package race tests and vet passed, and the internal documentation
+now accurately describes the compaction condition.
 
 Location: [file reader](../../internal/artifact/reader.go), lines 137–166.
 

internal/artifact/reader.go

@@ -158,7 +158,7 @@ func readFileArtifact(ctx context.Context, path string, open func(string) (artif
 			return nil, fmt.Errorf("failed to read file %s: %w", path, readErr)
 		}
 	}
-	if len(data) > 0 && cap(data)-len(data) > len(data) {
+	if cap(data)-len(data) > len(data) {
 		// A stale size hint should not make a small completed artifact retain a
 		// disproportionately large backing array.
 		compact := make([]byte, len(data))

internal/artifact/reader_benchmark_test.go

@@ -42,7 +42,20 @@ func BenchmarkArtifactFileRead(b *testing.B) {
 // BenchmarkRetainedArtifactFileRead measures live artifact bodies when an
 // opened file reports a size larger than the content that reaches EOF.
 func BenchmarkRetainedArtifactFileRead(b *testing.B) {
-	body := bytes.Repeat([]byte("x"), 256<<10)
+	for _, fixture := range []struct {
+		name string
+		body []byte
+	}{
+		{name: "small", body: bytes.Repeat([]byte("x"), 256<<10)},
+		{name: "empty", body: []byte{}},
+	} {
+		b.Run(fixture.name, func(b *testing.B) {
+			benchmarkRetainedArtifactFileRead(b, fixture.body)
+		})
+	}
+}
+
+func benchmarkRetainedArtifactFileRead(b *testing.B, body []byte) {
 	path := filepath.Join(b.TempDir(), "overreported.txt")
 	if err := os.WriteFile(path, body, 0o600); err != nil {
 		b.Fatal(err)

internal/artifact/reader_test.go

@@ -241,6 +241,7 @@ func TestFileReaderUsesOpenedSizeOnlyAsACapacityHint(t *testing.T) {
 		reportedSize int64
 	}{
 		{name: "overreported size", body: []byte("actual file content"), reportedSize: 128},
+		{name: "overreported size with empty content", body: []byte{}, reportedSize: 16 << 20},
 		{name: "underreported size", body: bytes.Repeat([]byte("x"), fileReadChunkSize+17), reportedSize: 1},
 		{name: "very large hint with small content", body: []byte("small actual content"), reportedSize: int64(^uint64(0) >> 1)},
 	}
@@ -280,6 +281,9 @@ func TestFileReaderUsesOpenedSizeOnlyAsACapacityHint(t *testing.T) {
 			if artifact.Size != int64(len(tc.body)) {
 				t.Fatalf("artifact size=%d, want %d", artifact.Size, len(tc.body))
 			}
+			if artifact.Name != filepath.Base(filePath) || artifact.URI != filePath || artifact.ContentType == "" {
+				t.Fatalf("unexpected artifact metadata: name=%q URI=%q content type=%q", artifact.Name, artifact.URI, artifact.ContentType)
+			}
 			wantHash := fmt.Sprintf("%x", sha256.Sum256(tc.body))
 			if artifact.Hash != wantHash {
 				t.Fatalf("artifact hash=%q, want %q", artifact.Hash, wantHash)