fix(processor): handle os.Remove errors for markdown inbox extras

When removing markdown inbox extras (embedded local images), os.Remove errors
were silently ignored. If removal failed, the image remained in the inbox and
was later published as a standalone image post.

- Check os.Remove errors and return a wrapped error.
- Rollback the already-saved post directory when extra removal fails.
- Deduplicate extras to avoid failing on duplicate references (e.g. same image
  referenced twice in one markdown).
- Add a negative test that verifies the error is returned and no post is
  persisted when removing an embedded image fails.

Fixes duplicate image posts caused by leftover inbox extras.

1 files changed, 55 insertions, 0 deletions

diff --git a/internal/processor/processor_test.go b/internal/processor/processor_test.go
index b5e8f20..df39008 100644
--- a/internal/processor/processor_test.go
+++ b/internal/processor/processor_test.go
@@ -6,6 +6,7 @@ import (
 	"image/png"
 	"os"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"testing"
 	"time"
@@ -318,3 +319,57 @@ func TestRun_duplicateImageClaimsInSameMarkdownAllowed(t *testing.T) {
 		t.Fatalf("n=%d; want 1", n)
 	}
 }
+
+func TestRun_markdownWithLocalImage_removeFails(t *testing.T) {
+	t.Parallel()
+	if runtime.GOOS == "windows" {
+		t.Skip("chmod does not reliably deny removal on Windows")
+	}
+
+	in := t.TempDir()
+	out := t.TempDir()
+
+	pngPath := filepath.Join(in, "embed.png")
+	f, err := os.Create(pngPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := png.Encode(f, image.NewRGBA(image.Rect(0, 0, 2, 2))); err != nil {
+		f.Close()
+		t.Fatal(err)
+	}
+	f.Close()
+
+	md := `![x](embed.png)
+text`
+	if err := os.WriteFile(filepath.Join(in, "post.md"), []byte(md), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	// Remove write permission from the inbox so os.Remove on the extra fails.
+	if err := os.Chmod(in, 0o555); err != nil {
+		t.Fatal(err)
+	}
+	defer os.Chmod(in, 0o755) // restore for cleanup
+
+	_, err = Run(ctx, &config.Config{InputDir: in, OutputDir: out, BaseURL: "https://x"})
+	if err == nil {
+		t.Fatal("expected error when inbox extra removal fails")
+	}
+	if !strings.Contains(err.Error(), "embed.png") {
+		t.Fatalf("error should mention embed.png, got: %v", err)
+	}
+
+	// Ensure nothing was persisted: post directory should have been rolled back.
+	entries, _ := os.ReadDir(filepath.Join(out, "posts"))
+	if len(entries) != 0 {
+		t.Fatalf("expected no posts after rollback, got %d", len(entries))
+	}
+
+	// Source files should still be in the inbox.
+	for _, name := range []string{"post.md", "embed.png"} {
+		if _, err := os.Stat(filepath.Join(in, name)); err != nil {
+			t.Fatalf("source %s should still exist: %v", name, err)
+		}
+	}
+}