P5a review: outlines from named destinations; pool race; fast over-limit; revalidation under the limiter; Accept pdf

- pdftext/outline: resolve named destinations through the catalog /Dests and the /Names /Dests
  tree, resolve indirect /Dest, /A and /Title, and treat reader.Null (what Dict.Get returns for
  a missing key) as absent. Before this every LaTeX and Acrobat PDF had an empty outline.
  pdftest gains NamedDests; TestOutlineNamedDestinations.
- api: pool() always goes through its Once (data race on concurrent first use);
  TestDefaultPoolConcurrentFirstUse. Revalidation of a stale cache entry counts against the
  caller/host limit.
- pdftext/runner: output over MaxText kills the child at once instead of waiting for the
  deadline; TestRunnerTooMuchTextFailsFast.
- fetch: Accept includes application/pdf;q=0.8.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/pdftest/pdftest.go

@@ -25,6 +25,10 @@ type Doc struct {
 	Pages   []string
 	Outline []Outline
 	Scanned []int
+	// NamedDests writes the outline the way LaTeX's hyperref and Acrobat do: each item is a
+	// /GoTo action to a named destination (resolved through the catalog's /Names /Dests tree)
+	// and its /Title is an indirect object. Without it items carry a direct /Dest array.
+	NamedDests bool
 }
 
 // Build returns the PDF bytes for d. It panics on a Doc it cannot express (an outline entry
@@ -51,9 +55,15 @@ func Build(d Doc) []byte {
 		scanned[p] = true
 	}
 
+	// With NamedDests the outline items are followed by one title object per item and then
+	// the name tree, so the numbers below stay fixed by position.
+	nameTree := outlineRoot + 1 + 2*len(d.Outline)
 	catalog := "<< /Type /Catalog /Pages 2 0 R"
 	if len(d.Outline) > 0 {
 		catalog += fmt.Sprintf(" /Outlines %d 0 R /PageMode /UseOutlines", outlineRoot)
+		if d.NamedDests {
+			catalog += fmt.Sprintf(" /Names << /Dests %d 0 R >>", nameTree)
+		}
 	}
 	obj(catalog + " >>")
 	var kids []string
@@ -93,6 +103,9 @@ func Build(d Doc) []byte {
 			}
 			n := first + i
 			item := fmt.Sprintf("<< /Title (%s) /Parent %d 0 R /Dest [%d 0 R /XYZ null null null]", esc(o.Title), outlineRoot, pageObj(o.Page-1))
+			if d.NamedDests {
+				item = fmt.Sprintf("<< /Title %d 0 R /Parent %d 0 R /A << /S /GoTo /D (dest.%d) >>", last+1+i, outlineRoot, i)
+			}
 			if i > 0 {
 				item += fmt.Sprintf(" /Prev %d 0 R", n-1)
 			}
@@ -101,6 +114,14 @@ func Build(d Doc) []byte {
 			}
 			obj(item + " >>")
 		}
+		if d.NamedDests {
+			var names []string
+			for i, o := range d.Outline {
+				obj(fmt.Sprintf("(%s)", esc(o.Title)))
+				names = append(names, fmt.Sprintf("(dest.%d) [%d 0 R /XYZ null null null]", i, pageObj(o.Page-1)))
+			}
+			obj(fmt.Sprintf("<< /Names [%s] >>", strings.Join(names, " ")))
+		}
 	}
 
 	xref := b.Len()