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/pdftext/runner.go

@@ -106,14 +106,17 @@ func (r *Runner) Run(ctx context.Context, pdf []byte) (*Doc, error) {
 	}
 
 	readErr := <-done
-	<-stderrDone
 
-	// Output over the limit: kill the child and report.
+	// Output over the limit: kill the child at once. Checked before waiting for stderr, which
+	// only closes when the child exits — and a child blocked on a full stdout pipe would not,
+	// until the deadline.
 	if int64(stdoutBuf.Len()) > maxText {
 		cancel()
+		<-stderrDone
 		_ = cmd.Wait()
 		return nil, ErrTooMuchText
 	}
+	<-stderrDone
 
 	waitErr := cmd.Wait()