fix: a damaged entry truncates the archive instead of failing it

a read error while copying one entry (a zip CRC mismatch, a corrupt deflate stream) was returned from `add`. That aborted the walk, and `Extract` threw away every entry already stored. So a large war with one damaged, irrelevant entry produced zero packages with the feature on, while java's legacy path (which reads only the entries it needs) still cataloged it.

- a read error on one entry now drops that entry and marks the resolver truncated (`entry "x" could not be read: ...`), and the walk continues
- if the stream itself breaks partway (a truncated `.tar.gz`), whatever was read before the break is kept and the archive is truncated. With nothing read it is still an error, as before
- disk limit and decompression budget errors still stop the walk

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

internal/archive/extract_test.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"io"
 	"io/fs"
+	"math/rand"
 	"os"
 	"path/filepath"
 	"strings"
@@ -344,6 +345,25 @@ func TestExtract_heldContentWrittenToDiskStaysUntilCleanup(t *testing.T) {
 	assert.Zero(t, disk)
 }
 
+func TestExtract_aTruncatedStreamKeepsWhatWasRead(t *testing.T) {
+	// a .tar.gz cut off partway breaks the stream for every entry after the cut; the ones before it are
+	// still good and must not be thrown away
+	noise := make([]byte, 64*1024)
+	rand.New(rand.NewSource(1)).Read(noise)
+	data := tarGzBytes(t, map[string]string{"a.txt": "first", "b.bin": string(noise)})
+	cut := data[:len(data)/2]
+
+	extracted, err := Extract(context.Background(), bytes.NewReader(cut), "", "app.tar.gz", NewLimiter(unboundedLimits), nil)
+	require.NoError(t, err)
+	require.NotNil(t, extracted)
+	t.Cleanup(extracted.Cleanup)
+
+	assert.True(t, extracted.Truncated)
+	locations, err := extracted.FilesByGlob("**")
+	require.NoError(t, err)
+	assert.Equal(t, []string{"a.txt"}, realPaths(locations))
+}
+
 func TestExtract_aPanicStillReleasesEverything(t *testing.T) {
 	// a decoder panicking on hostile bytes must not leak the charge or the spill file
 	ctx, root := scanContext(t)