fix(underlay): bound how far DWF packages and DGN streams inflate

The DWF package reader, the DGN stream inflater and the new DGN
ExtendedColors scan each read a zlib/zip payload to its end, so a
crafted or corrupt file could inflate until memory ran out. Cap them:
1 GiB for a whole DWF package, 512 MiB per DGN stream, 4 MiB per
ExtendedColors record candidate - far above real files.

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

src/scene/model/underlay_vector/dgn8.rs

@@ -157,10 +157,15 @@ impl<'a> Cfb<'a> {
 
 /// A DGN stream: raw, or zlib data after a 16-byte header.
 fn inflate(data: &[u8]) -> Vec<u8> {
+    // Far above any real element stream; stops a crafted one from
+    // inflating until memory runs out.
+    const STREAM_LIMIT: u64 = 512 << 20;
     for skip in [16usize, 0] {
         if let Some(z) = data.get(skip..) {
             let mut out = Vec::new();
-            if flate2::read::ZlibDecoder::new(z).read_to_end(&mut out).is_ok() && !out.is_empty() {
+            if flate2::read::ZlibDecoder::new(z).take(STREAM_LIMIT).read_to_end(&mut out).is_ok()
+                && !out.is_empty()
+            {
                 return out;
             }
         }
@@ -237,8 +242,16 @@ fn extended_colors(cfb: &Cfb) -> Vec<[u8; 3]> {
         if a & 0x0f != 8 || ((a as u16) << 8 | b as u16) % 31 != 0 {
             continue;
         }
+        // The record is a short XML list; the cap keeps a stream that
+        // inflates without end (or a crafted one) from exhausting memory.
+        const RECORD_LIMIT: u64 = 4 << 20;
         let mut out = Vec::new();
-        if flate2::read::ZlibDecoder::new(&attrs[at..]).read_to_end(&mut out).is_err() || out.len() < 2 {
+        if flate2::read::ZlibDecoder::new(&attrs[at..])
+            .take(RECORD_LIMIT)
+            .read_to_end(&mut out)
+            .is_err()
+            || out.len() < 2
+        {
             continue;
         }
         let units: Vec<u16> = out.chunks_exact(2).map(|c| u16::from_le_bytes([c[0], c[1]])).collect();

src/scene/model/underlay_vector/dwf.rs

@@ -14,11 +14,15 @@ fn unzip(bytes: &[u8]) -> Option<HashMap<String, Vec<u8>>> {
     // the offset itself.
     let mut archive = zip::ZipArchive::new(Cursor::new(bytes)).ok()?;
     let mut files = HashMap::new();
+    // Total inflated size a package may reach: far above any real sheet
+    // set, and a crafted archive cannot exhaust memory.
+    let mut budget: u64 = 1 << 30;
     for i in 0..archive.len() {
-        let mut file = archive.by_index(i).ok()?;
+        let file = archive.by_index(i).ok()?;
         let name = file.name().replace('\\', "/").trim_start_matches('/').to_string();
         let mut data = Vec::new();
-        file.read_to_end(&mut data).ok()?;
+        file.take(budget + 1).read_to_end(&mut data).ok()?;
+        budget = budget.checked_sub(data.len() as u64)?;
         files.insert(name, data);
     }
     Some(files)