From 2ae31ce2c6834051fda547d7ed86313efd42b2ec Mon Sep 17 00:00:00 2001
From: jay23606 <4602056+jay23606@users.noreply.github.com>
Date: Mon, 19 Oct 2026 21:07:16 -0400
Subject: [PATCH 1/2] fix(ascii85): reject short tail groups whose padded value
 overflows uint32

Short tail groups (2-4 chars) are padded with 'u' to five digits before
decoding. The uint32 overflow check only ran for full 5-char groups, so a
short tail whose padded value exceeds 0xFFFFFFFF wrapped silently and
emitted wrong bytes. The check now applies to every group and returns
null for such input.

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Signed-off-by: jay23606 <4602056+jay23606@users.noreply.github.com>
---
 lib/utils/ascii85.test.ts | 14 ++++++++++++++
 lib/utils/ascii85.ts      |  6 +++---
 2 files changed, 17 insertions(+), 3 deletions(-)
 create mode 100644 lib/utils/ascii85.test.ts

diff --git a/lib/utils/ascii85.test.ts b/lib/utils/ascii85.test.ts
new file mode 100644
index 00000000..e37aac1d
--- /dev/null
+++ b/lib/utils/ascii85.test.ts
@@ -0,0 +1,14 @@
+import { ascii85Decode } from './ascii85';
+
+describe('ascii85Decode', () => {
+  it('decodes a full 5-character group', () => {
+    expect(ascii85Decode('<~9jqo^~>')).toEqual(new Uint8Array([0x4d, 0x61, 0x6e, 0x20]));
+  });
+
+  it.each(['<~uu~>', '<~uuu~>', '<~uuuu~>'])(
+    'rejects the short tail group %s whose padded value overflows uint32',
+    (input) => {
+      expect(ascii85Decode(input)).toBeNull();
+    },
+  );
+});
diff --git a/lib/utils/ascii85.ts b/lib/utils/ascii85.ts
index 5a3a7fe2..0843ba80 100644
--- a/lib/utils/ascii85.ts
+++ b/lib/utils/ascii85.ts
@@ -34,10 +34,10 @@ export function ascii85Decode(input: string): Uint8Array | null {
       value = value * 85 + digit;
     }
 
-    if (chunkLen === 5 && value > 0xffffffff) return null;
+    // Applies to padded short tails too: a group whose value exceeds uint32 is invalid input.
+    if (value > 0xffffffff) return null;
 
-    // Use >>> 0 to simulate uint32 overflow for padded groups
-    const v = value >>> 0;
+    const v = value;
     const numBytes = chunkLen === 5 ? 4 : chunkLen - 1;
     if (numBytes >= 1) output.push((v >>> 24) & 0xff);
     if (numBytes >= 2) output.push((v >>> 16) & 0xff);

From 9b14489acbceb7696eddd6b3c122e389f66f82a9 Mon Sep 17 00:00:00 2001
From: jay23606 <4602056+jay23606@users.noreply.github.com>
Date: Mon, 19 Oct 2026 21:19:47 -0400
Subject: [PATCH 2/2] style(test): wrap the ascii85 tail-group expect call for
 prettier

ESLint's prettier/prettier rule flags the expect line in
lib/utils/ascii85.test.ts. Wrap it as prettier requires. No behaviour change.

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Signed-off-by: jay23606 <4602056+jay23606@users.noreply.github.com>
---
 lib/utils/ascii85.test.ts | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/utils/ascii85.test.ts b/lib/utils/ascii85.test.ts
index e37aac1d..b643c879 100644
--- a/lib/utils/ascii85.test.ts
+++ b/lib/utils/ascii85.test.ts
@@ -2,7 +2,9 @@ import { ascii85Decode } from './ascii85';
 
 describe('ascii85Decode', () => {
   it('decodes a full 5-character group', () => {
-    expect(ascii85Decode('<~9jqo^~>')).toEqual(new Uint8Array([0x4d, 0x61, 0x6e, 0x20]));
+    expect(ascii85Decode('<~9jqo^~>')).toEqual(
+      new Uint8Array([0x4d, 0x61, 0x6e, 0x20]),
+    );
   });
 
   it.each(['<~uu~>', '<~uuu~>', '<~uuuu~>'])(