Readability vectors: a legacy array with bytes after it

Rust's read path let a legacy envelope array with trailing bytes through when the
whole-array check was loosened, and no vector caught it. Add the vector; every
runtime refuses it.

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

packages/cultcache-py/tests/test_cultcache.py

@@ -913,7 +913,7 @@ class CultCacheTests(unittest.TestCase):
             for line in (root / "manifest.txt").read_text(encoding="utf-8").splitlines()
             if line and not line.startswith("#")
         ]
-        self.assertEqual(len(rows), 14)
+        self.assertEqual(len(rows), 15)
         envelopes = SingleFileMessagePackBackingStore(self._C2A_VECTORS / "v3-base.msgpack").pull_all()
         for vector, _, _, _, python in rows:
             content = (root / vector).read_bytes()

packages/cultcache-rs/src/lib.rs

@@ -4858,7 +4858,7 @@ mod tests {
                 }
             }
         }
-        assert_eq!(rows, 14);
+        assert_eq!(rows, 15);
         Ok(())
     }
 

packages/cultcache-ts/test/cult-cache.test.ts

@@ -1590,7 +1590,7 @@ test("SingleFileMessagePackBackingStore replaces a file exactly when it reads",
     .split(/\r?\n/u)
     .filter((line) => line.length > 0 && !line.startsWith("#"))
     .map((line) => line.split(/\s+/u));
-  assert.equal(rows.length, 14);
+  assert.equal(rows.length, 15);
   const dir = await mkdtemp(join(tmpdir(), "cultcache-readability-"));
   const seed = await copyVector(dir, join(c2aVectors, "v3-base.msgpack"), "seed.msgpack");
   const envelopes = await new SingleFileMessagePackBackingStore(seed).pullAll();

tests/vectors/document-variants-c2a/readability/generate.py

@@ -17,6 +17,7 @@ vectors = {
     "empty-array": pack([]),
     # A legacy envelope array: an array of maps. Rust, TypeScript and Python read it; C# has no legacy reader.
     "legacy-envelopes": pack([{"key": "old", "type": "old.type", "payload": pack([]), "storedAt": "2026-01-01T00:00:00Z"}]),
+    "legacy-trailing": None,  # filled below: the legacy array plus bytes after it
     "ints": pack([1, 2, 3]),
     "nil-first": pack([None, "x"]),
     "nested-array": pack([["cultcache.store.v9", [], []]]),
@@ -28,6 +29,7 @@ vectors = {
     "trailing-bytes": whole + b"\x01\x02\x03",
     "trailing-store": whole + whole,
 }
+vectors["legacy-trailing"] = vectors["legacy-envelopes"] + b"
"
 for name, data in vectors.items():
     (here / f"{name}.bin").write_bytes(data)
 print(len(vectors), "vectors")

tests/vectors/document-variants-c2a/readability/legacy-trailing.bin

@@ -0,0 +1 @@
+‘„£key£old¤type¨old.type§payloadÄ
<01>¨storedAt´2026-01-01T00:00:00Z


tests/vectors/document-variants-c2a/readability/manifest.txt

@@ -4,6 +4,7 @@
 zero-byte.bin       reads    reads    reads    reads
 empty-array.bin     reads    reads    reads    reads
 legacy-envelopes.bin refuses reads    reads    reads
+legacy-trailing.bin refuses refuses refuses refuses
 ints.bin            refuses  refuses  refuses  refuses
 nil-first.bin       refuses  refuses  refuses  refuses
 nested-array.bin    refuses  refuses  refuses  refuses