diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3bd9ffc..aeecdc4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -92,9 +92,9 @@ All notable changes to the CacheKit Protocol Specification.
 
 ### Test Vectors
 
-- 6 `bin`-encoded twins appended to `test-vectors/wire-format.json` (append-only;
-  the 6 legacy vectors are retained forever as legacy-read proof; fixture
-  1.0.0 → 1.1.0). Twins generated by the stdlib-only
+- 7 legacy/`bin` vector pairs in `test-vectors/wire-format.json` (append-only;
+  legacy vectors are retained forever as legacy-read proof; fixture
+  1.0.0 → 1.1.1). The original six `bin` twins were generated by the stdlib-only
   `tools/wire-format-reference.py` and byte-verified against rmp-serde output;
   `verify` now runs in CI (stdlib pass + `msgpack` third-encoder conformance) —
   the wire-format fixture's first protocol-side CI verification.
diff --git a/decisions/envelope-bin-encoding.md b/decisions/envelope-bin-encoding.md
index 738515d..9562556 100644
--- a/decisions/envelope-bin-encoding.md
+++ b/decisions/envelope-bin-encoding.md
@@ -164,13 +164,12 @@ giving the wire-format fixture its first protocol-side CI verification.
 the vector set matching the writer's current encoding (decode-identity keeps
 running against both sets, forever).
 
-**Deferred to the implementation PR:** all six `*_bin` twins exercise the
-`bin8` (`0xc4`) header — no legacy vector has `compressed_data` > 255 B, and a
-`bin16`/`bin32` twin cannot be derived from the existing pins (a new input
-needs real LZ4 output). The implementation PR MUST add at least one
-width-boundary vector (> 255 B compressed) generated by the real
-`cachekit-core` writer, so third-party readers get fixture coverage of the
-larger `bin` headers.
+**Discharged by LAB-868:** `width_boundary_bin16` is a real-`cachekit-core`
+writer vector with 303 B of `compressed_data`, and its canonical twin therefore
+uses the `bin16` (`0xc5`) header. This gives third-party readers pinned coverage
+of the larger `bin` header. A `bin32` fixture pair is deliberately omitted: its
+legacy array-of-integers twin would add roughly 590 KB of vendored hex data,
+while the runtime `width_boundary_bin16_bin32` test exercises that header.
 
 ## Links
 
diff --git a/spec/wire-format.md b/spec/wire-format.md
index 905026e..3d98225 100644
--- a/spec/wire-format.md
+++ b/spec/wire-format.md
@@ -6,7 +6,7 @@
 
 **LZ4 compression + xxHash3-64 integrity wrapping for cached payloads that use the envelope.**
 
-*Protocol Version 1.1 · Verified against `cachekit-core` v0.4.0 (`src/byte_storage.rs`); legacy envelope test vectors generated at v0.2.0 and unchanged since — `bin`-encoded twins added in protocol 1.1 ([decisions/envelope-bin-encoding.md](../decisions/envelope-bin-encoding.md))*
+*Protocol Version 1.1 · Verified against `cachekit-core` v0.4.0 (`src/byte_storage.rs`); six original legacy envelope test vectors were generated at v0.2.0, with the `width_boundary_bin16` legacy vector added by `cachekit-core` v0.5.0 — `bin`-encoded twins added in protocol 1.1 ([decisions/envelope-bin-encoding.md](../decisions/envelope-bin-encoding.md))*
 
 </div>
 
@@ -159,8 +159,8 @@ Canonical (bin, 1.1+ writers — vector `simple_string_bin`, 42 B):
 The two encodings are **mutually intelligible in both directions** under
 `rmp-serde` — this is a property of the deployed readers, not a migration
 promise. Toolchain-verified (rmp-serde 1.3.1, serde_bytes 0.11.19, rmp 0.8.15,
-serde 1.0.228) on all six byte-pinned vectors, including `bin` wire fed through
-the shipped `ByteStorage::retrieve()` with checksum validation and
+serde 1.0.228) on all seven byte-pinned vectors, including `bin` wire fed
+through the shipped `ByteStorage::retrieve()` with checksum validation and
 decompression-ratio guards intact (LAB-764):
 
 | Reader | Legacy wire (array-of-ints) | Canonical wire (`bin`) |
@@ -203,6 +203,14 @@ is append-only and verified in this repo's CI by
 provenance and the downstream re-pin plan live in
 [decisions/envelope-bin-encoding.md](../decisions/envelope-bin-encoding.md).
 
+The fixture deliberately includes the `bin8` → `bin16` boundary but not a
+`bin32` fixture pair. A pair with more than 65,535 compressed bytes would add
+roughly 590 KB of hex-encoded fixture data once the legacy array-of-integers
+twin is included, then be vendored into every SDK. The `bin16` pair verifies
+the generic shortest-width selection property at fixture level, while
+`cachekit-core/tests/dual_decode.rs::width_boundary_bin16_bin32` exercises
+`bin32` at runtime without that distribution cost.
+
 > [!WARNING]
 > **History.** Earlier revisions of this document described the envelope as a
 > MessagePack *map* with `bin`-encoded byte fields — **that was never what
diff --git a/test-vectors/wire-format.json b/test-vectors/wire-format.json
index 9be2ba0..fdc3cc5 100644
--- a/test-vectors/wire-format.json
+++ b/test-vectors/wire-format.json
@@ -2,7 +2,7 @@
   "checksum": "xxHash3-64, 8 bytes big-endian, computed on uncompressed input",
   "compression": "LZ4 block format (NOT frame)",
   "envelope_format": "MessagePack positional array (rmp_serde::to_vec): [compressed_data, checksum, original_size, format]. Vectors without an 'envelope_encoding' field use the legacy array-of-integers encoding for compressed_data and are retained forever as legacy-read proof; their '*_bin' twins use msgpack bin (canonical for protocol 1.1+ writers). checksum always encodes as an array of 8 integers. Normative rules: spec/wire-format.md, 'Byte Layout' / 'Encoding compatibility'.",
-  "generator": "legacy vectors: cachekit-core v0.2.0 (unchanged since); *_bin vectors: tools/wire-format-reference.py generate - deterministic re-encode of the legacy fields, byte-verified against rmp-serde 1.3.1 + serde_bytes 0.11.19 output (LAB-783)",
+  "generator": "six original legacy vectors: cachekit-core v0.2.0; width_boundary_bin16 legacy vector: cachekit-core v0.5.0 real writer; *_bin vectors: tools/wire-format-reference.py generate - deterministic re-encode of the legacy fields, byte-verified against rmp-serde 1.3.1 + serde_bytes 0.11.19 output (LAB-783)",
   "limits": {
     "max_compressed_size": 536870912,
     "max_compression_ratio": 1000,
@@ -63,6 +63,15 @@
       "input_size": 1,
       "name": "single_byte"
     },
+    {
+      "description": "300-byte deterministic xorshift64* incompressible payload (seed 0x9e3779b97f4a7c15, multiplier 0x2545f4914f6cdd1d; little-endian u64 output truncated to 300 bytes; real writer bin16 width boundary)",
+      "envelope_hex": "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",
+      "envelope_size": 478,
+      "format": "msgpack",
+      "input_hex": "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",
+      "input_size": 300,
+      "name": "width_boundary_bin16"
+    },
     {
       "description": "bin-encoded twin of 'empty': identical fields, compressed_data as msgpack bin (canonical writer encoding, protocol 1.1+)",
       "envelope_hex": "94c40100982d06cc800538ccd3cc94ccc200a76d73677061636b",
@@ -128,7 +137,18 @@
       "name": "single_byte_bin",
       "envelope_encoding": "bin",
       "derived_from": "single_byte"
+    },
+    {
+      "description": "bin-encoded twin of 'width_boundary_bin16': identical fields, compressed_data as msgpack bin (canonical writer encoding, protocol 1.1+)",
+      "envelope_hex": "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",
+      "envelope_size": 331,
+      "format": "msgpack",
+      "input_hex": "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",
+      "input_size": 300,
+      "name": "width_boundary_bin16_bin",
+      "envelope_encoding": "bin",
+      "derived_from": "width_boundary_bin16"
     }
   ],
-  "version": "1.1.0"
+  "version": "1.1.1"
 }
diff --git a/tools/wire-format-reference.py b/tools/wire-format-reference.py
index 99da3a5..7fa1a3a 100644
--- a/tools/wire-format-reference.py
+++ b/tools/wire-format-reference.py
@@ -38,7 +38,7 @@
 
 FIXTURE_PATH = Path(__file__).resolve().parent.parent / "test-vectors" / "wire-format.json"
 
-FIXTURE_VERSION = "1.1.0"
+FIXTURE_VERSION = "1.1.1"
 ENVELOPE_FORMAT = (
     "MessagePack positional array (rmp_serde::to_vec): "
     "[compressed_data, checksum, original_size, format]. Vectors without an "
@@ -49,7 +49,8 @@
     "spec/wire-format.md, 'Byte Layout' / 'Encoding compatibility'."
 )
 GENERATOR = (
-    "legacy vectors: cachekit-core v0.2.0 (unchanged since); *_bin vectors: "
+    "six original legacy vectors: cachekit-core v0.2.0; width_boundary_bin16 "
+    "legacy vector: cachekit-core v0.5.0 real writer; *_bin vectors: "
     "tools/wire-format-reference.py generate - deterministic re-encode of the "
     "legacy fields, byte-verified against rmp-serde 1.3.1 + serde_bytes 0.11.19 "
     "output (LAB-783)"