diff --git a/build-packages.sh b/build-packages.sh
index 1d635297..9ebd90d7 100755
--- a/build-packages.sh
+++ b/build-packages.sh
@@ -188,6 +188,7 @@ install_python_packages() {
         beautifulsoup4 \
         tabulate \
         xlrd \
+        python-calamine \
         numba \
         patsy \
         numexpr \
diff --git a/docker/package-init.sh b/docker/package-init.sh
index 4b96305f..19ad83c3 100644
--- a/docker/package-init.sh
+++ b/docker/package-init.sh
@@ -208,6 +208,7 @@ if [ -f "$PIP_PATH" ]; then
         beautifulsoup4 \
         tabulate \
         xlrd \
+        python-calamine \
         numba \
         patsy \
         numexpr \
diff --git a/packages/code/src/protocol.test.ts b/packages/code/src/protocol.test.ts
index 25c00cf3..9e1ac2b3 100644
--- a/packages/code/src/protocol.test.ts
+++ b/packages/code/src/protocol.test.ts
@@ -988,6 +988,15 @@ test('bridge artifact policy and media types match the hardened gateway contract
   assert.equal(bridgeArtifactMediaType('preview.png'), 'image/png');
   assert.equal(bridgeArtifactMediaType('reports/result.json'), 'application/json');
   assert.equal(bridgeArtifactMediaType('Dockerfile'), 'application/octet-stream');
+  // XLSB (Excel Binary Workbook) — sandboxed code can produce these via
+  // `pd.read_excel(path, engine='calamine')`-backed workflows; the egress
+  // gateway must accept them with the correct Content-Type rather than
+  // falling back to application/octet-stream.
+  assert.equal(isSupportedBridgeArtifactName('report.xlsb'), true);
+  assert.equal(
+    bridgeArtifactMediaType('report.xlsb'),
+    'application/vnd.ms-excel.sheet.binary.macroenabled.12',
+  );
 });
 
 test('linked-worktree lanes nest beneath their checkout key and conflict only with it', () => {
diff --git a/packages/code/src/protocol.ts b/packages/code/src/protocol.ts
index 1451986d..e6488c66 100644
--- a/packages/code/src/protocol.ts
+++ b/packages/code/src/protocol.ts
@@ -111,6 +111,7 @@ const BRIDGE_ARTIFACT_EXTENSIONS = new Set([
     '.pptx',
     '.xls',
     '.xlsx',
+    '.xlsb',
     '.odt',
     '.ods',
     '.odp',
@@ -241,8 +242,8 @@ const BRIDGE_ARTIFACT_MEDIA_TYPES: Readonly<Record<string, string>> = {
   '.woff': 'font/woff',
   '.woff2': 'font/woff2',
   '.xls': 'application/vnd.ms-excel',
-    '.xlsx':
-        'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
+  '.xlsx': 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
+  '.xlsb': 'application/vnd.ms-excel.sheet.binary.macroenabled.12',
   '.xml': 'application/xml',
   '.yaml': 'application/yaml',
   '.yml': 'application/yaml',