diff --git a/tests/test_content_packs_vst.py b/tests/test_content_packs_vst.py
index 8204f8c9..f1071d03 100644
--- a/tests/test_content_packs_vst.py
+++ b/tests/test_content_packs_vst.py
@@ -89,3 +89,30 @@ def test_unknown_platform_rejected(tmp_path):
         assert "unknown platform" in str(e)
     else:
         raise AssertionError("build_vst_pack accepted an unknown platform")
+
+
+def test_repo_flag_reaches_both_publish_target_and_manifest_url(tmp_path, monkeypatch):
+    # Load-bearing invariant: --repo must reach BOTH the upload target and the URL
+    # written into the manifest. If it reaches only one, a pack is downloaded from
+    # a repo it was never uploaded to → every client 404s. Capture the publish
+    # repo and assert the emitted manifest URL points at the same one.
+    import json
+
+    root = tmp_path / "vst"
+    _fake_vst_tree(root)
+    published_to = []
+    monkeypatch.setattr(
+        content_packs, "_publish_release",
+        lambda tag, zip_path, title, notes, repo=content_packs.REPO: published_to.append(repo))
+
+    manifest_path = tmp_path / "manifest.json"
+    rc = content_packs.main([str(root), "--vst", "--publish",
+                             "--repo", "acme/widgets", "--manifest", str(manifest_path)])
+    assert rc == 0
+    manifest = json.loads(manifest_path.read_text())
+
+    # Uploaded to acme/widgets for every platform...
+    assert set(published_to) == {"acme/widgets"}, published_to
+    # ...and every manifest URL points at that same repo (not the default core).
+    for plat, entry in manifest.items():
+        assert "/acme/widgets/releases/download/" in entry["url"], (plat, entry["url"])
diff --git a/tools/content_packs.py b/tools/content_packs.py
index 759905bc..d428e768 100644
--- a/tools/content_packs.py
+++ b/tools/content_packs.py
@@ -201,6 +201,12 @@ def main(argv=None) -> int:
                     help="slice one rig VST root (src[0]) into per-platform "
                          "vst-<plat>-v<N> packs; manifest keyed by platform "
                          "(the shape rig_builder's data/vst_packs.json wants)")
+    ap.add_argument("--repo", default=REPO,
+                    help=f"GitHub repo to publish releases to AND reference in the "
+                         f"emitted manifest URLs (default {REPO}). The upload "
+                         f"target and the URL always use this same repo — a pack "
+                         f"is downloaded from whatever the manifest says, so they "
+                         f"must not diverge.")
     ap.add_argument("--manifest", type=Path,
                     help="write the {id: {url,sha256,bytes}} map here (default: stdout)")
     ap.add_argument("--selfcheck", action="store_true", help="run the round-trip demo and exit")
@@ -219,10 +225,13 @@ def main(argv=None) -> int:
             zip_path = out_dir / vst_asset(plat, args.version)
             build_vst_pack(vst_root, zip_path, plat)
             if args.publish:
+                # --repo MUST reach both, or the manifest advertises a repo the
+                # asset was never uploaded to (every client download 404s).
                 _publish_release(vst_tag(plat, args.version), zip_path,
                                  f"Rig VST pack ({plat}) v{args.version}",
-                                 "Opt-in per-platform rig VST pack. Not a code release.")
-                url = vst_url(plat, args.version)
+                                 "Opt-in per-platform rig VST pack. Not a code release.",
+                                 args.repo)
+                url = vst_url(plat, args.version, args.repo)
             else:
                 url = (out_dir.resolve() / zip_path.name).as_uri()
             manifest[plat] = manifest_entry(zip_path, url)
@@ -232,8 +241,8 @@ def main(argv=None) -> int:
             zip_path = out_dir / pack_asset(pid, args.version)
             build_pack(src, zip_path)
             if args.publish:
-                publish(pid, args.version, zip_path)
-                url = pack_url(pid, args.version)
+                publish(pid, args.version, zip_path, args.repo)
+                url = pack_url(pid, args.version, args.repo)
             else:
                 url = (out_dir.resolve() / zip_path.name).as_uri()
             manifest[pid] = manifest_entry(zip_path, url)