diff --git a/.github/workflows/test-plugins.yml b/.github/workflows/test-plugins.yml
index d9e4e8d3..4c7cbc9e 100644
--- a/.github/workflows/test-plugins.yml
+++ b/.github/workflows/test-plugins.yml
@@ -97,6 +97,27 @@ jobs:
           done
           exit $fail
 
+      # The floor the store and loader actually read is versions[0]. Requiring
+      # the new spelling only on plugins that are already being bumped lets the
+      # migration finish organically, instead of rewriting 42 manifests and
+      # pushing 42 store updates for a field rename with no behaviour change.
+      - name: Check manifest version fields on changed plugins
+        if: steps.changed.outputs.ids != '' && github.event.inputs.all != 'true'
+        working-directory: plugins-repo
+        env:
+          IDS: ${{ steps.changed.outputs.ids }}
+        run: |
+          for pid in $IDS; do
+            case "$pid" in
+              '' | *[!a-z0-9._-]*) echo "::error::invalid plugin id '$pid'"; exit 1 ;;
+            esac
+          done
+          python scripts/check_manifest_version_fields.py $IDS
+          # The gate's own regression suite -- its failure mode is silent,
+          # so a manifest that looks migrated but resolves to no floor must
+          # not slip through.
+          python scripts/test_check_manifest_version_fields.py
+
       - name: Validate manifests against schema
         if: steps.changed.outputs.ids != ''
         env:
diff --git a/plugins/baseball-scoreboard/manifest.json b/plugins/baseball-scoreboard/manifest.json
index 960359d8..bcbb72e0 100644
--- a/plugins/baseball-scoreboard/manifest.json
+++ b/plugins/baseball-scoreboard/manifest.json
@@ -33,7 +33,7 @@
     {
       "released": "2026-08-03",
       "version": "1.21.1",
-      "ledmatrix_min": "2.0.0"
+      "ledmatrix_min_version": "2.0.0"
     },
     {
       "released": "2026-08-02",
diff --git a/plugins/football-scoreboard/manifest.json b/plugins/football-scoreboard/manifest.json
index 0c1ed8ca..7cbea4f9 100644
--- a/plugins/football-scoreboard/manifest.json
+++ b/plugins/football-scoreboard/manifest.json
@@ -27,7 +27,7 @@
     {
       "released": "2026-08-03",
       "version": "2.10.1",
-      "ledmatrix_min": "2.0.0"
+      "ledmatrix_min_version": "2.0.0"
     },
     {
       "released": "2026-08-02",
diff --git a/scripts/check_manifest_version_fields.py b/scripts/check_manifest_version_fields.py
new file mode 100644
index 00000000..bb758cb8
--- /dev/null
+++ b/scripts/check_manifest_version_fields.py
@@ -0,0 +1,156 @@
+#!/usr/bin/env python3
+"""Require the *newest* versions[] entry to use `ledmatrix_min_version`.
+
+Run over changed plugins in CI, or over everything with `--all`:
+
+    python scripts/check_manifest_version_fields.py baseball-scoreboard news
+    python scripts/check_manifest_version_fields.py --all      # audit, non-gating
+
+## Why only the newest entry
+
+`PluginStoreManager` and `PluginLoader` resolve a plugin's floor through
+`src/plugin_system/compatibility.py:declared_min_version`, which reads
+`versions[0]` and accepts either spelling. So the deprecated `ledmatrix_min`
+costs nothing functionally, and the store's own deprecation check is
+warnings-only and reachable only from the sideload path.
+
+Rewriting all 42 manifests to the new spelling would therefore change no
+behaviour while forcing 42 version bumps — 42 store updates pushed to every
+user for a field rename. Instead this gate asks each plugin to migrate the one
+entry that is actually read, at a moment when it is already being bumped for
+other reasons. The migration completes as plugins release, and cannot slide
+backwards.
+
+Historical entries are left alone: nothing reads them, and rewriting shipped
+release records to satisfy a linter is worse than the inconsistency.
+"""
+
+from __future__ import annotations
+
+import argparse
+import json
+import sys
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+PLUGINS = REPO_ROOT / "plugins"
+
+NEW = "ledmatrix_min_version"
+OLD = "ledmatrix_min"
+
+
+def _declares_floor_elsewhere(manifest: dict) -> bool:
+    """Does the manifest declare a floor above the `versions[]` array?
+
+    The core's `compatibility.declared_min_version` checks, in order:
+    top-level `min_ledmatrix_version`, then `requires.min_ledmatrix_version`,
+    and only then `versions[0]`. Four published plugins — flights, leaderboard,
+    music and stocks — use the top-level form, so demanding the key in
+    `versions[0]` unconditionally would fail manifests that are already
+    correct, and push them into declaring the floor twice.
+    """
+    if manifest.get("min_ledmatrix_version"):
+        return True
+    requires = manifest.get("requires")
+    return isinstance(requires, dict) and bool(
+        requires.get("min_ledmatrix_version"))
+
+
+def check_plugin(plugin_id: str) -> list[str]:
+    """Problems with this plugin's newest version entry (empty when fine)."""
+    path = PLUGINS / plugin_id / "manifest.json"
+    if not path.exists():
+        return []  # not a monorepo plugin; nothing to say
+
+    try:
+        manifest = json.loads(path.read_text(encoding="utf-8"))
+    except (OSError, ValueError) as e:
+        return [f"{plugin_id}: manifest.json could not be read ({e})"]
+
+    versions = [v for v in (manifest.get("versions") or []) if isinstance(v, dict)]
+    if not versions:
+        return []
+
+    head = versions[0]
+    version_label = head.get("version", "?")
+    problems: list[str] = []
+
+    # Values, not key presence. The core resolves the floor with
+    # `head.get(NEW) or head.get(OLD)`, so an empty string or null under either
+    # key is no floor at all -- and a gate that accepted the key while the core
+    # saw nothing would pass exactly the manifests it exists to catch.
+    # `_declares_floor_elsewhere` already worked this way; this brings the
+    # versions[0] check into line with it.
+    new_value = head.get(NEW)
+    old_value = head.get(OLD)
+
+    if not new_value and old_value:
+        problems.append(
+            f"{plugin_id}: versions[0] ({version_label}) uses the deprecated "
+            f"'{OLD}'. Rename it to '{NEW}' — this is the entry the store and "
+            f"loader actually read. Older entries can stay as they are."
+        )
+    elif not new_value and not _declares_floor_elsewhere(manifest):
+        # Neither spelling in versions[0], and nothing above it either. The
+        # core's declared_min_version() then resolves to None, so the install
+        # gate has no floor to enforce and the plugin can reach a core that
+        # cannot run it — the exact failure the B6 sunset turns fatal.
+        problems.append(
+            f"{plugin_id}: versions[0] ({version_label}) declares no minimum "
+            f"core version, and neither does the manifest above it. Add "
+            f"'{NEW}' so the install gate has a floor to enforce."
+        )
+
+    # compatible_versions is required by the core's manifest schema and is the
+    # only field that can express an upper bound; a missing one means the gate
+    # has nothing authoritative to evaluate.
+    compatible = manifest.get("compatible_versions")
+    if not isinstance(compatible, list) or not compatible:
+        problems.append(
+            f"{plugin_id}: 'compatible_versions' is missing or empty. The core "
+            f"manifest schema requires it, and it is the field the install "
+            f"gate evaluates for upper bounds."
+        )
+
+    return problems
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("plugin_ids", nargs="*", help="Plugin ids to check")
+    parser.add_argument("--all", action="store_true",
+                        help="Audit every plugin; reports without failing")
+    args = parser.parse_args()
+
+    if args.all:
+        ids = sorted(p.name for p in PLUGINS.iterdir()
+                     if (p / "manifest.json").exists())
+    else:
+        ids = args.plugin_ids
+        if not ids:
+            print("No plugins to check.")
+            return 0
+
+    problems = [p for pid in ids for p in check_plugin(pid)]
+
+    if not problems:
+        print(f"OK: {len(ids)} plugin(s) checked, newest version entries are current.")
+        return 0
+
+    for problem in problems:
+        print(f"  - {problem}", file=sys.stderr)
+
+    if args.all:
+        print(f"\n{len(problems)} plugin(s) still to migrate — audit only, "
+              f"not failing. They migrate at their next version bump.",
+              file=sys.stderr)
+        return 0
+
+    print(f"\n{len(problems)} problem(s). These plugins are being changed "
+          f"anyway, so the fix is a one-line rename in the entry you just "
+          f"added.", file=sys.stderr)
+    return 1
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/scripts/test_check_manifest_version_fields.py b/scripts/test_check_manifest_version_fields.py
new file mode 100644
index 00000000..e6374a37
--- /dev/null
+++ b/scripts/test_check_manifest_version_fields.py
@@ -0,0 +1,124 @@
+#!/usr/bin/env python3
+"""Regression tests for the manifest version-field gate.
+
+The gate exists to guarantee the install gate has a floor to enforce. Its
+failure mode is silent: a manifest that *looks* migrated but resolves to no
+floor passes here, then reaches a core that cannot run it — which the B6
+sunset turns from a degraded plugin into one that will not load at all.
+
+So these pin the two things that are easy to get wrong:
+
+- **Values, not key presence.** The core resolves the floor with
+  ``head.get(NEW) or head.get(OLD)``. An empty string or ``null`` under either
+  key is no floor, and a gate checking only for the key would accept exactly
+  the manifests it exists to catch.
+- **The floor may legitimately live above ``versions[]``.** Four published
+  plugins declare a top-level ``min_ledmatrix_version``, which the core checks
+  *first*. Demanding the key inside ``versions[0]`` would fail manifests that
+  are already correct.
+
+Exit codes follow the convention in `run_plugin_tests.py`: 0 pass, 1 fail.
+"""
+
+import json
+import shutil
+import sys
+import tempfile
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parent))
+import check_manifest_version_fields as gate  # noqa: E402
+
+BASE = {"id": "p", "compatible_versions": [">=2.0.0"]}
+
+CLEAN, DEPRECATED, MISSING = "clean", "deprecated", "missing-floor"
+
+
+def classify(manifest):
+    """Run the gate over a synthetic manifest and bucket the outcome."""
+    root = Path(tempfile.mkdtemp())
+    (root / "p").mkdir()
+    (root / "p" / "manifest.json").write_text(json.dumps(manifest))
+    original = gate.PLUGINS
+    gate.PLUGINS = root
+    try:
+        problems = [p for p in gate.check_plugin("p")
+                    if "compatible_versions" not in p]
+    finally:
+        gate.PLUGINS = original
+        shutil.rmtree(root, ignore_errors=True)
+
+    if not problems:
+        return CLEAN
+    if "deprecated" in problems[0]:
+        return DEPRECATED
+    if "declares no minimum" in problems[0]:
+        return MISSING
+    return f"unexpected: {problems[0]}"
+
+
+def entry(**kwargs):
+    return {**BASE, "versions": [{"version": "1.0.0", **kwargs}]}
+
+
+CASES = [
+    # (label, manifest, expected)
+    ("new spelling with a value",
+     entry(ledmatrix_min_version="2.0.0"), CLEAN),
+    ("deprecated spelling with a value",
+     entry(ledmatrix_min="2.0.0"), DEPRECATED),
+
+    # The regression this file was added for: a present-but-empty key.
+    ('new spelling, empty string, no floor elsewhere',
+     entry(ledmatrix_min_version=""), MISSING),
+    ("new spelling, null, no floor elsewhere",
+     entry(ledmatrix_min_version=None), MISSING),
+    ('deprecated spelling, empty string, no floor elsewhere',
+     entry(ledmatrix_min=""), MISSING),
+    ("deprecated spelling, null, no floor elsewhere",
+     entry(ledmatrix_min=None), MISSING),
+
+    # An empty NEW alongside a real OLD is what the core's `or` falls through
+    # to, so it is a spelling problem rather than a missing floor.
+    ("empty new spelling but a valid deprecated one",
+     entry(ledmatrix_min_version="", ledmatrix_min="2.0.0"), DEPRECATED),
+
+    # The floor may live above versions[]; the core checks there first.
+    ("no floor in versions[0], top-level declares it",
+     {**BASE, "min_ledmatrix_version": "2.0.0", "versions": [{"version": "1.0.0"}]},
+     CLEAN),
+    ("no floor in versions[0], requires{} declares it",
+     {**BASE, "requires": {"min_ledmatrix_version": "2.0.0"},
+      "versions": [{"version": "1.0.0"}]}, CLEAN),
+    ("empty key in versions[0], top-level declares it",
+     {**BASE, "min_ledmatrix_version": "2.0.0",
+      "versions": [{"version": "1.0.0", "ledmatrix_min_version": ""}]}, CLEAN),
+    ("top-level present but empty, nothing else",
+     {**BASE, "min_ledmatrix_version": "",
+      "versions": [{"version": "1.0.0"}]}, MISSING),
+
+    ("no floor anywhere", entry(), MISSING),
+]
+
+
+def main() -> int:
+    failures = []
+    for label, manifest, expected in CASES:
+        got = classify(manifest)
+        ok = got == expected
+        print(f"  [{'pass' if ok else 'FAIL'}] {label:52} -> {got}")
+        if not ok:
+            failures.append(f"{label}: expected {expected}, got {got}")
+
+    print()
+    if failures:
+        print(f"{len(failures)} failure(s):", file=sys.stderr)
+        for f in failures:
+            print(f"  - {f}", file=sys.stderr)
+        return 1
+    print(f"All {len(CASES)} cases passed.")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())