diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index 72d233bbb..3e2121269 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -172,7 +172,7 @@ jobs:
           nix flake check ./platform --no-build --show-trace
 
   flux-kustomize-check:
-    name: Flux kustomize build
+    name: Flux manifests
     needs: changes
     if: needs.changes.outputs.code == 'true'
     runs-on: ubuntu-latest
@@ -186,19 +186,22 @@ jobs:
         with:
           version: v1.34.0
 
-      - name: Render every flux overlay to catch schema / ordering bugs
+      - name: Install kubeconform
+        env:
+          KUBECONFORM_VERSION: v0.8.0
         run: |
           set -euo pipefail
-          for overlay in \
-            platform/cluster/flux/clusters/production \
-            platform/cluster/flux/apps/core \
-            platform/cluster/flux/apps/edge \
-            platform/cluster/flux/apps/utility-system
-          do
-            echo "::group::kustomize build $overlay"
-            kubectl kustomize "$overlay" > /dev/null
-            echo "::endgroup::"
-          done
+          curl -fsSL "https://github.com/yannh/kubeconform/releases/download/${KUBECONFORM_VERSION}/kubeconform-linux-amd64.tar.gz" \
+            | tar -xz -C /usr/local/bin kubeconform
+          kubeconform -v
+
+      # Before trusting a green validation run, prove the validator can still
+      # fail: it checks a deliberately broken Canary and expects a rejection.
+      - name: Prove the schema check can fail
+        run: ./scripts/check-flux-manifests.sh --self-test
+
+      - name: Build every flux overlay and validate it against real schemas
+        run: ./scripts/check-flux-manifests.sh
 
   fe-static:
     # Also the bundle build: the system tests serve this artifact with
diff --git a/scripts/check-flux-manifests.sh b/scripts/check-flux-manifests.sh
new file mode 100755
index 000000000..a560eb382
--- /dev/null
+++ b/scripts/check-flux-manifests.sh
@@ -0,0 +1,205 @@
+#!/usr/bin/env bash
+#
+# Builds every Flux overlay and validates the rendered objects against real
+# schemas, including the CRDs the charts install.
+#
+# The overlay list is derived from the Flux Kustomization CRs rather than
+# written here, so a path CI builds and a path the cluster applies cannot drift.
+# A directory that no Kustomization CR points at is reported as uncovered: it is
+# either dead or about to be applied by nobody.
+#
+# Requires: kubectl, kubeconform, python3.
+set -euo pipefail
+
+FLUX_ROOT=${FLUX_ROOT:-platform/cluster/flux}
+CATALOG=${CATALOG:-https://raw.githubusercontent.com/datreeio/CRDs-catalog/main}
+
+# Kinds whose schema must actually be found. kubeconform skips a resource it has
+# no schema for, and a skip is silent, so without this list the CRDs we most
+# want checked would pass by not being checked at all.
+REQUIRED_KINDS=${REQUIRED_KINDS:-Canary,IngressRoute,Middleware,VaultStaticSecret,HelmRelease,HelmRepository,Kustomization,GitRepository}
+
+command -v kubectl >/dev/null || { echo "::error::kubectl not found"; exit 1; }
+command -v kubeconform >/dev/null || { echo "::error::kubeconform not found"; exit 1; }
+
+RENDER_DIR=$(mktemp -d)
+trap 'rm -rf "$RENDER_DIR"' EXIT
+
+# -strict rejects unknown fields, which is what turns a misspelled Canary key
+# into a failed build rather than a field the cluster silently ignores.
+# -verbose because the JSON report otherwise lists only failures, and the
+# summary below needs to see which kinds were validated and which were skipped
+# for want of a schema.
+validate() {
+  kubeconform \
+    -strict \
+    -verbose \
+    -ignore-missing-schemas \
+    -schema-location default \
+    -schema-location "$CATALOG/{{.Group}}/{{.ResourceKind}}_{{.ResourceAPIVersion}}.json" \
+    "$@"
+}
+
+# `--self-test` proves the gate can still fail. A validator that has quietly
+# stopped validating — a lost schema location, an -ignore flag too many — passes
+# every real manifest, so the only way to trust a green run is to keep one
+# manifest that must go red. The fixture lives here rather than in the Flux tree,
+# where an intentionally invalid Canary would read as a mistake.
+if [[ ${1:-} == "--self-test" ]]; then
+  cat > "$RENDER_DIR/bad-canary.yaml" <<'EOF'
+apiVersion: flagger.app/v1beta1
+kind: Canary
+metadata:
+  name: deliberately-broken
+  namespace: default
+spec:
+  provider: kubernetes
+  targetRef:
+    apiVersion: apps/v1
+    kind: Deployment
+    name: api
+  service:
+    port: "8080"
+  analysis:
+    interval: 30s
+    iterations: 4
+    thresholdd: 3
+EOF
+  if validate "$RENDER_DIR/bad-canary.yaml" > "$RENDER_DIR/self-test.log" 2>&1; then
+    echo "::error::the validator accepted a Canary with a misspelled key and a string port; it is not validating CRDs"
+    cat "$RENDER_DIR/self-test.log"
+    exit 1
+  fi
+  echo "Self-test: a malformed Canary is rejected, as it should be."
+  sed 's/^/  /' "$RENDER_DIR/self-test.log"
+  exit 0
+fi
+
+[[ -d "$FLUX_ROOT" ]] || { echo "::error::$FLUX_ROOT not found; run this from the repository root"; exit 1; }
+
+# 1. The paths Flux actually applies. Written to a file rather than read through
+# a process substitution, so a YAML parse error fails the run instead of being
+# swallowed into an empty list.
+python3 - "$FLUX_ROOT" > "$RENDER_DIR/paths.txt" <<'PY'
+import os, posixpath, sys, yaml
+root = sys.argv[1]
+paths = set()
+for dirpath, _, files in os.walk(root):
+    for f in files:
+        if not f.endswith((".yaml", ".yml")):
+            continue
+        full = os.path.join(dirpath, f)
+        try:
+            docs = list(yaml.safe_load_all(open(full)))
+        except yaml.YAMLError as e:
+            print(f"::error file={full}::unparseable YAML: {e}", file=sys.stderr)
+            sys.exit(1)
+        for d in docs:
+            if not isinstance(d, dict):
+                continue
+            if d.get("kind") != "Kustomization":
+                continue
+            if not str(d.get("apiVersion", "")).startswith("kustomize.toolkit.fluxcd.io/"):
+                continue
+            p = (d.get("spec") or {}).get("path")
+            if p:
+                # normpath, not lstrip("./"): lstrip removes any leading '.' or
+                # '/' character, which would eat the first segment of a path
+                # into a dot-named directory.
+                paths.add(posixpath.normpath(p))
+for p in sorted(paths):
+    print(p)
+PY
+
+mapfile -t PATHS < "$RENDER_DIR/paths.txt"
+
+if [[ ${#PATHS[@]} -eq 0 ]]; then
+  echo "::error::no Flux Kustomization paths found under $FLUX_ROOT"
+  exit 1
+fi
+
+# 2. Build each one.
+echo "Overlays declared by Flux Kustomization CRs: ${#PATHS[@]}"
+for overlay in "${PATHS[@]}"; do
+  if [[ ! -d "$overlay" ]]; then
+    echo "::error::a Kustomization CR points at $overlay, which does not exist"
+    exit 1
+  fi
+  echo "::group::kustomize build $overlay"
+  out="$RENDER_DIR/$(echo "$overlay" | tr '/' '_').yaml"
+  kubectl kustomize "$overlay" > "$out"
+  printf '%s  %s objects\n' "$overlay" "$(grep -c '^kind:' "$out" || true)"
+  echo "::endgroup::"
+done
+
+# 3. Every buildable app directory must be covered by one of those paths.
+UNCOVERED=0
+for dir in "$FLUX_ROOT"/apps/*/ "$FLUX_ROOT"/clusters/*/; do
+  dir=${dir%/}
+  [[ -f "$dir/kustomization.yaml" ]] || continue
+  covered=0
+  for overlay in "${PATHS[@]}"; do
+    [[ "$dir" == "$overlay" ]] && covered=1 && break
+  done
+  if [[ $covered -eq 0 ]]; then
+    echo "::error::$dir builds but no Flux Kustomization CR applies it"
+    UNCOVERED=1
+  fi
+done
+[[ $UNCOVERED -eq 0 ]] || exit 1
+
+# 4. Validate the rendered objects.
+echo "::group::kubeconform"
+set +e
+validate -output json "$RENDER_DIR"/*.yaml > "$RENDER_DIR/report.json"
+KC=$?
+set -e
+echo "::endgroup::"
+
+# 5. Report what was checked, and fail on anything invalid or on a required kind
+# that had no schema to check against.
+python3 - "$RENDER_DIR/report.json" "$REQUIRED_KINDS" "$KC" <<'PY'
+import collections, json, sys
+
+report, required_csv, kc = sys.argv[1], sys.argv[2], int(sys.argv[3])
+required = {k.strip() for k in required_csv.split(",") if k.strip()}
+data = json.load(open(report))
+
+by_status = collections.defaultdict(collections.Counter)
+problems = []
+for r in data.get("resources", []):
+    status = r.get("status", "unknown")
+    by_status[status][r.get("kind", "?")] += 1
+    if status in ("statusInvalid", "statusError"):
+        problems.append(f"{r.get('kind')}/{r.get('name')}: {r.get('msg')}")
+
+validated = by_status["statusValid"]
+skipped = by_status["statusSkipped"]
+
+print("validated:")
+for kind, n in sorted(validated.items()):
+    print(f"  {kind} x{n}")
+if skipped:
+    print("no schema, not checked:")
+    for kind, n in sorted(skipped.items()):
+        print(f"  {kind} x{n}")
+
+failed = False
+for line in problems:
+    print(f"::error::{line}")
+    failed = True
+
+missing = required & set(skipped)
+if missing:
+    print(f"::error::no schema found for required kind(s): {', '.join(sorted(missing))}")
+    failed = True
+
+unseen = required - set(validated) - set(skipped)
+if unseen:
+    print(f"::notice::required kind(s) not present in any overlay: {', '.join(sorted(unseen))}")
+
+if failed or (kc != 0 and not problems):
+    sys.exit(1)
+PY
+
+echo "Flux manifests build and validate."