diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index 6762221..30b5467 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -11,9 +11,11 @@ on:
   workflow_dispatch:
 
 env:
-  # Bumped to 0.0.78: carries L3 build.mcpp native build program (build-mcpp member),
-  # compat.openblas Windows recipe (bin/libopenblas.dll staged beside the .exe).
-  MCPP_VERSION: "0.0.87"
+  # Bumped to 0.0.91: carries standard = "c++fly" (experimental playground
+  # mode) in the resolver grammar — required so descriptors declaring it get
+  # the lint WARN below instead of a hard grammar-parse rejection from an
+  # older pinned mcpp (admission policy: warn, don't reject).
+  MCPP_VERSION: "0.0.91"
 
 jobs:
   lint:
@@ -56,6 +58,17 @@ jobs:
             if ! lua5.4 tests/check_mirror_urls.lua "$f"; then
               fail=1
             fi
+            # 5. c++fly admission policy (mcpp design 2026-07-14 §11-Q2, v1):
+            #    c++fly means "toolchain's latest level + every experimental
+            #    gate" — deliberately toolchain-dependent, so a published
+            #    package built with it is not reproducible for consumers.
+            #    Policy: WARN (never fail) and observe ecosystem usage before
+            #    deciding whether to tighten. Two spellings: `language = ` is
+            #    the descriptor's inline mcpp-segment key; `standard = ` covers
+            #    mcpp.toml content embedded in heredoc/generated_files blocks.
+            if grep -nE '\b(language|standard)[[:space:]]*=[[:space:]]*"c\+\+fly"' "$f" >/dev/null; then
+              echo "::warning file=$f::declares C++ standard \"c++fly\" (experimental playground mode) — toolchain-dependent and non-reproducible for consumers; published packages should pin a concrete standard (c++23/c++26)"
+            fi
           done
           [ $fail -eq 0 ] && echo "All package files valid."
           exit $fail
@@ -133,22 +146,25 @@ jobs:
       fail-fast: false
       matrix:
         include:
+          # Archive names are derived from env.MCPP_VERSION in the Download
+          # step — bumping the pin is a ONE-line change (hardcoded versions
+          # here once 404'd a pin bump).
           - platform: linux
             os: ubuntu-latest
-            archive: mcpp-0.0.87-linux-x86_64.tar.gz
-            root: mcpp-0.0.87-linux-x86_64
+            suffix: linux-x86_64
+            ext: tar.gz
             mcpp: bin/mcpp
             xlings: registry/bin/xlings
           - platform: macos
             os: macos-15
-            archive: mcpp-0.0.87-macosx-arm64.tar.gz
-            root: mcpp-0.0.87-macosx-arm64
+            suffix: macosx-arm64
+            ext: tar.gz
             mcpp: bin/mcpp
             xlings: registry/bin/xlings
           - platform: windows
             os: windows-latest
-            archive: mcpp-0.0.87-windows-x86_64.zip
-            root: mcpp-0.0.87-windows-x86_64
+            suffix: windows-x86_64
+            ext: zip
             mcpp: bin/mcpp.exe
             xlings: registry/bin/xlings.exe
     steps:
@@ -165,8 +181,8 @@ jobs:
       - name: Download mcpp
         shell: bash
         env:
-          MCPP_ARCHIVE: ${{ matrix.archive }}
-          MCPP_ROOT: ${{ matrix.root }}
+          MCPP_ARCHIVE: mcpp-${{ env.MCPP_VERSION }}-${{ matrix.suffix }}.${{ matrix.ext }}
+          MCPP_ROOT: mcpp-${{ env.MCPP_VERSION }}-${{ matrix.suffix }}
         run: |
           curl -L -fsS -o "$MCPP_ARCHIVE" \
             "https://github.com/mcpp-community/mcpp/releases/download/v${MCPP_VERSION}/${MCPP_ARCHIVE}"