diff --git a/.agents/docs/2026-07-08-index-side-adoption-plan.md b/.agents/docs/2026-07-08-index-side-adoption-plan.md
new file mode 100644
index 0000000..a938ca6
--- /dev/null
+++ b/.agents/docs/2026-07-08-index-side-adoption-plan.md
@@ -0,0 +1,90 @@
+# Index-side adoption plan — mcpp 0.0.85 train (floor, strict lint, scan_overrides, long brackets)
+
+Companion to mcpp repo
+`.agents/docs/2026-07-08-descriptor-index-evolution-roadmap.md` (master) and
+its two design docs (same date). This doc is the mcpp-index execution detail.
+
+Rule of the whole rollout: **floor first, new grammar/keys after** — enforced
+mechanically by lint once P1 lands (lint parses with the pinned mcpp; before
+the pin reaches 0.0.85, new-grammar descriptors cannot merge).
+
+---
+
+## P0 — merge PR #63 as-is (pre-train)
+
+fmt 12.2.0 via `generated_files` works on today's 0.0.81 (verified locally
+2026-07-08: lint pass, sha256 match, member test green, generated file = 
+upstream `src/fmt.cc` minus exactly the `import std;` guard). Don't couple it
+to the train; migrate it in P2.
+
+## P1 — floor PR (single atomic PR)
+
+1. `index.toml` at repo root:
+
+   ```toml
+   [index]
+   spec        = "1"
+   min_mcpp    = "0.0.85"
+   latest_mcpp = "0.0.85"
+   ```
+
+2. `.github/workflows/validate.yml`: `MCPP_VERSION` 0.0.81 → 0.0.85.
+3. lint job: add the pinned-mcpp download step (same snippet as the workspace
+   job) and run `mcpp xpkg parse --strict` over changed (PR) / all (push,
+   nightly) descriptors — **in addition to** the existing `lua5.4 loadfile`
+   check (the xim side executes real Lua; both grammars stay guarded).
+4. `tools/publish_mcpp_index.sh`: pack `index.toml` into the artifact tree
+   (one `cp` next to the existing `pkgs/` copy). Pointer untouched.
+5. `docs/repository-and-schema.md`: floor paragraph (what breaks for
+   pre-0.0.85 clients, why now).
+
+## P2 — fmt: generated_files → scan_overrides
+
+`pkgs/f/fmtlib.fmt.lua` descriptor `mcpp` segment becomes:
+
+```lua
+mcpp = {
+    schema       = "0.1",
+    language     = "c++23",
+    import_std   = true,
+    modules      = { "fmt" },
+    include_dirs = { "*/include", "*/src" },
+    sources      = { "*/src/fmt.cc" },        -- upstream file, verbatim
+    cxxflags     = { "-DFMT_IMPORT_STD" },
+    scan_overrides = {
+        ["*/src/fmt.cc"] = { provides = { "fmt" }, imports = { "std" } },
+    },
+    targets      = { ["fmt"] = { kind = "lib" } },
+}
+```
+
+- Deletes the 3.4 KB escaped `generated_files` copy entirely.
+- `tests/examples/fmtlib.fmt/` member unchanged — it is the live CI proof
+  (also the matrix's first `import_std = true` package build on mac/win).
+- mcpp-side reconciliation (mandatory for override files) audits the declared
+  `(provides, imports)` against the compiler's `.ddi` every build.
+
+## P3 — long-bracket migrations (one PR per package)
+
+`pkgs/n/nlohmann.json.lua`, `pkgs/c/compat.eigen.lua`: `generated_files`
+escaped strings → `[==[ … ]==]`. Mechanical; reviewer checks the parity
+oracle output (content via lua5.4 == content via `mcpp xpkg parse --json`),
+which the lint step re-verifies anyway.
+
+## P4 — docs refresh
+
+`docs/repository-and-schema.md`:
+- replace "`generated_files` … 不支持 `[[…]]`" with: long brackets require
+  mcpp ≥ 0.0.85 (index floor guarantees this; lint enforces).
+- new row in the case-index table: "guarded-import module unit →
+  `scan_overrides`" pointing at `pkgs/f/fmtlib.fmt.lua` post-P2.
+- mention `mcpp xpkg parse --strict` as the local reproduction of lint.
+
+## Verification / rollback
+
+- Every PR rides the existing `mcpp test --workspace` 3-OS matrix.
+- P1 is the only PR with blast radius (floor + version bump together): if
+  0.0.85 misbehaves in CI, revert P1 alone restores the 0.0.81 world; P2/P3
+  cannot have merged yet (lint gate).
+- CN mirror for fmt (from PR #63 review) remains a separate follow-up via
+  gtc/mcpp-res — unrelated to this train.
diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index 32bef31..a23f2ad 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -13,7 +13,7 @@ on:
 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: "0.0.81"
+  MCPP_VERSION: "0.0.85"
 
 jobs:
   lint:
@@ -59,6 +59,30 @@ jobs:
           done
           [ $fail -eq 0 ] && echo "All package files valid."
           exit $fail
+      # ── Single-source-of-truth grammar check ─────────────────────────
+      # `mcpp xpkg parse` uses EXACTLY the resolver's parser, so what
+      # passes here is what builds for users of the pinned MCPP_VERSION.
+      # Strict by default: unknown mcpp-segment keys fail (they would be
+      # silently ignored at build time). This also mechanically enforces
+      # the rollout rule "floor first, new grammar after": descriptors
+      # needing a newer grammar cannot pass a lint pinned to an older mcpp.
+      - name: Download pinned mcpp
+        run: |
+          curl -L -fsS -o mcpp.tar.gz \
+            "https://github.com/mcpp-community/mcpp/releases/download/v${MCPP_VERSION}/mcpp-${MCPP_VERSION}-linux-x86_64.tar.gz"
+          tar -xzf mcpp.tar.gz
+          echo "MCPP=$PWD/mcpp-${MCPP_VERSION}-linux-x86_64/bin/mcpp" >> "$GITHUB_ENV"
+      - name: Parse descriptors with the resolver grammar (mcpp xpkg parse)
+        run: |
+          fail=0
+          for f in pkgs/*/*.lua; do
+            if ! "$MCPP" xpkg parse "$f" > /dev/null; then
+              echo "::error file=$f::mcpp xpkg parse failed (resolver grammar)"
+              fail=1
+            fi
+          done
+          [ $fail -eq 0 ] && echo "All descriptors parse with mcpp ${MCPP_VERSION}."
+          exit $fail
 
   mirror-cn-reachable:
     # Closed-loop guard for the CN mirror: every CN url referenced by a
@@ -111,20 +135,20 @@ jobs:
         include:
           - platform: linux
             os: ubuntu-latest
-            archive: mcpp-0.0.81-linux-x86_64.tar.gz
-            root: mcpp-0.0.81-linux-x86_64
+            archive: mcpp-0.0.85-linux-x86_64.tar.gz
+            root: mcpp-0.0.85-linux-x86_64
             mcpp: bin/mcpp
             xlings: registry/bin/xlings
           - platform: macos
             os: macos-15
-            archive: mcpp-0.0.81-macosx-arm64.tar.gz
-            root: mcpp-0.0.81-macosx-arm64
+            archive: mcpp-0.0.85-macosx-arm64.tar.gz
+            root: mcpp-0.0.85-macosx-arm64
             mcpp: bin/mcpp
             xlings: registry/bin/xlings
           - platform: windows
             os: windows-latest
-            archive: mcpp-0.0.81-windows-x86_64.zip
-            root: mcpp-0.0.81-windows-x86_64
+            archive: mcpp-0.0.85-windows-x86_64.zip
+            root: mcpp-0.0.85-windows-x86_64
             mcpp: bin/mcpp.exe
             xlings: registry/bin/xlings.exe
     steps:
diff --git a/docs/repository-and-schema.md b/docs/repository-and-schema.md
index 9e998d5..8fff690 100644
--- a/docs/repository-and-schema.md
+++ b/docs/repository-and-schema.md
@@ -47,13 +47,26 @@ tools/gtc                    gitcode CLI,见 cn-mirror.md
 | `c_standard` | C 源码:`"c99"` 或 `"c11"` |
 | `modules` | module 库:`{ "x.y" }` |
 | `include_dirs` | glob 列表,暴露给消费者的头目录 |
-| `generated_files` | `{ ["相对路径"]="内容字符串" }`;不支持 `[[…]]`,须以 `\n`、`\"` 转义 |
+| `generated_files` | `{ ["相对路径"]="内容字符串" }`;mcpp ≥ 0.0.85 支持 Lua 长括号 `[==[…]==]` 多行字符串(推荐,可读可 review);转义单行串仍兼容 |
+| `scan_overrides` | `{ ["glob"]={ provides={…}, imports={…} } }`;声明式扫描结果,命中文件跳过 M1 文本扫描(适用于带条件 import 守卫的上游模块单元,如 fmt 的 src/fmt.cc);构建期由编译器 P1689 输出自动对账,声明错误响亮失败(mcpp ≥ 0.0.85)|
 | `sources` | glob 列表,编入 lib 的源码 |
 | `cflags` / `cxxflags` / `ldflags` | 追加至对应规则 |
 | `targets` | `{ ["name"]={ kind="lib"/"bin", main=…, soname=… } }` |
 | `features` | `{ ["f"]={ sources={…} } }`,仅识别 sources |
 | `deps` | `{ ["ns.name"]="ver" }`,扁平或点号式 |
 
+## index 版本契约(index.toml)
+
+仓库根的 `index.toml` 声明 `[index] min_mcpp` —— 能解析本索引全部描述符的最老
+mcpp 版本。契约随树旅行:`publish_mcpp_index.sh` 把它打进 artifact,git clone 与
+`[indices] path =` 本地索引天然携带。mcpp ≥ 0.0.85 在打开索引树时检查,违反时报
+`E0006` + 升级指引(调试逃生口 `MCPP_INDEX_FLOOR=ignore`)。
+
+规则(由 lint 机械强制,非纪律):**floor 先行、新文法在后**——lint 用 CI pin 的
+mcpp 跑 `xpkg parse`(strict:未知键即失败),所以需要更新文法/键的描述符在
+`MCPP_VERSION` 与 `min_mcpp` 同步提升之前物理上合不进 main。本地复现:
+`mcpp xpkg parse pkgs/<x>/<name>.lua`。
+
 ## CI 行为(validate.yml)
 
 - 触发条件:PR(改动 `pkgs/**/*.lua`、`tests/**`、`README.md` 或本 workflow)、push 至 main、nightly cron、手动触发。
diff --git a/index.toml b/index.toml
new file mode 100644
index 0000000..3230b75
--- /dev/null
+++ b/index.toml
@@ -0,0 +1,11 @@
+# Index→client version contract (design: mcpp .agents/docs/2026-07-08-index-
+# version-semantics-and-descriptor-grammar-design.md D3). The contract travels
+# WITH the index tree: packed into the artifact, present in git checkouts and
+# path-indices alike. mcpp >= 0.0.85 checks it at the index-open choke point
+# (E0006 on violation). Bump min_mcpp ONLY together with the CI MCPP_VERSION
+# pin — lint parses descriptors with the pinned mcpp, which enforces the
+# "floor first, new grammar after" rollout rule mechanically.
+[index]
+spec        = "1"
+min_mcpp    = "0.0.85"
+latest_mcpp = "0.0.85"
diff --git a/tools/publish_mcpp_index.sh b/tools/publish_mcpp_index.sh
index 58eeec3..a157b2f 100755
--- a/tools/publish_mcpp_index.sh
+++ b/tools/publish_mcpp_index.sh
@@ -25,6 +25,9 @@ info() { echo "[mcpp-index] $*"; }
 TREE="$OUT/tree"; mkdir -p "$TREE"
 cp -a "$SRC/pkgs" "$TREE/"
 [ -f "$SRC/README.md" ] && cp "$SRC/README.md" "$TREE/" || true
+# index.toml carries the index→client version contract (min_mcpp floor);
+# it must travel with the tree so unpacked snapshots enforce it offline.
+[ -f "$SRC/index.toml" ] && cp "$SRC/index.toml" "$TREE/" || true
 tar --sort=name --owner=0 --group=0 --numeric-owner -czf "$OUT/$BASE.tar.gz" -C "$TREE" . 2>/dev/null \
   || tar -czf "$OUT/$BASE.tar.gz" -C "$TREE" .
 SHA="$(sha256sum "$OUT/$BASE.tar.gz" | awk '{print $1}')"