diff --git a/crates/cli/src/commands/install/loader.rs b/crates/cli/src/commands/install/loader.rs
index 4a7fb7c..630f275 100644
--- a/crates/cli/src/commands/install/loader.rs
+++ b/crates/cli/src/commands/install/loader.rs
@@ -26,8 +26,8 @@ use unlucky_core::game::install::execute;
 
 use super::report_loader::ProcessorSection;
 use super::{
-    build_engine, ensure_name_free, failure_error, loader_processors, map_install_error,
-    register_instance, report, report_loader, vanilla, CONCURRENCY,
+    build_engine, ensure_name_free, failure_error, loader_processors, map_install_error, progress,
+    register_instance, report_loader, vanilla, CONCURRENCY,
 };
 use crate::cli::InstallArgs;
 use crate::context::Ctx;
@@ -119,7 +119,7 @@ pub(super) fn run(ctx: &Ctx, args: &InstallArgs, kind: LoaderKind) -> Result<Rep
         }
     }
 
-    let sink = report::progress_sink(args.progress, args.json_progress, plan.files().len());
+    let sink = progress::progress_sink(args.progress, args.json_progress, plan.files().len());
     let install_report = block_on(execute(&engine, &plan.install, CONCURRENCY, sink))
         .map_err(|error| map_install_error(&error, ctx))?;
     if !install_report.is_complete() {
diff --git a/crates/cli/src/commands/install/loader_processors.rs b/crates/cli/src/commands/install/loader_processors.rs
index 60d1347..f609a88 100644
--- a/crates/cli/src/commands/install/loader_processors.rs
+++ b/crates/cli/src/commands/install/loader_processors.rs
@@ -25,7 +25,7 @@ use unlucky_core::download::DownloadEngine;
 use unlucky_core::game::arguments::Environment;
 use unlucky_core::game::install::InstallReport;
 
-use super::{failure_error, report, CONCURRENCY};
+use super::{failure_error, progress, CONCURRENCY};
 use crate::cli::InstallArgs;
 use crate::context::Ctx;
 use crate::error::CliError;
@@ -86,7 +86,7 @@ pub(super) fn execute(
     plan: &ProcessorPlan,
     args: &InstallArgs,
 ) -> Result<(InstallReport, ProcessorRun), CliError> {
-    let sink = report::progress_sink(args.progress, args.json_progress, plan.libraries.len());
+    let sink = progress::progress_sink(args.progress, args.json_progress, plan.libraries.len());
     let libraries = block_on(processors::download_libraries(
         engine,
         &plan.libraries,
diff --git a/crates/cli/src/commands/install/mod.rs b/crates/cli/src/commands/install/mod.rs
index 16452d3..fcd31f2 100644
--- a/crates/cli/src/commands/install/mod.rs
+++ b/crates/cli/src/commands/install/mod.rs
@@ -12,6 +12,7 @@
 
 mod loader;
 mod loader_processors;
+mod progress;
 mod report;
 mod report_loader;
 mod vanilla;
diff --git a/crates/cli/src/commands/install/progress.rs b/crates/cli/src/commands/install/progress.rs
new file mode 100644
index 0000000..204b2f7
--- /dev/null
+++ b/crates/cli/src/commands/install/progress.rs
@@ -0,0 +1,300 @@
+//! stderr 实时进度（原版安装 / 加载器库 / processor 依赖库三段共用）。
+//!
+//! **M210/D11 的教训**：进度行的数字必须是**已经发生的事实**（每个文件的 [`FileStatus`]），
+//! 不能拿「处理到第几个文件」冒充「下载了几个」。旧实现在回调里只累加一个 `done` 就打印
+//! `下载 {done}/{total}`，于是重装同版本（3961 个文件全部已就绪、一个字节都没下）时会连打
+//! `下载 32/3961 … 3961/3961`——进度条在跑，下载量是 0，用户在读一句假话。
+//!
+//! 现在分三个计数（下载 / 跳过 / 失败），人读行的措辞随计数走：下载数为 0 时**不出现「下载」
+//! 二字**，改说「已就绪 N/M（跳过 N 个）」。
+
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::Arc;
+
+use unlucky_core::game::install::{FileOutcome, FileStatus, ProgressSink};
+
+use crate::output::progress_line;
+
+/// 每处理多少个文件打一行进度（3000 个资源下约 90 行，够用又不刷屏）。
+const PROGRESS_EVERY: usize = 32;
+
+/// 进度里最多逐条打印几条失败（其余交给最终错误汇总）。
+const MAX_PROGRESS_FAILURES: usize = 5;
+
+/// 一次进度快照：每个字段都是**真实结局**的计数。
+#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
+pub(crate) struct Snapshot {
+    /// 已处理文件数（含跳过与失败）。
+    pub done: usize,
+    /// 计划文件总数。
+    pub total: usize,
+    /// 本次真的下载并落盘的文件数。
+    pub downloaded: usize,
+    /// 已存在且校验通过、本次跳过的文件数。
+    pub skipped: usize,
+    /// 失败文件数。
+    pub failed: usize,
+}
+
+impl Snapshot {
+    /// 人读进度行。
+    ///
+    /// 下载数为 0 时**不提「下载」**：本次一个字节都没下，再写「下载 0/N」也只是换个说法的假进度。
+    pub(crate) fn text(&self) -> String {
+        let failure = if self.failed > 0 {
+            format!(" / 失败 {}", self.failed)
+        } else {
+            String::new()
+        };
+        if self.downloaded == 0 {
+            format!(
+                "已就绪 {}/{}（跳过 {} 个{failure}）",
+                self.done, self.total, self.skipped
+            )
+        } else {
+            format!(
+                "下载 {} 个 / 跳过 {} 个（进度 {}/{}{failure}）",
+                self.downloaded, self.skipped, self.done, self.total
+            )
+        }
+    }
+
+    /// `--json` 模式的进度事件（字段名稳定，`done`/`total` 保持旧名以兼容脚本）。
+    fn json(&self) -> serde_json::Value {
+        serde_json::json!({
+            "event": "progress",
+            "done": self.done,
+            "total": self.total,
+            "downloaded": self.downloaded,
+            "skipped": self.skipped,
+            "failed": self.failed,
+        })
+    }
+}
+
+/// 计数：回调来自多个下载线程，全部原子累加。
+#[derive(Debug, Default)]
+struct Tally {
+    done: AtomicUsize,
+    downloaded: AtomicUsize,
+    skipped: AtomicUsize,
+    failed: AtomicUsize,
+    failure_lines: AtomicUsize,
+}
+
+impl Tally {
+    /// 记一个结局，返回记完之后的快照。
+    fn observe(&self, outcome: &FileOutcome, total: usize) -> Snapshot {
+        let done = self.done.fetch_add(1, Ordering::Relaxed) + 1;
+        match outcome.status {
+            FileStatus::Downloaded => {
+                self.downloaded.fetch_add(1, Ordering::Relaxed);
+            }
+            FileStatus::Skipped => {
+                self.skipped.fetch_add(1, Ordering::Relaxed);
+            }
+            FileStatus::Failed => {
+                self.failed.fetch_add(1, Ordering::Relaxed);
+            }
+        }
+        Snapshot {
+            done,
+            total,
+            downloaded: self.downloaded.load(Ordering::Relaxed),
+            skipped: self.skipped.load(Ordering::Relaxed),
+            failed: self.failed.load(Ordering::Relaxed),
+        }
+    }
+}
+
+/// 实时进度回调（只写 stderr，不污染 `--json` 的 stdout）。
+///
+/// 两种形态：人类模式打文本行；`--json` 模式打 **JSONL**（一行一条事件，`event` 字段分流），
+/// 这样脚本既能吃 stdout 的最终信封，也能实时跟进而不必解析文本。
+///
+/// 失败行只打前几条：整源不可达时会一口气失败上千个文件，全打出来既没用又淹没原因。
+pub fn progress_sink(enabled: bool, json: bool, total: usize) -> Option<ProgressSink> {
+    sink_with(enabled, json, total, Arc::new(progress_line))
+}
+
+/// 可注入输出端的构造器（测试据此抓行；生产只有一个调用者 [`progress_sink`]）。
+fn sink_with(
+    enabled: bool,
+    json: bool,
+    total: usize,
+    out: Arc<dyn Fn(&str) + Send + Sync>,
+) -> Option<ProgressSink> {
+    if !enabled {
+        return None;
+    }
+    let tally = Arc::new(Tally::default());
+    Some(Arc::new(move |outcome: &FileOutcome| {
+        let snapshot = tally.observe(outcome, total);
+        if let Some(failure) = &outcome.failure {
+            let seen = tally.failure_lines.fetch_add(1, Ordering::Relaxed);
+            if seen < MAX_PROGRESS_FAILURES {
+                emit(
+                    json,
+                    serde_json::json!({
+                        "event": "file_failed",
+                        "done": snapshot.done,
+                        "total": total,
+                        "name": outcome.name,
+                        "role": outcome.role.as_str(),
+                        "kind": failure.kind.as_str(),
+                        "message": failure.message,
+                    }),
+                    &format!(
+                        "失败 {}/{} {}：{}",
+                        snapshot.done, total, outcome.name, failure.message
+                    ),
+                    &out,
+                );
+            } else if seen == MAX_PROGRESS_FAILURES {
+                emit(
+                    json,
+                    serde_json::json!({
+                        "event": "progress_truncated",
+                        "suppressed_after": MAX_PROGRESS_FAILURES,
+                    }),
+                    "（更多失败不再逐条打印，见最终错误汇总）",
+                    &out,
+                );
+            }
+            return;
+        }
+        if snapshot.done.is_multiple_of(PROGRESS_EVERY) || snapshot.done == total {
+            emit(json, snapshot.json(), &snapshot.text(), &out);
+        }
+    }))
+}
+
+/// 一条进度：JSONL 模式打序列化后的一行，人类模式打短文本。
+fn emit(
+    json_mode: bool,
+    record: serde_json::Value,
+    text: &str,
+    out: &Arc<dyn Fn(&str) + Send + Sync>,
+) {
+    if json_mode {
+        let line = record.to_string();
+        out(&line);
+    } else {
+        out(text);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::Mutex;
+
+    use unlucky_core::download::DownloadErrorKind;
+    use unlucky_core::game::install::{FileFailure, FileRole};
+
+    use super::*;
+
+    /// 抓行的输出端。
+    fn recorder() -> (Arc<dyn Fn(&str) + Send + Sync>, Arc<Mutex<Vec<String>>>) {
+        let lines = Arc::new(Mutex::new(Vec::new()));
+        let sink_lines = Arc::clone(&lines);
+        let out: Arc<dyn Fn(&str) + Send + Sync> =
+            Arc::new(move |line: &str| sink_lines.lock().expect("锁").push(line.to_string()));
+        (out, lines)
+    }
+
+    fn outcome(name: &str, status: FileStatus) -> FileOutcome {
+        FileOutcome {
+            role: FileRole::Asset,
+            name: name.to_string(),
+            dest: std::path::PathBuf::from(format!("assets/{name}")),
+            status,
+            bytes: 1234,
+            source: Some("cache".to_string()),
+            failure: None,
+        }
+    }
+
+    /// **D11 用例**：全部已存在（重装同版本）⇒ 进度行里不出现「下载」，下载计数为 0。
+    ///
+    /// 抓得住：把「处理序号」当下载量打印的旧实现（它会打出 `下载 32/96` 这类行）；
+    /// 以及任何「下载数 > 0 却说没下载」的表述。抓不住：行里出现的其它夸张词（措辞审查），
+    /// 也不管单行是否真的落到 stderr（那是 [`crate::output::progress_line`] 的事）。
+    #[test]
+    fn all_skipped_progress_never_claims_downloads() {
+        const TOTAL: usize = 96; // 3 的倍数，必然跨过 PROGRESS_EVERY
+        let (out, lines) = recorder();
+        let sink = sink_with(true, false, TOTAL, out).expect("进度开关打开时必须有 sink");
+        for index in 0..TOTAL {
+            sink(&outcome(&format!("asset-{index}"), FileStatus::Skipped));
+        }
+        let lines = lines.lock().expect("锁").clone();
+        assert!(!lines.is_empty(), "应当有进度行");
+        for line in &lines {
+            assert!(
+                !line.contains("下载"),
+                "全部跳过时进度行不许提「下载」：{line}"
+            );
+        }
+        let last = lines.last().expect("至少一行");
+        assert!(
+            last.contains(&format!("已就绪 {TOTAL}/{TOTAL}"))
+                && last.contains(&format!("跳过 {TOTAL}")),
+            "全跳过应当说「已就绪 N/N（跳过 N 个）」：{last}"
+        );
+    }
+
+    /// 同一场景的 `--json` 形态：`downloaded` 必须是 0（脚本据此判断「其实没下」）。
+    #[test]
+    fn all_skipped_json_progress_reports_zero_downloads() {
+        const TOTAL: usize = 32;
+        let (out, lines) = recorder();
+        let sink = sink_with(true, true, TOTAL, out).expect("进度开关打开时必须有 sink");
+        for index in 0..TOTAL {
+            sink(&outcome(&format!("lib-{index}"), FileStatus::Skipped));
+        }
+        let records: Vec<serde_json::Value> = lines
+            .lock()
+            .expect("锁")
+            .iter()
+            .map(|line| serde_json::from_str(line).expect("JSONL"))
+            .collect();
+        let progress = records
+            .iter()
+            .find(|record| record["event"] == "progress")
+            .expect("应当有 progress 事件");
+        assert_eq!(progress["downloaded"], 0);
+        assert_eq!(progress["skipped"], TOTAL);
+        assert_eq!(progress["done"], TOTAL);
+        assert_eq!(progress["total"], TOTAL);
+    }
+
+    /// 真的有下载时，计数与措辞都跟着事实走（避免「一刀切不打印」这种假修复）。
+    #[test]
+    fn mixed_outcomes_report_real_counts() {
+        let (out, lines) = recorder();
+        let sink = sink_with(true, false, 4, out).expect("sink");
+        sink(&outcome("client.jar", FileStatus::Downloaded));
+        let failed = FileOutcome {
+            failure: Some(FileFailure {
+                kind: DownloadErrorKind::Network,
+                message: "连接被重置".to_string(),
+            }),
+            ..outcome("b", FileStatus::Failed)
+        };
+        sink(&failed);
+        sink(&outcome("c", FileStatus::Skipped));
+        sink(&outcome("d", FileStatus::Skipped));
+        let lines = lines.lock().expect("锁").clone();
+        // 失败有自己的行（`失败 2/4 b：…`），进度行不拿它冒充下载量。
+        assert!(
+            lines.iter().any(|line| line.starts_with("失败 2/4 b")),
+            "{lines:?}"
+        );
+        let last = lines.last().expect("至少一行");
+        // done == total 时无条件打最后一行。
+        assert!(last.contains("下载 1 个"), "{last}");
+        assert!(last.contains("跳过 2 个"), "{last}");
+        assert!(last.contains("失败 1"), "{last}");
+        assert!(last.contains("进度 4/4"), "{last}");
+    }
+}
diff --git a/crates/cli/src/commands/install/report.rs b/crates/cli/src/commands/install/report.rs
index af04893..750204b 100644
--- a/crates/cli/src/commands/install/report.rs
+++ b/crates/cli/src/commands/install/report.rs
@@ -1,84 +1,15 @@
-//! 安装结果的两种呈现形态：人类可读行 + `--json` 载荷，外加 stderr 实时进度。
+//! 安装结果的两种呈现形态：人类可读行 + `--json` 载荷（stderr 实时进度见 [`super::progress`]）。
 //!
 //! 拆出来是因为 `install` 的流程（规划 → 下载 → 登记）与排版彼此独立：
 //! 前者要能读懂，后者要能被脚本断言。`--dry-run` 与真实安装共用同一份排版，
 //! 差别只是多出逐文件清单与源选择。
 
-use std::sync::atomic::{AtomicUsize, Ordering};
-use std::sync::Arc;
-
 use serde_json::json;
 use unlucky_core::download::DownloadEngine;
-use unlucky_core::game::install::{
-    FileOutcome, InstallPlan, InstallReport, ProgressSink, Registration,
-};
+use unlucky_core::game::install::{FileOutcome, InstallPlan, InstallReport, Registration};
 
 use crate::context::Ctx;
-use crate::output::{progress_line, Report};
-
-/// 每处理多少个文件打一行进度（3000 个资源下约 90 行，够用又不刷屏）。
-const PROGRESS_EVERY: usize = 32;
-
-/// 进度里最多逐条打印几条失败（其余交给最终错误汇总）。
-const MAX_PROGRESS_FAILURES: usize = 5;
-
-/// 实时进度回调（只写 stderr，不污染 `--json` 的 stdout）。
-///
-/// 两种形态：人类模式打文本行；`--json` 模式打 **JSONL**（一行一条事件，`event` 字段分流），
-/// 这样脚本既能吃 stdout 的最终信封，也能实时跟进而不必解析文本。
-///
-/// 失败行只打前几条：整源不可达时会一口气失败上千个文件，全打出来既没用又淹没原因。
-pub fn progress_sink(enabled: bool, json: bool, total: usize) -> Option<ProgressSink> {
-    if !enabled {
-        return None;
-    }
-    let done = Arc::new(AtomicUsize::new(0));
-    let failures = Arc::new(AtomicUsize::new(0));
-    Some(Arc::new(move |outcome: &FileOutcome| {
-        let index = done.fetch_add(1, Ordering::Relaxed) + 1;
-        if let Some(failure) = &outcome.failure {
-            let seen = failures.fetch_add(1, Ordering::Relaxed);
-            if seen < MAX_PROGRESS_FAILURES {
-                emit(
-                    json,
-                    json!({
-                        "event": "file_failed",
-                        "done": index,
-                        "total": total,
-                        "name": outcome.name,
-                        "role": outcome.role.as_str(),
-                        "kind": failure.kind.as_str(),
-                        "message": failure.message,
-                    }),
-                    &format!("失败 {index}/{total} {}：{}", outcome.name, failure.message),
-                );
-            } else if seen == MAX_PROGRESS_FAILURES {
-                emit(
-                    json,
-                    json!({"event": "progress_truncated", "suppressed_after": MAX_PROGRESS_FAILURES}),
-                    "（更多失败不再逐条打印，见最终错误汇总）",
-                );
-            }
-            return;
-        }
-        if index.is_multiple_of(PROGRESS_EVERY) || index == total {
-            emit(
-                json,
-                json!({"event": "progress", "done": index, "total": total}),
-                &format!("下载 {index}/{total}"),
-            );
-        }
-    }))
-}
-
-/// 一条进度：JSONL 模式打序列化后的一行，人类模式打短文本。
-fn emit(json_mode: bool, record: serde_json::Value, text: &str) {
-    if json_mode {
-        progress_line(&record.to_string());
-    } else {
-        progress_line(text);
-    }
-}
+use crate::output::Report;
 
 /// 排版一次安装结果。
 #[allow(clippy::too_many_arguments)]
diff --git a/crates/cli/src/commands/install/vanilla.rs b/crates/cli/src/commands/install/vanilla.rs
index b0a074a..65b6157 100644
--- a/crates/cli/src/commands/install/vanilla.rs
+++ b/crates/cli/src/commands/install/vanilla.rs
@@ -21,7 +21,7 @@ use unlucky_core::game::install::{
 };
 
 use super::{
-    build_engine, ensure_name_free, failure_error, map_install_error, report, CONCURRENCY,
+    build_engine, ensure_name_free, failure_error, map_install_error, progress, report, CONCURRENCY,
 };
 use crate::cli::InstallArgs;
 use crate::context::Ctx;
@@ -142,7 +142,7 @@ pub(super) fn plan_and_install(
                 "旧版（pre-1.6）清单兜底待补；可先用官方启动器装好该版本再用 `%prog% launch`",
             ));
         }
-        let sink = report::progress_sink(progress, json_progress, plan.file_count());
+        let sink = progress::progress_sink(progress, json_progress, plan.file_count());
         let report = execute(engine, &plan, CONCURRENCY, sink).await?;
         Ok(Attempt {
             plan,
diff --git a/crates/core/src/download/mirrors.json b/crates/core/src/download/mirrors.json
index 8075108..722ffc8 100644
--- a/crates/core/src/download/mirrors.json
+++ b/crates/core/src/download/mirrors.json
@@ -117,7 +117,8 @@
     {
       "id": "bmclapi-libraries",
       "from": "https://libraries.minecraft.net",
-      "to": "https://bmclapi2.bangbang93.com"
+      "to": "https://bmclapi2.bangbang93.com",
+      "inject": "/maven"
     },
     {
       "id": "bmclapi-assets-objects",
diff --git a/crates/core/tests/download/mirrors_test.rs b/crates/core/tests/download/mirrors_test.rs
index c5eceeb..3ff95ba 100644
--- a/crates/core/tests/download/mirrors_test.rs
+++ b/crates/core/tests/download/mirrors_test.rs
@@ -30,15 +30,115 @@ fn prefix_rule_preserves_sub_path() {
         .expect("libraries 规则缺失");
     let candidate = rule.apply(LIBRARIES_URL).expect("重写失败");
     assert_eq!(candidate.source, "bmclapi");
+    // 子路径逐字保留（`/maven` 是镜像侧的固定前缀，不属于子路径）。
+    //
+    // M210/D1：这条断言此前写的是「换成 `https://bmclapi2.bangbang93.com` 就完事」，等于把
+    // **丢 inject 的 bug 钉成了期望**——实测 70/70 个库 404（无 `/maven` 回 404 + 9 B，
+    // 带 `/maven` 回 200、sha1 与官方逐字节一致）。现在把 `/maven` 写进期望值。
     assert_eq!(
         candidate.url,
         LIBRARIES_URL.replace(
             "https://libraries.minecraft.net",
-            "https://bmclapi2.bangbang93.com"
+            "https://bmclapi2.bangbang93.com/maven"
         )
     );
 }
 
+/// **守卫（M210/D1）**：每一条「给 libraries 用」的镜像规则，镜像前缀都必须带 `/maven`。
+///
+/// 官方库域名（`libraries.minecraft.net`）与各 loader 的 maven 在 BMCLAPI 上统一挂在 `/maven`
+/// 下；`apply()` 是纯前缀替换，`to` 里少了这一段就会把 `com/google/guava/...` 直接拼到镜像根上。
+///
+/// 抓得住：删掉/改错任一条库镜像规则的 `inject`（本用例对 `bmclapi-libraries` 的变异会红）。
+/// 抓不住：`/maven` **写歪**（如 `/maven2`、`/maven/` 之外的等价路径）只能靠行为用例
+/// [`library_urls_expand_to_the_maven_subpath_on_bmclapi`]；路径结构本就不同的镜像表（资源对象走
+/// `/assets`、元数据走 `/fabric-meta`）不在此判据内；新增但 `from` 不像 maven 仓库的库镜像也不在此列。
+#[test]
+fn every_library_mirror_rule_carries_the_maven_segment() {
+    let table = MirrorTable::builtin();
+    // 判据：「给 libraries 用」= `from` 指向 maven 仓库（host/路径里带 maven，或就是 Mojang 库域名）。
+    // 新增一条库镜像规则时这条自动纳入，不必改测试。
+    fn serves_maven(from: &str) -> bool {
+        host_of(from).unwrap_or_default().contains("maven")
+            || from.contains("maven")
+            || host_of(from) == Some("libraries.minecraft.net")
+    }
+    // 判据覆盖的规则 id（内置表里就是这 5 条；`bmclapi-liteloader` 的 `from` 不像 maven 仓库，不在列，
+    // 它指向的镜像路径另有一个「镜像上不存在」的观察，见 M210 报告的 §5）。
+    const EXPECTED: [&str; 5] = [
+        "bmclapi-libraries",
+        "bmclapi-forge-maven",
+        "bmclapi-forge-maven-net",
+        "bmclapi-neoforge",
+        "bmclapi-fabric-maven",
+    ];
+    let mut checked: Vec<&str> = Vec::new();
+    for rule in table.rules.iter().filter(|rule| serves_maven(&rule.from)) {
+        let prefix = format!("{}{}", rule.to, rule.inject);
+        assert!(
+            prefix.ends_with("/maven"),
+            "规则 {} 的镜像前缀 `{prefix}` 少了 `/maven`：官方 `{}` 在镜像上挂在 `/maven/` 下，\
+             丢了它整张表 404（M210/D1）",
+            rule.id,
+            rule.from
+        );
+        checked.push(rule.id.as_str());
+    }
+    // 判据失效（规则被改名/改形/删掉）时这里红：期望的规则一条都不能漏。
+    for expected in EXPECTED {
+        assert!(
+            checked.contains(&expected),
+            "库镜像规则 {expected} 没被形态判据覆盖到（被改名/改形/删掉了？）：{checked:?}"
+        );
+    }
+    // 多出来的（新增 maven 规则）也得登记进 EXPECTED，否则说明它绕过了这道判据的意图审查。
+    assert_eq!(
+        checked.len(),
+        EXPECTED.len(),
+        "库镜像规则数与预期不符（新增/删除了规则？）：{checked:?}"
+    );
+}
+
+/// **行为守卫（M210/D1）**：真实库 URL 展开后必须落在镜像的 `/maven/<子路径>` 上。
+///
+/// 与上一条互为补充：那条看规则形态，这条看用户实际会请求到的 URL。
+/// 抓得住：`inject` 丢失、`to` 里手写 `/maven` 被删、或 `from`/`to` 被改成拼不出 `/maven` 的形态。
+/// 抓不住：只覆盖这 4 个官方 maven 根（各处未必都写全）；镜像侧真实可达性（要网络，留给 e2e）。
+#[test]
+fn library_urls_expand_to_the_maven_subpath_on_bmclapi() {
+    let table = MirrorTable::builtin();
+    let region = RegionProfile::mirror_first(0);
+    let cases = [
+        (
+            LIBRARIES_URL,
+            "https://bmclapi2.bangbang93.com/maven/com/google/guava/guava/32.0.0/guava-32.0.0.jar",
+        ),
+        (
+            "https://maven.fabricmc.net/net/fabricmc/fabric-loader/0.15.11/fabric-loader-0.15.11.jar",
+            "https://bmclapi2.bangbang93.com/maven/net/fabricmc/fabric-loader/0.15.11/fabric-loader-0.15.11.jar",
+        ),
+        (
+            "https://maven.minecraftforge.net/net/minecraftforge/forge/1.20.1-47.2.0/forge-1.20.1-47.2.0-installer.jar",
+            "https://bmclapi2.bangbang93.com/maven/net/minecraftforge/forge/1.20.1-47.2.0/forge-1.20.1-47.2.0-installer.jar",
+        ),
+        (
+            "https://maven.neoforged.net/releases/net/neoforged/neoforge/21.1.80/neoforge-21.1.80-installer.jar",
+            "https://bmclapi2.bangbang93.com/maven/net/neoforged/neoforge/21.1.80/neoforge-21.1.80-installer.jar",
+        ),
+    ];
+    for (official, expected) in cases {
+        let candidates = table.expand(official, ResourceKind::Library, &region);
+        let mirror = candidates
+            .iter()
+            .find(|candidate| candidate.source == "bmclapi")
+            .unwrap_or_else(|| panic!("{official} 没有 bmclapi 候选：{candidates:?}"));
+        assert_eq!(
+            mirror.url, expected,
+            "库镜像 URL 形状不对（官方 {official}）"
+        );
+    }
+}
+
 #[test]
 fn asset_rule_injects_path_prefix() {
     let table = MirrorTable::builtin();