diff --git a/crates/core/src/download/config.rs b/crates/core/src/download/config.rs
index 20929a1..3de7b08 100644
--- a/crates/core/src/download/config.rs
+++ b/crates/core/src/download/config.rs
@@ -223,178 +223,5 @@ pub fn publish(cache_root: &Path, next: DownloadTuning) -> bool {
 }
 
 #[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::setting::keys::{launcher_schema, launcher_version};
-
-    /// **守门③**：schema 的默认值 / 区间 / 键名与 `EngineConfig::default()` / 调优默认值取同一组常量。
-    /// 变异证明（只改实现侧）：`EngineConfig::default()` 的并发写回 64、schema 默认值写成 16、
-    /// `MAX_CONCURRENCY` 改了而 schema 仍写 64 ⇒ 各自红。
-    #[test]
-    fn the_schema_contract_is_single_sourced() {
-        let schema = launcher_schema();
-        assert_eq!(schema.version(), launcher_version());
-        let cfg = EngineConfig::default();
-        let tune = DownloadTuning::default();
-
-        // 并发 1~64（0 张许可没意义）；尝试次数 **0**~10（P2-1：0 = 只试一次，旧配置里真有）。
-        let contract: [(&str, i64, i64, usize); 2] = [
-            (
-                KEY_CONCURRENCY,
-                i64::try_from(DEFAULT_MAX_CONCURRENCY).expect("装得下"),
-                1,
-                MAX_CONCURRENCY,
-            ),
-            (
-                KEY_RETRY_LIMIT,
-                i64::from(DEFAULT_MAX_ATTEMPTS_PER_SOURCE),
-                0,
-                usize::try_from(MAX_ATTEMPTS_PER_SOURCE).expect("装得下"),
-            ),
-        ];
-        for (key, default, min, max) in contract {
-            let spec = schema.spec(key).expect("键已登记");
-            assert_eq!(spec.default, serde_json::json!(default), "{key}");
-            assert_eq!(
-                spec.kind,
-                crate::setting::spec::ValueKind::Int {
-                    min,
-                    max: i64::try_from(max).expect("装得下"),
-                },
-                "{key}"
-            );
-        }
-        assert_eq!(cfg.max_concurrency, DEFAULT_MAX_CONCURRENCY);
-        assert_eq!(tune.max_concurrency, DEFAULT_MAX_CONCURRENCY);
-        assert_eq!(cfg.max_attempts_per_source, DEFAULT_MAX_ATTEMPTS_PER_SOURCE);
-        assert_eq!(
-            tune.max_attempts_per_source,
-            DEFAULT_MAX_ATTEMPTS_PER_SOURCE
-        );
-    }
-
-    /// `SettingSpec.doc` 是 `&'static str`（`concat!` 插不进常量），描述里的数字只能手写——这条钉住它，
-    /// 改常量不改文案就红（`catalog.rs` 会把这些 doc 当 JSON schema 的 description 发出去）。
-    #[test]
-    fn the_key_docs_quote_the_real_limits() {
-        let schema = launcher_schema();
-        let doc = |key: &str| schema.spec(key).expect("键已登记").doc;
-        assert!(doc(KEY_CONCURRENCY).contains(&format!("1~{MAX_CONCURRENCY}")));
-        assert!(doc(KEY_CONCURRENCY).contains(&format!("出厂 {DEFAULT_MAX_CONCURRENCY}")));
-        assert!(doc(KEY_RETRY_LIMIT).contains(&format!("出厂 {DEFAULT_MAX_ATTEMPTS_PER_SOURCE}")));
-    }
-
-    /// 未填 / 越界回落默认（不阻断下载）；**`retry_limit: 0` 是合法值**，语义 = 只试一次。
-    ///
-    /// 变异证明：把并发的区间过滤删掉 ⇒ `0` / `9999` 两条红；把尝试次数的 `.max(1)` 删掉 ⇒
-    /// `0 → 1` 那条红（引擎会拿到 0 次尝试）；把 `0` 判成越界 ⇒ 同样红。
-    #[test]
-    fn missing_or_illegal_values_fall_back_to_the_defaults() {
-        assert_eq!(
-            DownloadTuning::from_settings(None, None, None),
-            DownloadTuning::default()
-        );
-
-        let just_over = i64::try_from(MAX_CONCURRENCY).expect("上限装得下") + 1;
-        for bad in [0_i64, -1, 9_999, just_over] {
-            let tune = DownloadTuning::from_settings(Some(bad), None, None);
-            assert_eq!(tune.max_concurrency, DEFAULT_MAX_CONCURRENCY, "{bad}");
-        }
-        // 0 与 1 都 = 只试一次：旧配置里的 0 不许回落成出厂 3（那正是「界面 0、引擎 3」）。
-        for zero_or_one in [0_i64, 1] {
-            let tune = DownloadTuning::from_settings(None, Some(zero_or_one), None);
-            assert_eq!(tune.max_attempts_per_source, 1, "{zero_or_one}");
-        }
-        for bad in [-1_i64, 9_999] {
-            let tune = DownloadTuning::from_settings(None, Some(bad), None);
-            assert_eq!(
-                tune.max_attempts_per_source,
-                DEFAULT_MAX_ATTEMPTS_PER_SOURCE
-            );
-        }
-
-        let tune = DownloadTuning::from_settings(Some(2), Some(2), None);
-        assert_eq!(tune.max_concurrency, 2);
-        assert_eq!(tune.max_attempts_per_source, 2);
-    }
-
-    /// 三态：**空串 ≠ 关**（这条是「设置项说假话」的高发点，M197 的键语义同源）。
-    #[test]
-    fn empty_gh_proxy_means_follow_builtin_not_off() {
-        assert_eq!(gh_proxy_override(""), GhProxyOverride::Builtin);
-        assert_eq!(gh_proxy_override("   "), GhProxyOverride::Builtin);
-        for off in [
-            "off", "OFF", " none ", "direct", "disable", "disabled", "no",
-        ] {
-            assert_eq!(gh_proxy_override(off), GhProxyOverride::Off, "{off}");
-        }
-        assert_eq!(
-            gh_proxy_override(" https://gh.example/ "),
-            GhProxyOverride::Prefix("https://gh.example/".to_string())
-        );
-        // 未填（键不存在）也是 Builtin，不是 Off。
-        assert_eq!(
-            DownloadTuning::from_settings(None, None, None).gh_proxy,
-            GhProxyOverride::Builtin
-        );
-    }
-
-    /// `apply_gh_proxy` 的三档真的改到档案上、并且**改到候选链上**（`expand()` 读的就是档案里那个
-    /// 前缀；自定义前缀那一档的链断言在 `shared.rs`）。变异证明：`Off` 分支改成原样返回 ⇒ `off` 红。
-    #[test]
-    fn gh_proxy_override_reaches_the_profile_and_the_chain() {
-        use crate::download::mirrors::{MirrorTable, SOURCE_GH_PROXY};
-        use crate::download::types::ResourceKind;
-
-        let url = "https://github.com/o/r/releases/download/v1/a.jar";
-        let table = MirrorTable::builtin();
-        let sources = |profile: &RegionProfile| -> Vec<String> {
-            table
-                .expand(url, ResourceKind::Other, profile)
-                .into_iter()
-                .map(|candidate| candidate.source)
-                .collect()
-        };
-
-        let mirror_first = RegionProfile::mirror_first(0);
-        let kept = DownloadTuning::default().apply_gh_proxy(mirror_first.clone());
-        assert_eq!(kept.gh_proxy, mirror_first.gh_proxy, "Builtin 不该动档案");
-        assert!(
-            sources(&kept).contains(&SOURCE_GH_PROXY.to_string()),
-            "出厂套前缀"
-        );
-
-        let off = DownloadTuning::from_settings(None, None, Some("off"))
-            .apply_gh_proxy(mirror_first.clone());
-        assert!(
-            !sources(&off).contains(&SOURCE_GH_PROXY.to_string()),
-            "关了就没候选"
-        );
-
-        let prefix = DownloadTuning::from_settings(None, None, Some("https://gh.example/"))
-            .apply_gh_proxy(mirror_first);
-        assert_eq!(prefix.gh_proxy.as_deref(), Some("https://gh.example/"));
-        assert!(prefix.gh_proxy_enabled(), "前缀生效");
-    }
-
-    /// 每个数据根的调优互不串味（一个根改成 2 不该改另一个根的引擎）。
-    /// 变异证明：把 `wanted`/`publish` 的键改回单一进程级槽位 ⇒ 第二个根读到 2，红。
-    #[test]
-    fn tuning_is_per_cache_root_and_no_change_is_reported_as_such() {
-        let a = PathBuf::from("/tmp/ull-tuning-a");
-        let b = PathBuf::from("/tmp/ull-tuning-b");
-        assert_eq!(wanted(&a), DownloadTuning::default());
-
-        let changed = DownloadTuning::from_settings(Some(2), None, None);
-        assert!(publish(&a, changed.clone()), "真变了要报变更");
-        assert_eq!(wanted(&a), changed);
-        assert!(!publish(&a, changed.clone()), "同值不该报变更");
-        assert_eq!(wanted(&b), DownloadTuning::default(), "别的根不受影响");
-
-        assert!(
-            publish(&a, DownloadTuning::default()),
-            "恢复默认也是一次变更"
-        );
-        assert_eq!(wanted(&a), DownloadTuning::default());
-    }
-}
+#[path = "config/tests.rs"]
+mod tests;
diff --git a/crates/core/src/download/config/tests.rs b/crates/core/src/download/config/tests.rs
new file mode 100644
index 0000000..49d2add
--- /dev/null
+++ b/crates/core/src/download/config/tests.rs
@@ -0,0 +1,175 @@
+//! `download::config` 的单测：**从 `config.rs` 拆出只为守 400 行硬线**（M289 加超时字段前先纯搬移，逐字节未改）。
+
+use super::*;
+use crate::setting::keys::{launcher_schema, launcher_version};
+
+/// **守门③**：schema 的默认值 / 区间 / 键名与 `EngineConfig::default()` / 调优默认值取同一组常量。
+/// 变异证明（只改实现侧）：`EngineConfig::default()` 的并发写回 64、schema 默认值写成 16、
+/// `MAX_CONCURRENCY` 改了而 schema 仍写 64 ⇒ 各自红。
+#[test]
+fn the_schema_contract_is_single_sourced() {
+    let schema = launcher_schema();
+    assert_eq!(schema.version(), launcher_version());
+    let cfg = EngineConfig::default();
+    let tune = DownloadTuning::default();
+
+    // 并发 1~64（0 张许可没意义）；尝试次数 **0**~10（P2-1：0 = 只试一次，旧配置里真有）。
+    let contract: [(&str, i64, i64, usize); 2] = [
+        (
+            KEY_CONCURRENCY,
+            i64::try_from(DEFAULT_MAX_CONCURRENCY).expect("装得下"),
+            1,
+            MAX_CONCURRENCY,
+        ),
+        (
+            KEY_RETRY_LIMIT,
+            i64::from(DEFAULT_MAX_ATTEMPTS_PER_SOURCE),
+            0,
+            usize::try_from(MAX_ATTEMPTS_PER_SOURCE).expect("装得下"),
+        ),
+    ];
+    for (key, default, min, max) in contract {
+        let spec = schema.spec(key).expect("键已登记");
+        assert_eq!(spec.default, serde_json::json!(default), "{key}");
+        assert_eq!(
+            spec.kind,
+            crate::setting::spec::ValueKind::Int {
+                min,
+                max: i64::try_from(max).expect("装得下"),
+            },
+            "{key}"
+        );
+    }
+    assert_eq!(cfg.max_concurrency, DEFAULT_MAX_CONCURRENCY);
+    assert_eq!(tune.max_concurrency, DEFAULT_MAX_CONCURRENCY);
+    assert_eq!(cfg.max_attempts_per_source, DEFAULT_MAX_ATTEMPTS_PER_SOURCE);
+    assert_eq!(
+        tune.max_attempts_per_source,
+        DEFAULT_MAX_ATTEMPTS_PER_SOURCE
+    );
+}
+
+/// `SettingSpec.doc` 是 `&'static str`（`concat!` 插不进常量），描述里的数字只能手写——这条钉住它，
+/// 改常量不改文案就红（`catalog.rs` 会把这些 doc 当 JSON schema 的 description 发出去）。
+#[test]
+fn the_key_docs_quote_the_real_limits() {
+    let schema = launcher_schema();
+    let doc = |key: &str| schema.spec(key).expect("键已登记").doc;
+    assert!(doc(KEY_CONCURRENCY).contains(&format!("1~{MAX_CONCURRENCY}")));
+    assert!(doc(KEY_CONCURRENCY).contains(&format!("出厂 {DEFAULT_MAX_CONCURRENCY}")));
+    assert!(doc(KEY_RETRY_LIMIT).contains(&format!("出厂 {DEFAULT_MAX_ATTEMPTS_PER_SOURCE}")));
+}
+
+/// 未填 / 越界回落默认（不阻断下载）；**`retry_limit: 0` 是合法值**，语义 = 只试一次。
+///
+/// 变异证明：把并发的区间过滤删掉 ⇒ `0` / `9999` 两条红；把尝试次数的 `.max(1)` 删掉 ⇒
+/// `0 → 1` 那条红（引擎会拿到 0 次尝试）；把 `0` 判成越界 ⇒ 同样红。
+#[test]
+fn missing_or_illegal_values_fall_back_to_the_defaults() {
+    assert_eq!(
+        DownloadTuning::from_settings(None, None, None),
+        DownloadTuning::default()
+    );
+
+    let just_over = i64::try_from(MAX_CONCURRENCY).expect("上限装得下") + 1;
+    for bad in [0_i64, -1, 9_999, just_over] {
+        let tune = DownloadTuning::from_settings(Some(bad), None, None);
+        assert_eq!(tune.max_concurrency, DEFAULT_MAX_CONCURRENCY, "{bad}");
+    }
+    // 0 与 1 都 = 只试一次：旧配置里的 0 不许回落成出厂 3（那正是「界面 0、引擎 3」）。
+    for zero_or_one in [0_i64, 1] {
+        let tune = DownloadTuning::from_settings(None, Some(zero_or_one), None);
+        assert_eq!(tune.max_attempts_per_source, 1, "{zero_or_one}");
+    }
+    for bad in [-1_i64, 9_999] {
+        let tune = DownloadTuning::from_settings(None, Some(bad), None);
+        assert_eq!(
+            tune.max_attempts_per_source,
+            DEFAULT_MAX_ATTEMPTS_PER_SOURCE
+        );
+    }
+
+    let tune = DownloadTuning::from_settings(Some(2), Some(2), None);
+    assert_eq!(tune.max_concurrency, 2);
+    assert_eq!(tune.max_attempts_per_source, 2);
+}
+
+/// 三态：**空串 ≠ 关**（这条是「设置项说假话」的高发点，M197 的键语义同源）。
+#[test]
+fn empty_gh_proxy_means_follow_builtin_not_off() {
+    assert_eq!(gh_proxy_override(""), GhProxyOverride::Builtin);
+    assert_eq!(gh_proxy_override("   "), GhProxyOverride::Builtin);
+    for off in [
+        "off", "OFF", " none ", "direct", "disable", "disabled", "no",
+    ] {
+        assert_eq!(gh_proxy_override(off), GhProxyOverride::Off, "{off}");
+    }
+    assert_eq!(
+        gh_proxy_override(" https://gh.example/ "),
+        GhProxyOverride::Prefix("https://gh.example/".to_string())
+    );
+    // 未填（键不存在）也是 Builtin，不是 Off。
+    assert_eq!(
+        DownloadTuning::from_settings(None, None, None).gh_proxy,
+        GhProxyOverride::Builtin
+    );
+}
+
+/// `apply_gh_proxy` 的三档真的改到档案上、并且**改到候选链上**（`expand()` 读的就是档案里那个
+/// 前缀；自定义前缀那一档的链断言在 `shared.rs`）。变异证明：`Off` 分支改成原样返回 ⇒ `off` 红。
+#[test]
+fn gh_proxy_override_reaches_the_profile_and_the_chain() {
+    use crate::download::mirrors::{MirrorTable, SOURCE_GH_PROXY};
+    use crate::download::types::ResourceKind;
+
+    let url = "https://github.com/o/r/releases/download/v1/a.jar";
+    let table = MirrorTable::builtin();
+    let sources = |profile: &RegionProfile| -> Vec<String> {
+        table
+            .expand(url, ResourceKind::Other, profile)
+            .into_iter()
+            .map(|candidate| candidate.source)
+            .collect()
+    };
+
+    let mirror_first = RegionProfile::mirror_first(0);
+    let kept = DownloadTuning::default().apply_gh_proxy(mirror_first.clone());
+    assert_eq!(kept.gh_proxy, mirror_first.gh_proxy, "Builtin 不该动档案");
+    assert!(
+        sources(&kept).contains(&SOURCE_GH_PROXY.to_string()),
+        "出厂套前缀"
+    );
+
+    let off = DownloadTuning::from_settings(None, None, Some("off"))
+        .apply_gh_proxy(mirror_first.clone());
+    assert!(
+        !sources(&off).contains(&SOURCE_GH_PROXY.to_string()),
+        "关了就没候选"
+    );
+
+    let prefix = DownloadTuning::from_settings(None, None, Some("https://gh.example/"))
+        .apply_gh_proxy(mirror_first);
+    assert_eq!(prefix.gh_proxy.as_deref(), Some("https://gh.example/"));
+    assert!(prefix.gh_proxy_enabled(), "前缀生效");
+}
+
+/// 每个数据根的调优互不串味（一个根改成 2 不该改另一个根的引擎）。
+/// 变异证明：把 `wanted`/`publish` 的键改回单一进程级槽位 ⇒ 第二个根读到 2，红。
+#[test]
+fn tuning_is_per_cache_root_and_no_change_is_reported_as_such() {
+    let a = PathBuf::from("/tmp/ull-tuning-a");
+    let b = PathBuf::from("/tmp/ull-tuning-b");
+    assert_eq!(wanted(&a), DownloadTuning::default());
+
+    let changed = DownloadTuning::from_settings(Some(2), None, None);
+    assert!(publish(&a, changed.clone()), "真变了要报变更");
+    assert_eq!(wanted(&a), changed);
+    assert!(!publish(&a, changed.clone()), "同值不该报变更");
+    assert_eq!(wanted(&b), DownloadTuning::default(), "别的根不受影响");
+
+    assert!(
+        publish(&a, DownloadTuning::default()),
+        "恢复默认也是一次变更"
+    );
+    assert_eq!(wanted(&a), DownloadTuning::default());
+}
diff --git a/crates/core/src/download/engine.rs b/crates/core/src/download/engine.rs
index e782e78..8ad6173 100644
--- a/crates/core/src/download/engine.rs
+++ b/crates/core/src/download/engine.rs
@@ -35,6 +35,8 @@ use super::types::{
     SOURCE_OFFICIAL,
 };
 
+mod inspect;
+
 /// 一次成功尝试的产物描述。
 pub(crate) struct AttemptOk {
     /// 文件总字节数。
@@ -94,50 +96,6 @@ impl DownloadEngine {
         self
     }
 
-    /// 配置。
-    #[must_use]
-    pub fn config(&self) -> &EngineConfig {
-        &self.cfg
-    }
-
-    /// **真实并发闸门**此刻的许可数（探针，M193）：读 [`Self::acquire`] 会去抢的那张
-    /// `Semaphore`，**不是** `config().max_concurrency`。有下载在飞时偏小，空闲等于容量。
-    #[must_use]
-    pub fn concurrency_probe(&self) -> usize {
-        self.sem.available_permits()
-    }
-
-    /// HTTP 客户端（同一条连接池与超时配置）：给「一锤子查询」用（如 Adoptium 版本查询），
-    /// 没必要为了一个 GET 再造一个 client。
-    #[must_use]
-    pub fn client(&self) -> &reqwest::Client {
-        &self.http
-    }
-
-    /// 当前地区档案（设置页展示）。
-    #[must_use]
-    pub fn region(&self) -> &RegionProfile {
-        &self.region
-    }
-
-    /// 镜像表（`game::java` 的 Oracle / MS / Zulu 分发表在这里查）。
-    #[must_use]
-    pub fn mirrors(&self) -> &MirrorTable {
-        &self.mirrors
-    }
-
-    /// 健康度注册表（诊断页）。
-    #[must_use]
-    pub fn health(&self) -> &HealthRegistry {
-        &self.health
-    }
-
-    /// 内容寻址缓存。
-    #[must_use]
-    pub fn cache(&self) -> &ContentCache {
-        &self.cache
-    }
-
     /// 候选规划：镜像展开 → 官方位置保持不变 → 其余按健康度排序。
     #[must_use]
     pub fn plan(&self, req: &DownloadRequest, now_ms: u64) -> Vec<Candidate> {
diff --git a/crates/core/src/download/engine/inspect.rs b/crates/core/src/download/engine/inspect.rs
new file mode 100644
index 0000000..d03b2c4
--- /dev/null
+++ b/crates/core/src/download/engine/inspect.rs
@@ -0,0 +1,58 @@
+//! 引擎的只读查询面：**从 `engine.rs` 拆出只为守 400 行硬线**（M289 加失速诊断前先纯搬移，逐字节未改）。
+//!
+//! 这里只有「读」——配置、并发闸门探针、HTTP 客户端、地区档案、镜像表、健康度、内容缓存。
+//! 编排（候选循环、退避、落盘）仍在 [`super`]。
+
+use super::super::cache::ContentCache;
+use super::super::config::EngineConfig;
+use super::super::health::HealthRegistry;
+use super::super::mirrors::MirrorTable;
+use super::super::region::RegionProfile;
+use super::DownloadEngine;
+
+impl DownloadEngine {
+    /// 配置。
+    #[must_use]
+    pub fn config(&self) -> &EngineConfig {
+        &self.cfg
+    }
+
+    /// **真实并发闸门**此刻的许可数（探针，M193）：读 [`Self::acquire`] 会去抢的那张
+    /// `Semaphore`，**不是** `config().max_concurrency`。有下载在飞时偏小，空闲等于容量。
+    #[must_use]
+    pub fn concurrency_probe(&self) -> usize {
+        self.sem.available_permits()
+    }
+
+    /// HTTP 客户端（同一条连接池与超时配置）：给「一锤子查询」用（如 Adoptium 版本查询），
+    /// 没必要为了一个 GET 再造一个 client。
+    #[must_use]
+    pub fn client(&self) -> &reqwest::Client {
+        &self.http
+    }
+
+    /// 当前地区档案（设置页展示）。
+    #[must_use]
+    pub fn region(&self) -> &RegionProfile {
+        &self.region
+    }
+
+    /// 镜像表（`game::java` 的 Oracle / MS / Zulu 分发表在这里查）。
+    #[must_use]
+    pub fn mirrors(&self) -> &MirrorTable {
+        &self.mirrors
+    }
+
+    /// 健康度注册表（诊断页）。
+    #[must_use]
+    pub fn health(&self) -> &HealthRegistry {
+        &self.health
+    }
+
+    /// 内容寻址缓存。
+    #[must_use]
+    pub fn cache(&self) -> &ContentCache {
+        &self.cache
+    }
+
+}