chore(spec+checker): cleanup pass — trim docs, reorg Courseware, covers-as-data, fold DanglingReference (ADR-0012)

Spec母本噪音清理 + 一处 spec↔impl 对齐 + 一处契约自洽修正。

Part A — spec doc 瘦身:每条 doc 收到"语义点 + 标签 + ADR ref + 承载性 why",
把跨文件复读的方法论(element-kind 开放性对比、likec4 画不出、分歧点测试)上移到
module header。OPEN 框架保持清晰(RunState/Capability 完整性仍明示须 surface)。

Part B — Courseware/ 由 10 文件平铺重组为 Model/ Export/ Check/ Open/ 四子命名空间
(namespace Spec.Courseware 不变,零引用改动)+ 四个子 aggregator。lake build 绿(24 jobs)。

Part C — 渲染覆盖落为数据(ADR-0011 对齐):去掉 cph-check 里硬编码的
COVERED_TARGETS,改读 TargetConfig.covers。cph-model 新增 covers: Option<Vec<String>>
(None=未声明,由 cph-check 默认为全部 known kinds;显式 [] 表示不覆盖任何 kind)。
新增 3 个覆盖行为测试。

ADR-0012 — DanglingReference 退役(诊断 7→6 类):其两种情形(未解析 @ref、越界/缺失
相对 import)都是 typst 编译期失败,归 typstCompile。同步移除 Oracle.refsResolve
(被 compiles 蕴含),Legal 少一个合取项。impl 删去从未被发射的 DiagCode::DanglingReference,
闭合 named-but-unemitted 的 spec↔impl 缝。ADR-0010 加修订指针。

OPEN 点(RunState/Capability 完整性、QuestionBank、Course)按既定纪律保持 OPEN,本次
只改善其框架措辞,不决策。

验证:spec lake build 绿;cargo test 全绿(含新增覆盖测试);clippy 静默;
TH-141 check 0 errors/0 warnings 无回归。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/cph-diag/src/lib.rs

@@ -18,7 +18,7 @@ use serde::Serialize;
 /// Severity of a diagnostic.
 ///
 /// **Mirrors `Spec.Courseware.Diagnostic.Severity`** in the Lean semantic
-/// master (`spec/Spec/Courseware/Diagnostic.lean`), whose definition is
+/// master (`spec/Spec/Courseware/Check/Diagnostic.lean`), whose definition is
 /// exactly:
 ///
 /// ```text
@@ -76,12 +76,15 @@ pub enum DiagCode {
     UnknownKind,
     /// A required `content` `.typ` file (per the kind schema) is missing.
     MissingContentFile,
-    /// A reference (e.g. a relative import or cross-element link) does not
-    /// resolve.
-    DanglingReference,
     /// Instance data does not conform to its kind's JSON Schema.
     SchemaViolation,
-    /// A typst source failed to compile.
+    /// The assembled typst source failed to compile.
+    ///
+    /// Includes **reference-resolution** failures — an unresolved cross-reference
+    /// (`@ref`) or a relative `import`/`include` that escapes the import boundary
+    /// or names a missing file. typst detects all of these at compile time, so
+    /// they surface here rather than as a separate diagnostic (ADR-0012 folded
+    /// the former `DanglingReference` class into this one).
     TypstCompile,
     /// An element is ignored under a render target (ADR-0005: warning).
     RenderIgnored,
@@ -97,7 +100,6 @@ impl DiagCode {
             DiagCode::PartPathMissing => "E-PART-PATH",
             DiagCode::UnknownKind => "E-UNKNOWN-KIND",
             DiagCode::MissingContentFile => "E-MISSING-CONTENT",
-            DiagCode::DanglingReference => "E-DANGLING-REF",
             DiagCode::SchemaViolation => "E-SCHEMA",
             DiagCode::TypstCompile => "E-TYPST-COMPILE",
             DiagCode::RenderIgnored => "W-RENDER-IGNORED",