fix(manifest): Profile's dependency_linkage becomes two plain members

Windows CI could not compile `tests/unit/test_modgraph.cpp`:

  optional:262: error: no matching constructor for initialization of
  '_SMF_control<_Optional_construct_base<basic_string<char,...>>, ...>'

reached through `Manifest` -> `std::map<std::string, Profile>` ->
`Profile::dependencyLinkage`, an `std::optional<std::string>` DATA MEMBER of an
exported struct. `TargetEntry::sysroot`'s comment in the same file already
forbids that shape and prescribes the remedy -- two plain members -- after the
same error on an earlier occasion. `Profile` was the last member in the module
still shaped that way.

Semantics are unchanged: not declared still means "whatever [build] said", which
is what the optional carried and what `dependencyLinkageDeclared` carries now.

WHICH EDIT IN THIS BRANCH TIPS IT IS NOT ESTABLISHED. Two diagnoses were
refuted: that the new emptiness predicate's being an inline member was the cause
(made it a free function; CI failed identically), and that the runner image had
changed (re-ran main's own Windows job unchanged on today's image; it passed).
`test_modgraph.cpp` copies a Manifest by value on main too, so the landmine was
already armed; this removes the type that cannot be copied rather than the
perturbation that reached it.

Author: speak-agent

.agents/docs/2026-09-09-two-answers-and-two-silences.md

@@ -457,8 +457,33 @@ existed. That is #258's medicine applied one level further out, and it closed a
 fourth instance found while writing it — `xpkg.cppm`'s gate omitted
 `privateIncludeDirs`, which its own loop fills.
 
-**They are free functions, and that was forced by a measurement rather than
-chosen.** The first version made them members, which is the obvious shape and
+**A latent defect in this module had to be removed before any of it could
+land, and it is worth recording because the diagnosis went wrong twice.**
+Windows CI failed to compile `tests/unit/test_modgraph.cpp` with
+
+    optional:262: error: no matching constructor for initialization of
+    '_SMF_control<_Optional_construct_base<basic_string<char,...>>, ...>'
+
+reached through `Manifest` -> `std::map<std::string, Profile>` ->
+`Profile::dependencyLinkage`, an `std::optional<std::string>` DATA MEMBER of an
+exported struct. `TargetEntry::sysroot`'s comment, a few hundred lines above in
+the same file, already forbids that shape and gives the remedy — two plain
+members — after the same error on an earlier occasion. `Profile` was the last
+member in the module still shaped that way.
+
+The first attempt blamed the new emptiness predicate for being an inline member
+of an exported struct, and made it a free function. CI failed identically, which
+refuted that. The second attempt blamed the runner image, and was refuted by
+re-running main's own Windows job unchanged on today's image: it passed. So the
+trigger is somewhere in this change and the cause is the member, and those are
+different questions. **Which edit tips it is not established here** — the honest
+statement is that any perturbation of this module's interface can, and that
+removing the type which cannot be copied removes the class rather than the
+instance. `test_modgraph.cpp` copies a `Manifest` by value on main too
+(`scan_packages({PackageRoot{dir, m}})`), so the landmine was always armed.
+
+**The emptiness predicates are free functions, which was the first repair and is
+kept on its own merits.** The first version made them members, which is the obvious shape and
 the wrong one: adding an inline member to a struct this module exports changes
 what importers materialise from its BMI, and `Profile` carries a
 `std::optional<std::string>` that is already known to break under clang with the

CHANGELOG.md

@@ -71,6 +71,22 @@ GCC 的接口拼法本就是纯语言,因此同一个工程在 GCC 上能构建
 第四处随之关闭:xpkg 的闸门漏掉了它自己会填的 `privateIncludeDirs`。索引里 228 份
 descriptor 用新旧两个二进制解析,结果逐字节相同。
 
+### `Profile.dependency_linkage` 不再是 `std::optional<std::string>` 成员
+
+导出结构体的 `std::optional<std::string>` **数据成员**会迫使本模块的接口实例化该特化的
+特殊成员机制,在 clang + MSVC 标准库下无法编译:
+
+```
+optional:262: error: no matching constructor for initialization of
+'_SMF_control<_Optional_construct_base<basic_string<char,...>>, ...>'
+```
+
+路径是 `Manifest` -> `std::map<std::string, Profile>` -> `Profile`。同一文件里
+`TargetEntry::sysroot` 的注释早已禁止这个形状并给出修法(两个普通成员),`Profile` 是
+模块里最后一个仍是该形状的成员。现按同一修法改为
+`dependencyLinkage` + `dependencyLinkageDeclared`,语义不变:未声明仍表示「沿用
+`[build]` 的值」。
+
 ### `[runtime]` 与 `[target.<谓词>.runtime]` 的未知键会被报出
 
 不受支持的键被报出而不是丢弃,是 `[build]`、`[target.<triple>]` 与

modules/manifest/src/toml.cppm

@@ -705,8 +705,10 @@ std::expected<Manifest, ManifestError> parse_string(std::string_view content,
                         if (v.is_string()) out.push_back(v.as_string());
             };
             if (auto it = tt.find("dependency_linkage");
-                it != tt.end() && it->second.is_string())
+                it != tt.end() && it->second.is_string()) {
                 pr.dependencyLinkage = it->second.as_string();
+                pr.dependencyLinkageDeclared = true;
+            }
             read_list("cflags",   pr.cflags);
             read_list("cxxflags", pr.cxxflags);
             read_list("ldflags",  pr.ldflags);

modules/manifest/src/types.cppm

@@ -1401,12 +1401,29 @@ struct Profile {
     bool        strip    = false;
     // `dependency_linkage`, per profile (#519).
     //
-    // OPTIONAL, and that is load-bearing rather than stylistic: resolving a
-    // profile REPLACES the whole struct with the declared one, so a plain
-    // value would make `[profile.dev] opt = 0` silently reset a
-    // `[build] dependency_linkage = "shared"` back to the field default.
-    // Absent means "whatever [build] said".
-    std::optional<std::string> dependencyLinkage;
+    // DECLARED-OR-NOT IS LOAD-BEARING, and that is why there are two members
+    // rather than one: resolving a profile REPLACES the whole struct with the
+    // declared one, so a plain value alone would make `[profile.dev] opt = 0`
+    // silently reset a `[build] dependency_linkage = "shared"` back to the
+    // field default. Not declared means "whatever [build] said".
+    //
+    // TWO MEMBERS AND NOT AN `std::optional<std::string>`, for exactly the
+    // reason `TargetEntry::sysroot` gives above, and this was the last member
+    // in the module still shaped the way that note forbids. An
+    // `std::optional<std::string>` DATA MEMBER of an exported struct forces
+    // this module's interface to materialise that specialisation's
+    // special-member machinery, and under clang with the MSVC standard library
+    // it does not compile:
+    //
+    //     optional:262: error: no matching constructor for initialization of
+    //     '_SMF_control<_Optional_construct_base<basic_string<char,...>>, ...>'
+    //
+    // reached through `Manifest` -> `std::map<std::string, Profile>` ->
+    // `Profile`. The error names whichever translation unit happens to copy a
+    // Manifest -- `tests/unit/test_modgraph.cpp` is one -- and says nothing
+    // about the member that caused it.
+    std::string dependencyLinkage;
+    bool        dependencyLinkageDeclared = false;
     // Passthrough escape hatch (fixed keys, open values — I6 completeness):
     std::vector<std::string> cflags;
     std::vector<std::string> cxxflags;

src/build/prepare.cppm

@@ -2071,8 +2071,8 @@ prepare_build(bool print_fingerprint,
         // profile that does not mention it leaves `[build]` standing; a plain
         // value would reset it, because the block above REPLACES `pr` wholesale
         // with the declared profile.
-        if (pr.dependencyLinkage)
-            m->buildConfig.dependencyLinkage = *pr.dependencyLinkage;
+        if (pr.dependencyLinkageDeclared)
+            m->buildConfig.dependencyLinkage = pr.dependencyLinkage;
         m->buildConfig.optLevel = pr.optLevel;
         m->buildConfig.debug    = pr.debug;
         m->buildConfig.lto      = pr.lto;

tests/unit/test_manifest.cpp

@@ -3639,10 +3639,10 @@ dependency_linkage = "static"
 )");
     ASSERT_TRUE(m);
     ASSERT_TRUE(m->profiles.contains("dev"));
-    EXPECT_FALSE(m->profiles.at("dev").dependencyLinkage.has_value());
+    EXPECT_FALSE(m->profiles.at("dev").dependencyLinkageDeclared);
     ASSERT_TRUE(m->profiles.contains("fast"));
-    ASSERT_TRUE(m->profiles.at("fast").dependencyLinkage.has_value());
-    EXPECT_EQ(*m->profiles.at("fast").dependencyLinkage, "static");
+    ASSERT_TRUE(m->profiles.at("fast").dependencyLinkageDeclared);
+    EXPECT_EQ(m->profiles.at("fast").dependencyLinkage, "static");
 }
 
 TEST(Manifest, ADependencyEdgeLinkageIsAClosedVocabularyToo) {