fix: CapabilityProvider aggregate instead of std::pair (musl modules link)

The release (musl-gcc 15.1 static) link failed with an undefined reference to
vector<pair<string,string>>'s move ctor from the BuildPlan move ctor — the
instantiation wasn't emitted across the module boundary on that toolchain.
Use a named aggregate (capability, provider); structured bindings unchanged.
Verified: glibc build + musl-static self-build (the exact release path) link.

Author: d2learn-org

src/build/plan.cppm

@@ -66,7 +66,14 @@ struct BuildPlan {
     // in mcpp: providers (e.g. compat.glx-runtime) declare these per platform.
     std::vector<std::string>           runtimeDlopenLibs;   // union of deps' dlopen sonames
     std::vector<std::string>           runtimeCapabilities; // union of host capabilities
-    std::vector<std::pair<std::string, std::string>> runtimeProviders; // (capability, provider pkg)
+    // (capability, provider package). A named aggregate instead of std::pair:
+    // musl-gcc 15.1 modules failed to emit vector<pair<string,string>>'s
+    // move-ctor instantiation across the module boundary (release link error).
+    struct CapabilityProvider {
+        std::string capability;
+        std::string provider;
+    };
+    std::vector<CapabilityProvider>    runtimeProviders;
 };
 
 // Build a BuildPlan from already-validated inputs.
@@ -241,7 +248,7 @@ BuildPlan make_plan(const mcpp::manifest::Manifest&         manifest,
         for (auto const& cap : package.manifest.runtimeConfig.capabilities) {
             if (std::ranges::find(plan.runtimeCapabilities, cap) == plan.runtimeCapabilities.end())
                 plan.runtimeCapabilities.push_back(cap);
-            plan.runtimeProviders.emplace_back(cap, package.manifest.package.name);
+            plan.runtimeProviders.push_back({cap, package.manifest.package.name});
         }
     }
     // The same private runtime directories embedded as executable RUNPATH are

src/cli.cppm

@@ -3298,8 +3298,8 @@ prepare_build(bool print_fingerprint,
         bool found = false;
         std::stable_partition(ctx.plan.runtimeProviders.begin(),
                               ctx.plan.runtimeProviders.end(),
-                              [&](const std::pair<std::string, std::string>& pr) {
-            bool match = pr.first.rfind(capKey, 0) == 0 && pr.second == prov;
+                              [&](const auto& pr) {
+            bool match = pr.capability.rfind(capKey, 0) == 0 && pr.provider == prov;
             found = found || match;
             return match;
         });