fix(diagnostics): stop promising a remedy that does not work (2026.8.15.3)

沙箱真实验证抓到的:mcpp 在 SubOS 缺 `subos_info` 时建议 `xlings self update`,而实测它与 `self doctor --fix` 都不回填已存在的 SubOS,`xlings subos` 也无 repair 子命令。已开 openxlings/xlings#547;三处措辞改为陈述事实并指向它。这句话出自 xlings 的原始措辞,mcpp 一直在转述 —— 把「上游这么说」当成「这是对的」转述给用户,和自己写错一样。

Author: Sunrisepeak

mcpp.toml

@@ -1,6 +1,6 @@
 [package]
 name        = "mcpp"
-version     = "2026.8.15.2"
+version     = "2026.8.15.3"
 description = "Modern C++ build & package management tool"
 license     = "Apache-2.0"
 authors     = ["mcpp-community"]

src/platform/runtime_binding.cppm

@@ -284,7 +284,8 @@ resolve_runtime_binding(
             "       Where the C runtime comes from a payload, there is now no "
             "declared runtime to bind to — mcpp declines to guess a version, so "
             "the link falls back to the host and the hermeticity check will say "
-            "so. `xlings self update` writes the block.",
+            "so. Only a SubOS created by a current xlings carries the block "
+            "(openxlings/xlings#547).",
             selection.subosName,
             info.note.empty() ? "no `subos_info` block" : info.note));
     } else if (info.schema > mcpp::xlings::subos::kSupportedSchema) {

src/platform/xlings/subos_info.cppm

@@ -146,8 +146,10 @@ Info read(const std::filesystem::path& subosDir) {
         info.note = std::format(
             "subos '{}' does not describe itself (no `{}` block), so programs "
             "run from here get no environment it declares — a GL application "
-            "will not find its drivers. A newer xlings writes this block; "
-            "`xlings self update` adds it",
+            "will not find its drivers. A SubOS created by a current xlings "
+            "carries it; an existing one is NOT backfilled by `self update` or "
+            "`self doctor --fix` (openxlings/xlings#547), so recreating the "
+            "SubOS is what supplies it today",
             subosDir.string(), kBlock);
         return info;
     }

src/toolchain/lifecycle.cppm

@@ -615,8 +615,10 @@ export int toolchain_install(const mcpp::config::GlobalConfig& cfg,
             // the install itself succeeded.
             mcpp::ui::warning(std::format(
                 "installed, but not bound to a C runtime: {}.\n"
-                "         Run `xlings self update` to write the SubOS "
-                "description, then re-run this command to complete the wiring.",
+                "         The install itself succeeded. To complete the wiring, "
+                "use a SubOS created by a current xlings — an existing one is "
+                "not backfilled (openxlings/xlings#547) — then re-run this "
+                "command.",
                 fixed->skippedReason));
         }
 

src/version.cppm

@@ -31,6 +31,6 @@ import std;
 
 export namespace mcpp {
 
-inline constexpr std::string_view MCPP_VERSION = "2026.8.15.2";
+inline constexpr std::string_view MCPP_VERSION = "2026.8.15.3";
 
 } // namespace mcpp

tests/unit/test_post_install.cpp

@@ -160,8 +160,8 @@ TEST(PostInstallFixup, ADeclaredRuntimeThatCannotBeHonouredStillFails) {
 // No marker may be written for a fixup that did not happen. The marker is a
 // content fingerprint whose whole job is to answer "were these inputs ever
 // applied"; one written for "we did nothing" reads back as "already applied",
-// and the fixup would then never run again — including on the day the user runs
-// `xlings self update` and the identity finally becomes knowable.
+// and the fixup would then never run again — including on the day the user
+// moves to a SubOS that does describe itself and the identity becomes knowable.
 TEST(PostInstallFixup, ASkippedFixupLeavesNoMarkerBehind) {
     if constexpr (!mcpp::platform::is_linux) {
         GTEST_SKIP() << "the runtime binding gate is Linux-only";