feat(index): heal existing registry .xlings.json — org URL + artifact injection (#267-A #269)

Existing installs only run the text migration (seed is skipped when the
file exists), so it now rewrites the org URL and injects the artifact
declaration next to the canonical mcpplibs url. Idempotency gate: skip
injection when the res base is already present (plain replace_all would
re-inject every run). Covers both writer spacings (mcpp pretty / xlings
compact); unrelated keys (subos, bindings) are preserved byte-for-byte.

Author: Sunrisepeak

src/fallback/config_migration.cppm

@@ -1,8 +1,12 @@
-// mcpp.fallback.config_migration — legacy index name migration.
+// mcpp.fallback.config_migration — legacy index config migration.
 //
-// Older mcpp sandboxes used "mcpp-index" as the default index name.
-// These helpers rename it to "mcpplibs" in config.toml and .xlings.json
-// so xlings config/list output matches mcpp's default namespace.
+// Older mcpp sandboxes used "mcpp-index" as the default index name and the
+// pre-migration mcpp-community org URL. These helpers rename the index to
+// "mcpplibs", rewrite the org URL (#267), and inject the xlings >= 0.4.68
+// per-repo artifact declaration (#269) into config.toml / .xlings.json.
+// Deliberately text-based: .xlings.json carries xlings-owned state (subos,
+// version bindings) that a regeneration would destroy. This is a LEAF
+// module (no mcpp.config import), so the URL literals are repeated here.
 
 export module mcpp.fallback.config_migration;
 
@@ -83,6 +87,22 @@ bool migrate_xlings_json_index_names(const std::filesystem::path& path) {
     replace_all(updated, "https://github.com/mcpp-community/mcpp-index.git",
                          "https://github.com/mcpplibs/mcpp-index.git");
 
+    // Artifact injection (#269, xlings >= 0.4.68 per-repo artifact source).
+    // Existing installs never re-seed .xlings.json, so this migration is
+    // their only channel to the artifact declaration; older xlings safely
+    // ignores the key. Idempotency gate: the res base appearing anywhere
+    // means a previous run (or a fresh seed) already declared it — a plain
+    // replace_all would re-inject on every run. Both spacing variants
+    // because the file has two writers (mcpp pretty / xlings compact).
+    if (updated.find("xlings-res/mcpp-index") == std::string::npos) {
+        constexpr std::string_view art =
+            ", \"artifact\": \"https://github.com/xlings-res/mcpp-index\"";
+        for (std::string_view urlkv : {
+                "\"url\": \"https://github.com/mcpplibs/mcpp-index.git\"",
+                "\"url\":\"https://github.com/mcpplibs/mcpp-index.git\"" })
+            replace_all(updated, urlkv, std::string(urlkv) + std::string(art));
+    }
+
     return write_text_if_changed(path, original, updated);
 }
 

tests/unit/test_config.cpp

@@ -250,3 +250,64 @@ TEST(ConfigIndexMigration, CanonicalizeRespectsExplicitGitSourceAndCustomArtifac
     EXPECT_EQ(cfg.indexRepos[1].artifact, "https://example.com/my-mirror");
     EXPECT_TRUE(cfg.indexRepos[2].artifact.empty());        // foreign repo untouched
 }
+
+TEST(ConfigIndexMigration, XlingsJsonHealsPrettyLegacyEntry) {
+    auto dir = make_tempdir("mcpp-migrate-xj");
+    auto p = dir / ".xlings.json";
+    {
+        std::ofstream os(p);
+        os << "{\n  \"index_repos\": [\n"
+              "    { \"name\": \"mcpplibs\", \"url\": "
+              "\"https://github.com/mcpp-community/mcpp-index.git\" }\n"
+              "  ],\n  \"subos\": \"default\",\n  \"mirror\": \"auto\"\n}\n";
+    }
+    EXPECT_TRUE(mcpp::fallback::migrate_xlings_json_index_names(p));
+    auto text = read_all(p);
+    EXPECT_NE(text.find(
+        "\"url\": \"https://github.com/mcpplibs/mcpp-index.git\", "
+        "\"artifact\": \"https://github.com/xlings-res/mcpp-index\""),
+        std::string::npos) << text;
+    EXPECT_NE(text.find("\"subos\": \"default\""), std::string::npos);
+    EXPECT_EQ(text.find("mcpp-community/mcpp-index"), std::string::npos);
+    EXPECT_FALSE(mcpp::fallback::migrate_xlings_json_index_names(p));  // idempotent
+    EXPECT_EQ(read_all(p), text);
+    std::filesystem::remove_all(dir);
+}
+
+TEST(ConfigIndexMigration, XlingsJsonHealsCompactLegacyNameAndUrl) {
+    auto dir = make_tempdir("mcpp-migrate-xjc");
+    auto p = dir / ".xlings.json";
+    {
+        std::ofstream os(p);
+        os << "{\"index_repos\":[{\"name\":\"mcpp-index\","
+              "\"url\":\"https://github.com/mcpp-community/mcpp-index.git\"}],"
+              "\"mirror\":\"auto\"}";
+    }
+    EXPECT_TRUE(mcpp::fallback::migrate_xlings_json_index_names(p));
+    auto text = read_all(p);
+    EXPECT_NE(text.find("\"name\":\"mcpplibs\""), std::string::npos);
+    EXPECT_NE(text.find(
+        "\"url\":\"https://github.com/mcpplibs/mcpp-index.git\", "
+        "\"artifact\": \"https://github.com/xlings-res/mcpp-index\""),
+        std::string::npos) << text;
+    EXPECT_FALSE(mcpp::fallback::migrate_xlings_json_index_names(p));
+    std::filesystem::remove_all(dir);
+}
+
+TEST(ConfigIndexMigration, XlingsJsonSkipsInjectionWhenArtifactPresent) {
+    auto dir = make_tempdir("mcpp-migrate-xja");
+    auto p = dir / ".xlings.json";
+    std::string body =
+        "{\n  \"index_repos\": [\n"
+        "    { \"name\": \"mcpplibs\", \"url\": "
+        "\"https://github.com/mcpplibs/mcpp-index.git\", "
+        "\"artifact\": \"https://github.com/xlings-res/mcpp-index\" }\n"
+        "  ]\n}\n";
+    {
+        std::ofstream os(p);
+        os << body;
+    }
+    EXPECT_FALSE(mcpp::fallback::migrate_xlings_json_index_names(p));
+    EXPECT_EQ(read_all(p), body);
+    std::filesystem::remove_all(dir);
+}