fix(provider): read an xlings 1.10 payload_status as it meant it

A build whose vendored xlings cannot be updated (no newer source beside the
mcpp binary; the hermetic container lane) talks to xlings 2026.10.16.2,
whose payload_status reports no usable/current. Read as absent, every
payload was unusable and a fresh install reported success and then
'payload is not complete'. 1.10's complete already required the recipe's
revision, so it is both usable and current; the 1.10 behaviour is kept.
A payload of another revision is announced as an update, not as
incomplete.

Co-authored-by: speak-agent <248744407+speak-agent@users.noreply.github.com>

Author: Sunrisepeak

src/pm/package_fetcher.cppm

@@ -1147,7 +1147,7 @@ Fetcher::resolve_xpkg_path(std::string_view target,
     // currency; this function only maps them through the caller's intent.
     struct Here {
         std::filesystem::path dir;      // empty: nothing there
-        bool usable = false, current = false;
+        bool complete = false, usable = false, current = false;
         int installed = -1, revision = 0, floor = 0;
     };
     const auto here = [&]() -> Here {
@@ -1157,7 +1157,7 @@ Fetcher::resolve_xpkg_path(std::string_view target,
             // Present: a complete one (usable / current as the provider says),
             // or an interrupted install, or a success that installed nothing
             // (#533) -- the provider's verdicts say which.
-            return {st[0].dir, st[0].usable, st[0].current,
+            return {st[0].dir, st[0].complete, st[0].usable, st[0].current,
                     st[0].installedRevision, st[0].revision, st[0].floor};
         }
         // The provider could not say, or has nothing where the index's store
@@ -1168,7 +1168,7 @@ Fetcher::resolve_xpkg_path(std::string_view target,
         auto dir = provider->payload(ref);
         std::error_code ec;
         if (!dir.empty() && std::filesystem::is_directory(dir, ec) && !std::filesystem::is_empty(dir, ec))
-            return {dir, true, true};
+            return {dir, true, true, true};
         return {};
     };
 
@@ -1209,10 +1209,14 @@ Fetcher::resolve_xpkg_path(std::string_view target,
         if (now.usable)
             mcpp::ui::status("Updating", std::format("{}  packaging revision {} → {}",
                                                      label, now.installed, now.revision));
-        else if (now.installed >= 0 && now.installed < now.floor)
+        else if (now.complete && now.installed >= 0 && now.installed < now.floor)
             mcpp::ui::status("Updating", std::format(
                 "{}  packaging revision {} → {} (revision {} is below the index's floor {})",
                 label, now.installed, now.revision, now.installed, now.floor));
+        else if (now.installed >= 0 && now.installed != now.revision)
+            // A provider before 1.11 calls an older packaging incomplete.
+            mcpp::ui::status("Updating", std::format("{}  packaging revision {} → {}",
+                                                     label, now.installed, now.revision));
         else
             mcpp::ui::status("Reinstalling", std::format("{}  (the installed payload is incomplete)", label));
     }

src/provider/xlings/provider.cppm

@@ -247,8 +247,14 @@ public:
                     ps.installedRevision = t["installed_revision"].get<int>();
                 ps.complete = t.value("complete", false);
                 if (t.contains("floor") && t["floor"].is_number_integer()) ps.floor = t["floor"].get<int>();
-                ps.usable = t.value("usable", false);
-                ps.current = t.value("current", false);
+                // COMPAT(internal:provider-protocol-1.10): an xlings before
+                // 2026.10.17.1 reports no `usable` / `current`, and its
+                // `complete` already required the recipe's revision -- so it
+                // is both, read as 1.10 meant it. A vendored xlings that cannot
+                // be updated (no newer source beside this mcpp) keeps the
+                // behaviour it had.
+                ps.usable = t.contains("usable") ? t.value("usable", false) : ps.complete;
+                ps.current = t.contains("current") ? t.value("current", false) : ps.complete;
                 ps.error = str(t, "error");
                 out.push_back(std::move(ps));
             }