fix(build): keep custom index status visible

Author: Sunrisepeak

.agents/docs/2026-05-30-bmi-cache-custom-index-fix.md

@@ -80,4 +80,4 @@ There is also a cache-key correctness gap: all dependency cache entries currentl
 - Implemented regression as `tests/e2e/49_bmi_cache_nested_custom_index.sh` because the defect is in CLI dependency resolution plus build-plan artifact collection, not only the lower-level cache copy functions.
 - Local verification: `mcpp build` succeeded, then `MCPP=target/x86_64-linux-gnu/4d24c8b57fdbbbb4/bin/mcpp bash tests/e2e/49_bmi_cache_nested_custom_index.sh` returned `OK`.
 - `mcpp test -- --gtest_filter=BmiCache.*` initially exposed an unrelated local environment issue: `~/.mcpp/registry/data/xpkgs/xim-x-binutils/2.42` only had `.xpkg.lua` and no `bin/as`. Re-running with a temporary `MCPP_HOME` pointed at the complete installed mcpp registry passed: 15 test binaries ok, 0 failed.
-- Remote custom-index first-use sync now calls `update_index(..., quiet=true)` so `mcpp build` does not expose xlings update output. A non-zero update exits with a concise mcpp-level error.
+- Remote custom-index first-use sync keeps the mcpp-level `Fetching custom index repos (first use)` status, but calls `update_index(..., quiet=true)` so `mcpp build` does not expose xlings update output. A non-zero update exits with a concise mcpp-level error.

src/cli.cppm

@@ -1396,6 +1396,7 @@ prepare_build(bool print_fingerprint,
                         break;
                     }
                     if (needsRemoteUpdate) {
+                        mcpp::ui::status("Fetching", "custom index repos (first use)");
                         auto projEnv = mcpp::config::make_project_xlings_env(**cfg2, *root);
                         int rc = mcpp::xlings::update_index(projEnv, /*quiet=*/true);
                         if (rc != 0) {