test-build: make drop: satisfy a dep at resolution time

Previously drop: only filtered the resolved build order, so an external dep
with no dir in the tree (a 15.0-only SBo package like rust-opt) was flagged
UNMET before the order filter ran, and drop: could never rescue it. Move the
OV_DROP check into _resolve_visit: a dropped token is now skipped entirely
(no recurse, no UNMET, no order entry), satisfying 15.0-only deps that the
-current base already provides. Still inert on 15.0. Add self-check coverage
and clarify overrides.example.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/.extras/test-build b/.extras/test-build
index 8057683..90d45ac 100755
--- a/.extras/test-build
+++ b/.extras/test-build
@@ -231,6 +231,12 @@ _resolve_visit() {
       continue
     fi
     tok="$(apply_rename "$tok")"
+    # drop: satisfied by the -current base (e.g. a 15.0-only dep like rust-opt
+    # whose payload ships in current's full-install image). Skip it entirely:
+    # no recurse, no UNMET, no order entry. Inert on 15.0 (overrides are).
+    if [[ "${OV_DROP[$tok]:-}" == "1" ]]; then
+      continue
+    fi
     if [[ "${OV_FETCH[$tok]:-}" == "1" ]]; then
       FETCH_DEPS["$tok"]=1
       continue