fix(local): make trial-build-patch.R detect non-throwing build failures (#134)

`local/trial-build-patch.R` -- the single-package acceptance gate the proposer prints for humans to run (`PGPASS=... Rscript local/trial-build-patch.R <pkg>`) -- reported **`Trial build OK`** for rstan even though rstan.so failed to load (`symbol not found: tbb::detail::r1::observe`).

Same false-green as the registry gate before #130: `build_binary_package()` catches failures internally and returns `"error"` rather than throwing, so a `tryCatch` that only treats a thrown exception as failure passes a broken build. Now inspects the return value (mirrors trial-build-registry.R). Found while verifying the rstan/oneTBB unblock.

Reviewed-on: #134

local/trial-build-patch.R

@@ -40,23 +40,26 @@ cat(sprintf(
   patches_dir
 ))
 
-ok <- tryCatch(
-  {
-    bincraft::build_binary_package(
-      package,
-      tag_limit = 1L,
-      patches = patches_dir,
-      archive = FALSE,
-      upload = FALSE,
-      store_build_metadata = FALSE
-    )
-    TRUE
-  },
+# build_binary_package() catches build failures internally and RETURNS "error"
+# for the failed tag rather than throwing (bincraft >= v4.4.7), so inspect the
+# return value -- checking only for a thrown exception reports a broken build as
+# passing (false green).
+res <- tryCatch(
+  bincraft::build_binary_package(
+    package,
+    tag_limit = 1L,
+    patches = patches_dir,
+    archive = FALSE,
+    upload = FALSE,
+    store_build_metadata = FALSE
+  ),
   error = function(e) {
-    cat(sprintf("Trial build FAILED: %s\n", conditionMessage(e)))
-    FALSE
+    cat(sprintf("Trial build FAILED (threw): %s\n", conditionMessage(e)))
+    "error"
   }
 )
+flat <- as.character(unlist(res))
+ok <- length(flat) > 0L && !("error" %in% flat)
 
 if (ok) {
   cat(sprintf("Trial build OK: %s builds with the proposed patch.\n", package))