Merge origin/main (PR #8: corpus URL trailing-slash normalization) into feat/expenditure-concept

Local main was stale at fa40266 when this branch was created, so it was
missing 748ca4a. Merging rather than rebasing to preserve the reviewed
commit SHAs recorded in the SDD ledger.

tests/testthat/test-config.R

@@ -26,3 +26,41 @@ test_that(".resolve_cache_dir falls back to R_user_dir", {
     })
   })
 })
+
+# ---------------------------------------------------------------------------
+# Trailing-slash normalization (uscogdata #3 follow-up).
+#
+# EVERY consumer builds paths by concatenation: paste0(url, "manifest.json")
+# (manifest.R), paste0(url, e$path) (mirror.R), and the parquet glob in
+# views.R. mirror.R:104 even comments 'url ends in "/"' -- an assumption the
+# package documents and relies on but never enforced.
+#
+# A URL missing its trailing slash therefore fails SILENTLY and confusingly:
+#   HTTPS -> ".../downloadmanifest.json" -> the host answers with an HTML 404
+#            page -> the jsonlite lexical error that issue #3 reported;
+#   local -> ".../corpusdata/long/**/*.parquet" -> DuckDB "No files found".
+# Neither message points at the real cause. Normalize once, at resolution.
+# ---------------------------------------------------------------------------
+
+test_that(".resolve_url appends a missing trailing slash", {
+  withr::local_envvar(USCOGDATA_URL = "https://example.org/s/TOKEN/download")
+  expect_equal(.resolve_url(), "https://example.org/s/TOKEN/download/")
+})
+
+test_that(".resolve_url leaves an existing trailing slash alone", {
+  withr::local_envvar(USCOGDATA_URL = "https://example.org/s/TOKEN/download/")
+  expect_equal(.resolve_url(), "https://example.org/s/TOKEN/download/")
+})
+
+test_that(".resolve_url normalizes a local path without a trailing slash", {
+  withr::local_envvar(USCOGDATA_URL = "/tmp/corpus")
+  expect_equal(.resolve_url(), "/tmp/corpus/")
+})
+
+test_that(".resolve_url does not invent a slash for an empty setting", {
+  # An unset/empty URL must stay empty so the "not configured" guard in
+  # manifest.R still fires, rather than degrading into a bare "/" root.
+  withr::local_envvar(USCOGDATA_URL = "")
+  withr::local_options(uscogdata.url = "")
+  expect_equal(.resolve_url(), "")
+})