fix(build): stop per-minor objects masking the per-minor candidate list (#189)

## Motivation

`arm64/alpine324` (pipeline 11953) finished in minutes having uploaded 57 packages, and reported:

```
Skipped 0 package versions already attempted under R 4.4; 0 remaining
Skipped 0 package versions already attempted under R 4.6; 3 remaining
```

The same run's index step dropped **2407** packages as missing for 4.4 and **2436** for 4.6. Nothing to build, and thousands missing — the candidate list is wrong.

## Two omissions

**1. Per-minor objects mask the per-minor candidates.**

```r
s3_pkgs <- s3fs::s3_dir_ls(".../latest/src/contrib", recurse = TRUE)
file_names <- basename(s3_pkgs)
```

`recurse = TRUE` walks `4.4/`, `4.5/`, `4.6/`; `basename()` throws the directory away. `4.5/curl_1.0.tar.gz` and `curl_1.0.tar.gz` collapse to one name, so a package present under **any** R minor counts as built for **all** of them — pruning exactly the packages a per-minor pass exists to build.

Per-minor objects are now excluded, and presence in a specific minor is decided downstream where the running R version is known: `build-all.R` filters on it, and `build_binary_package()` checks the per-minor path per package and skips what is already there.

`Archive/` is kept. Those are versions built and later superseded; dropping them would make every archived version look unbuilt.

Validated against real path shapes:

| path | |
|---|---|
| `curl_1.0.tar.gz` | keep |
| `4.4/curl_1.0.tar.gz` | exclude |
| `4.6/rlang_1.3.0.tar.gz` | exclude |
| `Archive/curl/curl_0.9.tar.gz` | keep |
| `PACKAGES.gz` | keep |

**2. The error query ignores `r_version`.**

```sql
SELECT error_occurred FROM single_builds
 WHERE name = $1 AND tag = $2 AND platform = $3 AND arch = $4
```

A failure under the primary minor drops the package from every other minor's candidate list. This is the same omission fixed in `local/build-all.R` (#187) and in bincraft's `check_package_error()` (rpkgs/bincraft#119). This is the third and last consumer of that table — I have grepped the rest; `bincraft::R/cran-internal.R` also reads it, but to list packages present rather than to skip, where the R minor does not apply.

## Expected effect

The per-minor passes get real candidate lists. Expect slots that reported "0 remaining" to report thousands, and correspondingly long runs.

There is a cost: the list is no longer pruned by per-minor presence, so each pass asks `build_binary_package()` about packages that may already exist, and it answers `already exists in S3 ... Skipping build` per package. Slower per pass, and correct — the pruning it replaces was removing the wrong things.

Reviewed-on: #189

local/packages-to-build.R

@@ -116,7 +116,28 @@ s3_pkgs <- s3fs::s3_dir_ls(
   recurse = TRUE
 )
 
-file_names <- basename(s3_pkgs)
+# `recurse = TRUE` walks the per-minor slots as well, and `basename()` throws
+# the directory away - so `4.5/curl_1.0.tar.gz` and `curl_1.0.tar.gz` collapse
+# to one name and a package present under *any* R minor counts as built for
+# *all* of them. The candidate list then prunes exactly the packages a
+# per-minor pass exists to build: arm64/alpine324 reported "0 remaining" for
+# both 4.4 and 4.6 while its indexes were dropping 2400+ packages as missing.
+#
+# Per-minor objects are therefore excluded here. Presence in a specific minor
+# is decided downstream, where the running R version is known: build-all.R
+# filters on it, and `build_binary_package()` checks the per-minor path per
+# package and skips what is already there.
+#
+# Archive/ is kept. Those are versions that were built and then superseded;
+# dropping them would make every archived version look unbuilt.
+per_minor_object <- grepl("/[0-9]+\\.[0-9]+/[^/]+$", s3_pkgs)
+if (any(per_minor_object)) {
+  cat(sprintf(
+    "Excluding %d per-minor object(s) from the presence check; those are decided per pass\n",
+    sum(per_minor_object)
+  ))
+}
+file_names <- basename(s3_pkgs[!per_minor_object])
 
 # An object occupying a key is not proof a binary was built: a package whose
 # build failed has its CRAN source published under exactly that name. Left in
@@ -179,11 +200,22 @@ s3_dt <- data.table(
 
 ### Get all packages with build errors
 
+# Scoped to the R minor this snapshot is computed under. A failure is a fact
+# about one interpreter: without the scope a package that failed under the
+# primary minor is dropped from the candidate list for every other minor too,
+# which is the same omission fixed in local/build-all.R and in bincraft's
+# check_package_error().
+snapshot_r_minor <- paste(
+  R.version$major,
+  strsplit(R.version$minor, ".", fixed = TRUE)[[1L]][1L],
+  sep = "."
+)
 sql_query <- paste0(
   # nolint
   "SELECT error_occurred FROM ",
   "single_builds",
-  " WHERE name = $1 AND tag = $2 AND platform = $3 AND arch = $4"
+  " WHERE name = $1 AND tag = $2 AND platform = $3 AND arch = $4",
+  " AND substring(r_version from '^[0-9]+[.][0-9]+') = $5"
 )
 # Function to query for a single package-version
 query_error <- function(pkg, ver) {
@@ -191,7 +223,7 @@ query_error <- function(pkg, ver) {
     ~ DBI::dbGetQuery(
       con,
       sql_query,
-      params = list(pkg, ver, platform, arch)
+      params = list(pkg, ver, platform, arch, snapshot_r_minor)
     ),
     rate = purrr::rate_backoff(
       pause_base = 1L,