diff --git a/.crow/auto-apply-patches.yaml b/.crow/auto-apply-patches.yaml
new file mode 100644
index 0000000..15cc1ee
--- /dev/null
+++ b/.crow/auto-apply-patches.yaml
@@ -0,0 +1,65 @@
+# Auto-apply registry patches (issue #115, step 3 automation).
+# Classifies `single_builds` failures and, for the top-N auto-proposable
+# candidates by failure volume, writes the registry entries onto the reused
+# `auto/registry-patch-proposals` branch and opens/updates a single PR.
+# Nothing merges: the `trial-build-registry` pipeline is the merge gate, and a
+# human reviews the PR. Novel source diffs / unknown signatures are never
+# proposed. Global across platforms, so a single job -- no matrix.
+#
+# Needs a write token (REPO_RW_TOKEN) to push and FORGEJO_TOKEN to open the PR.
+# Register the `auto-apply-patches` cron in the crow UI, or run manually:
+#   woodpecker-cli pipeline create --var task=auto-apply-patches --branch=main 7
+variables:
+  patch_limit:
+    description: 'Max candidates to propose per run (top by failure volume).'
+    default: '10'
+
+when:
+  - event: manual
+    evaluate: 'task == "auto-apply-patches"'
+  - event: cron
+    cron: auto-apply-patches
+
+skip_clone: true
+
+labels:
+  group: rpkgs-amd64
+
+steps:
+  - name: 'Auto-apply registry patches'
+    image: reg.devxy.io/rpkgs/build-env-alpine:3.24
+    pull: true
+    environment:
+      PGPASS:
+        from_secret: PGPASS
+      REPO_RO_TOKEN:
+        from_secret: REPO_RO_TOKEN
+      REPO_RW_TOKEN:
+        from_secret: REPO_RW_TOKEN
+      FORGEJO_TOKEN:
+        from_secret: FORGEJO_TOKEN
+      GIT_USER: devxy-bot
+      GIT_EMAIL: bot@devxy.io
+      PATCH_LIMIT: ${patch_limit}
+      R_VERSION: 4.5.3
+      R_LIBS_USER: /mnt/cache/R-pkgs
+    commands:
+      - git clone -q https://pat-s:$$REPO_RO_TOKEN@git.devxy.io/devxy/build-cran-binaries.git .
+      - mkdir -p /mnt/cache/R-pkgs
+      - rm -rf /mnt/cache/R-pkgs/00LOCK-*
+      - /opt/R/$R_VERSION/bin/R -q -e 'pak::pak(c("httr2", "jsonlite"))'
+      - /opt/R/$R_VERSION/bin/Rscript local/propose-patches.R --open-pr --limit $PATCH_LIMIT
+    backend_options:
+      kubernetes:
+        resources:
+          requests:
+            memory: 1Gi
+            cpu: 2000m
+          limits:
+            memory: 2Gi
+            cpu: 2000m
+        tolerations:
+          - key: 'CI'
+            operator: 'Equal'
+            value: 'true'
+            effect: 'NoSchedule'
diff --git a/.crow/trial-build-registry.yaml b/.crow/trial-build-registry.yaml
new file mode 100644
index 0000000..1ac71e8
--- /dev/null
+++ b/.crow/trial-build-registry.yaml
@@ -0,0 +1,140 @@
+# Merge gate for the auto-patch PR (issue #115, step 3).
+# For each platform, trial-builds every registry entry the auto-patch branch
+# ADDS (vs main) in that platform's own `reg.devxy.io/rpkgs/build-env-*` image,
+# with the registry applied. A row with no new entries for its platform is a
+# fast no-op. The pipeline is green only if every new entry builds, so it gates
+# the PR before merge. Nothing is uploaded/archived/recorded.
+#
+# The repo uses no `pull_request` triggers, so this runs manually against the
+# branch (or on a cron); point it at the auto-patch branch via `patch_branch`:
+#   woodpecker-cli pipeline create --var task=trial-build-registry \
+#     --var patch_branch=auto/registry-patch-proposals --branch=main 7
+variables:
+  patch_branch:
+    description: 'Branch whose new registry entries to trial-build.'
+    default: auto/registry-patch-proposals
+
+when:
+  - event: manual
+    evaluate: 'task == "trial-build-registry"'
+  - event: cron
+    cron: trial-build-registry
+
+skip_clone: true
+
+labels:
+  group: rpkgs-${ARCH}
+
+matrix:
+  include:
+    - OS: alpine-322
+      ARCH: amd64
+      R_VERSION: 4.5.3
+      IMG: alpine:3.24
+    - OS: alpine-322
+      ARCH: arm64
+      R_VERSION: 4.5.3
+      IMG: alpine:3.24
+    - OS: alpine-323
+      ARCH: amd64
+      R_VERSION: 4.5.3
+      IMG: alpine:3.24
+    - OS: alpine-323
+      ARCH: arm64
+      R_VERSION: 4.5.3
+      IMG: alpine:3.24
+    - OS: alpine-324
+      ARCH: amd64
+      R_VERSION: 4.5.3
+      IMG: alpine:3.24
+    - OS: alpine-324
+      ARCH: arm64
+      R_VERSION: 4.5.3
+      IMG: alpine:3.24
+    - OS: redhat-8
+      ARCH: amd64
+      R_VERSION: 4.4.3
+      IMG: redhat:8
+    - OS: redhat-8
+      ARCH: arm64
+      R_VERSION: 4.4.3
+      IMG: redhat:8
+    - OS: redhat-9
+      ARCH: amd64
+      R_VERSION: 4.4.3
+      IMG: redhat:9
+    - OS: redhat-9
+      ARCH: arm64
+      R_VERSION: 4.4.3
+      IMG: redhat:9
+    - OS: redhat-10
+      ARCH: amd64
+      R_VERSION: 4.5.3
+      IMG: redhat:10
+    - OS: redhat-10
+      ARCH: arm64
+      R_VERSION: 4.5.3
+      IMG: redhat:10
+    - OS: ubuntu-2204
+      ARCH: amd64
+      R_VERSION: 4.4.3
+      IMG: ubuntu:jammy
+    - OS: ubuntu-2204
+      ARCH: arm64
+      R_VERSION: 4.4.3
+      IMG: ubuntu:jammy
+    - OS: ubuntu-2404
+      ARCH: amd64
+      R_VERSION: 4.4.3
+      IMG: ubuntu:noble
+    - OS: ubuntu-2404
+      ARCH: arm64
+      R_VERSION: 4.4.3
+      IMG: ubuntu:noble
+    - OS: ubuntu-2604
+      ARCH: amd64
+      R_VERSION: 4.5.3
+      IMG: ubuntu:resolute
+    - OS: ubuntu-2604
+      ARCH: arm64
+      R_VERSION: 4.5.3
+      IMG: ubuntu:resolute
+
+steps:
+  - name: 'Trial-build new registry entries'
+    image: reg.devxy.io/rpkgs/build-env-${IMG}
+    pull: true
+    environment:
+      B2_S3_ACCESS_KEY:
+        from_secret: B2_S3_ACCESS_KEY
+      B2_S3_SECRET_KEY:
+        from_secret: B2_S3_SECRET_KEY
+      REPO_RO_TOKEN:
+        from_secret: REPO_RO_TOKEN
+      GITHUB_PAT:
+        from_secret: GITHUB_PAT
+      PLATFORM: ${OS}
+      ARCH: ${ARCH}
+      R_VERSION: ${R_VERSION}
+      R_LIBS_USER: /mnt/cache/R-pkgs
+    commands:
+      - git clone -q --branch ${patch_branch} https://pat-s:$$REPO_RO_TOKEN@git.devxy.io/devxy/build-cran-binaries.git .
+      - git fetch -q origin main
+      - mkdir -p /mnt/cache/R-pkgs
+      - rm -rf /mnt/cache/R-pkgs/00LOCK-*
+      - /opt/R/$R_VERSION/bin/Rscript local/install-bincraft.R
+      - /opt/R/$R_VERSION/bin/Rscript local/trial-build-registry.R origin/main
+    backend_options:
+      kubernetes:
+        resources:
+          requests:
+            memory: 2Gi
+            cpu: 2000m
+          limits:
+            memory: 4Gi
+            cpu: 2000m
+        tolerations:
+          - key: 'CI'
+            operator: 'Equal'
+            value: 'true'
+            effect: 'NoSchedule'
diff --git a/local/patches/README.md b/local/patches/README.md
index 992395f..455a96c 100644
--- a/local/patches/README.md
+++ b/local/patches/README.md
@@ -81,6 +81,19 @@ Run the trial build inside the failing platform's build-env image; it uploads/ar
 Rscript local/trial-build-patch.R <package>
 ```
 
+#### Autonomous PR + trial-build gate
+
+`--open-pr` closes the loop: it writes the top-N candidates (by failure volume) onto the reused `auto/registry-patch-proposals` branch and opens/updates a single PR.
+`.crow/auto-apply-patches.yaml` runs this on a cron (needs `FORGEJO_TOKEN` and a write-scoped `REPO_RW_TOKEN`).
+
+```bash
+# Bounded batch; opens/updates one PR.
+PGPASS=... FORGEJO_TOKEN=... REPO_RW_TOKEN=... Rscript local/propose-patches.R --open-pr --limit 10
+```
+
+The merge gate is `.crow/trial-build-registry.yaml`: matrixed over the build-env images, each platform trial-builds only the entries the branch **adds** (`local/trial-build-registry.R`, which diffs the registry against `main`) and is green only if every new entry builds.
+The repo uses no `pull_request` triggers, so this gate runs manually or on a cron against the auto-patch branch (`--var patch_branch=...`); wiring it to fire on the PR needs `event: pull_request` enabled on the forge.
+
 `--write` and `--open-issue` also append to `local/patches/proposals-log.json`, a ledger of what was proposed.
 
 ### Feedback loop (step 4)
diff --git a/local/proposal-tracking-lib.R b/local/proposal-tracking-lib.R
index 5efc87c..80c4ab2 100644
--- a/local/proposal-tracking-lib.R
+++ b/local/proposal-tracking-lib.R
@@ -175,4 +175,37 @@ blocked_summary <- function(report, max_pkgs = 15L) {
   })
 }
 
+# Does a registry entry's `platforms` apply to a build on `os` (e.g.
+# "ubuntu-2604")? Mirrors bincraft's token match: an entry applies if any of its
+# platform tokens is "*", the OS codename, or the distro family ("ubuntu").
+entry_applies_to_os <- function(entry_platforms, os) {
+  toks <- as.character(unlist(entry_platforms))
+  family <- sub("-.*$", "", os) # ubuntu-2604 -> ubuntu
+  any(toks %in% c("*", os, family))
+}
+
+# Registry entries present in `current` but not in `base` (matched on
+# package|platforms|versions), optionally restricted to those that apply to a
+# given `os`. Used by the trial-build gate to build only the entries a PR adds.
+new_registry_packages <- function(current, base, os = NULL) {
+  key <- function(e) {
+    sprintf(
+      "%s|%s|%s",
+      e$package %||% "?",
+      paste(sort(as.character(unlist(e$platforms))), collapse = ","),
+      e$versions %||% "?"
+    )
+  }
+  base_keys <- vapply(base %||% list(), key, character(1L))
+  added <- Filter(function(e) !(key(e) %in% base_keys), current %||% list())
+  if (!is.null(os)) {
+    added <- Filter(function(e) entry_applies_to_os(e$platforms, os), added)
+  }
+  unique(vapply(
+    added,
+    function(e) as.character(e$package %||% ""),
+    character(1L)
+  ))
+}
+
 `%||%` <- function(a, b) if (is.null(a)) b else a
diff --git a/local/propose-patches.R b/local/propose-patches.R
index 7ff195b..fb45ea9 100644
--- a/local/propose-patches.R
+++ b/local/propose-patches.R
@@ -15,10 +15,17 @@
 #
 # Usage:
 #   PGPASS=... Rscript local/propose-patches.R [--platform P] [--arch A] [--min N]
+#                                              [--limit N]
 #       (default)        print candidates + validation, take no action
 #       --write          append candidates to local/patches/registry.json and
 #                        the proposals ledger (commit + open a PR yourself)
 #       --open-issue     post/update a Forgejo tracking issue (needs FORGEJO_TOKEN)
+#       --open-pr        write the entries, push the `auto/registry-patch-proposals`
+#                        branch, and open/update a PR autonomously (needs
+#                        FORGEJO_TOKEN, and REPO_RW_TOKEN to push in CI). The
+#                        `trial-build-registry` pipeline is the merge gate.
+#       --limit N        only act on the top-N candidates by failure volume
+#                        (bounded batch; the rest are picked up on the next run)
 #       --json PATH      also write the machine-readable candidate list to PATH
 
 options(error = function() {
@@ -58,6 +65,8 @@ if (is.na(min_count)) {
 }
 do_write <- "--write" %in% args
 do_issue <- "--open-issue" %in% args
+do_pr <- "--open-pr" %in% args
+limit <- suppressWarnings(as.integer(opt_val("--limit", NA_character_)))
 
 if (nchar(Sys.getenv("PGPASS")) == 0L) {
   stop("PGPASS env var is not set; a DB password is required.")
@@ -65,6 +74,8 @@ if (nchar(Sys.getenv("PGPASS")) == 0L) {
 
 registry_file <- file.path(script_dir, "patches", "registry.json")
 ledger_file <- file.path(script_dir, "patches", "proposals-log.json")
+# Branch the autonomous PR reuses, so re-runs update one PR instead of piling up.
+pr_branch <- "auto/registry-patch-proposals"
 
 # ---------------------------------------------------------------------------
 # Query failing builds (same shape as failing-builds-report.R)
@@ -118,7 +129,8 @@ registered_pkgs <- unique(vapply(
 report <- build_triage_report(failures, registered_pkgs)
 report <- Filter(function(r) r$build_count >= min_count, report)
 
-# Flatten auto-proposable groups into candidate records.
+# Flatten auto-proposable groups into candidate records, carrying the group's
+# build volume so we can prioritise the highest-impact fixes.
 candidates <- list()
 for (r in report) {
   if (is.null(r$proposed_entries)) {
@@ -130,6 +142,7 @@ for (r in report) {
       signature = r$signature,
       confidence = r$confidence,
       tier = r$tier,
+      build_count = r$build_count,
       entry = r$proposed_entries[[pkg]]
     )
   }
@@ -173,6 +186,22 @@ if (length(candidates) == 0L) {
   q(status = 0)
 }
 
+# Prioritise by failure volume, then apply --limit so one run tackles a bounded
+# batch (the rest are picked up on the next run).
+candidates <- candidates[order(
+  -vapply(candidates, function(c) c$build_count %||% 0L, integer(1L))
+)]
+deferred <- 0L
+if (!is.na(limit) && limit >= 0L && length(candidates) > limit) {
+  deferred <- length(candidates) - limit
+  candidates <- utils::head(candidates, limit)
+  cat(sprintf(
+    "\nLimiting to top %d candidate(s) by failure volume; %d deferred to a later run.\n",
+    limit,
+    deferred
+  ))
+}
+
 cat(sprintf(
   "\n%d candidate registry %s:\n",
   length(candidates),
@@ -386,8 +415,163 @@ if (do_write) {
     cat(sprintf("Opened tracking issue #%d.\n", created$number))
   }
   save_ledger(merge_ledger(load_ledger(), new_ledger_records))
+} else if (do_pr) {
+  forgejo_token <- Sys.getenv("FORGEJO_TOKEN")
+  if (nchar(forgejo_token) == 0L) {
+    stop("--open-pr requires FORGEJO_TOKEN (to open the PR).")
+  }
+  suppressPackageStartupMessages(library(httr2, quietly = TRUE))
+  forgejo_base <- "https://git.devxy.io/api/v1"
+  repo <- "devxy/build-cran-binaries"
+
+  # Write the entries + ledger, then commit them onto the reused auto branch.
+  jsonlite::write_json(
+    merged,
+    registry_file,
+    auto_unbox = TRUE,
+    pretty = TRUE,
+    null = "null"
+  )
+  save_ledger(merge_ledger(load_ledger(), new_ledger_records))
+
+  git <- function(...) {
+    st <- system2("git", c(...), stdout = TRUE, stderr = TRUE)
+    if (!identical(attr(st, "status"), NULL)) {
+      stop(sprintf(
+        "git %s failed:\n%s",
+        paste(..., collapse = " "),
+        paste(st, collapse = "\n")
+      ))
+    }
+    invisible(st)
+  }
+  git("config", "user.name", Sys.getenv("GIT_USER", "devxy-bot"))
+  git(
+    "config",
+    "user.email",
+    Sys.getenv("GIT_EMAIL", "bot@devxy.io")
+  )
+  git("checkout", "-B", pr_branch)
+  git(
+    "add",
+    file.path(script_dir, "patches", "registry.json"),
+    ledger_file
+  )
+  git(
+    "commit",
+    "-m",
+    sprintf(
+      "feat(patches): auto-propose %d registry %s from classified failures",
+      length(candidate_entries),
+      if (length(candidate_entries) == 1L) "entry" else "entries"
+    )
+  )
+  # Push with a write token when provided (CI); otherwise rely on origin creds.
+  rw_token <- Sys.getenv("REPO_RW_TOKEN")
+  push_target <- if (nchar(rw_token) > 0L) {
+    sprintf(
+      "https://%s:%s@git.devxy.io/%s.git",
+      Sys.getenv("GIT_USER", "devxy-bot"),
+      rw_token,
+      repo
+    )
+  } else {
+    "origin"
+  }
+  git("push", "-f", push_target, sprintf("HEAD:refs/heads/%s", pr_branch))
+
+  pr_title <- sprintf(
+    "feat(patches): auto-proposed registry patches (%s)",
+    now
+  )
+  body_lines <- c(
+    sprintf(
+      "_Auto-generated %s by `local/propose-patches.R --open-pr` from classified `single_builds` failures._",
+      now
+    ),
+    "",
+    sprintf(
+      "Adds %d known-lever registry %s (top by failure volume%s).",
+      length(candidate_entries),
+      if (length(candidate_entries) == 1L) "entry" else "entries",
+      if (deferred > 0L) {
+        sprintf("; %d deferred to a later run", deferred)
+      } else {
+        ""
+      }
+    ),
+    "",
+    "**Merge gate:** the `trial-build-registry` pipeline builds each new entry in its target build-env image; merge only once it is green.",
+    "Novel source diffs and unknown signatures are never auto-proposed.",
+    "",
+    "| package | signature | platforms |",
+    "| --- | --- | --- |"
+  )
+  for (c in candidates) {
+    body_lines <- c(
+      body_lines,
+      sprintf(
+        "| %s | %s | %s |",
+        c$package,
+        c$signature,
+        toString(as.character(c$entry$platforms))
+      )
+    )
+  }
+  new_body <- paste(body_lines, collapse = "\n")
+
+  # One PR per reused branch: update if open, else create.
+  pulls_url <- sprintf(
+    "%s/repos/%s/pulls?state=open&limit=50",
+    forgejo_base,
+    repo
+  )
+  open_pulls <- httr2::request(pulls_url) |>
+    httr2::req_headers(Authorization = paste("token", forgejo_token)) |>
+    httr2::req_perform() |>
+    httr2::resp_body_json(simplifyVector = FALSE)
+  match_idx <- which(vapply(
+    open_pulls,
+    function(p) identical(p$head$ref, pr_branch),
+    logical(1L)
+  ))
+  if (length(match_idx) > 0L) {
+    num <- open_pulls[[match_idx[1]]]$number
+    httr2::request(sprintf("%s/repos/%s/pulls/%d", forgejo_base, repo, num)) |>
+      httr2::req_headers(
+        Authorization = paste("token", forgejo_token),
+        `Content-Type` = "application/json"
+      ) |>
+      httr2::req_body_json(list(title = pr_title, body = new_body)) |>
+      httr2::req_method("PATCH") |>
+      httr2::req_perform()
+    cat(sprintf("\nUpdated auto-patch PR #%d (branch %s).\n", num, pr_branch))
+  } else {
+    created <- httr2::request(sprintf(
+      "%s/repos/%s/pulls",
+      forgejo_base,
+      repo
+    )) |>
+      httr2::req_headers(
+        Authorization = paste("token", forgejo_token),
+        `Content-Type` = "application/json"
+      ) |>
+      httr2::req_body_json(list(
+        title = pr_title,
+        head = pr_branch,
+        base = "main",
+        body = new_body
+      )) |>
+      httr2::req_perform() |>
+      httr2::resp_body_json()
+    cat(sprintf(
+      "\nOpened auto-patch PR #%d (branch %s).\n",
+      created$number,
+      pr_branch
+    ))
+  }
 } else {
   cat(
-    "\nDry run: no changes made. Re-run with --write or --open-issue to act.\n"
+    "\nDry run: no changes made. Re-run with --write, --open-issue, or --open-pr to act.\n"
   )
 }
diff --git a/local/tests/test-proposal-tracking-lib.R b/local/tests/test-proposal-tracking-lib.R
index 02a29f1..05cd0e9 100644
--- a/local/tests/test-proposal-tracking-lib.R
+++ b/local/tests/test-proposal-tracking-lib.R
@@ -162,6 +162,57 @@ test_that("blocked_summary lists each dependency and its dependent count", {
   expect_true(b[[1L]]$packages_truncated)
 })
 
+test_that("entry_applies_to_os matches codename, family, and wildcard", {
+  expect_true(entry_applies_to_os(list("ubuntu-2604"), "ubuntu-2604"))
+  expect_true(entry_applies_to_os(list("ubuntu"), "ubuntu-2604")) # family
+  expect_true(entry_applies_to_os(list("*"), "ubuntu-2604"))
+  expect_true(entry_applies_to_os(list("alpine", "ubuntu-2604"), "ubuntu-2604"))
+  expect_false(entry_applies_to_os(list("alpine-324"), "ubuntu-2604"))
+  expect_false(entry_applies_to_os(list("ubuntu-2404"), "ubuntu-2604")) # other codename
+})
+
+test_that("new_registry_packages returns only added entries for the platform", {
+  base <- list(
+    list(
+      package = "RcppParallel",
+      platforms = list("alpine", "ubuntu-2604"),
+      versions = "*"
+    )
+  )
+  current <- list(
+    base[[1L]], # unchanged -> not "new"
+    list(package = "BFpack", platforms = list("ubuntu-2604"), versions = "*"),
+    list(
+      package = "someAlpinePkg",
+      platforms = list("alpine-324"),
+      versions = "*"
+    )
+  )
+  # For ubuntu-2604: only the newly-added BFpack (RcppParallel is unchanged,
+  # someAlpinePkg does not apply to this OS).
+  expect_identical(
+    new_registry_packages(current, base, os = "ubuntu-2604"),
+    "BFpack"
+  )
+  # For alpine-324: the alpine package is new and applies.
+  expect_identical(
+    new_registry_packages(current, base, os = "alpine-324"),
+    "someAlpinePkg"
+  )
+  # Without an OS filter, both additions are returned.
+  expect_setequal(
+    new_registry_packages(current, base),
+    c("BFpack", "someAlpinePkg")
+  )
+  # A changed platform set on the same package counts as a new entry.
+  widened <- list(list(
+    package = "RcppParallel",
+    platforms = list("*"),
+    versions = "*"
+  ))
+  expect_identical(new_registry_packages(widened, base), "RcppParallel")
+})
+
 test_that("retirement_candidates flags entries whose package no longer fails", {
   entries <- list(
     list(package = "RcppParallel"),
diff --git a/local/trial-build-registry.R b/local/trial-build-registry.R
new file mode 100644
index 0000000..f649b62
--- /dev/null
+++ b/local/trial-build-registry.R
@@ -0,0 +1,145 @@
+#!/usr/bin/env Rscript
+
+# Merge gate for the auto-patch PR (issue #115, step 3): for every registry
+# entry the PR ADDS that applies to this platform, trial-build the package with
+# the registry applied, in this platform's own build-env image. Nothing is
+# uploaded, archived, or written to the metadata DB.
+#
+# Exit 0 only if every new entry's package builds; exit 1 if any fails, so it
+# gates the PR. A platform with no new entries is a fast no-op.
+#
+# Usage (inside a build-env image):
+#   PLATFORM=ubuntu-2604 Rscript local/trial-build-registry.R [base_ref]
+#     base_ref  git ref to diff the registry against (default: origin/main)
+
+options(error = function() {
+  cat("ERROR:", geterrmessage(), "\n", file = stdout())
+  q(status = 1)
+})
+
+suppressPackageStartupMessages({
+  library(jsonlite, quietly = TRUE)
+  library(bincraft, quietly = TRUE)
+})
+
+script_path <- local({
+  a <- commandArgs(trailingOnly = FALSE)
+  f <- sub("^--file=", "", a[grepl("^--file=", a)])
+  if (length(f) == 1L && nzchar(f)) normalizePath(f) else NA_character_
+})
+script_dir <- if (is.na(script_path)) "local" else dirname(script_path)
+source(file.path(script_dir, "proposal-tracking-lib.R"))
+
+args <- commandArgs(trailingOnly = TRUE)
+base_ref <- if (length(args) >= 1L) {
+  args[[1L]]
+} else {
+  Sys.getenv("BASE_REF", "origin/main")
+}
+os <- Sys.getenv("PLATFORM", "")
+if (!nzchar(os)) {
+  stop("PLATFORM env var is not set (e.g. ubuntu-2604).")
+}
+
+patches_dir <- file.path(script_dir, "patches")
+registry_file <- file.path(patches_dir, "registry.json")
+current <- if (file.exists(registry_file)) {
+  jsonlite::fromJSON(registry_file, simplifyVector = FALSE)
+} else {
+  list()
+}
+# Read the registry at base_ref. Fail loud if the ref or file can't be read:
+# silently treating the base as empty would trial-build the WHOLE registry
+# instead of just the entries the branch adds.
+registry_rel <- "local/patches/registry.json"
+ref_ok <- suppressWarnings(system2(
+  "git",
+  c("rev-parse", "--verify", "--quiet", sprintf("%s^{commit}", base_ref)),
+  stdout = TRUE,
+  stderr = FALSE
+))
+if (!is.null(attr(ref_ok, "status"))) {
+  stop(sprintf("base ref %s does not resolve to a commit.", base_ref))
+}
+in_base <- suppressWarnings(system2(
+  "git",
+  c("ls-tree", base_ref, "--", registry_rel),
+  stdout = TRUE,
+  stderr = FALSE
+))
+file_in_base <- length(in_base) > 0L && any(nzchar(in_base))
+base_json <- suppressWarnings(system2(
+  "git",
+  c("show", sprintf("%s:%s", base_ref, registry_rel)),
+  stdout = TRUE,
+  stderr = FALSE
+))
+show_ok <- is.null(attr(base_json, "status"))
+if (file_in_base && !show_ok) {
+  stop(sprintf(
+    "could not read %s at %s; refusing to build the whole registry.",
+    registry_rel,
+    base_ref
+  ))
+}
+base <- if (show_ok && length(base_json) > 0L) {
+  jsonlite::fromJSON(paste(base_json, collapse = "\n"), simplifyVector = FALSE)
+} else {
+  list() # file genuinely absent at base -> every entry is new
+}
+
+pkgs <- new_registry_packages(current, base, os = os)
+if (length(pkgs) == 0L) {
+  cat(sprintf(
+    "No new registry entries apply to %s; nothing to trial-build.\n",
+    os
+  ))
+  q(status = 0)
+}
+
+cat(sprintf(
+  "Trial-building %d new registry %s on %s (vs %s):\n  %s\n",
+  length(pkgs),
+  if (length(pkgs) == 1L) "entry" else "entries",
+  os,
+  base_ref,
+  toString(pkgs)
+))
+
+results <- vapply(
+  pkgs,
+  function(pkg) {
+    cat(sprintf("\n=== trial build: %s ===\n", pkg))
+    tryCatch(
+      {
+        bincraft::build_binary_package(
+          pkg,
+          tag_limit = 1L,
+          patches = patches_dir,
+          archive = FALSE,
+          upload = FALSE,
+          store_build_metadata = FALSE
+        )
+        TRUE
+      },
+      error = function(e) {
+        cat(sprintf("FAILED %s: %s\n", pkg, conditionMessage(e)))
+        FALSE
+      }
+    )
+  },
+  logical(1L)
+)
+
+failed <- pkgs[!results]
+cat(sprintf(
+  "\n%d/%d passed on %s.%s\n",
+  sum(results),
+  length(results),
+  os,
+  if (length(failed) > 0L) sprintf(" Failed: %s", toString(failed)) else ""
+))
+if (length(failed) > 0L) {
+  q(status = 1)
+}
+q(status = 0)