build(deps): group every ecosystem into one pull request

.github/dependabot.yml

@@ -1,12 +1,23 @@
 # Dependency updates for every ecosystem this repository ships.
 #
-# Each ecosystem is ONE catch-all group covering minor, patch and major, with
-# open-pull-requests-limit 1, so a week yields at most one pull request per
-# ecosystem instead of one per dependency. Dependabot cannot group across
-# ecosystems, so the number of entries below is the floor on weekly PRs.
+# Each ecosystem is ONE catch-all group with open-pull-requests-limit 1, so a
+# week yields at most one pull request per ecosystem instead of one per
+# dependency. Dependabot cannot group ACROSS ecosystems, so the entries below
+# are the floor on what Dependabot itself opens; .github/workflows/combine-
+# deps.yml runs afterwards and folds whatever is open into a single pull
+# request.
 #
-# The github-actions entry exists because every action is pinned by commit SHA;
-# nothing else would ever move those pins.
+# The groups deliberately carry NO `update-types:` filter. That filter only
+# recognises semver update types, so a Docker base image pinned by digest
+# matches none of them and falls OUT of the group into its own ungrouped pull
+# request, one per directory. Omitting the filter makes `patterns: "*"` mean
+# what it says: everything, digests included. For the same reason majors are
+# not split into a second group — that is a guaranteed extra pull request.
+#
+# Security updates keep their own group where one is defined: `applies-to`
+# separates them from version updates and they are not capped by
+# open-pull-requests-limit, because an urgent fix should not queue behind
+# routine work.
 version: 2
 
 updates:
@@ -18,12 +29,7 @@ updates:
     groups:
       pip:
         patterns:
-          - "*"
-        update-types:
-          - minor
-          - patch
-          - major
-
+          - '*'
   - package-ecosystem: github-actions
     directory: /
     schedule:
@@ -32,8 +38,4 @@ updates:
     groups:
       github-actions:
         patterns:
-          - "*"
-        update-types:
-          - minor
-          - patch
-          - major
+          - '*'

.github/scripts/combine-deps.sh

@@ -0,0 +1,111 @@
+#!/usr/bin/env bash
+# combine-deps — fold every open Dependabot pull request into a single one.
+#
+# Dependabot groups within an ecosystem but never across them, so even a
+# correctly grouped repository still opens one pull request per ecosystem.
+# This replays all of them onto one branch and closes the originals against it.
+#
+# Re-running is safe: the branch is rebuilt from the base branch every time, so
+# a pull request that has since merged or closed simply drops out.
+#
+# A repository with artefacts that must be regenerated after a bump (a lockfile
+# in a second module, a checked-in hash manifest) puts that in
+# .github/scripts/combine-deps-local.sh, which runs after the replay and before
+# the pull request is opened. Anything it commits rides along.
+#
+# One caveat before you close the combined pull request: closing a Dependabot
+# pull request tells Dependabot not to re-open one for that same version.
+# Merging moves the dependency, so the next pass proposes the next version and
+# nothing is lost. Abandoning it instead forfeits that batch until a newer
+# version ships.
+set -euo pipefail
+
+BRANCH="deps/combined"
+BASE="$(gh repo view --json defaultBranchRef --jq .defaultBranchRef.name)"
+
+git fetch --quiet origin "$BASE"
+
+mapfile -t ROWS < <(
+  gh pr list --state open --author "app/dependabot" --base "$BASE" \
+    --limit 100 --json number,title --jq '.[] | [.number, .title] | @tsv' | sort -n
+)
+
+if [ "${#ROWS[@]}" -eq 0 ]; then
+  echo "combine-deps: no open Dependabot pull requests; nothing to combine."
+  exit 0
+fi
+
+git config user.name "github-actions[bot]"
+git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+git checkout --quiet -B "$BRANCH" "origin/$BASE"
+
+combined=()
+skipped=()
+
+for row in "${ROWS[@]}"; do
+  number="${row%%$'\t'*}"
+  title="${row#*$'\t'}"
+
+  git fetch --quiet origin "refs/pull/${number}/head:refs/combine/${number}"
+  base_point="$(git merge-base "origin/$BASE" "refs/combine/${number}")"
+
+  if git cherry-pick --allow-empty "${base_point}..refs/combine/${number}" >/dev/null 2>&1; then
+    combined+=("${number}"$'\t'"${title}")
+    echo "combine-deps: replayed #${number} — ${title}"
+  else
+    git cherry-pick --abort >/dev/null 2>&1 || true
+    skipped+=("${number}"$'\t'"${title}")
+    echo "combine-deps: SKIPPED #${number} (conflicts with an earlier bump) — ${title}"
+  fi
+done
+
+if [ "${#combined[@]}" -eq 0 ]; then
+  echo "combine-deps: every pull request conflicted; leaving them all open."
+  exit 0
+fi
+
+if [ -x .github/scripts/combine-deps-local.sh ]; then
+  echo "combine-deps: running repository-local post-processing."
+  .github/scripts/combine-deps-local.sh
+fi
+
+body_file="$(mktemp)"
+{
+  echo "Every open Dependabot pull request, replayed onto one branch by"
+  echo "\`.github/workflows/combine-deps.yml\` so the week's dependency work is"
+  echo "reviewed and merged once instead of per ecosystem."
+  echo
+  echo "### Combined"
+  echo
+  for row in "${combined[@]}"; do
+    echo "- #${row%%$'\t'*} — ${row#*$'\t'}"
+  done
+  if [ "${#skipped[@]}" -gt 0 ]; then
+    echo
+    echo "### Left open (conflicted on replay, merge these by hand)"
+    echo
+    for row in "${skipped[@]}"; do
+      echo "- #${row%%$'\t'*} — ${row#*$'\t'}"
+    done
+  fi
+} > "$body_file"
+
+git push --quiet --force-with-lease origin "$BRANCH"
+
+existing="$(gh pr list --state open --head "$BRANCH" --json number --jq '.[0].number // empty')"
+if [ -n "$existing" ]; then
+  gh pr edit "$existing" --body-file "$body_file"
+  combined_pr="$existing"
+else
+  gh pr create --base "$BASE" --head "$BRANCH" \
+    --title "build(deps): combined dependency updates" --body-file "$body_file"
+  combined_pr="$(gh pr list --state open --head "$BRANCH" --json number --jq '.[0].number')"
+fi
+
+for row in "${combined[@]}"; do
+  number="${row%%$'\t'*}"
+  gh pr comment "$number" --body "Superseded by #${combined_pr}, which carries this bump together with the rest of the week's dependency updates."
+  gh pr close "$number"
+done
+
+echo "combine-deps: combined ${#combined[@]} pull request(s) into #${combined_pr}."

.github/workflows/combine-deps.yml

@@ -0,0 +1,58 @@
+# Folds every open Dependabot pull request into a single one.
+#
+# Dependabot groups within an ecosystem but never across them (see the comment
+# in .github/dependabot.yml), so its best case is one pull request per
+# ecosystem. This runs after its weekly pass and combines whatever is open.
+#
+# REQUIRES the DEPS_COMBINE_TOKEN secret — a PAT (or GitHub App token) with
+# `repo` scope. The built-in GITHUB_TOKEN is not usable here for two separate
+# reasons: this organisation has "Allow GitHub Actions to create and approve
+# pull requests" turned off, so it cannot open the combined pull request at
+# all; and even with that enabled, a branch pushed or a pull request opened by
+# GITHUB_TOKEN does not trigger workflow runs, so the combined pull request
+# would sit with no CI and never go green. An organisation-level secret covers
+# every repository at once.
+name: combine-deps
+
+on:
+  schedule:
+    # Mondays, a few hours after Dependabot's weekly pass has opened its pull
+    # requests. Off the hour: :00 is the busiest minute on the shared runners.
+    - cron: '23 9 * * 1'
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+
+concurrency:
+  group: combine-deps
+  cancel-in-progress: false
+
+jobs:
+  combine:
+    name: Combine open Dependabot pull requests
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+    steps:
+      # The secrets context is not available to `if:`, so this is checked in the
+      # step body rather than as a condition.
+      - name: Require a token that can open a pull request and trigger CI
+        env:
+          COMBINE_TOKEN: ${{ secrets.DEPS_COMBINE_TOKEN }}
+        run: |
+          if [ -z "$COMBINE_TOKEN" ]; then
+            echo "::error::DEPS_COMBINE_TOKEN is not set. Add it as an organisation secret (a PAT with 'repo' scope)."
+            echo "GITHUB_TOKEN cannot be used here: Actions is not permitted to create pull requests in"
+            echo "this organisation, and a pull request it opens does not trigger CI, so the combined"
+            echo "pull request would never go green."
+            exit 1
+          fi
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          fetch-depth: 0
+          token: ${{ secrets.DEPS_COMBINE_TOKEN }}
+      - name: Combine
+        env:
+          GH_TOKEN: ${{ secrets.DEPS_COMBINE_TOKEN }}
+        run: bash .github/scripts/combine-deps.sh