build: releases fetch their signing keys from Proton Pass into memory, never onto the disk

tool/with_signing_keys.sh downloads the app's Android keystore and the
F-Droid index's from the vault Infra · Signing into a folder under
$XDG_RUNTIME_DIR, runs tool/release.dart with their paths, and removes
the folder however the run ends. The passwords are asked for as ever.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

tool/with_signing_keys.sh

@@ -0,0 +1,72 @@
+#!/usr/bin/env bash
+# Runs a release with its signing keys fetched from Proton Pass, where alone they are
+# kept (vault "Infra · Signing"): the app's Android keystore and the F-Droid index's,
+# each a note's attachment, downloaded into a folder in memory ($XDG_RUNTIME_DIR, a
+# tmpfs only the own user reads), handed to the release tool by the variables it reads
+# their paths from, and removed however the run ends. The keystores' passwords stay in
+# Pass: the release tool asks for them, as ever.
+#
+#   tool/with_signing_keys.sh <app> [release.dart's arguments]
+#   tool/with_signing_keys.sh train minor --dry-run
+#
+# Needs pass-cli, logged in (pass-cli login), and jq. Reads of the items take only their
+# IDs and their attachments' names, never a field.
+set -euo pipefail
+cd "$(git rev-parse --show-toplevel)"
+
+readonly vault='Infra · Signing'
+
+fail() {
+  echo "✗ $*" >&2
+  exit 1
+}
+
+[ $# -ge 1 ] || fail 'Usage: tool/with_signing_keys.sh <app> [release arguments]'
+app="$1"
+shift
+
+# Each app released (tool/src/release/apps.dart): the variable its keystore's path goes
+# in (its AndroidSigning's keystoreVariable) and the item keeping it.
+case "$app" in
+  learn) app_variable=HALKYON_ANDROID_KEYSTORE app_item='Halkyon Learn – Android release keystore' ;;
+  train) app_variable=HALKYON_TRAIN_ANDROID_KEYSTORE app_item='Halkyon Train – Android release keystore' ;;
+  *) fail "No signing key known for $app." ;;
+esac
+# The F-Droid repository's index key, the same for every app listed there.
+readonly fdroid_item='Halkyon Learn – F-Droid index keystore'
+
+for tool in pass-cli jq; do
+  command -v "$tool" >/dev/null || fail "$tool is missing."
+done
+[ -n "${XDG_RUNTIME_DIR:-}" ] && [ -d "$XDG_RUNTIME_DIR" ] ||
+  fail 'No $XDG_RUNTIME_DIR to keep the keys in memory.'
+
+keys=$(mktemp -d -p "$XDG_RUNTIME_DIR")
+trap 'rm -rf "$keys"' EXIT
+trap 'exit 130' INT TERM HUP
+
+# Downloads the attachment named $2 of the item titled $1 to $3.
+fetch() {
+  local item="$1" name="$2" to="$3" ids
+  ids=$(pass-cli item view --vault-name "$vault" --item-title "$item" --output json |
+    jq -r --arg name "$name" \
+      '[.item.share_id, .item.id, (.attachments[] | select(.content.name == $name) | .id)]
+       | select(length == 3) | @tsv') ||
+    fail "Can't read the item \"$item\" in $vault (pass-cli login?)."
+  [ -n "$ids" ] || fail "The item \"$item\" in $vault has no attachment $name."
+  local share item_id attachment
+  IFS=$'\t' read -r share item_id attachment <<<"$ids"
+  pass-cli item attachment download --share-id "$share" --item-id "$item_id" \
+    --attachment-id "$attachment" --output "$to" >/dev/null
+  [ -s "$to" ] || fail "The attachment $name of \"$item\" came empty."
+}
+
+echo "▸ Fetching the signing keys from $vault"
+fetch "$app_item" android-release.p12 "$keys/android-release.p12"
+fetch "$fdroid_item" fdroid-index.p12 "$keys/fdroid-index.p12"
+
+export "$app_variable=$keys/android-release.p12"
+export HALKYON_FDROID_KEYSTORE="$keys/fdroid-index.p12"
+status=0
+dart run tool/release.dart "$app" "$@" || status=$?
+exit "$status"