fix: Push to public mirrors after merge (#614)

Add fire-and-forget mirror push support so merges to the primary branch
are automatically pushed to configured public mirrors (GitHub, Codeberg,
etc.). Mirror failures are logged but never block the pipeline.

- lib/mirrors.sh: new shared mirror_push() helper
- lib/load-project.sh: parse [mirrors] TOML section into MIRROR_* env vars
- dev/phase-handler.sh: call mirror_push after do_merge() success
- dev/dev-poll.sh: call mirror_push after try_direct_merge() success
- gardener/gardener-run.sh: call mirror_push after _gardener_merge() success
- bin/disinto: set up mirror remotes during init, add commented mirrors to
  generated TOML
- projects/*.toml.example: show [mirrors] section (commented out)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/load-project.sh

@@ -8,7 +8,8 @@
 #   PROJECT_NAME, FORGE_REPO, FORGE_API, FORGE_WEB, FORGE_URL,
 #   PROJECT_REPO_ROOT, PRIMARY_BRANCH, WOODPECKER_REPO_ID,
 #   PROJECT_CONTAINERS, CHECK_PRS, CHECK_DEV_AGENT,
-#   CHECK_PIPELINE_STALL, CI_STALE_MINUTES
+#   CHECK_PIPELINE_STALL, CI_STALE_MINUTES,
+#   MIRROR_NAMES, MIRROR_URLS, MIRROR_<NAME> (per configured mirror)
 #   (plus backwards-compat aliases: CODEBERG_REPO, CODEBERG_API, CODEBERG_WEB)
 #
 # If no argument given, does nothing (allows poll scripts to work with
@@ -71,6 +72,14 @@ mon = cfg.get('monitoring', {})
 for key in ['check_prs', 'check_dev_agent', 'check_pipeline_stall']:
     if key in mon:
         emit(key.upper(), mon[key])
+
+# [mirrors] section
+mirrors = cfg.get('mirrors', {})
+for name, url in mirrors.items():
+    emit(f'MIRROR_{name.upper()}', url)
+if mirrors:
+    emit('MIRROR_NAMES', list(mirrors.keys()))
+    emit('MIRROR_URLS', list(mirrors.values()))
 " "$_PROJECT_TOML" 2>/dev/null) || {
   echo "WARNING: failed to parse project TOML: $_PROJECT_TOML" >&2
   return 1 2>/dev/null || exit 1

lib/mirrors.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+# mirrors.sh — Push primary branch + tags to configured mirror remotes.
+#
+# Usage: source lib/mirrors.sh; mirror_push
+# Requires: PROJECT_REPO_ROOT, PRIMARY_BRANCH, MIRROR_* vars from load-project.sh
+
+# shellcheck disable=SC2154  # globals set by load-project.sh / calling script
+
+mirror_push() {
+  [ -z "${MIRROR_NAMES:-}" ] && return 0
+  [ -z "${PROJECT_REPO_ROOT:-}" ] && return 0
+  [ -z "${PRIMARY_BRANCH:-}" ] && return 0
+
+  local name url
+  for name in $MIRROR_NAMES; do
+    url=$(eval "echo \"\$MIRROR_$(echo "$name" | tr '[:lower:]' '[:upper:]')\"") || true
+    [ -z "$url" ] && continue
+
+    # Ensure remote exists with correct URL
+    if git -C "$PROJECT_REPO_ROOT" remote get-url "$name" &>/dev/null; then
+      git -C "$PROJECT_REPO_ROOT" remote set-url "$name" "$url" 2>/dev/null || true
+    else
+      git -C "$PROJECT_REPO_ROOT" remote add "$name" "$url" 2>/dev/null || true
+    fi
+
+    # Fire-and-forget push (background, no failure propagation)
+    git -C "$PROJECT_REPO_ROOT" push "$name" "$PRIMARY_BRANCH" --tags 2>/dev/null &
+    log "mirror: pushed to ${name} (pid $!)"
+  done
+}