Fix filter reconciliation for pre-v1.2 state and unrelated histories

Three bugs found during first CI run after enabling :exclude:

- Derive old filter (:/subfolder) when state has no josh_filter stored
  (pre-v1.2 upgrade path)
- Detect unrelated histories in forward_sync() and fall back to
  reconcile_filter_change() instead of creating a useless conflict PR
- Skip state update on conflict result (prevents storing wrong filter
  and mono SHA that blocks retries)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

bin/josh-sync

@@ -214,6 +214,18 @@ _sync_direction() {
         local prev_filter
         prev_filter=$(echo "$state" | jq -r '.last_forward.josh_filter // empty')
 
+        # If no filter stored (pre-v1.2 state) but a previous sync exists,
+        # the old filter was the simple :/subfolder (before exclude was added)
+        if [ -z "$prev_filter" ]; then
+          local prev_mono_sha
+          prev_mono_sha=$(echo "$state" | jq -r '.last_forward.mono_sha // empty')
+          if [ -n "$prev_mono_sha" ]; then
+            local subfolder
+            subfolder=$(echo "$TARGET_JSON" | jq -r '.subfolder')
+            prev_filter=":/${subfolder}"
+          fi
+        fi
+
         if [ -n "$prev_filter" ] && [ "$prev_filter" != "$JOSH_FILTER" ]; then
           log "WARN" "Josh filter changed — reconciling histories"
           log "INFO" "Old: ${prev_filter}"
@@ -225,6 +237,13 @@ _sync_direction() {
       else
         result=$(reverse_sync)
       fi
+      # If forward sync hit unrelated histories, fall back to reconciliation
+      if [ "$result" = "unrelated" ]; then
+        log "WARN" "Unrelated histories detected — falling back to filter reconciliation"
+        result=$(reconcile_filter_change)
+        log "INFO" "Reconciliation result: ${result}"
+      fi
+
       log "INFO" "Result: ${result}"
 
       # Handle warnings
@@ -234,6 +253,7 @@ _sync_direction() {
       fi
       if [ "$result" = "conflict" ]; then
         echo "::warning::Target ${target_name}, branch ${branch}: merge conflict — PR created on subrepo"
+        continue
       fi
       if [ "$result" = "josh-rejected" ]; then
         echo "::error::Target ${target_name}, branch ${branch}: josh rejected push — check proxy logs"