fix: file-based source of truth for worker + backup protocol

- Worker: check {uuid}.{processor}.json existence before starting processor
- Worker: timestamp-copy backup existing output files before re-run (no delete, no overwrite)
- Executor: partial output saved as .json.partial (not .json) to avoid false completion
- Start script: removed set-e, log dir changed to momentry/logs, Qdrant collection status fix
- docs: M4 release incident report + M4/M5 collaboration protocol

src/core/processor/executor.rs

@@ -244,8 +244,10 @@ impl PythonExecutor {
                             .and_then(|c| serde_json::from_str::<serde_json::Value>(&c).ok())
                             .is_some();
                         if is_valid {
-                            let _ = std::fs::rename(tmp, out);
-                            tracing::warn!("[Executor] Partial output preserved: {:?}", out);
+                            let mut partial_path = out.to_path_buf();
+                            partial_path.set_extension("json.partial");
+                            let _ = std::fs::rename(tmp, &partial_path);
+                            tracing::warn!("[Executor] Partial output preserved: {:?}", partial_path);
                         } else {
                             let mut err_path = out.to_path_buf();
                             err_path.set_extension("json.err");