fix(investigation): persist large results and require graph links

Full-network pressure comparisons exceeded the worker limit before saved-result previews could run. Preserve complete calculation results and keep read-time summaries and pagination.

Incremental graph publication accepted isolated nodes after flow-authoring rules were lost. Require new steps to connect explicitly while retaining historical snapshots and status-only patches. Regression tests reproduce both failures on the previous code.

app/services/calculation_worker.py

@@ -93,8 +93,8 @@ async def execute_child(input_path: str, output_path: str):
             category = 'EXECUTION_CONTEXT_UNAVAILABLE'
         payload = {'status': 'failed', 'error': {'code': category}}
     encoded = json.dumps(payload, allow_nan=False)
-    if len(encoded.encode()) > 8 * 1024 * 1024:
-        encoded = json.dumps({'status': 'failed', 'error': {'code': 'RESULT_TOO_LARGE'}})
+    # Keep the complete calculation for persistence. MCP result reads apply
+    # their own summary/page budgets after the result has been saved.
     Path(output_path).write_text(encoded)
 
 
@@ -212,8 +212,6 @@ class CalculationWorker:
                         terminal = {'status': 'timed_out', 'error': {'code': 'EXECUTION_TIMEOUT'}}
                     elif process.returncode is not None:
                         try:
-                            if output_path.stat().st_size > 8 * 1024 * 1024:
-                                raise ValueError('Result exceeds persistence limit')
                             terminal = json.loads(output_path.read_text())
                         except (OSError, ValueError):
                             terminal = {'status': 'failed', 'error': {'code': 'CHILD_PROCESS_FAILED'}}