fix: add truncation awareness to loop output and warn on data loss

Address review feedback: the sliding window on allIterationOutputs
silently truncated the final loop output passed to downstream blocks.

- Track totalIterationCount on LoopScope so the true iteration count
  is preserved even after pruning
- Include totalIterations and truncated flag in the loop block output
  so downstream blocks can detect when data was pruned
- Log a warning with discarded/retained counts when truncation occurs

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

Author: MaxwellCalkin

apps/sim/executor/execution/state.ts

@@ -16,6 +16,8 @@ export interface LoopScope {
   skipFirstConditionCheck?: boolean
   /** Error message if loop validation failed (e.g., exceeded max iterations) */
   validationError?: string
+  /** Total number of iterations completed (may exceed allIterationOutputs.length when truncated) */
+  totalIterationCount?: number
 }
 
 export interface ParallelScope {

apps/sim/executor/orchestrators/loop.ts

@@ -248,11 +248,18 @@ export class LoopOrchestrator {
 
     if (iterationResults.length > 0) {
       scope.allIterationOutputs.push(iterationResults)
+      scope.totalIterationCount = (scope.totalIterationCount ?? 0) + 1
 
       // Sliding window: discard oldest iteration outputs to bound memory (fixes #2525)
       if (scope.allIterationOutputs.length > DEFAULTS.MAX_LOOP_ITERATION_HISTORY) {
         const excess = scope.allIterationOutputs.length - DEFAULTS.MAX_LOOP_ITERATION_HISTORY
         scope.allIterationOutputs.splice(0, excess)
+        logger.warn('Loop iteration history truncated to prevent OOM', {
+          loopId,
+          totalIterations: scope.totalIterationCount,
+          retained: DEFAULTS.MAX_LOOP_ITERATION_HISTORY,
+          discarded: scope.totalIterationCount - DEFAULTS.MAX_LOOP_ITERATION_HISTORY,
+        })
       }
     }
 
@@ -281,7 +288,12 @@ export class LoopOrchestrator {
     scope: LoopScope
   ): LoopContinuationResult {
     const results = scope.allIterationOutputs
-    const output = { results }
+    const totalIterations = scope.totalIterationCount ?? results.length
+    const output = {
+      results,
+      totalIterations,
+      ...(totalIterations > results.length && { truncated: true }),
+    }
     this.state.setBlockOutput(loopId, output, DEFAULTS.EXECUTION_TIME)
 
     if (this.contextExtensions?.onBlockComplete) {