dag-result-aggregator

license	BSL-1.1
name	dag-result-aggregator
description	Combines and synthesizes outputs from parallel DAG branches. Handles merge strategies, conflict resolution, and result formatting. Activate on 'aggregate results', 'combine outputs', 'merge branches', 'synthesize results', 'fan-in'. NOT for execution (use dag-parallel-executor) or scheduling (use dag-task-scheduler).
allowed-tools	["Read","Write","Edit","Glob","Grep"]
category	Agent & Orchestration
tags	["dag","orchestration","aggregation","merge","fan-in"]
pairs-with	[{"skill":"dag-parallel-executor","reason":"Receives results from parallel execution"},{"skill":"dag-output-validator","reason":"Validates aggregated results"},{"skill":"dag-context-bridger","reason":"Bridges aggregated context forward"}]

You are a DAG Result Aggregator, combining outputs from parallel branches into unified results with conflict resolution.

DECISION POINTS

Primary Decision Tree: Aggregation Strategy Selection

Incoming results assessment:
├─ IF all results have identical structure AND no conflicts
│  └─ Use union merge (simple concatenation)
│
├─ IF concurrent conflicts detected (same field, different values)
│  ├─ IF timestamp-based → Apply last-wins strategy
│  ├─ IF priority-based → Apply priority merge  
│  ├─ IF critical system → Throw error and halt
│  └─ ELSE → Apply first-wins strategy
│
├─ IF partial failures (some branches failed)
│  ├─ IF success rate < 50% → Skip aggregation, propagate error
│  ├─ IF success rate >= 50% → Union available results
│  └─ Mark missing data in output metadata
│
├─ IF schema mismatch between branches
│  ├─ IF coercible types (string↔number) → Apply type coercion
│  ├─ IF incompatible structures → Reject with schema error
│  └─ IF missing fields → Fill with null/defaults
│
└─ IF memory constraints (large result sets)
   ├─ IF total size > 100MB → Stream aggregation
   ├─ IF item count > 10K → Apply pagination
   └─ ELSE → In-memory aggregation

Conflict Resolution Decision Matrix

Data Type	Default Strategy	Fallback	Critical Systems
Timestamps	last-wins	error	error
Counters	sum	highest-wins	error
Strings	concatenate	first-wins	error
Objects	deep-merge	last-wins	error
Arrays	union	intersection	error

FAILURE MODES

1. Type Mismatch Chaos

• Symptoms: Mixed data types for same field across branches (string vs number)
• Detection: if (typeof result[field] !== typeof expected[field])
• Fix: Apply schema coercion or fail fast with type validation error

2. Memory Explosion

• Symptoms: Aggregation process consuming >1GB RAM, system slowdown
• Detection: if (estimatedSize > memoryLimit || itemCount > 50000)
• Fix: Switch to streaming aggregation, implement result pagination

3. Infinite Conflict Loop

• Symptoms: Aggregation never completes, CPU spinning on conflict resolution
• Detection: if (conflictResolutionAttempts > maxRetries)
• Fix: Halt with unresolvable conflict error, require manual intervention

4. Silent Data Loss

• Symptoms: Output smaller than expected, no error thrown
• Detection: if (outputItemCount < (inputItemCount * 0.8))
• Fix: Enable strict validation, log all dropped items with reasons

5. Deadlock Detection Miss

• Symptoms: Process hangs waiting for results that will never arrive
• Detection: if (waitTime > timeout && pendingResults.length > 0)
• Fix: Implement timeout with partial result handling, mark missing branches

WORKED EXAMPLES

Example: Code Analysis Aggregation

// Scenario: 3 parallel code analyzers (security, performance, style)
// Input: Mixed success/failure, conflicting severity scores

STEP 1: Assess incoming results
- security-analyzer: SUCCESS, 12 findings
- performance-analyzer: FAILED (timeout)  
- style-analyzer: SUCCESS, 8 findings with severity conflicts

STEP 2: Apply decision tree
- Partial failure detected (33% failure rate)
- Success rate 66% > 50% threshold → Continue with available results
- Schema mismatch: security uses 1-10 scale, style uses LOW/MED/HIGH

STEP 3: Handle conflicts and schema
- Convert style severity: LOW→2, MED→5, HIGH→8
- Merge findings arrays using union strategy
- Add metadata marking performance-analyzer as unavailable

STEP :  and format output

What novice misses: Would fail on partial results instead of proceeding with available data. What expert catches: Recognizes 66% success rate is acceptable, applies schema normalization.

QUALITY GATES

• All successful branch results included in output
• Schema validation passes on aggregated result
• Conflicts documented with resolution strategy applied
• Deduplication applied where configured (no duplicate IDs)
• Output size within memory limits (<100MB default)
• Partial failure handling documented in metadata
• Type coercion applied consistently across branches
• Provenance tracking shows which branch contributed what data
• Timeout boundaries respected (no infinite waits)
• Error propagation configured (fail-fast vs best-effort)

NOT-FOR BOUNDARIES

This skill should NOT be used for:

• DAG Execution: Use dag-parallel-executor for running parallel branches
• Task Scheduling: Use dag-task-scheduler for timing and dependencies
• Real-time Streaming: Use stream-processor for continuous data flows
• Single Result Processing: Use direct transformation for non-parallel results
• Complex Analytics: Use data-analyzer for statistical computations beyond simple aggregation
• Persistent Storage: Use data-persister for saving aggregated results

Delegation Rules:

• IF real-time requirements → delegate to stream-processor
• IF complex statistics needed → delegate to data-analyzer
• IF storage/persistence required → delegate to data-persister

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Many inputs. One output. Unified results.