# Lens [Pro]: <Target Concept / Pattern / Mechanism>

## 1. Architectural Role & Invariant Contract
- **System Classification**: <e.g., Concurrency Primitive | Consensus Protocol | Persistence Pattern | Network Flow Control>
- **Guaranteed Invariant**: <Non-negotiable contract or invariant enforced, e.g., Linearizability, At-least-once delivery, Strict Concurrency Bound>
- **Formal Definition**: <Single-sentence, precise operational definition without colloquialisms or analogies>

## 2. Runtime Mechanics & Execution Path
1. **Ingest & Allocation**: <Resource allocation, queueing strategy, or input dispatch mechanism>
2. **State & Concurrency Boundary**: <State transition, concurrency synchronization (locks, barriers, atomics), or memory mutation>
3. **Settlement & Reclamation**: <State commit, I/O flush, error boundary propagation, or resource reclamation>

## 3. Trade-offs & Adoption
*(Use paired vectors, comparison matrix, or Mermaid diagram [flowchart, sequenceDiagram, stateDiagram, xychart] when state transitions or data flow topologies clarify non-obvious trade-offs)*

- **Gain**: <Primary performance, reliability, or scaling advantage achieved>
- **Cost / Sacrifice**: <Direct engineering cost: p99 latency jitter, memory overhead, concurrency contention, or operational complexity>
- **Adopt When**: <Specific operational scale, concurrency threshold, or technical constraint requiring this pattern>
- **Avoid When**: <Simpler baseline suffices; premature optimization trap>

## 4. Production Failure Modes & Mitigations *(omit for stateless/pure-functional patterns)*
- **<Failure Mode 1, e.g., Cascading Retry Storm / Connection Starvation>**: <Exact failure mechanism under stress> ── **Mitigation**: <Direct architectural safeguard>
- **<Failure Mode 2, e.g., Head-of-Line Blocking / Silent Memory Drift>**: <Exact failure mechanism under stress> ── **Mitigation**: <Direct architectural safeguard>