lfe-perf-check - SKILL.md Agent Skill

name: lfe-perf-check description: Inspector sub-skill. Analyses the implementation diff for common performance anti-patterns — resource leaks, N+1 queries, unbounded growth, algorithmic complexity. Pure LLM reasoning, no profilers. Writes .plans/checks/perf_findings.md. Called by lfe-inspector when enabled in inspector-config.md.

LFE Performance Check — Prompt-Based Anti-Pattern Analysis

Position in Pipeline

Phase: 3 (Inspector sub-skill)
Persona: Inspector (read-only; no src/ writes)
Trigger: Invoked by /lfe-inspector Sub-Skill Dispatch when lfe-perf-check: true in .docs/quality/inspector-config.md
Output: .plans/checks/perf_findings.md — aggregated by Inspector into critique.md

Mission

Detect performance anti-patterns introduced by the current implementation through structured LLM reasoning over the diff. Findings are advisory unless a pattern is provably unbounded (e.g. O(n²) in a hot path with no upper bound on n).

Hard Rules

Dispatch Context Required (refuse direct invocation): This skill is dispatched by /lfe-inspector Step 6 — it is not a Brain-typeable skill (per LLM_AGENT_GUIDE.md §8.8 Skill Invocation Authority). If invoked without .plans/builder_done.md for the current slice, halt immediately and reply: "/lfe-perf-check is an Inspector sub-skill dispatched by /lfe-inspector. It cannot be run standalone. Run /lfe-inspector — the dispatcher will invoke this sub-skill if it is enabled in .docs/quality/inspector-config.md (or via an ## Inspector Overrides section in active_plan.md)." Direct invocation produces orphaned findings files and breaks the Inspector's aggregation logic.
Prompt-Only: No profiling tools, no benchmarks, no execution. Reasoning over code only.
Diff-Scoped: Analyse only files listed in builder_done.md; skip unchanged code.
Severity: Critical (provably unbounded, certain production impact) / High (likely hot-path) / Medium (probable overhead) / Low (style concern).
Cite Line: Every finding quotes the specific pattern from the code.

Inputs

.plans/builder_done.md — list of changed files
.plans/active_plan.md — domain context and scope boundary
.docs/domain/ — domain rules that might imply expected data volumes

Workflow

Step 1: Extract Diff Scope

From builder_done.md, identify and read modified files.

Step 2: Anti-Pattern Checklist

Reason through each category against the changed code:

Category	Patterns to Detect
Resource Leaks	Unclosed file handles, DB connections, sockets; missing `finally`/`defer`/`using` blocks; objects allocated in loops without release
N+1 Query	DB or API calls inside a loop; queries that could be batched; ORM lazy-load inside iteration
Unbounded Growth	Lists/maps that grow with no size limit; recursive calls with no guaranteed termination; caches with no eviction policy
Algorithmic Complexity	Nested loops over the same collection; sorting inside a frequently-called function; repeated full-scan where an index would help
Blocking I/O	Synchronous network or disk calls in async context; missing pagination on large result sets; missing timeouts on external calls
Memory Anti-Patterns	Large objects copied rather than referenced; excessive intermediate allocations in hot paths

Step 3: Write Findings File

Path: .plans/checks/perf_findings.md

Begin the file with a YAML frontmatter block — the Inspector's dispatcher relies on status: complete to detect successful runs and skip them on crash recovery.

---
phase: inspector
step: perf-check
kind: sub-skill
status: complete
timestamp: <ISO-8601>
source: .plans/builder_done.md
slice: <copied from active_plan.md>
---

Body:

## Performance Check Findings

**Scope**: <list of analysed files>
**Clean categories**: <categories with no findings>

### Critical
- <Pattern — description — quoted code evidence>

### High
- <finding>

### Medium
- <finding>

### Low / Informational
- <finding>

### Summary
- Critical issues: <N>
- Advisory issues: <N>

If no findings: write No performance anti-patterns identified in the analysed diff.

Handoff

Return control to /lfe-inspector. Inspector aggregates this file's content into critique.md under a ## Performance section. Write only this findings file; leave critique.md to the Inspector.