Ln 628 Concurrency Correctness Auditor

Paths: File paths (references/, ../ln-*) are relative to this skill directory.

Concurrency Correctness Auditor (L3 Worker)

Type: L3 Worker

Specialized worker auditing concurrency correctness, async hazards, and cross-process resource access.

Purpose & Scope

• Audit concurrency (Category 11: High Priority)
• 7 checks: async races, thread safety, TOCTOU, deadlocks, blocking I/O, resource contention, cross-process races
• Two-layer detection: grep finds candidates, agent reasons about context
• Emit FIX_RACE, FIX_DEADLOCK, or CONTROL_ASYNC_SIDE_EFFECT
• Calculate compliance score (X/10)

Inputs

MANDATORY READ: Load references/audit_worker_core_contract.md and references/mcp_tool_preferences.md. Tool policy: You may run as an isolated subagent where host AGENTS.md is not in scope, so default to hex-line MCP first for file reads, search, and edits. Load references/mcp_integration_patterns.md only when MCP behavior is unclear.

Receives contextStore with: tech_stack, best_practices, codebase_root, output_dir.

Use hex-graph first when dataflow or call-path analysis materially improves concurrency findings. Use hex-line first for local code reads when available. If MCP is unavailable, unsupported, or not indexed, continue with built-in Read/Grep/Glob/Bash and state the fallback in the report.

Workflow

Detection policy: use two-layer detection (candidate scan, then context verification); load references/two_layer_detection.md only when the verification method is ambiguous.

1. Parse context -- extract tech_stack, language, output_dir from contextStore
2. Per check (1-7):
   • Layer 1: Grep/Glob scan to find candidates
   • Layer 2: Read 20-50 lines around each candidate. Apply check-specific critical questions. Classify: confirmed / false positive / needs-context
3. Collect confirmed findings with severity, location, effort, recommendation
4. Calculate score per references/audit_scoring.md
5. Write Report -- build in memory, write to {output_dir}/ln-628--global.md (atomic single Write)
6. Return Summary

Audit Rules

Unified severity escalation: For ALL checks -- if finding affects payment/auth/financial code -> escalate to CRITICAL regardless of other factors.

1. Async/Event-Loop Races (CWE-362)

What: Shared state corrupted across await/yield boundaries in single-threaded async code.

Layer 1 -- Grep patterns:

Layer 2 -- Critical questions:

• Is the variable shared (module/global scope) or local?
• Can two async tasks interleave at this await point?
• Is there a lock/mutex/semaphore guarding the access?

Severity: CRITICAL (payment/auth) | HIGH (user-facing) | MEDIUM (background)

Safe pattern exclusions: Local variables, const declarations, single-use await (no interleaving possible).

Effort: M

2. Thread/Goroutine Safety (CWE-366)

What: Shared mutable state accessed from multiple threads/goroutines without synchronization.

Layer 1 -- Grep patterns:

Layer 2 -- Critical questions:

• Is this struct/object actually shared between threads? (single-threaded code -> FP)
• Is mutex/lock in embedded struct or imported module? (grep may miss it)
• Is go func capturing by value (safe) or by reference (unsafe)?

Severity: CRITICAL (payment/auth) | HIGH (data corruption possible) | MEDIUM (internal)

Safe pattern exclusions: Go map in init() or main() before goroutines start. Rust Arc<Mutex<T>> (already safe). Java Collections.synchronizedMap().

Effort: M

3. TOCTOU -- Time-of-Check Time-of-Use (CWE-367)

What: Resource state checked, then used, but state can change between check and use.

Layer 1 -- Grep patterns:

Layer 2 -- Critical questions:

• Is the check used for control flow (vulnerable) or just logging (safe)?
• Is there a lock/retry around the check-then-use sequence?
• Is the file in a temp directory controlled by the application (lower risk)?
• Could an attacker substitute the file (symlink attack)?

Severity: CRITICAL (security-sensitive: permissions, auth tokens, configs) | HIGH (user-facing file ops) | MEDIUM (internal/background)

Safe pattern exclusions: Check inside try/catch with retry. Check for logging/metrics only. Check + use wrapped in file lock.

Effort: S-M (replace check-then-use with direct use + error handling)

4. Deadlock Potential (CWE-833)

What: Lock acquisition in inconsistent order, or lock held during blocking operation.

Layer 1 -- Grep patterns:

Layer 2 -- Critical questions:

• Are these the same lock (reentrant = OK) or different locks (deadlock risk)?
• Is the lock ordering consistent across all call sites?
• Does the external call inside lock have a timeout?

Severity: CRITICAL (payment/auth) | HIGH (app freeze risk)

Safe pattern exclusions: Reentrant locks (same lock acquired twice). Locks with explicit timeout (asyncio.wait_for, tryLock).

Effort: L (lock ordering redesign)

5. Blocking I/O in Async Context (CWE-400)

What: Synchronous blocking calls inside async functions or event loop handlers.

Layer 1 -- Grep patterns:

Layer 2 -- Critical questions:

• Is this in a hot path (API handler) or cold path (startup script)?
• Is the blocking duration significant (>100ms)?
• Is there a legitimate reason (e.g., sync read of small config at startup)?

Severity: HIGH (blocks event loop/async context) | MEDIUM (minor blocking <100ms)

Safe pattern exclusions: Blocking call in if __name__ == "__main__" (startup). readFileSync in config loading at init time. Sync crypto for small inputs.

Effort: S-M (replace with async alternative)

6. Resource Contention (CWE-362)

What: Multiple concurrent accessors compete for same resource without coordination.

Layer 1 -- Grep patterns:

Layer 2 -- Critical questions:

• Are multiple writers actually concurrent? (Sequential = safe)
• Is there OS-level atomicity guarantee? (e.g., O_APPEND for small writes)
• Is ordering important for correctness?

Severity: HIGH (data corruption) | MEDIUM (ordering issues)

Safe pattern exclusions: Single writer pattern. OS-guaranteed atomic operations (small pipe writes, O_APPEND). Message queues with ordering guarantees.

Effort: M

7. Cross-Process & Invisible Side Effects (CWE-362, CWE-421)

What: Multiple processes or process+OS accessing same exclusive resource, including operations with non-obvious side effects on shared OS resources.

Layer 1 -- Grep entry points:

Layer 2 -- This check relies on reasoning more than any other:

1. Build Resource Inventory:

   Resource	Exclusive?	Accessor 1	Accessor 2	Sync present?

2. Trace Timeline:

   t=0ms  operation_A() -> resource_X accessed
   t=?ms  side_effect   -> resource_X accessed by external process
   t=?ms  operation_B() -> resource_X accessed again -> CONFLICT?
   

3. Critical Questions:

   • Can another process (terminal, OS, child) access this resource simultaneously?
   • Does this operation have invisible side effects on shared OS resources?
   • What happens if the external process is slower/faster than expected?
   • What happens if user triggers this action twice rapidly?

Severity: CRITICAL (two accessors to exclusive OS resource without sync) | HIGH (subprocess + shared file without lock) | HIGH (invisible side effect detected via reasoning)

Safe pattern exclusions: Single accessor. Retry/backoff pattern present. Operations sequenced with explicit delay/await.

Effort: M-L (may require removing redundant access path)

Scoring Algorithm

MANDATORY READ: Load references/audit_scoring.md.

Output Format

MANDATORY READ: Load references/templates/audit_worker_report_template.md.

Write JSON summary per references/audit_summary_contract.md. In managed mode the caller passes both runId and summaryArtifactPath; in standalone mode the worker generates its own run-scoped artifact path per shared contract.

Write report to {output_dir}/ln-628--global.md with category: "Concurrency" and checks: async_races, thread_safety, toctou, deadlock_potential, blocking_io, resource_contention, cross_process_races.

Return summary per references/audit_summary_contract.md.

When summaryArtifactPath is absent, write the standalone runtime summary under .hex-skills/runtime-artifacts/runs/{run_id}/evaluation-worker/{worker}--{identifier}.json and optionally echo the same summary in structured output.

Report written: .hex-skills/runtime-artifacts/runs/{run_id}/audit-report/ln-628--global.md
Score: X.X/10 | Issues: N (C:N H:N M:N L:N)

Critical Rules

Apply the already-loaded references/audit_worker_core_contract.md.

• Do not auto-fix: Report only -- concurrency fixes require careful human review
• Two-layer detection: Always apply Layer 2 reasoning after Layer 1 grep. Never report raw grep matches without context analysis
• Language-aware detection: Use language-specific patterns per check
• Unified CRITICAL escalation: Any finding in payment/auth/financial code = CRITICAL
• Effort realism: S = <1h, M = 1-4h, L = >4h
• Exclusions: Skip test files, skip single-threaded CLI tools, skip generated code
• Unique angle: Audit concurrency correctness only. Do not audit lifecycle readiness, layer ownership, or local code style.
• Action required: Every finding uses FIX_RACE, FIX_DEADLOCK, or CONTROL_ASYNC_SIDE_EFFECT.

Definition of Done

Apply the already-loaded references/audit_worker_core_contract.md.

• contextStore parsed (language, concurrency model, output_dir)
• All 7 checks completed with two-layer detection:
  • async races, thread safety, TOCTOU, deadlock potential, blocking I/O, resource contention, cross-process races
• Layer 2 reasoning applied to each candidate (confirmed / FP / needs-context)
• Findings collected with severity, location, effort, action, recommendation
• Score calculated per references/audit_scoring.md
• Report written to {output_dir}/ln-628--global.md (atomic single Write call)
• Summary written per contract

Reference Files

• Two-layer detection methodology: references/two_layer_detection.md
• Audit output schema: references/audit_output_schema.md

Version: 4.0.0 Last Updated: 2026-03-04