test: mutation testing for dispute resolution module

[mostronatorcoder]

Context

Follow-up from #618. Implement mutation testing coverage for dispute resolution — critical for trust and fairness in the P2P trading system.

Scope

Target modules:

• src/app/dispute.rs — Dispute creation and management
• src/app/admin_take_dispute.rs — Admin taking disputes
• src/app/admin_settle.rs — Admin settling disputes
• src/app/admin_cancel.rs — Admin cancelling disputed orders
• src/app/admin_add_solver.rs — Adding dispute solvers

Goal

• Run mutation testing on dispute modules
• Document baseline mutation score
• Kill surviving mutants
• Target: >70% mutation score

Priority Mutants to Kill

• Dispute state transitions
• Admin permission checks
• Solver assignment logic
• Settlement amount calculations
• Dispute timeout handling

Acceptance Criteria

• Baseline mutation report for dispute modules
• All critical mutants in admin permission checks killed
• All critical mutants in settlement logic killed
• Mutation score documented in PR

Ref: #618

[mostronatorcoder]

Baseline Mutation Testing Results

Date: 2026-03-10
Tool: cargo-mutants v27.0.0

Metric	Count
Total Mutants	34
✅ Killed	1
❌ Survived	31
⏱️ Timeout	2
Score	2.9%

Breakdown by file

File	Survived
src/app/dispute.rs	15
src/app/admin_settle.rs	7
src/app/admin_cancel.rs	4
src/app/admin_take_dispute.rs	3
src/app/admin_add_solver.rs	2

Root Cause

Same as #630 — async handlers depending on global state (get_db_pool(), get_nostr_client(), Settings). See #639 for the dependency injection refactoring needed.

The 1 killed mutant was caught by an existing test that exercises dispute-related logic indirectly.