# Evidence Size Budgets with Retention Tiers

## Module
__Libraries

## Status
VERIFIED

## Description
Implements evidence storage budgets with tiered retention (Hot/Warm/Cold/Archive), auto-pruning policies, and usage tracking. Distinct from "Evidence TTL and staleness policy" (expiration) and "DSSE Envelope Size Management" (single envelope sizing). This is a full lifecycle budget management system with compression tiers.

## Implementation Details
- **EvidenceBudgetService**: `src/__Libraries/StellaOps.Evidence/EvidenceBudgetService.cs` -- multi-partial implementation: `.Usage.cs` (track per-tenant/per-type usage against budgets), `.Status.cs` (budget status reporting), `.Prune.cs` (auto-pruning based on retention policies)
- **IEvidenceBudgetService**: `src/__Libraries/StellaOps.Evidence/IEvidenceBudgetService.cs` -- interface for budget management
- **EvidenceBudget**: `src/__Libraries/StellaOps.Evidence/EvidenceBudget.cs` -- budget configuration model
- **BudgetCheckResult/BudgetStatus**: `src/__Libraries/StellaOps.Evidence/BudgetCheckResult.cs`, `BudgetStatus.cs` -- budget check outcomes
- **RetentionPolicy**: `src/__Libraries/StellaOps.Evidence/RetentionPolicy.cs` -- per-tier retention configuration
- **RetentionTier**: `src/__Libraries/StellaOps.Evidence/RetentionTier.cs` -- tier enum (Hot/Warm/Cold/Archive)
- **RetentionTierManager**: `src/__Libraries/StellaOps.Evidence/RetentionTierManager.cs` -- multi-partial: `.CurrentTier.cs` (determine current tier), `.Migrate.cs` (migrate between tiers), `.Compress.cs` (tier-specific compression), `.Audit.cs` (audit trail for migrations)
- **IRetentionTierManager/IArchiveStorage**: `src/__Libraries/StellaOps.Evidence/IRetentionTierManager.cs`, `IArchiveStorage.cs` -- interfaces
- **TierMigrationResult/MigratedItem**: `src/__Libraries/StellaOps.Evidence/TierMigrationResult.cs`, `MigratedItem.cs` -- migration tracking
- **UsageStats/PruneResult**: `src/__Libraries/StellaOps.Evidence/UsageStats.cs`, `PruneResult.cs` -- reporting models
- **EvidenceItem/EvidenceType**: `src/__Libraries/StellaOps.Evidence/EvidenceItem.cs`, `EvidenceType.cs` -- evidence models
- **CompressionLevel/BudgetExceededAction**: `src/__Libraries/StellaOps.Evidence/CompressionLevel.cs`, `BudgetExceededAction.cs` -- configuration enums
- **Validation**: `src/__Libraries/StellaOps.Evidence/` -- `EvidenceIndexValidator.cs`, `IEvidenceIndexValidator.cs`, `SchemaLoader.cs`, `ValidationError.cs`, `ValidationResult.cs`
- **Source**: SPRINT_7000_0004_0002_evidence_size_budgets.md

## E2E Test Plan
- [ ] Verify budget tracking reports accurate usage per tenant and evidence type
- [ ] Test budget exceeded action triggers auto-pruning of oldest items
- [ ] Verify retention tier migration (Hot -> Warm -> Cold -> Archive) with compression
- [ ] Test RetentionTierManager applies tier-specific compression ratios
- [ ] Verify PruneResult reports number of items pruned and space reclaimed
- [ ] Test budget status API returns current usage vs. configured limits
- [ ] Verify tier migration audit trail records all migrations
- [ ] Test evidence index validation catches schema violations


## Verification

- **Verified**: 2026-02-13T20:30:00Z
- **Run**: run-001
- **Tier**: Tier 2d (Library/Internal)
- **Verdict**: PASS