feat: Policy Store DB for Self-Healing Remediation Policies (PHO-5)

[JustAGhosT]

Summary

Implements PHO-5: a persistent, versioned policy store for self-healing remediation policies, plus a decision engine in the AgencyLayer that consumes it.

What's new

FoundationLayer — PolicyStore sub-project

Models/RemediationAction.cs	[Flags] enum: Retry, Rollback, Reassign, Restart, Escalate
Models/RemediationPolicy.cs	Versioned policy entity with full audit fields
Models/PolicyAuditEntry.cs	Audit trail entry written on every create/update/delete
Ports/IRemediationPolicyPort.cs	Port interface: Get, List, Upsert, Delete, GetPolicyHistory
Options/PolicyStoreOptions.cs	Config: CosmosDB connection, container IDs, cache TTL
Adapters/CosmosDbRemediationPolicyAdapter.cs	CosmosDB adapter with IMemoryCache read path, safe fallback policy when DB is unavailable, and full audit trail
Seed/DefaultPolicySeed.cs	16 default policies (4 categories × 4 severities)
Seed/PolicyStoreInitializer.cs	Idempotent startup seeder
Extensions/PolicyStoreServiceExtensions.cs	AddPolicyStore(services, config) DI registration

AgencyLayer — SelfHealing sub-project

Ports/IRemediationDecisionPort.cs	Returns (RemediationAction, Dictionary<string,double>) tuple
Engines/RemediationPolicyDecisionEngine.cs	Delegates to IRemediationPolicyPort cached read path
Extensions/SelfHealingServiceExtensions.cs	AddSelfHealingServices(services) DI registration

Tests

• tests/FoundationLayer/PolicyStore/ — 8 tests: versioning (v1 on create, v+1 on update), previous version deactivation, fallback on missing policy, delete, list, seed (empty + idempotent)
• tests/AgencyLayer/SelfHealing/ — 6 tests: action resolution, fallback non-None, security/critical contains Escalate, null/empty args throw ArgumentException, port called exactly once

Key design decisions

• Partition key = IncidentCategory — hot path queries are always partition-scoped
• Soft versioning — old policy records kept with IsActive=false, not physically deleted; GetPolicyHistoryAsync surfaces all versions
• Cache TTL configurable via PolicyStoreOptions.CacheTtl (default 5 min)
• Safe fallback — if CosmosDB is unavailable, GetPolicyAsync returns a permissive Retry|Escalate policy and logs a warning; no exception propagated to callers
• Secrets — CosmosDbConnectionString must be provided via environment variable or Key Vault; never hardcoded

Checklist

• All public types have XML doc comments

• ILogger<T> on all classes

• Constructor null guards

• All public methods async with CancellationToken

• No circular layer references

• No secrets in code

• Solution file updated

• FoundationLayer.csproj and AgencyLayer.csproj updated

Closes PHO-5

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PHO-5 Create Policy Store DB for Self-Healing Remediation Policies

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