feat: Add comprehensive product advisories for improved scanner functionality

- Introduced a blueprint for explainable quiet alerts, detailing phases for SBOM, VEX readiness, and attestations.
- Developed a roadmap for deterministic diff-aware rescans, enhancing scanner speed and efficiency.
- Implemented a hash-based SBOM layer cache to optimize container scans by reusing previous results.
- Created a multi-runtime reachability corpus to validate function-level reachability across various programming languages.
- Proposed a stable SBOM model using SPDX 3.0.1 for persistence and CycloneDX 1.6 for interchange.
- Established a validation plan for quiet scans, focusing on provenance and CI integration.
- Documented guidelines for the Findings Ledger module, outlining roles, execution rules, and testing protocols.

docs/implplan/archived/updates/2025-10-20-authority-identity-registry.md

@@ -0,0 +1,14 @@
+# 2025-10-20 — Authority Identity Provider Registry & DPoP nonce updates
+
+## Summary
+- Authority host now resolves identity providers through the new metadata/handle pattern introduced in `StellaOps.Authority.Plugins.Abstractions`. Runtime handlers (`ValidateClientCredentialsHandler`, `ValidatePasswordGrantHandler`, `ValidateAccessTokenHandler`, bootstrap endpoints) acquire providers with `IAuthorityIdentityProviderRegistry.AcquireAsync` and rely on metadata (`AuthorityIdentityProviderMetadata`) for capability checks.
+- Unit and integration tests build lightweight `ServiceProvider` instances with test plugins, matching production DI behaviour and ensuring the new registry contract is exercised.
+- DPoP nonce enforcement now prefers `NormalizedAudiences` when populated and gracefully falls back to the configured `RequiredAudiences`, eliminating the runtime type mismatch that previously surfaced during test runs.
+
+## Operator impact
+- No configuration changes are required; existing YAML and environment-based settings continue to function.
+- Documentation examples referencing password/mTLS bootstrap flows remain accurate. The new registry logic simply ensures providers advertised in configuration are resolved deterministically and capability-gated before use.
+
+## Developer notes
+- When adding new identity providers or tests, register plugins via `ServiceCollection` and call `new AuthorityIdentityProviderRegistry(serviceProvider, logger)`.
+- For DPoP-required endpoints, populate `security.senderConstraints.dpop.nonce.requiredAudiences` or rely on defaults; both now funnel through the normalized set.