# 50 legacy-to-agent bridge patterns All entries below are design patterns, not shipped HELLO OS capabilities. Select and threat-model a specific use case before implementation. Use read-only access first; writes require an explicit policy gate and, for high-impact actions, human approval bound to the exact action. ## 1. MCP Wrapper Pattern **Area:** Architecture & Protocol Wrappers (1–10) **Status:** Design pattern only; not implemented. Expose a narrow, typed MCP facade over approved REST or SOAP operations. Start read-only and validate every argument. ## 2. Reverse Proxy Intent Interceptor **Area:** Architecture & Protocol Wrappers (1–10) **Status:** Design pattern only; not implemented. Put a typed, allowlisted API facade in front of legacy services. Do not translate arbitrary natural-language text directly into requests that mutate state. ## 3. Database Change Data Capture (CDC) Bridge **Area:** Architecture & Protocol Wrappers (1–10) **Status:** Design pattern only; not implemented. Use CDC with schema validation, data minimization, source permission checks, retention, and deletion propagation before forwarding events into a memory service. ## 4. Agent Card Metadata Injection **Area:** Architecture & Protocol Wrappers (1–10) **Status:** Design pattern only; not implemented. Publish an accurate static capability manifest at /.well-known/agent.json. Treat discovery metadata as untrusted input, not as authorization. ## 5. Async Event Bus Adapter **Area:** Architecture & Protocol Wrappers (1–10) **Status:** Design pattern only; not implemented. Bridge legacy message queues (RabbitMQ, Kafka, ActiveMQ) into the `hello.mesh` A2A protocol using event schema adapters. ## 6. OAuth-to-DID Token Exchanger **Area:** Architecture & Protocol Wrappers (1–10) **Status:** Design pattern only; not implemented. Use a token-exchange gateway to issue a short-lived, scoped credential after validating the OAuth session. A DID is a separate identifier and does not inherit proof of identity automatically. ## 7. GraphQL Federation Layer **Area:** Architecture & Protocol Wrappers (1–10) **Status:** Design pattern only; not implemented. Federate only the fields and operations each caller is allowed to access; query batching and round-trip counts depend on the schema and implementation. ## 8. JSON-RPC Schema Reflector **Area:** Architecture & Protocol Wrappers (1–10) **Status:** Design pattern only; not implemented. Generate candidate tool schemas from reviewed OpenAPI documents; manually review authorization, side effects, and input constraints before exposing them. ## 9. Webhook-to-Intent Transpiler **Area:** Architecture & Protocol Wrappers (1–10) **Status:** Design pattern only; not implemented. Parse signed or authenticated webhooks into typed event records. Validate source, timestamp, replay protection, and payload schema before any downstream action. ## 10. Headless Browser DOM Wrapper **Area:** Architecture & Protocol Wrappers (1–10) **Status:** Design pattern only; not implemented. Use browser automation only against explicitly allowlisted pages and accounts, with scoped sessions and human approval for state-changing actions. ## 11. Vector Embedding Backfill **Area:** Data & Memory Integration (11–20) **Status:** Design pattern only; not implemented. Backfill embeddings only for data with an approved purpose and retention policy; preserve source permissions and deletion requests. ## 12. Causal Dead-End Log Extractor **Area:** Data & Memory Integration (11–20) **Status:** Design pattern only; not implemented. Seed a failure registry only from authorized, redacted incident history, with provenance, retention, and correction/deletion handling. ## 13. Shadow Database Cloning **Area:** Data & Memory Integration (11–20) **Status:** Design pattern only; not implemented. Use database-native snapshots or isolated replicas when supported. Copy-on-write behavior and creation time depend on the provider and workload; no fixed latency is promised. ## 14. Document Chunking & Semantic Indexing **Area:** Data & Memory Integration (11–20) **Status:** Design pattern only; not implemented. Chunk authorized documents while preserving source access controls and citations. Do not treat model confidence scores as verified facts. ## 15. Incremental Cache Invalidation **Area:** Data & Memory Integration (11–20) **Status:** Design pattern only; not implemented. Map cache keys from legacy Redis clusters to agent memory pointers to prevent stale context retrieval. ## 16. Log-to-Episodic Memory Parser **Area:** Data & Memory Integration (11–20) **Status:** Design pattern only; not implemented. Ingest unstructured log files (JSON/Syslog) and parse them into structured episodic memory records. ## 17. Schema Version Fingerprinting **Area:** Data & Memory Integration (11–20) **Status:** Design pattern only; not implemented. Compute SHA-256 hashes of database schemas to detect silent breaking changes before agents run queries. ## 18. Dead-Letter Queue (DLQ) Introspection **Area:** Data & Memory Integration (11–20) **Status:** Design pattern only; not implemented. Expose dead-letter messages read-only first. Retrying or replaying a message requires idempotency checks and explicit approval. ## 19. Audit Trail Normalizer **Area:** Data & Memory Integration (11–20) **Status:** Design pattern only; not implemented. Normalize audit events into a documented receipt format. A hash alone is not a digital signature or proof of execution. ## 20. State snapshot serialization **Area:** Data & Memory Integration (11–20) **Status:** Design pattern only; not implemented. Serialize only approved, minimized state with schema versions, retention rules, and encryption; do not copy session secrets into memory blobs. ## 21. API Key Vault Mapping **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Keep API keys in a secret manager and expose narrow operations through a server-side capability proxy. Never return raw keys to prompts or model output. ## 22. RBAC-to-Guardian Tier Mapper **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Map roles conservatively to a documented permission matrix with explicit deny rules and owner review; Guardian tiers are not automatically equivalent to an external RBAC system. ## 23. Circuit Breaker Cost Governor **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Set hard request, rate, and spend limits, then stop calls on policy thresholds. P99 monitoring is a signal, not a spending-control substitute. ## 24. Untrusted Content Isolation and Policy Checks **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Keep external content explicitly marked as untrusted and apply context-specific validation. No sanitizer can reliably remove prompt injection from arbitrary text. ## 25. Cryptographic Receipt Stamping **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Use a digital signature over a canonical receipt with a protected signing key. A SHA-256 digest is an identifier, not a signature. ## 26. Automated Least-Privilege Scoping **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Use observed usage to recommend permission reductions; require an owner to review before changing grants because rare capabilities may still be necessary. ## 27. Human-in-the-Loop Webhook Gate **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Require explicit human authorization for high-impact changes, bound to the exact action, target, amount, and expiry. A chat notification alone is not an approval. ## 28. Session Continuity Tokenizer **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Store session continuity only in a dedicated encrypted secret store, with short expiry and explicit account scope. Prefer server-issued OAuth over browser-cookie portability. ## 29. Ephemeral Sandbox Isolation **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Run untrusted code in a properly configured isolation boundary with resource limits and deny-by-default network egress. Containers alone are not a security boundary equivalent to a VM. ## 30. Deterministic Replay Recording **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Record deterministic inputs and stubbed external responses for repeatable tests. Replay must not repeat real-world side effects. ## 31. Multi-Model Consensus Firewall **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Use independent policy checks and human approval for high-impact actions. Multiple model outputs are not a security boundary or authorization mechanism. ## 32. Compliance Guardrail Injector **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Apply compliance controls in data access, retention, and audit systems. Adding policy text to a prompt does not establish regulatory compliance. ## 33. Self-Revoking Capability Passports **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Use signed, scoped, expiring capabilities with revocation. Do not base authorization on a model confidence score. ## 34. Audit Log Merkle Tree Anchoring **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Merkle-root anchoring can make later tampering detectable only when roots are published to a trusted independent system and verification is retained. ## 35. Zero-Trust Egress Filtering **Area:** Security, Identity & Governance (21–35) **Status:** Design pattern only; not implemented. Apply deny-by-default egress at the network boundary, with DNS/IP controls, logging, and a reviewed allowlist. ## 36. AST Symbol Reflector **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Parse source files into AST symbol nodes using a project-specific parser and validated repository scope; `src/engine/ast.ts` is an example location, not a shipped path. ## 37. Pre-Commit TypeScript Compiler Gate **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Run the project’s configured TypeScript compiler as a pre-commit or CI gate. A pre-commit hook is optional and can be bypassed; CI remains authoritative. ## 38. Automated Test Runner Wrapper **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Wrap legacy test suites (Jest, PyTest, JUnit) in MCP tools so agents receive clean JSON test receipts. ## 39. Dependency Graph Visualizer **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Map imports and exports across legacy codebases to guide multi-agent refactoring tasks. ## 40. AML Transpilation Pipeline **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Use a model or parser to draft AML from a specification, then validate and review it. AML v1 is static and this pipeline must never execute generated source. ## 41. N+1 Query Detector **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Detect likely N+1 query patterns and propose measured alternatives; do not automatically rewrite locking or transaction semantics. ## 42. Dead Code Pruner **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Identify likely unreferenced code and submit a reviewed patch with build and test evidence. Never delete code automatically based only on static heuristics. ## 43. Automated Patch Reverter **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Automate rollback only when side effects are known to be reversible and reconciliation is tested; database backups and external actions need separate recovery plans. ## 44. Cross-Language Fuzzing Bridge **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Fuzz documented API boundaries with bounded, isolated test inputs and explicit authorization. Keep fuzz traffic out of production unless approved. ## 45. Model Arbitrage Optimizer **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Route work using measured task quality, latency, privacy, and cost. Cheap/local models still require validation and policy controls. ## 46. Token-Budgeted Context Packer **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Pack context to a measured model/tokenizer budget and preserve source references; approximate counts can differ from the provider tokenizer. ## 47. Sleep-Cycle Code Refinement **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Schedule maintenance only with a bounded change scope, tests, review, and rollback path; background agents must not silently rewrite production code. ## 48. Multi-Agent Git Merge Arbiter **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Use tools to propose conflict resolutions, then require normal tests and human review before merging. Model votes do not prove a merge is correct. ## 49. Documentation-to-Spec Generator **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Parse markdown READMEs and API docs into structured JSON contract schemas. ## 50. Zero-Downtime Blue/Green DNS Swap **Area:** Code, CI/CD & Compilation (36–50) **Status:** Design pattern only; not implemented. Use staged, health-checked traffic switching with explicit rollback. A DNS update is not inherently atomic and DNS caches may delay propagation.