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+# Architecture & data flow
+
+Reversible PII de-identification round trip for HNCB. An advisor query with a real
+name is tokenized before it leaves for the cloud; the AgentCore agent reasons on
+tokens only; identity is restored on-prem before the advisor sees the answer.
+
+Everything runs in **one AWS account** (`ap-southeast-1`); the trust zones are
+**logical**, represented by tags (`Zone=on-prem-VPC-A` vs `Zone=cloud-VPC-B`) — the
+demo proves data-flow behaviour, not physical residency.
+
+> **Core invariant:** cloud-zone components (AgentCore Runtime, Gateway, Bedrock)
+> never receive the real name. Proven live — for one session the token `CUST_*`
+> appeared in 13 CloudWatch trace events while `王小明` / `A123456789` appeared in 0.
+
+## Component reference
+
+| # | Component | Repo | AWS resource | Zone | Sees real PII? |
+|---|---|---|---|---|---|
+| UI | Advisor split-view UI | `ui/` | S3 + CloudFront | cloud (host) | shows restored answer to the advisor |
+| entry | Orchestration | `fusion/` (prod) · `gateway_api/orchestrator/` (dry run) | Fusion SaaS · `/demo` Lambda | — | ✅ owns the flow |
+| 2 | `/tokenize` | `gateway_api/tokenize/` | Lambda (in-VPC) + API Gateway | on-prem | ✅ mints the map |
+| 2 | PII detector | `presidio/` | Fargate (private, SG-locked `:5001`) | on-prem | typed findings only |
+| 2,4,8 | Token vault | `terraform/main.tf` | DynamoDB `…-vault` | on-prem | ✅ reversible map |
+| 4-6 | Customer records | `seed/` | DynamoDB `…-customers` | on-prem | ✅ never leave zone |
+| 3,7 | Cloud agent + model | `agent/` | AgentCore Runtime + Bedrock (apac Claude 3.5 Sonnet v2) | **cloud** | ❌ tokens only |
+| 4 | Tool bridge | `scripts/agentcore_setup.sh` | AgentCore Gateway (MCP, AWS_IAM) | **cloud** | ❌ tokens only |
+| 4-6 | RAG tool | `lambda_rag/` | Lambda | on-prem | ✅ resolves token, returns none |
+| 8 | `/restore` | `gateway_api/restore/` | Lambda + API Gateway | on-prem | ✅ re-attaches identity |
+
+## Flow diagram
+
+```mermaid
+flowchart TB
+ advisor(["Advisor (browser)"])
+ ui["Advisor UI
S3 + CloudFront
(split view)"]
+
+ subgraph entry["Entry / orchestration"]
+ fusion["Fusion SaaS (prod)
— or —
/demo Lambda (Fusion-less dry run)"]
+ end
+
+ subgraph cloudzone["CLOUD zone (Zone=cloud-VPC-B) — sees TOKENS only"]
+ runtime["AgentCore Runtime
Strands agent + Bedrock
apac Claude 3.5 Sonnet v2"]
+ gateway["AgentCore Gateway
MCP · AWS_IAM / SigV4"]
+ end
+
+ subgraph onprem["ON-PREM zone (Zone=on-prem-VPC-A) — holds the reversible map + PII"]
+ tokenize["/tokenize Lambda (in-VPC)
detect → mint → vault → splice"]
+ presidio["Presidio detector
Fargate (PRIVATE, SG-locked :5001)"]
+ vault[("DynamoDB VAULT
token <-> PII (+customer_id)")]
+ customers[("DynamoDB CUSTOMERS
raw records — never leave")]
+ rag["RAG tool Lambda
token -> evidence (no PII out)"]
+ restore["/restore Lambda
re-attach identity"]
+ end
+
+ advisor -- "1 query: 王小明 + A123456789" --> ui
+ ui -- "POST {query}" --> fusion
+ fusion -- "2 {query}" --> tokenize
+ tokenize -- "POST /analyze" --> presidio
+ presidio -- "typed findings" --> tokenize
+ tokenize -- "write {token,type,value,session}" --> vault
+ tokenize -- "3 deidentified_prompt (CUST_*)" --> runtime
+ runtime -- "4 tools/call get_customer_activity_summary(CUST_*)" --> gateway
+ gateway -- "5 invoke (SigV4)" --> rag
+ rag -- "6 resolve token" --> vault
+ rag -- "read record" --> customers
+ rag -- "7 evidence package (token-keyed, no PII)" --> runtime
+ runtime -- "talking points (tokens only)" --> fusion
+ fusion -- "8 {session_id, text}" --> restore
+ restore -- "lookup session tokens" --> vault
+ restore -- "final: (客戶:王小明)…" --> fusion
+ fusion -- "{final, deidentified_prompt, agent_tokenized}" --> ui
+ ui -- "split view: restored vs tokenized" --> advisor
+```
+
+## Sequence (the 8-step round trip)
+
+```mermaid
+sequenceDiagram
+ autonumber
+ actor A as Advisor
+ participant UI as UI (S3/CloudFront)
+ participant F as Fusion or demo
+ participant TK as tokenize (on-prem)
+ participant PR as Presidio (private)
+ participant V as Vault (DynamoDB)
+ participant RT as AgentCore Runtime + Bedrock (cloud)
+ participant GW as AgentCore Gateway (cloud)
+ participant RG as RAG Lambda (on-prem)
+ participant RS as restore (on-prem)
+
+ A->>UI: query with 王小明 + A123456789
+ UI->>F: POST {query}
+ F->>TK: {query}
+ TK->>PR: POST /analyze
+ PR-->>TK: typed findings
+ TK->>V: write token to PII map (session)
+ TK-->>F: deidentified_prompt (CUST_*)
+ F->>RT: {prompt: CUST_*}
+ Note over RT,GW: cloud sees TOKENS only
+ RT->>GW: tools/call get_customer_activity_summary(CUST_*)
+ GW->>RG: invoke (SigV4)
+ RG->>V: resolve token to customer_id
+ RG-->>RT: de-identified evidence package
+ RT-->>F: talking points (tokens only)
+ F->>RS: {session_id, text}
+ RS->>V: lookup session tokens
+ RS-->>F: final (王小明 restored)
+ F-->>UI: {final, deidentified_prompt, agent_tokenized}
+ UI-->>A: split view (restored vs tokenized)
+```
+
+## ASCII fallback
+
+```
+ ┌──────────────────────────────────────────────┐
+ Advisor │ "請問客戶 王小明 (A123456789) 最近三個月…" │ ← REAL PII
+ (browser) └──────────────────────────────────────────────┘
+ │ │
+ │ 1 │
+ ▼ ▼
+ ┌─────────────────┐ ┌───────────────────────────┐
+ │ Advisor UI │ │ Entry / orchestration │
+ │ S3 + CloudFront │──POST─────▶│ • Fusion SaaS (prod) │ stands in for Fusion
+ │ (split view) │ {query} │ • /demo Lambda (dry run) │ only, in the demo
+ └─────────────────┘◀───────────│ tokenize→agent→restore │
+ ▲ {final, └───────────┬───────────────┘
+ │ deidentified, │
+ │ agent_tokenized} │ 2 {query}
+════════╪════════════════════════════════════╪════════ TRUST BOUNDARY (public HTTPS + x-api-key)
+ ON-PREM│ (Zone=on-prem-VPC-A) ▼
+ │ ┌───────────────────────┐ findings ┌────────────────────┐
+ │ │ /tokenize Lambda │────────────▶│ Presidio detector │
+ │ │ (in VPC) │◀────────────│ Fargate (PRIVATE, │
+ │ │ detect→mint→vault→splice│ │ SG-locked :5001) │
+ │ └───────┬───────────────┘ └────────────────────┘
+ │ │ write {token,type,value,session}
+ │ ▼
+ │ ┌───────────────────────┐ (VPC gateway endpoint)
+ │ │ DynamoDB VAULT │◀────────────────┐
+ │ │ token ⇄ PII (+cust_id) │ │
+ │ └───────────────────────┘ │
+ │ deidentified_prompt = "…CUST_317499…" ← TOKENS ONLY │
+════════╪═════════════════════════════════│═════════════════════════════════╪══════════════
+ CLOUD │ (Zone=cloud-VPC-B) │ 3 │ resolve token
+ │ ▼ │
+ │ ┌────────────────────────┐ │
+ │ │ AgentCore RUNTIME │ │
+ │ │ Strands agent + Bedrock│ │
+ │ │ (apac Claude 3.5 Sonnet)│ │
+ │ └───────────┬────────────┘ │
+ │ │ 4 tools/call (MCP, SigV4) │
+ │ ▼ get_customer_activity_summary │
+ │ ┌────────────────────────┐ │
+ │ │ AgentCore GATEWAY (MCP) │ │
+ │ │ AWS_IAM auth │ │
+ │ └───────────┬────────────┘ │
+ │ ← trace shows ONLY tokens │ 5 invoke │
+════════╪══(王小明: 0 hits, CUST_: 13)═══│═════════════════════════════════════╪══════════════
+ ON-PREM│ ▼ │
+ │ ┌────────────────────────┐ 6 reads │
+ │ │ RAG tool Lambda │─────────────────────┘
+ │ │ token→customer_id→ │ ┌────────────────────┐
+ │ │ de-identified evidence │─────▶│ DynamoDB CUSTOMERS │ ← raw PII
+ │ │ (raw record stays here) │ read │ (never leaves zone)│ stays put
+ │ └───────────┬────────────┘ └────────────────────┘
+ │ │ 7 evidence package (token-keyed, no PII)
+ │ ▼ → agent writes talking points (tokens only)
+ │ ┌────────────────────────┐
+ │ 8 {session_id, │ /restore Lambda │
+ └───────────────────▶│ vault lookup by session │ prepend 王小明 + swap inline tokens
+ final = "(客戶:王小明)…" │ re-attach identity │
+ ← PII restored on-prem └────────────────────────┘
+```
+
+## Auth & network per hop
+
+| Hop | Transport | Auth |
+|---|---|---|
+| UI → entry | public HTTPS | `/demo` (dry run) or Fusion SaaS (prod) |
+| entry → `/tokenize`, `/restore` | public API Gateway (HTTPS) | shared secret (`x-api-key` / bearer, checked in-handler) |
+| `/tokenize` → Presidio | private (in-VPC) | Presidio SG allows only the tokenize Lambda's SG |
+| `/tokenize`,`/restore`,RAG → DynamoDB | AWS API | IAM (tokenize reaches it via a VPC gateway endpoint) |
+| Runtime → Gateway → RAG | MCP over HTTPS | SigV4 (`AWS_IAM`); runtime role has `bedrock-agentcore:InvokeGateway`, gateway role has `lambda:InvokeFunction` |
+
+Notes:
+- The **UI is cloud-hosted** but only ever displays the *restored* answer to the
+ authorized advisor; the cloud *reasoning* path (Runtime/Gateway/Bedrock) is the
+ part that never sees PII.
+- **Fusion is shared SaaS** and is never built or hosted here. The `/demo`
+ orchestrator only stands in for Fusion's orchestration in the Fusion-less dry run.
+- Tokens are **random per request** (`CUST_` for a PERSON, `TW_` for a
+ Taiwan ROC ID); the reversible map lives only in the on-prem vault.