Add MVP demo interview runbook

mvp/demo/interview-walkthrough.md

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+# Interview Walkthrough: MVP Diagnosis Agent
+
+This walkthrough is the Plan C demo story. It is meant for a short Agent Engineer interview, not as exhaustive system documentation.
+
+## 30-Second Summary
+
+```text
+This is an enterprise diagnosis Agent MVP.
+It takes a payment-timeout question, plans the investigation, calls evidence tools,
+checks the answer through a verifier, persists the full trace, and accepts feedback.
+```
+
+The important claim is not "the model answered once." The claim is:
+
+```text
+The system can show what evidence was used, how the answer was checked, and how to replay the session.
+```
+
+## Demo Flow
+
+1. Start the service with the `mvp-demo` profile.
+2. Run the fixed payment-timeout request.
+3. Open `mvp/demo/output/chat-response.json`.
+4. Open `mvp/demo/output/trace-response.json`.
+5. Point to evidence tools and verifier evaluation.
+6. Submit feedback and show it is attached to the same session.
+
+## Commands
+
+Start service:
+
+```powershell
+mvn spring-boot:run "-Dspring-boot.run.profiles=mvp-demo"
+```
+
+Run the demo from another terminal:
+
+```powershell
+powershell -ExecutionPolicy Bypass -File mvp/demo/scripts/run-payment-timeout-demo.ps1
+```
+
+Optional custom session:
+
+```powershell
+powershell -ExecutionPolicy Bypass -File mvp/demo/scripts/run-payment-timeout-demo.ps1 -SessionId "mvp-demo-payment-timeout-002"
+```
+
+## What To Show
+
+### 1. User-Facing Answer
+
+File:
+
+```text
+mvp/demo/output/chat-response.json
+```
+
+Say:
+
+```text
+This is the answer the user sees. The session id is stable, so I can trace this exact answer later.
+```
+
+### 2. Evidence Trace
+
+File:
+
+```text
+mvp/demo/output/trace-response.json
+```
+
+Say:
+
+```text
+This is the important Agent engineering part.
+I can inspect which tools were called, what inputs they received,
+whether they succeeded, and what evidence preview was persisted.
+```
+
+Point to:
+
+- `data.toolInvocations[*].toolName`
+- `data.toolInvocations[*].inputParams`
+- `data.toolInvocations[*].outputPreview`
+- `data.toolInvocations[*].success`
+
+### 3. Verifier / Self-Evaluation
+
+Point to:
+
+- `data.session.selfEvaluation`
+- `data.summary.hasVerifierEvaluation`
+
+Say:
+
+```text
+The final answer is not just raw Executor output.
+It is checked by a verifier or self-evaluation layer using the persisted trace.
+That lets the system return PASS, LOW_CONFID, or REJECT-style behavior instead of pretending all answers are equally certain.
+```
+
+### 4. Feedback Loop
+
+File:
+
+```text
+mvp/demo/output/feedback-response.json
+```
+
+Then re-query trace if needed.
+
+Say:
+
+```text
+Feedback is attached to the same diagnosis session.
+That makes it possible to mine useful / not useful cases later.
+```
+
+### 5. Regression Story
+
+Mention, do not deep dive unless asked:
+
+```text
+For repeatability, I also built an offline eval baseline.
+The demo proves the runtime trace; the eval baseline proves fixed-case regression.
+The two are separate on purpose: demo for human review, eval for automated signal.
+```
+
+## Strong Interview Framing
+
+Use this phrasing:
+
+```text
+I focused on the Agent engineering surface:
+traceability, evidence persistence, verifier gating, feedback, and regression checks.
+The model answer is only one part of the system.
+The more important part is whether we can audit and improve the answer after it is produced.
+```
+
+## Known Limits To Say Proactively
+
+```text
+This MVP still depends on configured MySQL, Redis, Milvus, and model credentials.
+The mvp-demo profile mocks logs and metrics, but not the full application runtime.
+Secret cleanup and fully isolated default tests are separate production-hardening tasks.
+```