Demo: Investigate sample security alert before agent assignment

## Goal
Triage the sample security alert and decide whether implementation work is required.

## Context
Review `demo/python_app_demo/alerts/sample-alert.md`, which represents an input validation scanner finding.

## Acceptance criteria
- Determine whether the alert is a true positive or false positive.
- Document the evidence and affected area.
- Describe the potential blast radius.
- If valid, propose a narrowly scoped remediation and tests.
- Do not merge a remediation without human security review and approval.

## Demo workflow
Use this issue to demonstrate that not every task should be assigned directly to an implementation agent. A human should lead the initial judgment-heavy triage. An agent may later help with evidence gathering or a scoped fix only after the human defines the required behavior.

Start by reading demo/python_app_demo/alerts/sample-alert.md and identify the reported input-validation finding and affected area. Gather evidence to classify it as a true or false positive, document the blast radius, and record any narrowly scoped remediation and tests if it is valid. Do not merge remediation without human security review and approval.

Written by the indexing model from the issue text.