[v1.0] Enable repository secret, dependency, and code-scanning controls

[codeforester]

Goal

Enable defense-in-depth repository controls for vulnerable dependencies, committed secrets, and static code-scanning findings.

Background

Live repository settings on 2026-08-30 report dependabot_security_updates disabled and secret scanning, non-provider patterns, push protection, and validity checks disabled. The code-scanning alerts endpoint reports that no analysis exists.

The repository's Ruff, Bandit, pip-audit, redaction, and threat-model gates are valuable, but they do not prevent a credential from being pushed, open reviewed security-update pull requests, or provide CodeQL-style cross-file analysis.

Scope

• Enable the dependency graph, Dependabot alerts/security updates, and a reviewed update policy.
• Enable secret scanning, push protection, validity checks, and supported non-provider patterns.
• Enable CodeQL default or advanced setup for the supported Python surface.
• Make actionable security checks required on protected main.
• Document triage, false-positive dismissal, SLA, and emergency response ownership.
• Record any organization/plan control that cannot be enabled and its compensating control.

Acceptance Criteria

• Repository settings read back the intended dependency, secret, and code-scanning features as enabled.
• A safe test secret pattern is blocked or detected in a documented rehearsal.
• Code scanning produces a successful analysis for main and pull requests.
• Dependabot security updates open a reviewed PR when a test fixture/rehearsal dependency is vulnerable, or equivalent evidence proves configuration.
• Security checks are required by branch protection and cannot be silently skipped on release-source changes.
• Dismissals require reason, reviewer, and audit trail; ownership and remediation SLAs are documented.
• Existing Bandit and pip-audit gates remain in place and are not treated as substitutes for repository controls.

Validation

Read back GitHub security settings and branch protection; inspect the first successful code-scanning run; execute safe secret/dependency rehearsal cases; verify alert and dismissal workflows.

Non-Goals

• Do not commit a real credential or known exploitable production dependency.
• Do not replace the runtime threat model, trusted publishing, or artifact attestations.

Dependencies

• [v1.0] Gate releases on protected main lineage and independent approval #271
• [v1.0] Pin and verify the release build toolchain #278

Project Fields

• Status: Backlog
• Priority: P1
• Area: Security
• Initiative: v1.0 Readiness
• Size: M

Ownership

• Assignee: @codeforester