docs: define the trusted-local Codex Security threat model

[mldangelo-oai]

Summary

Codex Security runs with your local permissions. This PR explains the practical security model: scan only repositories you trust and either own or are authorized to assess.

It also makes the scanner's behavior clear:

• Scans use the codex_security_scan filesystem profile and approvalPolicy: "never".
• --codex and codexOverrides do not make that profile or approval policy more restrictive.
• Local workbench processes can inherit other credentials from your environment.
• The scanner must use the target and output paths you authorize and report its actual coverage.

Why

Permission to assess a repository is not the same as trusting it. Configuration settings are not security guarantees when the scan does not apply them. Users should be able to see which actions and data flows are authorized before starting a scan.

Scope

The PR changes only:

• SECURITY.md
• sdk/typescript/README.md

It does not change skills, scanner behavior, or runtime configuration.

Validation

• 385 tests passed; 3 expected skips.
• Full Markdown formatting and SDK type checks passed.
• Generated models and the production TypeScript build passed.
• The packed npm artifact passed the public SDK, installed CLI, and bundled-plugin integrity checks.
• The PR contains only the two documentation files listed above.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 01e3cdb4da

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: ea18cb11a4

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".