Harden js_repl emitImage to accept only data: URLs

[fjord-oai]

Motivation

• Prevent untrusted js_repl code from supplying arbitrary external URLs that the host would forward into model input and cause external fetches / data exfiltration. This change narrows the emitImage contract to safe, self-contained data URLs.

Description

• Kernel: added normalizeEmitImageUrl and enforce that string-valued codex.emitImage(...) inputs and input_image/content-item paths only accept non-empty data: URLs; byte-based paths still produce data URLs as before (kernel.js).
• Host: added validate_emitted_image_url and check EmitImage requests before creating FunctionCallOutputContentItem::InputImage, returning an error to the kernel if the URL is not a data: URL (mod.rs).
• Tests/docs: added a runtime test js_repl_emit_image_rejects_non_data_url to assert rejection of non-data URLs and updated user-facing docs/instruction text to state data URL support instead of generic direct image URLs (mod.rs, docs/js_repl.md, project_doc.rs).

Testing

• Ran just fmt in codex-rs; it completed successfully.
• Added a runtime test (cargo test -p codex-core js_repl_emit_image_rejects_non_data_url) but executing the test in this environment failed due to a missing system dependency required by codex-linux-sandbox (the vendored bubblewrap build requires libcap.pc via pkg-config), so the test could not be run here.
• Attempted a focused cargo test invocation with and without default features; both compile/test attempts were blocked by the same missing system libcap dependency in this environment.

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Codex Task

[fjord-oai]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 2e69ea53d0

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[fjord-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Swish!

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".