🤖 fix: support JSON attachments

[LeonidasZhak]

Summary

Allow JSON files to be attached in the chat composer while keeping the shared provider attachment allowlist restricted to model-supported media types.

Background

Fixes #3546. JSON files were rejected by the chat composer even though they can be carried through the existing generic file-part send path. The agent-facing attach_file tool must still reject JSON so agents use file_read for text files.

Implementation

• Adds a chat-scoped attachment helper that accepts application/json and .json without expanding the shared provider attachment allowlist.
• Includes JSON in the chat file picker accept list and tooltip copy.
• Adds focused coverage for JSON MIME handling, extension-based detection when macOS drag/drop provides an empty MIME type, and the attach_file boundary.

Validation

• Focused attachment tests: 40 passed
• Focused ESLint and Prettier checks passed
• tsgo --noEmit --project tsconfig.json passed
• git diff --check passed
• make static-check passed

Risks

Low. JSON support is scoped to user-selected chat attachments. The provider media allowlist and agent attach_file behavior remain unchanged.

---

Generated with mux • Model: GPT-5 • Thinking: unknown • Cost: $unknown

[LeonidasZhak]

@codex review

Please review this small JSON attachment support fix for #3546. The diff only expands the attachment media-type allowlist and file picker copy, with focused coverage for application/json and empty-MIME .json drag/drop handling.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Already looking forward to the next diff.

Reviewed commit: 834e8e47c2

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[LeonidasZhak]

@codex review

Rebased this PR onto the latest main and resolved the attachment conflicts by preserving upstream staged ZIP attachment support while keeping JSON as a provider-supported attachment type.

Validation:

• bun test --timeout=10000 src/browser/utils/attachmentsHandling.test.ts src/common/utils/attachments/supportedAttachmentMediaTypes.test.ts - 19 tests passed
• focused ESLint for AttachFileButton, attachment handling tests, and supported media-type files
• ./node_modules/.bin/tsgo --noEmit --project tsconfig.json
• git diff --check origin/main...HEAD
• make static-check

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 4cf1aa10ac

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[LeonidasZhak]

@codex review

Addressed the JSON allowlist feedback. JSON remains supported for user-selected chat attachments through a chat-scoped helper, but the shared provider attachment allowlist no longer treats application/json or .json as model media attachments. This keeps attach_file({ path: "package.json" }) rejected so the agent can use file_read.

Validation:

• bun test --timeout=10000 src/common/utils/attachments/supportedAttachmentMediaTypes.test.ts src/browser/utils/attachmentsHandling.test.ts src/node/services/tools/attach_file.test.ts - 39 tests passed
• focused ESLint for attachment helpers, browser attachment handling, AttachFileButton, and attach_file tests
• ./scripts/generate-version.sh && ./node_modules/.bin/tsgo --noEmit --project tsconfig.json
• git diff --check origin/main...HEAD
• make static-check

[chatgpt-codex-connector]

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

Reviewed commit: 35ff6ea336

ℹ️ About Codex in GitHub

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• Mark a draft as ready
• Comment "@codex review".

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[LeonidasZhak]

@codex review

Rebased onto the latest main and resolved the attachment conflict by preserving upstream display-only handling for unsupported source files. JSON remains supported only for user-selected chat attachments; attach_file still treats it as display-only rather than a model attachment.

Validation: 40 focused tests passed; focused ESLint, Prettier, and TypeScript checks passed; git diff --check passed; full make static-check passed.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 9181e190d3

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[LeonidasZhak]

@codex review

Addressed the generic-MIME JSON feedback in 3c26cff31. Chat attachments now fall back to the filename when a non-empty MIME is unsupported, and the data URL is canonicalized to the resolved media type. Provider/agent attachment boundaries remain unchanged.

Validation: 41 focused tests passed; focused ESLint, Prettier, and TypeScript checks passed; git diff --check passed; full make static-check passed.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Already looking forward to the next diff.

Reviewed commit: 3c26cff31d

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".