🧱 refactor: Read Message Content Siblings Through the Parts Host

[berry-13]

Summary

The message part components read the app only through MessagePartsHost, but their siblings in components/Chat/Messages/Content still reached for Recoil, ~/store, useMessageContext and useToastContext directly: 16 of 115 files. A sibling that reads app state that way cannot move into @librechat/chat with the parts, and it ignores whatever host the view supplied.

This routes nine of them through the host. MarkdownComponents, SiblingHeader, MessageContent, Markdown, BackgroundTaskCard and hydration read the message, user, toast, user-text preferences and LaTeX setting from useMessagePartsHost(). For that, MessagePartMessage gains the optional conversationId and partIndex the app's message context already carries, MessagePartsUser gains id, and the host gains useLaTeXParsing. ApprovalContext reads the ephemeral agent from ChatSettings, which already exposes the same Recoil reader. The two benches only swap their inline RecoilRoot for an AppStores wrapper in client/test/harness.tsx; that is a harness-only change.

The remaining siblings follow in two stacked PRs, and ActivityPhaseGroup waits for #17138.

Type of change

• Refactor

Testing

Tested environments/configuration:

Local jest and typecheck; no runtime configuration matters for this change.

Automated tests:

• cd client && npx jest src/components/Chat/Messages src/components/Chat/Input src/hooks/Input src/components/Chat/Subagents src/components/Share src/Providers: 201 suites, 3,729 tests pass.
• cd packages/chat && npx jest: 36 suites, 388 tests pass; every host fixture carries the new member.
• Both benches run explicitly (npx jest --runInBand --coverage=false --testMatch '**/ContentParts.bench.tsx', and the same for MarkdownBlocks.bench.tsx): 2 and 3 cases pass.
• npx tsc --noEmit for client and packages/chat, and the package build, are clean. ESLint, Prettier and import sorting are clean on every changed file.
• The audit's parts-context.sh over Messages/Content reports 7 of 115 files (from 16), and 0 of 44 under Parts.

Screenshots / recordings

No user-facing change.

Risk / compatibility

Low. Each new read is the same store or context the component read before, through the app's host. useResumeSubmit now takes getEphemeralAgent from ChatSettings, which every caller has above it under routes/Root.tsx.

Checklist

• I reviewed my own changes
• Relevant tests have been added or updated
• Existing relevant tests pass
• The change does not introduce new warnings or errors

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-15T17:58:03.997716Z	6fcd281	Draft marked ready
🔒 Security Review	✅ Completed 2026-10-15T17:58:23.961134Z	6fcd281	Draft marked ready

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