fix: preserve RAG upload limits and block unsafe iframes

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Pull Request Checklist

Before submitting, make sure you've checked the following:

• Target branch: Automation branch is based on main per run configuration.
• Description: Fixes two high-severity regressions found in recent behavioral changes.
• Changelog: Not added; targeted critical bugfix automation PR.
• Documentation: Not applicable for these internal correctness/security fixes.
• Dependencies: No new dependencies.
• Testing: Focused regression tests and validation commands run successfully.
• Code review: Self-reviewed changed code and caller paths.
• Prefix: PR title uses fix:.

Changelog Entry

Description

• Preserve existing RAG file upload and image compression limits when admins submit partial RAG config updates, such as saving only Web Search settings.
• Restrict generic markdown iframe rendering to external HTTP(S) origins so chat content cannot trigger same-origin authenticated requests via iframe src values.

Added

• Dependency-light regression test for partial RAG config update preservation.
• getSafeIframeSrc utility and Vitest coverage for external, same-origin, backend-origin, and script/data/file iframe sources.

Changed

• /api/v1/retrieval/config/update now treats omitted nullable upload/compression fields consistently with the surrounding optional config fields.
• Generic markdown iframe rendering now validates src before creating an iframe.

Deprecated

• None.

Removed

• None.

Fixed

• Admin saving Web Search settings no longer silently clears FILE_MAX_SIZE, FILE_MAX_COUNT, FILE_IMAGE_COMPRESSION_WIDTH, or FILE_IMAGE_COMPRESSION_HEIGHT.
• Raw markdown iframe content can no longer embed relative/same-origin/WebUI-backend URLs such as /api/v1/auths/signout, or script/data/file schemes.

Security

• Blocks same-origin iframe request abuse from model-generated or shared chat markdown.

Breaking Changes

• None.

---

Additional Information

Bug and impact:

• Partial RAG update data loss: saving a partial RAG config payload ({ web: ... }) overwrote upload limits and image compression settings with None, disabling admin-enforced upload controls.
• Unsafe iframe rendering: raw markdown iframes bypassed sanitized HTML and rendered arbitrary src values, allowing authenticated same-origin GET side effects from viewed chat content.

Root cause:

• Four optional upload/compression fields were assigned directly from form_data instead of preserving existing values when omitted.
• HTMLToken.svelte extracted iframe URLs from unsanitized token.text and rendered them without origin/scheme validation.

Fix and validation performed:

• Added non-None preservation for the four RAG upload/compression fields.
• Added external-origin iframe URL validation and wired it into generic iframe rendering.
• Ran python3 -m py_compile backend/open_webui/routers/retrieval.py tests/test_rag_config_update.py.
• Manually executed test_partial_rag_updates_preserve_file_upload_settings() because pytest is unavailable in the base image.
• Ran npm ci to install pinned frontend dependencies.
• Ran npx vitest run src/lib/utils/iframe.test.ts (4 tests passed).
• Ran npx prettier --check src/lib/components/chat/Messages/Markdown/HTMLToken.svelte src/lib/utils/iframe.ts src/lib/utils/iframe.test.ts.
• Ran git diff --check origin/main..HEAD.

Screenshots or Videos

• Not applicable.

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