fix: preserve existing abstract during reindex

[yc111233]

Problem

When index_resource() rebuilds the vector index (e.g. after switching embedding models via reindex with regenerate=False), it passes an empty summary_dict to vectorize_file:

await vectorize_file(
    file_path=file_uri,
    summary_dict={"name": file_name},  # no "summary" key
    ...
)

This causes Context(abstract=""), which overwrites the existing VLM-generated abstract in the vector index with an empty string.

Impact: Rerank relies on the abstract field to differentiate documents. With empty abstracts, all documents sent to the rerank API are identical ("[empty]" after the DashScope safety filter), resulting in uniform scores and no meaningful ranking.

Root Cause

index_resource and the normal write path use different code paths for the abstract field:

• Normal write: semantic processor (VLM) generates summary → passed as summary_dict["summary"] → stored as abstract in vector index
• Reindex: no summary available → summary_dict has no "summary" key → abstract="" → overwrites old value via upsert

Reindex and VLM summary generation are independent concerns, but the current implementation couples them by discarding the old abstract during reindex.

Fix

Before calling vectorize_file, query the existing vector index entry via fetch_by_uri (which already includes abstract in its output fields) and carry forward the old value:

existing_abstract = ""
if vector_store:
    try:
        existing = await vector_store.fetch_by_uri(file_uri, ctx=ctx)
        if existing:
            existing_abstract = existing.get("abstract", "") or ""
    except Exception:
        pass

await vectorize_file(
    file_path=file_uri,
    summary_dict={"name": file_name, "summary": existing_abstract},
    ...
)

Test Plan

• Verified on OpenViking 0.3.5 with 8600+ vectors
• Reindex with new embedding model (BGE-M3 → text-embedding-v4) preserves all VLM abstracts
• Rerank scores show proper differentiation after reindex (10 unique scores vs all-identical before fix)
• No impact on regenerate=True path (which uses summarize() instead of build_index())

[github-actions]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 2 🔵🔵⚪⚪⚪

🏅 Score: 90

🧪 No relevant tests

🔒 No security concerns identified

📝 TODO sections openviking/utils/embedding_utils.py [372]: Recursive indexing? Skip subdirectories to match previous behavior

🔀 No multiple PR themes

⚡ Recommended focus areas for review Error Handling Bare except Exception: swallows all errors without logging, potentially hiding real issues when fetching existing abstracts. This could lead to silent failures to preserve abstracts without observability. except Exception: pass

[github-actions]

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