Drive vectorsdb dimension from the embeddings column only

[abnegate]

Addresses the P1 on #211: the placeholder-only guard left a stale archived dimension uncorrected when it disagreed with the actual vector column size, while the pre-#211 behavior overwrote it from any vector column (the P1 on #210).

The embeddings column is the schema-defining vector of a vectorsdb collection, so it alone now drives dimension: mismatches (including the pre-dimension-archive placeholder) are corrected from its size, and other vector columns never touch the value. This satisfies both review findings simultaneously.

🤖 Generated with Claude Code

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[greptile-apps]

Greptile Summary

This PR changes how vectorsdb collection dimensions are restored during Appwrite migrations.

• Adds a constant for the embeddings vector key.
• Limits dimension sync to the embeddings column.
• Updates stale dimensions when the archived value differs from the column size.

Confidence Score: 5/5

This looks safe to merge after checking the non-standard vector-column case.

• The main changed flow matches the intended embeddings-driven dimension behavior.
• A collection without an embeddings vector can keep a stale archived dimension.

src/Migration/Destinations/Appwrite.php

Important Files Changed

Filename	Overview
src/Migration/Destinations/Appwrite.php	Updates vectorsdb dimension reconciliation so embeddings alone drives the stored collection dimension.

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
src/Migration/Destinations/Appwrite.php:1338
**Non-Embeddings Dimension Stays Stale**

When an archived vectorsdb collection has no serialized `dimension` and its vector column is named anything other than `embeddings`, this guard skips the only size-based correction path. The table keeps the placeholder or stale dimension, so the migrated collection can reject later vector writes because its stored dimension no longer matches the actual vector column size.

_{Reviews (1): Last reviewed commit: "fix: drive vectorsdb dimension from the ..." | Re-trigger Greptile}