Fix VectorSessionFunctions element grow/shrink corruption (VectorSet Attributes) + tests

[tiagonapoli]

What

Fixes a VectorSet element corruption bug in VectorSessionFunctions.InPlaceWriter, and adds a unit test over the element sub-store write path that pins it.

The bug

InPlaceWriter did newValue.CopyTo(value) straight into the existing record's value span with no capacity or content-length handling. For a variable-length per-element value (the SETATTR Attributes blob), an in-place overwrite in the mutable region would:

• Grow (e.g. 9 -> 11 bytes) -> ArgumentException: Destination is too short.
• Shrink (e.g. 11 -> 9 bytes) -> stale trailing bytes remain and the content length is never shortened, so the read returns the old length.

The base contract computes a RecordSizeInfo and returns false when the new value won't fit, letting Tsavorite allocate a fresh record — the Vector override skipped all of it.

The fix

Mirror the main-store pattern: build the RecordSizeInfo for the new value, PopulateRecordSizeInfo, then TrySetContentLengths, which resizes/shortens the value in place and returns false when it cannot grow within the allocated record. On false, return false so Tsavorite falls back to a fresh, correctly-sized record via InitialWriter. Only copy once the length is set.

var sizeInfo = new RecordSizeInfo() { FieldInfo = GetUpsertFieldInfo(logRecord, newValue, ref input) };
functionsState.storeWrapper.store.Log.PopulateRecordSizeInfo(ref sizeInfo);
if (!logRecord.TrySetContentLengths(sizeInfo.FieldInfo.ValueSize, in sizeInfo))
    return false;   // -> Tsavorite RCU -> InitialWriter (fresh record)

Test

VectorElementUpsertResizePreservesValue([Values(false, true)] inReadOnlyRegion) drives a dedicated Vector session directly (mirroring VectorManager's DiskANN write callback) and walks a single element through initial write -> equal-size overwrite -> grow -> shrink, verifying the exact round-trip after each stage. It covers both the mutable region (InPlaceWriter) and the read-only region (fresh InitialWriter record). Plus VectorElementUpsertRoundTrips as a baseline.

Before the fix, the mutable-region case failed at the grow stage; with the fix both regions pass.

Validation

• New VectorElement* tests: 6/6 pass (both TestFixtures).
• Full Garnet.test.vectorset suite: 143 passed, 22 skipped, 0 failed — no regressions.

Scope note

Only the Upsert/InPlaceWriter path is fixed here — that is the path attributes actually use (WriteCallbackUnmanaged -> Upsert) and the one the repro hit. The RMW/Updater callback path (InitialUpdater/InPlaceUpdater/CopyUpdater) has the same latent shape but is only invoked by DiskANN with fixed-size data and isn't reachable variable-size through any command, so it is intentionally left unchanged.

[Copilot]

Pull request overview

Fixes a variable-length VectorSet element Upsert corruption/exception issue by ensuring VectorSessionFunctions.InPlaceWriter correctly resizes (or declines in-place growth) before copying the new payload, and adds a regression test that exercises create → same-size overwrite → grow → shrink across both mutable and read-only regions.

Changes:

• Update VectorSessionFunctions.InPlaceWriter to build/populate RecordSizeInfo and call TrySetContentLengths(...) prior to copying, so grow/shrink updates don’t overflow or leave stale trailing bytes.
• Add VectorElementUpsertResizePreservesValue test that drives the element sub-store Upsert/Read path and validates exact round-trips after each resize stage (mutable in-place vs read-only reallocation).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
test/standalone/Garnet.test.vectorset/RespVectorSetTests.cs	Adds a regression test covering element Upsert value resizing (create/overwrite/grow/shrink) in both mutable and read-only regions.
libs/server/Storage/Functions/VectorStore/VectorSessionFunctions.cs	Fixes InPlaceWriter to resize/shorten in-place safely via RecordSizeInfo + TrySetContentLengths, falling back to reallocation when needed.

Comments suppressed due to low confidence (1)

test/standalone/Garnet.test.vectorset/RespVectorSetTests.cs:3984

• If the Read goes pending, calling CompletePending(wait:true) does not update the local status/input/output. Subsequent asserts will still see the original Pending status (Found will be false) and may miss the updated ReadDesiredSize recorded by the Reader. Use CompletePendingWithOutputs to retrieve the completed Status (and Input/Output) before asserting.

                                var status = context.Read(elementKey, ref input, ref output);
                                if (status.IsPending)
                                    _ = context.CompletePending(wait: true);

                                ClassicAssert.IsTrue(status.Found, "reading a written element must find the record");
                                ClassicAssert.IsTrue(output.SpanByteAndMemory.IsSpanByte, "the element read must stay on the pinned span");