[mgravell]

Fixes #3278.

Problem

Since 3.4.0 the HELLO reply has been a source of the server version, and both the interactive and subscription connections issue HELLO. The handler assigned version straight to the Redis API version, but the two conventions in the wild differ (measured against real servers):

Server	server	version	extra
Garnet 2.2.2	redis	7.4.3 (Redis API version)	garnet_version => 2.2.2
Valkey 9.1.2	valkey	9.1.2 (Valkey's own version)	INFO: redis_version:7.2.4

On Valkey the detected version therefore depended on whether the last reply processed was HELLO (9.1.2) or INFO (7.2.4), so version-gated commands (e.g. DELEX in LockRelease) were sometimes sent to a server that does not have them.

Rule

Decided once the whole HELLO map has been read:

• server => redis (or absent): version is the Redis API version; a <vendor>_version key, if present, sets the product variant (Garnet shape).
• server is a recognised non-Redis name (valkey, redict, ...): version is the vendor version and only feeds the product variant; the API version is left to INFO's redis_version.
• server is unrecognised: version is ignored (logged). Conservative by design: if INFO is unavailable too, the version falls back to DefaultVersion rather than guessing.
• A plain Redis HELLO never touches the product variant, so it cannot clobber INFO's KeyDB detection (which comes from executable, not a *_version key).

Verification

• Patched library against real Valkey 9.1.2 and Garnet 2.2.2, 20 connections each: stable at API 7.2.4 / vendor 9.1.2 and API 7.4.3 / vendor 2.2.2 respectively.
• The in-process test server can now emulate both shapes (HelloServerName, HelloVersionString, HelloExtraFields). ProductVariantUnitTests and ValkeyUnitTests run per protocol and assert the API version as well as the variant.
• New DetectProductVariantFromHelloAlone disables INFO so HELLO is the only source; it fails deterministically on RESP2 and RESP3 with the fix reverted. The test vendor version is now 9.1.2 rather than 1.2.3-preview4, because an unparseable version was hiding the bug.
• Full Build.csproj Release build with CI=true is green.

[mgravell]

👍