refactor(tiering): introduce FragmentRef abstraction for serialization

[romange]

Summary

• Moves DetermineSerializationParams logic into a new FragmentRef class in the tiering namespace
• FragmentRef wraps a CompactValue* and exposes IsOffloaded, HasStashPending, ClearStashPending, ObjType, and GetSerializationDescr
• StashDescriptor now inherits from FragmentRef::SerializationDescr
• CancelStash and ShouldStash updated to accept FragmentRef instead of PrimeValue*

🤖 Generated with Claude Code

[augmentcode]

🤖 Augment PR Summary

Summary: This PR refactors tiering offload/stash code by centralizing serialization-descriptor computation behind a new abstraction.

Changes:

• Introduces tiering::FragmentRef (wrapping a CompactValue) to query offload/stash state and compute serialization descriptors
• Moves the old DetermineSerializationParams logic into new src/core/tiering_types.{h,cc} and wires it into the core build
• Updates TieredStorage stashing, cancellation, and eligibility checks to use FragmentRef
• Makes TieredStorageBase::StashDescriptor reuse FragmentRef::SerializationDescr via inheritance

Technical Notes: Behavior for stashing strings and listpack-encoded hashes is preserved while reusing the descriptor in both scheduling and completion paths.

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[augmentcode]

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[Copilot]

Pull request overview

This PR introduces a FragmentRef class in the dfly::tiering namespace that encapsulates value introspection and serialization description logic previously spread across a free function (DetermineSerializationParams) and the StashDescriptor struct. FragmentRef wraps a CompactValue* and exposes methods like IsOffloaded, HasStashPending, ClearStashPending, ObjType, and GetSerializationDescr. StashDescriptor now inherits from FragmentRef::SerializationDescr, and CancelStash/ShouldStash signatures are updated to accept FragmentRef.

Changes:

• New FragmentRef class added to src/core/tiering_types.h/.cc, centralizing serialization introspection
• TieredStorage::StashDescriptor updated to inherit from FragmentRef::SerializationDescr; CancelStash and ShouldStash signatures updated to accept tiering::FragmentRef
• tiering_types.cc added to the dfly_core CMake library target

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/core/tiering_types.h	Defines new FragmentRef class and nested SerializationDescr struct
src/core/tiering_types.cc	Implements FragmentRef::GetDescr (moved from DetermineSerializationParams)
src/core/CMakeLists.txt	Adds tiering_types.cc to dfly_core build target
src/server/tiered_storage.h	Updates StashDescriptor, ShouldStash, CancelStash, and adds unimplemented GetStashParams private method
src/server/tiered_storage.cc	Updates call sites to use FragmentRef, removes DetermineSerializationParams

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.