Treat a pack-less v2 fetch response as an error, not success

[Soph]

Problem

consumeV2FetchPack returned nil when the protocol-v2 fetch response ended — a bare flush or EOF — without ever delivering a packfile section. So a truncated or pack-less response let a fetch report success having stored nothing. Its streaming sibling openV2PackStream correctly treats the same situation as io.ErrUnexpectedEOF.

By the time control reaches either function, wants is non-empty (fetchToStoreV2/fetchPackV2 both return git.NoErrAlreadyUpToDate early when there's nothing to fetch), so the server genuinely owes us a packfile section — a response without one is anomalous.

Fix

Return io.ErrUnexpectedEOF on the no-packfile flush/EOF paths in consumeV2FetchPack, matching openV2PackStream. The expectPackfile (post-ready) branch keeps its existing, more specific message, and an empty-but-present pack still flows through the normal packfile path unchanged.

Tests

• TestStoreV2FetchPackRejectsResponseWithoutPackfile — a bare flush yields io.ErrUnexpectedEOF.
• TestStoreV2FetchPackRejectsTruncatedResponse — EOF before any packfile yields io.ErrUnexpectedEOF.

These mirror the existing openV2PackStream rejection tests. Full go test ./... passes.

🤖 Generated with Claude Code

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Note

Medium Risk
Changes error semantics on the v2 fetch-to-store path (core replication/fetch), but replaces incorrect silent success with a detectable failure.

Overview
consumeV2FetchPack no longer returns success when a protocol v2 fetch response ends with a bare flush or EOF and never sends a packfile section. Those paths now return io.ErrUnexpectedEOF, aligned with openV2PackStream, so store-based fetches cannot report success after storing nothing from a truncated or empty response.

The post-ready case still uses the existing explicit “expected packfile after ready” errors; acknowledgments-without-packfile behavior is unchanged.

Tests cover a flush-only wire and an empty reader, both expecting io.ErrUnexpectedEOF.

^{Reviewed by Cursor Bugbot for commit 74a2fd5. Configure here.}