GitBlobstore: remote-managed fetch/merge/push sync

[coffeegoddd]

No description provided.

[Copilot]

Pull request overview

Adds a “remote-managed” synchronization mode to GitBlobstore so local reads/writes automatically fetch from a configured remote, merge remote-tracking state into the local ref, and push updates back using --force-with-lease. This is supported by new git plumbing APIs and a new gitrebase helper that performs key/path-granularity merges with atomic handling for chunked trees.

Changes:

• Introduce remote-managed fetch/merge/push workflows in GitBlobstore (including lease-based push retries).
• Add new git plumbing methods (FetchRef, PushRefWithLease, MergeBase, ListTreeRecursive, CommitTreeWithParents) and associated tests.
• Add gitrebase merge helper + tests, and switch chunked-part naming to 4 digits (0001, 0002, …).

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
go/store/blobstore/internal/gitrebase/temp_index.go	Adds temp index helper for merge operations.
go/store/blobstore/internal/gitrebase/merge.go	Implements merge logic for remote-tracking -> local ref with conflict hooks and chunked-tree atomicity.
go/store/blobstore/internal/gitrebase/merge_test.go	Adds test coverage for fast-forward, merge commits, and conflict policies.
go/store/blobstore/internal/git/api.go	Extends GitAPI with fetch/push-with-lease and merge/list/commit helpers.
go/store/blobstore/internal/git/impl.go	Implements new GitAPI methods via git CLI plumbing commands.
go/store/blobstore/internal/git/errors.go	Adds MergeConflictError type and helpers.
go/store/blobstore/internal/git/impl_test.go	Refactors test setup and adds tests for new git API methods.
go/store/blobstore/git_blobstore.go	Adds remote-managed mode + integrates fetch/merge/push sync; switches chunk part width to 4 digits.
go/store/blobstore/git_blobstore_test.go	Adds integration tests for remote-managed behavior and retries.
go/store/blobstore/git_blobstore_helpers_test.go	Updates test fake to satisfy extended GitAPI interface.
go/store/blobstore/git_blobstore_chunked_put_test.go	Updates expectations to 4-digit chunk part names.

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[coffeegoddd]

@coffeegoddd DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
3bc5c6d	ok	5937471

version	total_tests
3bc5c6d	5937471

correctness_percentage
100.0

[coffeegoddd]

@coffeegoddd DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
0b9a547	ok	5937471

version	total_tests
0b9a547	5937471

correctness_percentage
100.0

[Copilot]

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 5 comments.

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[Copilot]

Exists now always calls syncForRead(), which will run a git fetch and mutate local refs even for callers that only expect local reads. Consider gating syncForRead() behind an explicit remote-managed option (or a no-op when no remote is configured) to avoid unexpected network/IO and side effects on read-only use cases.

[Copilot]

RemoteName defaults to "origin" here, which effectively makes remote-managed behavior the default for all GitBlobstores. If local-only operation should still be supported, consider leaving remoteName empty by default and only enabling remote fetch/push when the caller explicitly opts in (or provide a separate flag/enum to control sync behavior).

[Copilot]

Returning RefNotFoundError when the remote-tracking ref doesn't exist makes an uninitialized remote (no refs/dolt/data yet) fail hard, instead of behaving like an empty store (e.g., manifest missing). If empty remotes are valid, consider treating !okRemote as an empty state (no-op sync) and letting the existing NotFound / missing-ref logic handle it.

Suggested change

	return &git.RefNotFoundError{Ref: gbs.remoteTrackingRef}
	// Treat an uninitialized remote (no remote-tracking ref yet) as an empty store.
	// This makes syncForRead a no-op in that case, allowing existing NotFound logic
	// elsewhere to handle the absence of data.
	return nil

[coffeegoddd]

@coffeegoddd DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
dc5cea6	ok	5937471

version	total_tests
dc5cea6	5937471

correctness_percentage
100.0

[reltuk]

LGTM, one comment about separating local vs. remote ref name and making a unique local ref for this blobstore instance.

[coffeegoddd]

@coffeegoddd DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
adfab24	ok	5937471

version	total_tests
adfab24	5937471

correctness_percentage
100.0