Fix rank merges on delta vibe

[tomasMizera]

Related to https://github.com/MerginMaps/server-private/issues/3221

• added update action if delete create, this is handling all cases.

• added improvment to rules for mergin to fix edge cases when global checkpoints are merging together

• we just added UPDATE action when DELETE + CREATE

[Copilot]

Pull request overview

This PR addresses incorrect delta results when merging cached delta checkpoints across rank/chunk boundaries, particularly around delete+create/recreate edge cases (“rank merges on delta vibe”). It adjusts change-merge rules to preserve correct client outcomes and adds regression coverage for the cross-checkpoint scenarios.

Changes:

• Updates ProjectVersionDelta.merge_changes/_compare_changes to better handle CREATE/DELETE/CREATE sequences across checkpoints (including introducing a “force update” path).
• Adds regression tests for cross-checkpoint create→delete→recreate and recreate→delete scenarios.
• Updates existing delta-change expectations where delete+create sequences should be represented as UPDATE rather than CREATE.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
server/mergin/sync/models.py	Adjusts delta merge comparison rules and introduces a FORCE_UPDATE action to avoid losing delete+create semantics across checkpoints.
server/mergin/tests/test_public_api_v2.py	Adds cross-checkpoint regression tests and updates expected delta change types for delete+create behavior.

Comments suppressed due to low confidence (1)

server/mergin/tests/test_public_api_v2.py:35

• This file now imports from .utils twice (with overlapping names) and the PR adds another symbol to the second block. Consider consolidating into a single .utils import to avoid duplicate/overlapping imports (which can also hide unused-import issues).

from .utils import (
    add_user,
    create_blank_version,
    create_project,
    create_workspace,
    diffs_are_equal,
    execute_query,
    login_as_admin,
    push_change,
)

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[coveralls]

Pull Request Test Coverage Report for Build 22226588552

Details

• 57 of 57 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 94.614%

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Totals
Change from base Build 21514078503:	0.03%
Covered Lines:	8872
Relevant Lines:	9377

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💛 - Coveralls