Unify checks when applying merge action in editable mapping

[fm3]

Since #7917 we look up the agglomerate ids for a merge action by the segment ids. This means that there is no “sane” case where the segments are not contained in the agglomerates anymore. So rather than going for a no-op in this case, we should move to assertions. This was already partially done, now I’m cleaning this up.

Steps to test:

• Proofread some, should work as before

Issues:

• fixes Double-check if we still need to handle segment1IsValid && segment2IsValid in mergeGraph #8368

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• Considered common edge cases

[coderabbitai]

📝 Walkthrough

Walkthrough

This change updates the EditableMappingUpdater.scala file by adding an explicit validation in the applyMergeAction method to check that segmentId1 exists within agglomerateGraph1, mirroring the existing check for segmentId2 in agglomerateGraph2. Additionally, the mergeGraph method is simplified by removing the conditional check for segment existence and now always merges the two agglomerate graphs when they are distinct. No changes were made to public entity signatures.

Changes

Files	Change Summary
webknossos-tracingstore/app/com/.../EditableMappingUpdater.scala	Added validation for segmentId1 in applyMergeAction; simplified mergeGraph by removing segment existence checks and unconditionally merging graphs.

Assessment against linked issues

Objective	Addressed	Explanation
Remove obsolete segment existence checks from mergeGraph and ensure equivalent assertion for segmentId1 (#8368)	✅

Possibly related PRs

• Fix merging editable mappings where self-merge is generated; fix compacted update action writes #8367: Both PRs update validation and merging logic in EditableMappingUpdater.scala, focusing on segment existence checks and agglomerate merging behavior.

Suggested labels

bug

Suggested reviewers

• MichaelBuessemeyer

Poem

A rabbit hopped through code so bright,
Checking segments left and right.
With careful eyes, it merged the graphs,
Ensuring checks for both the halves.
Now bugs are gone, the path is clear—
The code is safe, let's give a cheer!
🐇✨

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📜 Recent review details

Configuration used: CodeRabbit UI
Review profile: CHILL
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 756b023 and 26878ca.

📒 Files selected for processing (1)

• webknossos-tracingstore/app/com/scalableminds/webknossos/tracingstore/tracings/editablemapping/EditableMappingUpdater.scala (2 hunks)

🚧 Files skipped from review as they are similar to previous changes (1)

• webknossos-tracingstore/app/com/scalableminds/webknossos/tracingstore/tracings/editablemapping/EditableMappingUpdater.scala

⏰ Context from checks skipped due to timeout of 90000ms (3)

• GitHub Check: build-smoketest-push
• GitHub Check: backend-tests
• GitHub Check: frontend-tests

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