test(network): add a regression test for #1079 (EntityRef.copy on a client)

[soloturn]

AI-assisted change proposal. Filed by agent driven by @soloturn via GDD.

Investigated #1079 ("EntityManager::copy works incorrectly on a remote client" - copying a networked entity and modifying the copy also modified the original, attributed at the time to the copy's EntityRef getting redirected via net-id lookup).

Traced the mechanism the original report described: NetworkEntitySystem#onAddNetworkComponent is what registers a NetworkComponent-bearing entity into the netId→entity lookup (NetworkSystemImpl#netIdToEntityId). It's gated @NetFilterEvent(netFilter = RegisterMode.AUTHORITY) - a client never runs it, including for a locally-created copy that happens to carry a (copied) NetworkComponent. That's the mechanism the 2014 report needed to exist for the redirection to happen, and it doesn't apply client-side.

Confirmed by running an actual test against a real client context via the MTE integration environment (ModuleTestingHelper#createClient()): creating a NetworkComponent-bearing entity on a client, copying it, and mutating a component on the copy leaves the original untouched.

No production code change - the bug doesn't reproduce against current develop. Adding the test as a permanent regression guard and documentation of why, since the entity system has been substantially rewritten since 2014 and nothing currently links back to this issue.

Test plan

• EntityCopyOnClientTest (1/1 pass) via :engine-tests:integrationTest.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 67d054c7-5960-450e-8dbf-ed72e46a1caa

📥 Commits

Reviewing files that changed from the base of the PR and between 338d7dd and 190838f.

📒 Files selected for processing (1)

• engine-tests/src/test/java/org/terasology/engine/integrationenvironment/EntityCopyOnClientTest.java

Included review availability: Your plan provides up to 8 included reviews per hour; 4 remain after this review.

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📝 Walkthrough

Summary by CodeRabbit

• Tests
  • Added a regression test confirming that copying a networked entity on a client creates an independent entity.
  • Verified that modifying a component on the copied entity does not change the original entity.

Walkthrough

Adds an integration regression test for copying a networked entity on a client. The test verifies that changing a component on the copy does not change the original entity.

Changes

Client entity copy isolation

Layer / File(s)	Summary
Client copy isolation test engine-tests/src/test/java/org/terasology/engine/integrationenvironment/EntityCopyOnClientTest.java	Creates a networked entity on a client, copies it, changes the copy’s component value, and verifies that the original retains its value.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 19083

This is a localized regression-test-only change with no production behavior change, and the reported integration test passes. No actionable merge-blocking risk remains beyond normal checks and review.

Poem

A rabbit copied an entity with care,
Its values stayed safely paired.
The copy changed from forty-two to ninety-nine,
While the original kept its own design.
“Separate refs!” the rabbit cheered,
“The regression test is cleared!”

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the regression test, its network scope, and issue #1079.
Description check	✅ Passed	The description explains the issue, investigation, test behavior, and verification result, and it matches the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch soloturn-entity-copy-client-test-1079

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