fix(BA-5974): remove deployment name uniqueness constraint

[fregataa]

Summary

• Drop the partial unique index ix_endpoints_unique_name_when_active on (name, domain, project) and the application-level _check_endpoint_name_exists pre-check, so deployment names are no longer unique within a project.
• The previous constraint scope (domain, project) did not match the my_deployments list scope (created_user), so a deployment created by another user in the same project blocked the create yet stayed invisible to the caller — leaving the user unable to choose the name and unable to locate the conflicting record.
• Remove the now-unused DeploymentNameAlreadyExists exception and the duplicate-name test. Routing keys on route_id, and the inference session name template f"{endpoint.name}-{route_id}" already disambiguates downstream.

Test plan

• Apply the new alembic migration on a database that holds the existing index and verify \d endpoints no longer lists ix_endpoints_unique_name_when_active.
• Create two deployments with the same name in the same project (different and same created_user) and confirm both succeed.
• Confirm my_deployments and project-scoped list queries return both rows as expected.
• Downgrade the migration and verify the index is recreated with predicate lifecycle_stage NOT IN ('destroying', 'destroyed').

Resolves BA-5974

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Removes the endpoint/deployment name uniqueness constraint so users can reuse deployment names within the same project without being blocked by deployments created by other users.

Changes:

• Dropped the partial unique index on (name, domain, project) from the ORM model and added an Alembic migration to drop/recreate it.
• Removed the application-level “duplicate name” pre-check and the DeploymentNameAlreadyExists exception.
• Removed the unit test that asserted duplicate-name creation fails.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/unit/manager/repositories/deployment/test_deployment_repository.py	Removes the duplicate-name rejection test.
src/ai/backend/manager/repositories/deployment/db_source/db_source.py	Removes the app-level duplicate-name pre-check.
src/ai/backend/manager/models/endpoint/row.py	Removes the partial unique index definition from the model.
src/ai/backend/manager/models/alembic/versions/c7d58e2a4f93_drop_endpoint_name_unique_index.py	Adds migration to drop the index and recreate it on downgrade.
src/ai/backend/common/exception.py	Removes DeploymentNameAlreadyExists exception type.
changes/11507.fix.md	Adds changelog entry documenting behavior change.

Comments suppressed due to low confidence (1)

tests/unit/manager/repositories/deployment/test_deployment_repository.py:3663

• This PR changes behavior to allow duplicate deployment names within the same project, but the test that enforced uniqueness was removed without adding a new test asserting the new behavior. Please add a unit test that creates two endpoints with the same name in the same (domain, project) and asserts both creations succeed (and optionally both are returned by relevant list queries if those are unit-tested here).

    async def test_create_endpoint_succeeds_with_different_name(
        self,
        deployment_repository: DeploymentRepository,
        test_domain: DomainRow,
        test_group: GroupRow,
        test_scaling_group: ScalingGroupRow,
        test_image_id: uuid.UUID,
    ) -> None:

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[jopemachine]

Would it be better to remove the unique constraint entirely rather than applying it per scope?