feat(code-mappings): Allow multiple source roots per stack root

[romtsn]

Summary

• Change unique constraint on RepositoryProjectPathConfig from (project, stack_root) to (project, stack_root, source_root)
• Update single-mapping serializer validation to include source_root in duplicate check
• Update bulk endpoint upsert key to match on (stack_root, source_root) instead of just stack_root

This allows the same stack trace root (e.g. io/sentry/opentelemetry) to map to multiple source paths in the repo (e.g. sentry-opentelemetry-core/src/... and sentry-opentelemetry-bootstrap/src/...), which is needed for monorepos with shared package prefixes across modules.

Stack trace resolution already handles this correctly — it iterates all mappings sorted by specificity and uses the first match that resolves to a real file.

Test plan

• All 63 existing tests pass (bulk + single endpoints)
• Updated tests to reflect new constraint semantics
• Deploy migration and verify with real monorepo upload

🤖 Generated with Claude Code

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/migrations/1058_change_code_mapping_unique_constraint.py

for 1058_change_code_mapping_unique_constraint in sentry

--
-- Custom state/database change combination
--
CREATE UNIQUE INDEX CONCURRENTLY "sentry_repositoryproject_project_id_stack_root_so_c371dfa7_uniq" ON "sentry_repositoryprojectpathconfig" ("project_id", "stack_root", "source_root");
ALTER TABLE "sentry_repositoryprojectpathconfig" ADD CONSTRAINT "sentry_repositoryproject_project_id_stack_root_so_c371dfa7_uniq" UNIQUE USING INDEX "sentry_repositoryproject_project_id_stack_root_so_c371dfa7_uniq";
ALTER TABLE "sentry_repositoryprojectpathconfig" DROP CONSTRAINT "sentry_repositoryproject_project_id_stack_root_e376b891_uniq";

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[github-actions]

Backend Test Failures

Failures on e9b55a7 in this run:

tests/sentry/api/endpoints/issues/test_organization_derive_code_mappings.py::OrganizationDeriveCodeMappingsTest::test_post_existing_code_mapping — log

tests/sentry/api/endpoints/issues/test_organization_derive_code_mappings.py:324: in test_post_existing_code_mapping
    new_code_mapping = RepositoryProjectPathConfig.objects.get(
.venv/lib/python3.13/site-packages/django/db/models/manager.py:87: in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
.venv/lib/python3.13/site-packages/django/db/models/query.py:638: in get
    raise self.model.MultipleObjectsReturned(
E   sentry.integrations.models.repository_project_path_config.RepositoryProjectPathConfig.MultipleObjectsReturned: get() returned more than one RepositoryProjectPathConfig -- it returned 2!

[armenzg]

I really like this change.
We will see a huge uptick on code mappings for monorepos but I believe it will make a lot of things better.