Add endpoint for accessing the aggregate per-branch limits

This is required to check on branch creation/modification within which
bounds the operation may be conducted.

Author: mxsrc

src/api/_util/resourcelimit.py

@@ -716,3 +716,18 @@ async def project_available(session: AsyncSession, project: Project) -> Resource
         (await project_limits(project)).total - await project_allocations(session, project),
         await organization_available(session, await project.awaitable_attrs.organization),
     )
+
+
+async def project_branch_maxima(session: AsyncSession, project: Project) -> Resources:
+    """Minimum per-branch limit across the hierarchy (project > organization > system).
+
+    Returns None for any field where no per-branch limit has been configured at any level.
+    """
+    organization = await project.awaitable_attrs.organization
+    return Resources.min(
+        Resources.min(
+            (await project_limits(project)).per_branch,
+            (await organization_limits(organization)).per_branch,
+        ),
+        (await system_limits(session)).per_branch,
+    )

src/api/organization/project/resources.py

@@ -2,7 +2,14 @@
 
 from ....models.resources import EntityType
 from ..._util import Forbidden, NotFound, Unauthenticated
-from ..._util.resourcelimit import Limits, Resources, project_allocations, project_available, project_limits
+from ..._util.resourcelimit import (
+    Limits,
+    Resources,
+    project_allocations,
+    project_available,
+    project_branch_maxima,
+    project_limits,
+)
 from ...dependencies import ProjectDep, SessionDep
 
 api = APIRouter()
@@ -49,3 +56,12 @@ async def allocations(session: SessionDep, project: ProjectDep) -> Resources:
 )
 async def available(session: SessionDep, project: ProjectDep) -> Resources:
     return await project_available(session, project)
+
+
+@api.get(
+    "/branch-maxima/",
+    name="organizations:projects:resources:branch-maxima",
+    responses={401: Unauthenticated, 403: Forbidden, 404: NotFound},
+)
+async def branch_maxima(session: SessionDep, project: ProjectDep) -> Resources:
+    return await project_branch_maxima(session, project)