fix: allow a task related node to have no kind

[pa-lem]

Problem

Reading tasks with include_related_nodes=True raises a Pydantic ValidationError when a task
references a node that no longer exists in the graph.

A task outlives the nodes it references. When a related node's vertex is gone, the server cannot
resolve a kind for it and returns kind: null. TaskRelatedNode.kind was typed as a required
str, so Task.from_graphql failed while constructing the model:

pydantic_core._pydantic_core.ValidationError: 1 validation error for TaskRelatedNode
kind
  Input should be a valid string [type=string_type, input_value=None, input_type=NoneType]

The path is manager.py selecting {"id": None, "kind": None} for related_nodes, then
Task.from_graphql doing TaskRelatedNode(**item) on each entry.

This turns a server-side condition the API now handles gracefully into a client-side crash.

Server side

Infrahub previously declared TaskRelatedNode.kind non-null, so this case surfaced as a GraphQL
error rather than a null value. That is being corrected in
opsmill/infrahub#10075, which makes the field nullable. This change is the SDK half: without it,
the same tasks fail with a validation error instead.

The two are intentionally not coupled by a submodule bump, so this can land and be released on its
own schedule.

Change

TaskRelatedNode.kind is now str | None = None.

Tests

Added test_from_graphql_related_node_without_kind, which parses a task carrying one resolvable
and one unresolvable related node. Verified to fail before the change with the exact
ValidationError above.

tests/unit/sdk/test_task.py passes 16/16. ruff check, ruff format --check and mypy are
clean on the touched files.

The full unit suite reports 3 failures — test_repository_app.py::test_repo_list,
test_repository_app.py::test_repo_init and test_task_app.py::test_task_list_command — which
reproduce identically on unmodified stable, so they are pre-existing and unrelated.

Backporting

Targeting stable. To be backported to develop and infrahub-develop, both of which still carry
the required kind: str.

🤖 Generated with Claude Code

---

Summary by cubic

Make TaskRelatedNode.kind optional to prevent crashes when reading tasks with include_related_nodes=True that reference deleted nodes. The SDK now accepts kind: null from the server without a validation error.

• Bug Fixes
  • Set TaskRelatedNode.kind to str | None = None in infrahub_sdk/task/models.py.
  • Added test_from_graphql_related_node_without_kind to cover null kind values.

^{Written for commit 1cb2a6d. Summary will update on new commits.}

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@           Coverage Diff           @@
##           stable    #1219   +/-   ##
=======================================
  Coverage   82.47%   82.47%           
=======================================
  Files         138      138           
  Lines       12186    12186           
  Branches     1833     1833           
=======================================
  Hits        10051    10051           
  Misses       1572     1572           
  Partials      563      563           

Flag	Coverage Δ
integration-tests	40.56% <0.00%> (-0.01%)	⬇️
python-3.10	56.27% <0.00%> (+0.01%)	⬆️
python-3.11	56.26% <0.00%> (-0.02%)	⬇️
python-3.12	56.26% <0.00%> (ø)
python-3.13	56.27% <0.00%> (+0.01%)	⬆️
python-3.14	56.27% <0.00%> (ø)
python-filler-3.12	22.21% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
infrahub_sdk/task/models.py	98.27% <100.00%> (ø)

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[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}