fix: preserve context during child graph init

[mturac]

Summary

Fixes #34511.

Child workflow engines inherit the parent GraphRuntimeState.execution_context, but the child Graph.init(...) call creates node instances before the engine starts running. LLM node construction can load model/provider configuration during that init step, which requires the captured Flask app context.

This wraps child graph initialization in the inherited execution context so node factories and subsequent child engine execution use the same context boundary.

Screenshots

Not applicable; backend workflow runtime change.

Validation

• uv run --project api --dev pytest api/tests/unit_tests/core/workflow/test_workflow_entry.py::TestWorkflowEntry::test_child_engine_enters_execution_context_while_initializing_graph -q
• uv run --project api --dev pytest api/tests/unit_tests/core/workflow/test_workflow_entry.py -q
• uv run --project api --dev pytest api/tests/unit_tests/core/workflow/nodes/iteration/test_iteration_child_engine_errors.py -q
• uv run --project api --dev pytest api/tests/unit_tests/core/workflow/test_workflow_entry_helpers.py::TestWorkflowChildEngineBuilder::test_build_child_engine_constructs_graph_engine_with_quota_layer_only -q
• uv run --project api --dev pytest api/tests/unit_tests/core/workflow/test_workflow_entry.py api/tests/unit_tests/core/workflow/test_workflow_entry_helpers.py api/tests/unit_tests/core/workflow/nodes/iteration/test_iteration_child_engine_errors.py -q
• uv run --project api --dev ruff check api/core/workflow/workflow_entry.py api/tests/unit_tests/core/workflow/test_workflow_entry.py api/tests/unit_tests/core/workflow/test_workflow_entry_helpers.py
• uv run --project api --dev ruff format --check api/core/workflow/workflow_entry.py api/tests/unit_tests/core/workflow/test_workflow_entry.py api/tests/unit_tests/core/workflow/test_workflow_entry_helpers.py
• ./dev/pyrefly-check-local api/core/workflow/workflow_entry.py
• git diff --check

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

[github-actions]

Pyrefly Diff

base → PR

--- /tmp/pyrefly_base.txt	2026-06-29 10:15:24.675149800 +0000
+++ /tmp/pyrefly_pr.txt	2026-06-29 10:15:13.665100222 +0000
@@ -6226,7 +6226,7 @@
 ERROR Object of class `object` has no attribute `tool` [missing-attribute]
    --> tests/unit_tests/core/workflow/test_node_runtime.py:654:12
 ERROR Argument `TestWorkflowEntry.test_single_step_run_injects_code_limits.StubWorkflow` is not assignable to parameter `workflow` with type `Workflow` in function `core.workflow.workflow_entry.WorkflowEntry.single_step_run` [bad-argument-type]
-   --> tests/unit_tests/core/workflow/test_workflow_entry.py:145:22
+   --> tests/unit_tests/core/workflow/test_workflow_entry.py:241:22
 ERROR Object of class `_FakeModelNodeMixin` has no attribute `node_data` [missing-attribute]
   --> tests/unit_tests/core/workflow/test_workflow_entry_helpers.py:73:35
 ERROR Object of class `_FakeModelNodeMixin` has no attribute `node_data` [missing-attribute]

[github-actions]

Pyrefly Type Coverage

Metric	Base	PR	Delta
Type coverage	51.49%	51.49%	-0.00%
Strict coverage	51.01%	51.01%	-0.00%
Typed symbols	30,846	30,847	+1
Untyped symbols	29,332	29,333	+1
Modules	2931	2931	0