Python: Kernel JSON Schema Builder support for Forward Refs #6464

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1. Evan Mattson (moonbox3)

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2. Evan Mattson (moonbox3)

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   This issue is stale because it has been open for 90 days with no activity.
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8. Evan Mattson (moonbox3)

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10. grvnmttl commented on Jul 26, 2026

    

    Gaurav Naresh Mittal (grvnmttl)

    on Jul 26, 2026

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    Picking this back up — it was auto-closed as stale but the gap is still present on main today.

    I dug into the exact failure mode: plain (non-cyclic) forward references already resolve correctly in KernelJsonSchemaBuilder.build_model_schema today. The real bug is that a self-referential or mutually-recursive KernelBaseModel (e.g. a tree node, linked list, or two models that reference each other) causes KernelJsonSchemaBuilder.build() to recurse infinitely and crash with RecursionError: maximum recursion depth exceeded, rather than a NameError on the unresolved name.

    I have a fix ready that detects the cycle and emits a standard JSON Schema $defs/$ref pair instead of recursing — the same mechanism Pydantic's own model_json_schema() uses for recursive models. It only activates when a cycle is actually present, so today's fully-inlined schema output for non-recursive models is unchanged. Added test coverage for the simple forward-ref case, self-reference, a mutual two-model cycle, and the structured_output=True path — none of which were covered before. Opening a PR shortly.