fix(server): propagate render context to sync handlers in executor#38
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Az107 merged 1 commit intoJul 12, 2026
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run_in_executor does not carry contextvars into the worker thread, so the render context set by init_render_ctx was invisible to sync route handlers: use_state() and @js registered nothing and pages shipped without their <script> blocks or state initializers, silently. Running the handler through contextvars.copy_context() makes the executor thread see the same RenderContext object, whose mutations the main thread then renders. Async handlers are unaffected.
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Problem
use_state()and@jsare silently broken inside sync route handlers.The response ships an empty
<head />— noLocalStateinitializer, no transpiled function — so the page shows a raw{{localstate_…}}placeholder andonclickcalls an undefined function. The same handler declaredasync defworks.Cause
handle_requeststores the render context in aContextVar(init_render_ctx) and then runs sync handlers vialoop.run_in_executor(...).run_in_executordoes not propagatecontextvars, so inside the worker threadget_render_ctx()returnsNoneand every registration is dropped without error.Fix
Run the handler through
contextvars.copy_context():The copied context sees the same
RenderContextobject, so registrations made in the executor thread are visible when the main thread renders the response. Async handlers are unaffected.Verification
Reproduced on
develop(60e7e1f) with uvicorn + curl: before the patch the sync handler renders<head />; after it, both<script>blocks (state initializer + transpiledincrement) are injected and identical to the async handler's output.ruff checkpasses.