fix(react-router): Key server middleware counter by root span, not OTel context - #22982
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…el context The server instrumentation-API middleware index counter was stored on the OpenTelemetry context. Without a tracer provider the context does not propagate, so the counter reset to 0 on every middleware and all middleware spans reported index 0. Key the counter by the request's root span (the single transaction all of a request's middlewares run under) in a WeakMap instead, so the index increments in every mode. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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What
Store the server instrumentation-API middleware index counter in a WeakMap keyed by the request's root span, instead of on the OpenTelemetry context.
Why
The counter lived on the OTel context, which does not propagate when no tracer provider is set up. In that case it reset to 0 for every middleware, so all middleware spans on a route reported
react_router.middleware.index: 0instead of 0, 1, 2, .... The root span is the single transaction all of a request's middlewares run under, so keying on it increments correctly regardless of whether a provider is active.