chore(buglog): bug-1871 fixed (754d5bcf); log bug-1890 (Nagle tail latency)

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

.wolf/bugs/bug-1890.md

@@ -0,0 +1,55 @@
+---
+id: "bug-1890"
+status: "open"
+status_updated: "2026-09-29"
+status_note: "newly logged"
+component: "lib"
+severity: "noise"
+timestamp: "2026-09-29T14:01:08Z"
+last_seen: "2026-09-29T14:01:08Z"
+occurrences: 1
+files: ["src/lib/netio.c (socket_create, socket_connect, endpoint_accept)"]
+tags: ["netio", "tcp", "latency", "ha", "snapshot"]
+related: ["bug-1871"]
+---
+
+# bug-1890: netio sockets leave Nagle on: last TLS records of a message burst arrive ~40 ms late
+
+## Description
+**Observed:** a 9-chunk HA snapshot transfer is fully written by the primary within 1 ms, but the standby reads the last chunks ~40 ms later. Primary trace (xce-1871-fs1, ctrl-1) shows the final send drained at 13:20:33.967 (`bug1871 upd ... 0x5->0x1 outq_empty=1 fsm_out=5`); the standby logs:
+```
+[2026-09-29 13:20:33,969] ... ha_handle_snapshot_chunk: chunk crc32 checkpoint_lsn=114 chunk_index=6 ...
+[2026-09-29 13:20:34,010] ... ha_handle_snapshot_chunk: chunk crc32 checkpoint_lsn=114 chunk_index=7 ...
+```
+
+**Expected:** on loopback the whole burst arrives within a few ms (most runs: max inter-chunk gap 1-4 ms).
+**Impact:** latency only, ~40 ms on the tail of a burst (snapshot/WAL batches, request-reply pairs after bulk data); no loss. `grep -rn TCP_NODELAY src/lib` finds nothing, so every netio TCP socket runs with Nagle, and a small trailing TLS record waits for the receiver's delayed ACK.
+**Found by:** soak -- bug-1871's instrumented force-snapshot runs, 2026-09-29. Suspected (not yet proven with TCP_NODELAY on): Nagle + delayed ACK.
+
+## Environment
+- OS: no /etc/os-release; Docker container; NixOS kernel; kernel Linux 6.18.33 x86_64
+- libc: glibc 2.42-47 (interpreter /nix/store/wb6rhpznjfczwlwx23zmdrrw74bayxw4-glibc-2.42-47/lib/ld-linux-x86-64.so.2)
+- Toolchain: gcc (GCC) 15.2.0, meson 1.9.1
+- Build: asan (src/xce.build.bug1871, with temporary netio TRACE instrumentation)
+- Code: scheduler-framework @ 3444cf16
+- Deployment: local 3-node HA controller cluster (xce-test-ha --force-snapshot), localhost:9991-9993, 32 CPUs
+
+## Reproduction
+1. `nix develop ./src --command bash .claude/skills/xce-test-ha/run-ha-soak.sh --force-snapshot <dir>`
+2. On the rejoined standby's log, compute the gap between consecutive `ha_handle_snapshot_chunk: chunk crc32` lines of one transfer; a ~40 ms gap (while the primary finished sending 1 ms earlier) is the symptom.
+- Frequency: 5/40 transfers had a 39-41 ms gap, 2026-09-29 (xce-1871-fs1..fs16)
+- Evidence: /home/claude/tmp/xce-1871-fs1, /home/claude/tmp/xce-1871-fs5, /home/claude/tmp/xce-1871-fs16 (ctrl-*.log)
+
+## Root cause
+TODO: required for fixed/partial
+
+## Fix
+TODO: required for fixed/partial
+
+## Verification
+- Test: TODO: name + file; RED before the fix, GREEN after
+- Suites: TODO: suite results and build profile
+- Live: TODO: soak/deploy run, or n/a and why
+
+## References
+- Related: none