--- id: "bug-1971" status: "fixed" status_updated: "2026-10-22" status_note: "two-choke archive in xce-build.sh; test harness green" component: "build" severity: "wrong-result" timestamp: "2026-10-22T07:50:00Z" last_seen: "2026-10-22T07:50:00Z" occurrences: 2 files: ["src/tools/xce-build.sh"] tags: ["test", "flaky", "observability", "build"] related: [] fix_commits: ["68c3ccd7"] --- # bug-1971: next xce-build.sh run destroys the prior testlog — flaky-failure evidence unrecoverable ## Description **Observed:** (t2, 2026-10-22) a full `make build` (asan profile) failed on a controller test case; a following `make clean` + `make build` passed 134/134. The failing run's `meson-logs/testlog.{txt,json,junit.xml}` had been destroyed twice over: `setup_build`'s unconditional `rm -rf "$BUILD_DIR"` deletes the whole build dir (meson-logs included) before the retry, and meson itself overwrites `testlog.*` on every `meson test` invocation regardless. Nothing in the surviving tree identifies which case failed: the worker suite's daemon logs (`/tmp/test_xcecd_resync.log` and rotations) showed no failure signature, and no `sched_test`/Go test output is retained anywhere. Reconstruction from filesystem timestamps alone (`/tmp/test_*.log` rotations, `meson-log.txt` build options line, `/usr/local/go` ctime, bash history) established the two-run timeline but could not name the failed case. The same evidence-loss shape hit t1 earlier (2026-10-21, the two controller flakes fixed in 5b9d7270) — there the testlog happened to still exist because no clean rebuild ran in between; that was luck, not design. **Expected:** when a build/test run fails, its meson-logs (testlog.txt/json/junit.xml) and any per-case fixtures it kept (the mkdtemp sweep contract deliberately preserves FAILED cases' `/tmp/xce_*` dirs) survive at least until the next run starts — so a flaky failure can be diagnosed from disk afterwards without re-running and hoping to reproduce. **Impact:** intermittent/flaky test failures (the exact class this project keeps hitting: 5b9d7270's two flakes, bug-1521's random heap corruption, the t2 2026-10-22 case) leave zero durable evidence. Each recurrence costs a full rebuild cycle and often fails to reproduce. Also buries the mkdtemp "failed cases keep their dirs for post-mortem" contract, since the next `make build` never looks for those dirs and a clean build gives the appearance of none existing. **Found by:** user report (t2 build failure, 2026-10-22) + post-mortem on the t2 filesystem. ## Environment - OS: Ubuntu 24.04.2 LTS (t1 and t2); kernel Linux 6.8.0-139-generic x86_64 - libc: glibc 2.39 (host ldd) - Toolchain: gcc 13.3.0 (Ubuntu 13.3.0-6ubuntu2~24.04.1), meson 1.12.1 - Build: asan (xce.build) - Code: build/de-nix @ 5b9d7270 (t2 checkout), e8cb6d57 (t1) - Deployment: n/a — dev-loop build/test on t1 (workstation) and t2 (8-core/8GB test node) ## Reproduction 1. On any machine: `make build` (or `bash src/tools/xce-build.sh`) and let the test phase fail (e.g. by patching a test to fail). 2. Note `src/xce.build/meson-logs/testlog.txt` contains the failure. 3. Run `make clean && make build` again: the previous testlog is gone (build dir was rm -rf'd), and even without `make clean`, a successful `meson test` run overwrites testlog.* in place. - Frequency: deterministic — every subsequent run destroys the prior run's evidence. - Evidence: t2 `/tmp/myxce` 2026-10-22: failing run ~05:46, passing rerun 05:52 (its testlog survives at `/tmp/myxce/src/xce.build/meson-logs/testlog.txt`, 134/134 OK); the failing run's testlog was deleted by the `make clean` at ~05:5x. ## Root cause `setup_build()` in `src/tools/xce-build.sh` unconditionally `rm -rf "$BUILD_DIR"` on every non-incremental invocation, and `meson test` overwrites `$BUILD_DIR/meson-logs/testlog.*` on every run. xce-build.sh never copies failure state anywhere durable, and nothing else in the tree does either. ## Fix Two chokes in `src/tools/xce-build.sh` (this commit): 1. `archive_previous_failure()` — runs at script start, before `setup_build`'s wipe. If the marker `.meson_test_failed_rc` (written by the previous run's EXIT trap) exists, the previous run's `meson-logs` are MOVED to `$SRC_DIR/testlogs.archive//prev--rc/` — outside the build dir, so the wipe can't touch them. It also sweeps aged (>5 min, i.e. not a concurrent session's) `/tmp/xce_*` FAILED-case fixture DIRS into `prev--fixtures/`, and caps the archive at the newest 10 entries per build dir. 2. `finalize_failure_evidence()` — the EXIT trap (replaces the old lock-release trap, which becomes its last statement). On rc≠0 with RUN_TESTS=1, COPIES `meson-logs` to `testlogs.archive//this--rc/` and writes the marker. Copy-not-move: meson-logs still belongs to the live build dir for this run's own inspection; the next run moves the copy out at its start. Configure/compile failures (RUN_TESTS unset) archive nothing — those are deterministic and self-explanatory on rerun; it's the testlog-bearing flaky failures that need preservation. Additionally `-type d` added to BOTH `/tmp/xce_*` sweeps (this one and bug-924's `prune_stale_tmp_fixtures`): mkdtemp fixtures are always directories (`/tmp/xce_