test(hardlink): report the mutation families, don't assert one of them

CI's nightly is 1.100.0-nightly (2026-08-25); the machine this suite was written on had 1.96.0-nightly (2026-02-24). On the newer one the control's `cp -al` clone mutates only the build/ and *.d families — upstream appears to have stopped rewriting `.fingerprint/*/dep-*` in place under checksum freshness — so the suite went red on the *absence* of a hazard. That is the wrong shape for a gate. The control's job is to prove the hazard exists at all, which a non-empty mutated set already does; naming one family as mandatory makes the suite red whenever upstream stops doing something we never wanted it to do, and red in the CONTROL, where a failure reads as "the hazard is gone" rather than "upstream changed". It is now a note either way. Nothing is given up. The fix scenario asserts the source is byte-identical after a full rebuild in the clone, which covers every family the running Cargo has, named or not — and the checksum-freshness scenario after it tests the stale-reuse hazard directly. The dep-* line only ever documented which family was in play. `unshare_mutable_paths` keeps unsharing dep-* regardless, and its measurement block now records both observations with their versions: 22 MB of a 6.9 GB tree against a failure mode that is a wrong answer rather than a slow one.
2026-08-26 12:50:42 -05:00
parent 3f97d3d1e7
commit 5e8e773f78
3 changed files with 30 additions and 5 deletions
@@ -332,7 +332,17 @@ _unshare_files() {
 #   <profile>/.fingerprint/<unit>/dep-<target>   (only under
 #                                                CARGO_UNSTABLE_CHECKSUM_FRESHNESS,
 #                                                where this file carries the
-#                                                per-source blake3 checksums)
+#                                                per-source blake3 checksums.
+#                                                NOT reproduced on
+#                                                1.100.0-nightly (2026-08-25),
+#                                                measured by this repo's own CI
+#                                                — upstream appears to have
+#                                                stopped writing it in place.
+#                                                Kept in the unshared set
+#                                                anyway: it costs 22 MB of a
+#                                                6.9 GB tree, and the failure
+#                                                it guards is a wrong answer,
+#                                                not a slow one.)
 #   <profile>/build/<pkg>/output, root-output   (Cargo build-script metadata)
 #   <profile>/build/<pkg>/out/**                (whatever the build script
 #                                                writes into OUT_DIR — build