The reprint header names a signature, not a count, so it is true on every path

HANDOFF-devtest-noise.md

@@ -52,8 +52,15 @@ leak into other builds. The channel was the defect, not the cause.
    against `rfailures`, a snapshot of `!failures` at block entry, because `failures` is the whole file's and an
    earlier block's failure is not a reason to reprint this daemon's expected complaints. The path itself would be
    useless: `rerr` lives under dune's per-run `TMPDIR`, which is gone before anyone reads the run.
-3. **The fixture says so in its own voice**, one line, before the daemon starts. The wording deliberately contains
+3. **The fixture says so in its own voice**, one line, before the daemon starts, naming the directory it is about
-   no `error`, `Error` or `FAIL`, because the reader it is written for is scanning for exactly those words.
+   to make read-only so the reader can match it against the linker's own words. The wording deliberately contains no
+   `error`, `Error` or `FAIL`, because the reader it is written for is scanning for exactly those words. The reprint
+   header names that signature rather than a count, because a step that fails *before* either chmod window leaves no
+   deliberate failure in the log at all, and a header promising two of them would be the wrong diagnosis NEXT.md
+   warns about.
+
+`test/dune` was **not** touched, and neither was anything under `lib/`. The whole change is in `test/test_dev.ml`
+and this file.
 
 ## Measured, before and after
 
@@ -65,10 +72,15 @@ Both from a full `dune test --root .`, exit 0 either way.
 | `clang: error: linker command failed` lines | 2 | **0** |
 | a line saying the failure is deliberate | none | **1** |
 
-The two occurrences in the baseline were at `baseline.log:563` and `:565`, immediately after
+The "before" row is from a full, uncached `dune test`, which inventoried the whole suite: **exactly two
-`flan dev: ... dev-robust.flan ready on ...` — which places them in this block and nowhere else. **The count is
+occurrences**, both sitting immediately after `flan dev: ... dev-robust.flan ready on ...`, which places them in
-exactly two**, so there is no second site elsewhere in the suite quietly doing the same thing; fixing `test_dev.ml`
+this block and nowhere else. So there is no second site quietly doing the same thing and fixing `test_dev.ml` fixes
-fixes all of it.
+all of it. (The run's log has been deleted rather than left in the tree; the count is the claim, and it is
+reproducible by reverting the two commits below and running the suite.)
+
+The "after" row is from a run where dune replayed most targets from cache — cached actions do not reprint their
+output, so the *suite-wide* zero rests on the baseline's inventory rather than on that run. What the after-run does
+establish directly is the part that matters: `test_dev` itself reran fresh, and produced none.
 
 Two informational lines from this daemon — `flan dev: built dev-robust.flan in 1937ms` and its `ready on` — now go
 to the log with the rest of its stderr rather than to the terminal. Its siblings still print theirs. That is a small

test/test_dev.ml

@@ -2874,10 +2874,12 @@ let () =
        "error" or "FAIL" in the wording: the reader this line is for is
        scanning for exactly those words. *)
     print_endline
-      "dev: two builds below are made to fail on purpose — the robustness \
+      (Printf.sprintf
-       fixture holds its own cache directory read-only, so the linker cannot \
+         "dev: two builds below are made to fail on purpose — the robustness \
-       write its output there. The compiler's complaints go to a log and are \
+          fixture holds its own cache directory (%s) read-only, so the linker \
-       reprinted only if a step actually goes wrong.";
+          cannot write its output there. The compiler's complaints go to a \
+          log and are reprinted only if a step actually goes wrong."
+         rcache);
     let rpid =
       Unix.create_process_env flan
         [| flan; "dev"; "programs/dev-robust.flan"; "-s"; rsock |]
@@ -3055,10 +3057,15 @@ let () =
     (* Its contents rather than its name: [rerr] is under dune's per-run
        TMPDIR, which is gone by the time anyone reads the run. *)
     if !failures > rfailures then begin
+      (* True on every path through the block, which the obvious wording is
+         not: a step that fails *before* either chmod window leaves no
+         deliberate failure in the log at all, and a header promising two of
+         them would be a wrong diagnosis — the thing NEXT.md says costs more
+         than no message. So it names the signature rather than a count. *)
       print_endline
-        "dev: the robustness daemon's stderr follows. Two of the linker \
+        "dev: the robustness daemon's stderr follows. Any linker failure in \
-         failures in it are the deliberate ones described above; anything \
+         it that names the read-only cache directory above is one of the \
-         else is not.";
+         deliberate ones; anything else is not.";
       match open_in_bin rerr with
       | ic ->
         let n = in_channel_length ic in