fix(tooling): three findings from reviewing this branch against itself

1. A self-test case that was a duplicate wearing different clothes. "a heading
cargo's listing does not carry is an orphan however the source reads" passed on
an empty listing -- which is the first case in the table, already. Once defined
comes from cargo, the Rust beside a fixture is not read at all, so four cases
for the four source shapes would be four copies of one assertion dressed as
coverage. Deleted; the evidence for those shapes is the real-tree injection, and
context/code/tooling.md now says which half a fixture can carry and which it
cannot. This is exactly the shape improvise-84wp's prose, applied two commits
ago, tells a reviewer to look for.

2. assemble-stamp.sh grepped its patterns as REGEXES, inherited from the inline
version it was extracted from. The `.` in improvise_wasm_client.js?v=abc matches
any character, so a stamp corrupted in that position read as present -- a pass in
the one direction a guard must not fail in. grep -F, plus a case proved by
injection: dropping the -F flips it.

3. A missing cargo raised a traceback out of --check-evidence. It now names the
flag that takes a saved listing instead.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FC2jVn8Au7E9JPkw6bwXXH

scripts/assemble-stamp-test.sh

@@ -64,6 +64,13 @@ run_case "a file that does not exist is a miss, not an abort" 1 "vanished.js" \
 
 # A caller that drops one argument would otherwise have the last FILE read as
 # a PATTERN over the file before it -- a check that passes by accident.
+# The pattern is a literal. As a regex, `.` matches any character, so a stamp
+# corrupted in exactly that position would read as present -- the one direction
+# a guard must not fail in.
+printf 'import "./pkg/improvise_wasm_clientXjs?v=abc";\n' > "$work/corrupt.js"
+run_case "a pattern is matched literally, not as a regex" 1 "corrupt.js" \
+  "$work/corrupt.js" "pkg/improvise_wasm_client.js?v=abc"
+
 run_case "an odd number of arguments is a usage error" 2 "pairs" \
   "$work/stamped.js" "pkg/improvise_wasm_client.js?v=abc" "$work/bare.js"
 

scripts/assemble-stamp.sh

@@ -24,8 +24,10 @@ while [ $# -ge 2 ]; do
   file=$1
   pattern=$2
   shift 2
-  if [ -f "$file" ] && grep -q "$pattern" "$file"; then
-    grep -n "$pattern" "$file"
+  # -F, because every pattern is a literal and `.` as "any character" would
+  # let a corrupted stamp match -- a pass in the direction that looks like one.
+  if [ -f "$file" ] && grep -qF "$pattern" "$file"; then
+    grep -nF "$pattern" "$file"
   else
     echo "assemble: $file is missing the cache-bust stamp: $pattern" >&2
     missing="${missing} $file"

scripts/check-comment-runs.py

@@ -313,7 +313,12 @@ def cargo_test_names(listing, ignored_listing=""):
 
 def _cargo_listing(extra):
     cmd = ["cargo", "test", "--workspace", "--", "--list", *extra]
-    run = subprocess.run(cmd, capture_output=True, text=True)
+    try:
+        run = subprocess.run(cmd, capture_output=True, text=True)
+    except OSError as e:
+        raise SystemExit(f"error: cannot run cargo ({e}).\n"
+                         "--check-evidence needs a toolchain, or --rust-tests FILE "
+                         "holding a saved `cargo test --workspace -- --list`.")
     if run.returncode != 0:
         raise SystemExit(f"error: {' '.join(cmd)} failed:\n{run.stderr}")
     return run.stdout
@@ -754,11 +759,6 @@ SELF_TEST_EVIDENCE = [
     ("a ### naming a helper rather than a test is still an orphan",
      "### a_helper\n", "fn a_helper() {}\n", "", "", ["a_helper"], []),
 
-    ("a heading cargo's listing does not carry is an orphan however the source reads",
-     "### a_test_that_is_only_text\n",
-     'pub const S: &str = r#"\n#[test]\nfn a_test_that_is_only_text() {}\n"#;\n',
-     "", "", ["a_test_that_is_only_text"], []),
-
     ("a test that cites the evidence file and has no entry is caught",
      "", "/// See `context/test-evidence/clients.md`.\n#[test]\nfn a_cited_test() {}\n",
      "", "m::a_cited_test: test\n", [], ["a_cited_test"]),