the refusal carries its code, because something reads it

The mcpp-index compatibility measurement distinguishes "this graph does not
supply what the member asked for" from "the member did not build" --- a
distinction that decides whether a member counts against a compatibility
figure --- and it was written to do so on the refusal code
`interface-not-provided`. That code reached no output: `refusal::record` is
read by `mcpp doctor` and by one branch of the build-database path, and a
`mcpp build` prints none of it. The consumer's judge could never fire.

The code is now printed in the diagnostic, the way E0006 is, and e2e 743
asserts it. A refusal that only a person can recognise forces every machine
consumer to match prose --- and prose that a package's own compile error could
coincidentally contain.

Found by running the consumer's own criterion against the engine rather than
reading it: a mechanism with no way to trigger is the defect class this whole
branch exists to remove, and it had one of its own.

Co-authored-by: Claude Code <noreply@anthropic.com>

Author: speak-agent

src/build/prepare.cppm

@@ -11227,9 +11227,18 @@ prepare_build(bool print_fingerprint,
                     names += "\n         ";
                     names += mI;
                 }
+                // THE CODE IS PRINTED, THE WAY E0006 IS, BECAUSE SOMETHING
+                // READS THIS. A refusal that only a person can recognise
+                // forces every machine consumer to match prose --- and prose
+                // that a package's own compile error could coincidentally
+                // contain. The mcpp-index compatibility measurement
+                // distinguishes "this graph does not supply what the member
+                // asked for" from "the member did not build" on exactly this
+                // token, and that distinction decides whether a member counts
+                // against a compatibility figure.
                 return std::unexpected(std::format(
                     "'{}' requires interfaces the resolved implementation does "
-                    "not provide.{}\n"
+                    "not provide. [interface-not-provided]{}\n"
                     "       provided by  {} ({} interface{})\n"
                     "       This is refused before anything is compiled "
                     "because dependency resolution is the earliest time the "

tests/e2e/743_kernel_abi_interfaces_are_resolved_not_preprocessed.sh

@@ -134,6 +134,16 @@ echo "$out" | grep -q "fakekernel" || {
     echo "$out" >&2
     exit 1
 }
+# AND THE CODE, BECAUSE SOMETHING READS THIS. mcpp-index's compatibility
+# measurement tells "this graph does not supply what the member asked for"
+# from "the member did not build" on this token; without it that consumer has
+# to match prose, and the distinction decides whether a member counts against
+# a compatibility figure.
+echo "$out" | grep -q "\[interface-not-provided\]" || {
+    echo "FAIL: the refusal must carry its code the way E0006 does" >&2
+    echo "$out" >&2
+    exit 1
+}
 # Nothing compiled: the answer exists before the compiler is reached, and a
 # refusal that arrives after an object file has been written has answered at
 # the wrong time even when it answers correctly.