diff --git a/openfut-blaze-host/build.rs b/openfut-blaze-host/build.rs
index f6eea38..0a465d0 100644
--- a/openfut-blaze-host/build.rs
+++ b/openfut-blaze-host/build.rs
@@ -66,4 +66,13 @@ fn main() {
             println!("cargo:rerun-if-changed={p}");
         }
     }
+    // Committing updates refs/heads/<branch>, NOT the HEAD file, so watching
+    // HEAD alone leaves the stamp one commit behind. Observed: the banner read
+    // a84a72e immediately after committing 2337431.
+    if let Some(rf) = git(&["symbolic-ref", "-q", "HEAD"]) {
+        let path = format!("../.git/{rf}");
+        if std::path::Path::new(&path).exists() {
+            println!("cargo:rerun-if-changed={path}");
+        }
+    }
 }
diff --git a/openfut-blaze-host/sidecar.sh b/openfut-blaze-host/sidecar.sh
index 2cc00a9..1c47e96 100755
--- a/openfut-blaze-host/sidecar.sh
+++ b/openfut-blaze-host/sidecar.sh
@@ -116,6 +116,12 @@ cmd_start() {
     die "port $OPENFUT_BLAZE_HOST_PORT is already in use"
   fi
 
+  # The binary's stamp can lag the tree (cargo cannot know about every source
+  # change). Compare it with the tree's real HEAD at launch and say so, because
+  # an evidence artefact that names the wrong commit is worse than one that
+  # names none.
+  HEAD_NOW="$(git -C "$ROOT" rev-parse --short=7 HEAD 2>/dev/null || echo unknown)"
+
   local tree
   tree="$(tree_state)"
   if [[ "$tree" == "DIRTY" ]]; then
@@ -141,7 +147,15 @@ cmd_start() {
     fi
     if port_listening "$OPENFUT_BLAZE_HOST_PORT"; then
       echo "sidecar started: pid $pid, port $OPENFUT_BLAZE_HOST_PORT"
-      grep -m1 'openfut-blaze-host v' "$LOGFILE" 2>/dev/null | sed 's/^/  /'
+      local banner stamped
+      banner="$(grep -m1 'openfut-blaze-host v' "$LOGFILE" 2>/dev/null)"
+      echo "  ${banner}"
+      stamped="$(sed -n 's/.*commit=\([0-9a-f]*\).*/\1/p' <<<"$banner")"
+      if [[ -n "$stamped" && "$stamped" != "unknown" && "$stamped" != "$HEAD_NOW" ]]; then
+        echo "  !! STALE BUILD STAMP: binary says $stamped, HEAD is $HEAD_NOW" >&2
+        echo "     Rebuild before treating this run as evidence:" >&2
+        echo "       touch openfut-blaze-host/build.rs && cargo build -p openfut-blaze-host" >&2
+      fi
       if grep -q 'WARNING: built from a modified working tree' "$LOGFILE" 2>/dev/null; then
         echo "  !! DIRTY BUILD — results are not parity evidence" >&2
       fi