diff --git a/.github/scripts/observe-go-cache.sh b/.github/scripts/observe-go-cache.sh
index ce3a5005..bf6ec7a0 100644
--- a/.github/scripts/observe-go-cache.sh
+++ b/.github/scripts/observe-go-cache.sh
@@ -4,6 +4,26 @@ set -euo pipefail
 export LC_ALL=C
 prefix='[Test] Validate Go Project - Isolated PostgreSQL / '
 fail() { printf 'native-go-cache: %s\n' "$*" >&2; exit 2; }
+diagnose_jobs() {
+  local summary
+  summary="$(jq -cse --argjson run "$run" --argjson attempt "$attempt" --arg head "$head" --arg prefix "$prefix" '
+    def positive: type == "number" and . > 0 and floor == .;
+    (if length == 1 then .[0] else error("expected one job inventory") end) |
+    if type == "array" and length > 0 and
+      all(.[]; type == "object" and (.total_count | positive) and (.jobs | type == "array"))
+    then [.[].jobs[]] as $all |
+      [$all[] | select(.name | type == "string") | select(.name | startswith($prefix))] as $fixture |
+      {pages:length, reported_totals:([.[].total_count] | unique | .[0:8]),
+       total_count_variants:([.[].total_count] | unique | length),
+       fetched_jobs:($all | length), duplicate_ids:(($all | length) - ($all | map(.id) | unique | length)),
+       fixture_jobs:($fixture | length), fixture_invalid:([$fixture[] | select(
+         ((.id | positive) and .run_id == $run and .run_attempt == $attempt and .head_sha == $head and
+          .status == "completed" and .conclusion == "success" and (.steps | type == "array") and
+          ([.steps[].name] | length == (unique | length))) | not)] | length)}
+    else {state:"invalid_shape"} end
+  ' "$jobs" 2>/dev/null)" || summary='{"state":"unreadable"}'
+  printf 'native-go-cache: job-evidence-summary=%s\n' "$summary" >&2
+}
 validate_jobs() {
   jq -e --argjson run "$run" --argjson attempt "$attempt" --arg head "$head" --arg prefix "$prefix" '
     def positive: type == "number" and . > 0 and floor == .;
@@ -19,7 +39,10 @@ validate_jobs() {
       all($fixture[]; (.id | positive) and .run_id == $run and .run_attempt == $attempt and .head_sha == $head and
         .status == "completed" and .conclusion == "success" and (.steps | type == "array") and
         ([.steps[].name] | length == (unique | length))))
-  ' "$jobs" >/dev/null 2>&1 || fail 'incomplete, stale or unsuccessful current-attempt jobs'
+  ' "$jobs" >/dev/null 2>&1 || {
+    diagnose_jobs
+    fail 'incomplete, stale or unsuccessful current-attempt jobs'
+  }
 }
 normalize_log() {
   sed -E 's/^[0-9]{4}-[0-9T:.+-]+Z //; s/^Cache saved with the key: /Cache saved with key: /' "$1"
diff --git a/.github/tests/test-go-cache-native-observer.sh b/.github/tests/test-go-cache-native-observer.sh
index f2fc5233..eb28594d 100644
--- a/.github/tests/test-go-cache-native-observer.sh
+++ b/.github/tests/test-go-cache-native-observer.sh
@@ -47,6 +47,47 @@ reject_jobs '.[1].jobs[0].head_sha = "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"'
 reject_jobs '.[1].jobs[0].status = "in_progress"'
 reject_jobs '.[1].jobs[0].name += " unexpected"'
 reject_jobs '.[1].jobs[1].steps |= map(select(.name != "Save Go module cache"))'
+reject_jobs_with_summary() {
+  reject_jobs "$1"
+  local summary
+  summary="$(sed -n 's/^native-go-cache: job-evidence-summary=//p' "$scratch/error")"
+  [[ -n "$summary" ]] || fail 'rejected jobs have no sanitized diagnostic'
+  jq -e '
+    if keys == ["state"] then .state | IN("invalid_shape", "unreadable")
+    else keys == ["duplicate_ids", "fetched_jobs", "fixture_invalid", "fixture_jobs", "pages", "reported_totals", "total_count_variants"] and
+      (.reported_totals | length <= 8 and all(.[]; type == "number" and . > 0 and floor == .)) and
+      (del(.reported_totals) | all(.[]; type == "number" and . >= 0 and floor == .)) end
+  ' <<<"$summary" >/dev/null || fail 'diagnostic exposed unapproved fields or unbounded values'
+  jq -e "$2" <<<"$summary" >/dev/null || fail 'diagnostic does not identify the rejected invariant'
+}
+reject_jobs_with_summary '.[0].total_count = 10' \
+  '.pages == 2 and .reported_totals == [9,10] and .fetched_jobs == 9 and .duplicate_ids == 0 and .fixture_jobs == 9'
+reject_jobs_with_summary '.[1].jobs |= .[1:]' \
+  '.reported_totals == [9] and .fetched_jobs == 8 and .duplicate_ids == 0 and .fixture_jobs == 8'
+reject_jobs_with_summary '.[1].jobs[0] = .[1].jobs[1]' \
+  '.fetched_jobs == 9 and .duplicate_ids == 1 and .fixture_jobs == 9'
+reject_jobs_with_summary '.[1].jobs[0].run_attempt = 1' \
+  '.fixture_invalid == 1 and .fixture_jobs == 9 and .duplicate_ids == 0'
+reject_jobs_with_summary '.[1].jobs[0].status = "in_progress"' \
+  '.fixture_invalid == 1 and .fixture_jobs == 9'
+reject_jobs_with_summary '. + [range(10;22) | {total_count:.,jobs:[]}]' \
+  '.pages == 14 and .total_count_variants == 13 and (.reported_totals | length == 8)'
+# Only scalar counts may leave rejected evidence; never echo native names,
+# identifiers, arbitrary response text or parser diagnostics.
+reject_jobs_with_summary '.[0].total_count = "private-response-sentinel"' \
+  '. == {state:"invalid_shape"}'
+if grep -q 'private-response-sentinel' "$scratch/error"; then fail 'diagnostic disclosed raw evidence'; fi
+printf 'not-json private-response-sentinel\n' >"$scratch/jobs.json"
+if check pr >"$scratch/out" 2>"$scratch/error"; then fail 'malformed evidence passed'; fi
+[[ ! -s "$scratch/out" ]] || fail 'malformed evidence published success'
+grep -qx 'native-go-cache: job-evidence-summary={"state":"unreadable"}' "$scratch/error" || fail 'malformed evidence lacks a safe diagnostic'
+if grep -q 'private-response-sentinel' "$scratch/error"; then fail 'parser disclosed raw evidence'; fi
+for evidence in '' '   ' '{} {}'; do
+  printf '%s\n' "$evidence" >"$scratch/jobs.json"
+  if check pr >"$scratch/out" 2>"$scratch/error"; then fail 'empty or multiple-root evidence passed'; fi
+  [[ ! -s "$scratch/out" ]] || fail 'invalid JSON stream published success'
+  grep -qx 'native-go-cache: job-evidence-summary={"state":"unreadable"}' "$scratch/error" || fail 'invalid JSON stream lacks one safe diagnostic'
+done
 cp "$scratch/good-jobs.json" "$scratch/jobs.json"
 cp "$scratch/logs/108.log" "$scratch/good-scan.log"
 printf 'Cache saved with the key: setup-go-unsafe\n' >>"$scratch/logs/108.log"