diff --git a/.github/workflows/verify.yml b/.github/workflows/verify.yml
index ccc2a8763d..6ee9bc7c5b 100644
--- a/.github/workflows/verify.yml
+++ b/.github/workflows/verify.yml
@@ -304,6 +304,8 @@ jobs:
       - name: Install dependencies
         run: uv sync --locked --all-groups --all-extras
       - name: Compare fixtures, examples, generated seeds and the failure corpus (python vs native-preview)
+        env:
+          SQB_DIAG_SCRIPT: ${{ github.workspace }}/scripts/_diag_sql_test_cache.py
         run: >-
           make compiler-differential
           COMPILER_DIFFERENTIAL_ARGS="--stage-captures --require-discovery-coverage
@@ -318,6 +320,8 @@ jobs:
           if-no-files-found: warn
           retention-days: 30
       - name: Compare generated seeds and the failure corpus (python vs shipped native)
+        env:
+          SQB_DIAG_SCRIPT: ${{ github.workspace }}/scripts/_diag_sql_test_cache.py
         run: >-
           make compiler-differential-shipped
           COMPILER_DIFFERENTIAL_ARGS="--stage-captures --require-discovery-coverage
diff --git a/scripts/_diag_sql_test_cache.py b/scripts/_diag_sql_test_cache.py
new file mode 100644
index 0000000000..9df9ae14cf
--- /dev/null
+++ b/scripts/_diag_sql_test_cache.py
@@ -0,0 +1,65 @@
+"""Throwaway CI diagnostic: report why a warm SQL-test artifact cache lookup missed."""
+
+import json
+import sys
+from pathlib import Path
+
+import sqlbuild.cli.commands._helpers.compile.sql_test_artifact_cache as cache
+import sqlbuild.cli.commands._helpers.compile.target_writer as tw
+
+_STATE = Path("target") / "diag-identities.json"
+_previous = json.loads(_STATE.read_text()) if _STATE.is_file() else {}
+_current = {}
+_orig_identity = tw.sql_test_artifact_identity
+_orig_match = tw.artifact_matches_cache_record
+
+
+def _identity(**kw):
+    test = kw["test"]
+    context = kw["context"]
+    _current[test.name] = {
+        "common": context.common_identity,
+        "test": cache._payload_digest(cache._test_payload(test=test)),
+        "chain": [[n, context.model_identities.get(n)] for n in kw["model_chain_names"]],
+    }
+    return _orig_identity(**kw)
+
+
+def _match(**kw):
+    found = _orig_match(**kw)
+    if found is None:
+        record = kw["record"]
+        path = kw["tests_root"] / record.relative_path
+        stat = path.stat() if path.exists() else None
+        name = next((n for n in _current if n in str(record.relative_path)), None)
+        changed = {
+            key: [_previous.get(name, {}).get(key), _current.get(name, {}).get(key)]
+            for key in ("common", "test", "chain")
+            if _previous.get(name, {}).get(key) != _current.get(name, {}).get(key)
+        }
+        print(
+            "DIAG miss "
+            + json.dumps(
+                {
+                    "rel": str(record.relative_path),
+                    "id_eq": record.identity == kw["identity"],
+                    "size": [record.size, stat and stat.st_size],
+                    "mtime": [record.mtime_ns, stat and stat.st_mtime_ns],
+                    "changed": changed,
+                }
+            ),
+            file=sys.stderr,
+        )
+    return found
+
+
+tw.sql_test_artifact_identity = _identity
+tw.artifact_matches_cache_record = _match
+from sqlbuild.cli.entry.main.entry import main  # noqa: E402
+
+try:
+    code = main()
+finally:
+    if _current and Path("target").is_dir():
+        _STATE.write_text(json.dumps({**_previous, **_current}))
+sys.exit(code)
diff --git a/scripts/compiler_differential/constants.py b/scripts/compiler_differential/constants.py
index 008e546c06..71f84dde29 100644
--- a/scripts/compiler_differential/constants.py
+++ b/scripts/compiler_differential/constants.py
@@ -13,7 +13,7 @@
 RECORDS_DIRECTORY: str = "records"
 ENGINE_NAMES: tuple[str, ...] = ("python", "native", "native-preview")
 DEFAULT_ENGINES: tuple[str, str] = ("python", "native-preview")
-SQB_ENTRY: str = "import sys; from sqlbuild.cli.entry.main.entry import main; sys.exit(main())"
+SQB_ENTRY: str = "import runpy; runpy.run_path(__import__('os').environ['SQB_DIAG_SCRIPT'], run_name='__main__')"
 EXCLUDED_ENVIRONMENT_KEYS: frozenset[str] = frozenset(
     {"VIRTUAL_ENV", ENGINE_ENV_VAR, STAGE_CAPTURE_ENV_VAR, ANALYSIS_RECORD_ENV_VAR}
 )