fix: harden evidence secret file handoff

harness/tests/test_registry_evidence_config.py

@@ -223,6 +223,37 @@ def test_signed_http_rejects_reordered_extra_mismatch_userinfo_and_duplicate_pro
     assert_no_canaries(caught.value)
 
 
+def test_s3_rejects_inline_credentials_and_never_discloses_them(tmp_path):
+    path = write_config(tmp_path, {
+        "type": "s3", "bucket": "clinical-evidence",
+        "access_key": ACCESS_CANARY,
+        "secret_key": SECRET_CANARY,
+        "session_token": TOKEN_CANARY,
+    })
+
+    with pytest.raises(ConfigError) as caught:
+        load_config(path)
+    assert "file" in str(caught.value).lower()
+    assert_no_canaries(caught.value)
+    assert_no_canaries("".join(traceback.format_exception(caught.value)))
+
+
+def test_s3_scalar_secret_files_are_bounded(tmp_path):
+    access = tmp_path / "oversized-access-key"
+    access.write_bytes(b"A" * (64 * 1024 + 1))
+    secret = tmp_path / "secret-key"
+    secret.write_text("bounded-secret")
+    path = write_config(tmp_path, {
+        "type": "s3", "bucket": "clinical-evidence",
+        "access_key_file": str(access), "secret_key_file": str(secret),
+    })
+
+    with pytest.raises(ConfigError) as caught:
+        load_config(path)
+    assert "secret file" in str(caught.value).lower()
+    assert "bounded-secret" not in str(caught.value)
+
+
 def test_s3_ambient_and_static_file_credentials_are_secret_typed(tmp_path):
     ambient = load_config(write_config(tmp_path, {
         "type": "s3", "bucket": "clinical-evidence", "prefix": "published/",

harness/tht/config.py

@@ -49,13 +49,17 @@ def _expand_env(value: Any) -> Any:
 _MAX_SIGNED_URL_FILE_BYTES = 1024 * 1024
 
 
-def _resolve_http_signed_url_files(value: Any) -> Any:
+def _resolve_evidence_secret_files(value: Any) -> Any:
     """Resolve only signed HTTP URL arrays, keeping their values out of public errors."""
     if isinstance(value, dict):
         resolved = {
-            key: _resolve_http_signed_url_files(item)
+            key: _resolve_evidence_secret_files(item)
             for key, item in value.items()
         }
+        if resolved.get("type") == "s3" and any(
+            name in resolved for name in ("access_key", "secret_key", "session_token")
+        ):
+            raise ConfigError("S3 Evidence credentials require *_file references")
         if resolved.get("type") != "http" or "signed_urls_file" not in resolved:
             return resolved
         if "urls" in resolved:
@@ -94,10 +98,13 @@ def _resolve_http_signed_url_files(value: Any) -> Any:
         resolved["urls"] = parsed
         return resolved
     if isinstance(value, list):
-        return [_resolve_http_signed_url_files(item) for item in value]
+        return [_resolve_evidence_secret_files(item) for item in value]
     return value
 
 
+_MAX_SCALAR_SECRET_FILE_BYTES = 64 * 1024
+
+
 def _resolve_secret_files(value: Any) -> Any:
     if isinstance(value, dict):
         resolved = {key: _resolve_secret_files(item) for key, item in value.items()}
@@ -109,9 +116,13 @@ def _resolve_secret_files(value: Any) -> Any:
                 raise ConfigError(f"{secret_name} and {file_name} are mutually exclusive")
             path = Path(resolved.pop(file_name))
             try:
-                secret = path.read_text()
-            except (OSError, UnicodeError) as exc:
-                raise ConfigError(f"Cannot read secret file: {path}") from exc
+                with path.open("rb") as stream:
+                    payload = stream.read(_MAX_SCALAR_SECRET_FILE_BYTES + 1)
+                if len(payload) > _MAX_SCALAR_SECRET_FILE_BYTES:
+                    raise OSError
+                secret = payload.decode("utf-8")
+            except (OSError, UnicodeError):
+                raise ConfigError(f"Cannot read secret file: {path}") from None
             if not secret or any(char.isspace() for char in secret) or "\x00" in secret:
                 raise ConfigError(f"Invalid secret file: {path}")
             resolved[secret_name] = secret
@@ -532,7 +543,7 @@ def load_config(path: Path) -> Config:
         raise ConfigError(f"Configurazione YAML non valida: {path}") from exc
     if not isinstance(raw, dict):
         raise ConfigError(f"Configurazione non valida (atteso un mapping YAML): {path}")
-    expanded = _resolve_secret_files(_resolve_http_signed_url_files(_expand_env(raw)))
+    expanded = _resolve_secret_files(_resolve_evidence_secret_files(_expand_env(raw)))
     _validate_internal_embedding_contract(expanded, path)
     _validate_internal_vector_contract(expanded, path)
     translated, used_legacy = translate_legacy_config(expanded)