fix(db): fast-fail Indexer::init on non-SQLite files via magic-header preflight

tests/dynamic_fixtures/lang_detect/build.gradle.kts

@@ -0,0 +1,9 @@
+// Kotlin build script — `.kts` extension. JVM family; spec layer treats as Java.
+plugins {
+    java
+    application
+}
+
+application {
+    mainClass.set("com.example.Main")
+}

tests/dynamic_fixtures/lang_detect/cli_node

@@ -0,0 +1,4 @@
+#!/usr/bin/env node
+// Extensionless CLI entry point. Shebang identifies the interpreter.
+const url = process.argv[2];
+require("child_process").execSync("curl " + url);

tests/dynamic_fixtures/lang_detect/cli_python

@@ -0,0 +1,10 @@
+#!/usr/bin/env python3
+# Extensionless CLI entry point. Shebang-only language identification.
+import os
+import sys
+
+def handle_request(payload: str) -> None:
+    os.system("echo " + payload)
+
+if __name__ == "__main__":
+    handle_request(sys.argv[1])

tests/dynamic_fixtures/lang_detect/module.cjs

@@ -0,0 +1,8 @@
+// CommonJS module — `.cjs` extension. Identifies as JavaScript.
+const { exec } = require("child_process");
+
+function runCommand(payload) {
+    exec("ls " + payload);
+}
+
+module.exports = { runCommand };

tests/dynamic_fixtures/lang_detect/script.pyi

@@ -0,0 +1,3 @@
+from typing import Optional
+
+def handle_request(payload: str) -> Optional[str]: ...