SQLite: Make foreign key errors on txn commit visible to app.

I noticed the test was testing for an "internal error", which is always a bug, and implies that in prod an error would have been logged to Sentry. We can make this throw an application-visible error instead. This also makes the test output look less bad.

src/workerd/api/sql-test.js

@@ -1379,7 +1379,7 @@ export default {
     // Test defer_foreign_keys (explodes the DO)
     await assert.rejects(async () => {
       await doReq('sql-test-foreign-keys');
-    }, /Error: internal error/);
+    }, /constraints were violated: FOREIGN KEY constraint failed: SQLITE_CONSTRAINT/);
 
     // Some increments.
     assert.equal(await doReq('increment'), 1);

src/workerd/io/BUILD.bazel

@@ -140,6 +140,9 @@ wd_cc_library(
         "@capnp-cpp//src/capnp:capnp-rpc",
         "@capnp-cpp//src/kj:kj-async",
     ],
+    implementation_deps = [
+        "@sqlite3",
+    ],
 )
 
 wd_cc_library(

src/workerd/io/actor-sqlite.c++

@@ -10,6 +10,7 @@
 #include <workerd/util/sentry.h>
 
 #include <algorithm>
+#include <sqlite3.h>
 
 namespace workerd {
 
@@ -648,6 +649,21 @@ kj::Maybe<kj::Promise<void>> ActorSqlite::onNoPendingFlush() {
   return outputGate.wait();
 }
 
+void ActorSqlite::TxnCommitRegulator::onError(
+    kj::Maybe<int> sqliteErrorCode, kj::StringPtr message) const {
+  KJ_IF_SOME(c, sqliteErrorCode) {
+    if (c == SQLITE_CONSTRAINT) {
+      JSG_ASSERT(false, Error,
+          "Durable Object was reset and rolled back to its last known good state because the "
+          "application left the database in a state where constraints were violated: ",
+          message);
+    }
+  }
+
+  // For any other type of error, fall back to the default behavior (throwing a non-JSG exception)
+  // as we don't know for sure that the problem is the application's fault.
+}
+
 const ActorSqlite::Hooks ActorSqlite::Hooks::DEFAULT = ActorSqlite::Hooks{};
 
 kj::Promise<void> ActorSqlite::Hooks::scheduleRun(kj::Maybe<kj::Date> newAlarmTime) {

src/workerd/io/actor-sqlite.h

@@ -90,8 +90,16 @@ class ActorSqlite final: public ActorCacheInterface, private kj::TaskSet::ErrorH
   SqliteKv kv;
   SqliteMetadata metadata;
 
+  // Define a SqliteDatabase::Regulator that is similar to TRUSTED but turns certain SQLite errors
+  // into application errors as appropriate when committing an implicit transaction.
+  class TxnCommitRegulator: public SqliteDatabase::Regulator {
+  public:
+    void onError(kj::Maybe<int> sqliteErrorCode, kj::StringPtr message) const;
+  };
+  static constexpr TxnCommitRegulator TRUSTED_TXN_COMMIT;
+
   SqliteDatabase::Statement beginTxn = db->prepare("BEGIN TRANSACTION");
-  SqliteDatabase::Statement commitTxn = db->prepare("COMMIT TRANSACTION");
+  SqliteDatabase::Statement commitTxn = db->prepare(TRUSTED_TXN_COMMIT, "COMMIT TRANSACTION");
 
   kj::Maybe<kj::Exception> broken;