Merge pull request #875 from SceneTech/fix/indexeddb-readwrite-serialization-269

Serialize IndexedDB readwrite commits

Author: wieslawsoltes

docs/validation/indexeddb-readwrite-serialization-269.md

@@ -0,0 +1,39 @@
+# IndexedDB read/write transaction serialization
+
+## Consumer failure
+
+The unchanged VS Code OSS 1.137 workbench opens several `readwrite`
+transactions against its `vscode-web-state-db-global` database during startup
+and state flush. WebScene previously let every transaction commit from the
+revision visible when the transaction was created. More than four overlapping
+writes could exhaust the compatibility layer's conflict retry limit and reject
+a valid transaction with `AbortError`.
+
+The exact AppScene `cd0a02e` / WebScene `98077f23` Release package reproduced
+this while saving the encrypted MCP input metadata. The native log reported
+`IndexedDB database changed before this transaction committed` before the
+reload lifecycle began. The encrypted key survived, while the workspace
+`mcpInputs` record did not.
+
+## Contract
+
+WebScene now serializes `readwrite` commits per database inside one runtime.
+Each transaction retains its isolated mutation log. When it reaches the head of
+the queue, the existing optimistic concurrency path reloads the newest durable
+revision, replays the mutations, and commits atomically. A transaction aborted
+while queued is skipped. The native revision check remains in place for writes
+from separate runtimes or processes.
+
+Serialization is database scoped, so independent databases continue in
+parallel. Request delivery and readonly transaction behavior are unchanged.
+
+## Focused gate
+
+`webscene_native_indexeddb_contract` starts twelve overlapping read/write
+transactions after the initial database write. This exceeds the former
+four-retry ceiling and requires all fourteen records to be visible through the
+normal cursor path. The focused Release/V8 test passes in 1.31 seconds.
+
+The final consumer gate is the exact packaged Code OSS MCP store, reload, and
+reopen sequence. It remains tracked by WebScene #269 and the Code OSS release
+acceptance epic.

experiments/WebScene.NativeEngine.Probe/native/webscene_indexeddb_compatibility.h

@@ -11,6 +11,7 @@ inline constexpr std::string_view indexeddb_compatibility_source = R"JS(
   if (typeof nativeStorage !== 'function') return;
   const openConnections = new Map();
   const loadedDatabases = new Map();
+  const writeTails = new Map();
   const clone = value => structuredClone(value);
   const failure = (message, name) => new DOMException(message, name);
   const event = (type, fields = {}) => Object.assign({
@@ -233,6 +234,7 @@ R"JS(  class IDBTransaction extends EventTarget {
       this._active = true;
       this._pending = 0;
       this._finishScheduled = false;
+      this._commitQueued = false;
       this._mutations = [];
       this._settled = versionchange ? new Promise((resolve, reject) => {
         this._settleResolve = resolve;
@@ -289,7 +291,23 @@ R"JS(  class IDBTransaction extends EventTarget {
         else this._commit();
       }, 0);
     }
-    async _commit(attempt = 0) {
+    async _commit() {
+      if (this._commitQueued) return;
+      this._commitQueued = true;
+      const name = this.db.name;
+      const previous = writeTails.get(name) ?? Promise.resolve();
+      let release;
+      const current = new Promise(resolve => { release = resolve; });
+      writeTails.set(name, current);
+      await previous.catch(() => {});
+      try {
+        if (this._active) await this._commitNow();
+      } finally {
+        release();
+        if (writeTails.get(name) === current) writeTails.delete(name);
+      }
+    }
+    async _commitNow(attempt = 0) {
       try {
         const revision = await nativeStorage(
           'store', this.db.name, this._revision, this._state);
@@ -321,7 +339,7 @@ R"JS(  class IDBTransaction extends EventTarget {
             }
             this._state = state;
             this._revision = latest.revision;
-            return this._commit(attempt + 1);
+            return this._commitNow(attempt + 1);
           } catch (reloadError) { error = reloadError; }
         }
         this._fail(error);

experiments/WebScene.NativeEngine.Probe/tests/native_v8_runtime_indexeddb_tests.inc

@@ -388,6 +388,16 @@ void test_indexeddb_persistence_and_transaction_contract()
         write.objectStore('ItemTable').put('second', 'beta');
         await transactionDone(write);
 
+        stage = 'concurrent-writes';
+        const concurrentWrites = [];
+        for (let index = 0; index < 12; ++index) {
+          const transaction = database.transaction('ItemTable', 'readwrite');
+          transaction.objectStore('ItemTable').put(
+            `value-${index}`, `parallel-${index}`);
+          concurrentWrites.push(transactionDone(transaction));
+        }
+        await Promise.all(concurrentWrites);
+
         stage = 'abort-v1';
         const rolledBack = database.transaction('ItemTable', 'readwrite');
         rolledBack.objectStore('ItemTable').put('must-not-commit', 'alpha');
@@ -441,7 +451,9 @@ void test_indexeddb_persistence_and_transaction_contract()
         "indexedDbProbe.upgradeOld===0&&indexedDbProbe.abortName==='AbortError'"
         "&&indexedDbProbe.versionChange==='1->2'&&indexedDbProbe.version===2"
         "&&indexedDbProbe.stores.join(',')==='ItemTable,SecondTable'"
-        "&&indexedDbProbe.cursorValues.length===2"
+        "&&indexedDbProbe.cursorValues.length===14"
+        "&&indexedDbProbe.cursorValues.filter(item=>"
+        "item[0].startsWith('parallel-')).length===12"
         "&&indexedDbProbe.cursorValues[0][0]==='alpha'"
         "&&indexedDbProbe.cursorValues[0][1].nested.enabled"
         "&&indexedDbProbe.cursorValues[0][1].bytes[2]===255"