fix(sessions): title app-created sessions from the first user message

App-created sessions (started by sending a message from cloudcli) were
titled with placeholder names — "Untitled Codex Session" from the disk
indexer and, briefly, "New session" from the empty canonical upsert —
before a later sync finally settled on the right text, causing the
sidebar title to flicker.

- Codex/OpenCode synchronizers now title app-created sessions (distinct
  app id mapped to a provider id) from the first user message, while
  sessions found purely by indexing keep their existing setup. Claude
  keeps its AI-generated titles; Cursor already used the first message.
- Decode OpenCode's JSON-string-literal prompts so titles no longer
  surface wrapped in quotes; hoist unwrapJsonStringLiteral into
  shared/utils since it's now used by both the reader and synchronizer.
- Guard the sidebar upsert merge so an empty summary can never blank out
  a title that is already set.
- Add codex/opencode synchronizer tests for the app-created vs indexed
  naming paths.

server/shared/utils.ts

@@ -1066,6 +1066,30 @@ export function getOpenCodeDatabasePath(): string {
   return path.join(os.homedir(), '.local', 'share', 'opencode', 'opencode.db');
 }
 
+/**
+ * Decodes an OpenCode text payload that was persisted as a JSON string literal.
+ *
+ * OpenCode can store the first user prompt (and other text parts) as `"hello"`
+ * instead of `hello`. Used by both the OpenCode session reader (transcript
+ * history) and the OpenCode synchronizer (session titling) so a session name or
+ * message body never surfaces with surrounding quote characters. Only fully
+ * quoted, valid JSON string literals are unwrapped; ordinary prose that merely
+ * happens to start/end with a quote is returned untouched.
+ */
+export function unwrapJsonStringLiteral(value: string): string {
+  const trimmed = value.trim();
+  if (!trimmed.startsWith('"') || !trimmed.endsWith('"')) {
+    return value;
+  }
+
+  try {
+    const parsed = JSON.parse(trimmed);
+    return typeof parsed === 'string' ? parsed : value;
+  } catch {
+    return value;
+  }
+}
+
 // ---------------------------
 //----------------- SAFE DIRECTORY NAME UTILITIES ------------
 /**