fix: add parentId to appendAssistantTranscriptMessage to preserve history chain

Messages appended via /status (and other assistant transcript injections)
were written with no parentId, breaking the tree structure that history
reconstruction walks. This caused context to be truncated at these
injection points.

The fix reads the current leaf message ID before appending and includes
it as parentId in the new entry, preserving the chain.

src/gateway/server-methods/chat.ts

@@ -82,6 +82,36 @@ function ensureTranscriptFile(params: { transcriptPath: string; sessionId: strin
   }
 }
 
+/**
+ * Find the leaf (last message) ID from a transcript file.
+ * Returns null if file doesn't exist, is empty, or has no messages (header only).
+ */
+function findTranscriptLeafId(transcriptPath: string): string | null {
+  if (!fs.existsSync(transcriptPath)) return null;
+
+  try {
+    const content = fs.readFileSync(transcriptPath, "utf-8");
+    const lines = content.split(/\r?\n/).filter((line) => line.trim());
+    if (lines.length === 0) return null;
+
+    // Walk backwards to find the last message entry with an id
+    for (let i = lines.length - 1; i >= 0; i--) {
+      try {
+        const parsed = JSON.parse(lines[i]);
+        // Skip non-message entries (like session headers)
+        if (parsed?.type === "message" && typeof parsed?.id === "string") {
+          return parsed.id;
+        }
+      } catch {
+        // Skip malformed lines
+      }
+    }
+    return null;
+  } catch {
+    return null;
+  }
+}
+
 function appendAssistantTranscriptMessage(params: {
   message: string;
   label?: string;
@@ -112,6 +142,9 @@ function appendAssistantTranscriptMessage(params: {
     }
   }
 
+  // Find the current leaf ID before we append
+  const parentId = findTranscriptLeafId(transcriptPath);
+
   const now = Date.now();
   const messageId = randomUUID().slice(0, 8);
   const labelPrefix = params.label ? `[${params.label}]\n\n` : "";
@@ -125,6 +158,7 @@ function appendAssistantTranscriptMessage(params: {
   const transcriptEntry = {
     type: "message",
     id: messageId,
+    parentId,
     timestamp: new Date(now).toISOString(),
     message: messageBody,
   };