feat(ai): add session history with visual state restoration

Add the ability to browse, resume, and delete past AI chat sessions.
Sessions are stored per-project using StateManager metadata and JSON
files on disk. The history dropdown shows recent sessions with relative
timestamps, and clicking one restores the full visual state (messages,
tool indicators, edits, errors, questions). Resumed sessions continue
the Claude conversation via the SDK resume option.

Also adds a project-switch warning when AI is streaming, resets the
chat UI on project open, and saves partial history when a query is
cancelled so it can be resumed later.

Author: abose

src-node/claude-code-agent.js

@@ -220,6 +220,21 @@ exports.answerQuestion = async function (params) {
     return { success: true };
 };
 
+/**
+ * Resume a previous session by setting the session ID.
+ * The next sendPrompt call will use queryOptions.resume with this session ID.
+ */
+exports.resumeSession = async function (params) {
+    if (currentAbortController) {
+        currentAbortController.abort();
+        currentAbortController = null;
+    }
+    _questionResolve = null;
+    _queuedClarification = null;
+    currentSessionId = params.sessionId;
+    return { success: true };
+};
+
 /**
  * Destroy the current session (clear session ID).
  */
@@ -832,11 +847,13 @@ async function _runQuery(requestId, prompt, projectPath, model, signal, locale,
 
         if (isAbort) {
             _log("Cancelled");
-            // Query was cancelled — clear session so next query starts fresh
+            // Send sessionId so browser side can save partial history for later resume
+            const cancelledSessionId = currentSessionId;
+            // Clear session so next query starts fresh
             currentSessionId = null;
             nodeConnector.triggerPeer("aiComplete", {
                 requestId: requestId,
-                sessionId: null
+                sessionId: cancelledSessionId
             });
             return;
         }