fix: correct canResume logic to avoid showing spurious Resume button

- Initialize finishReason to "stop" in new sessions (was undefined)
- Fix canResume to only be true when there's actually something to resume:
  - tool_calls: model called tools, waiting for results
  - length: response was truncated
  - null with streamingContent: user aborted mid-stream

Previously, undefined finishReason passed the check (undefined !== "stop")
causing Resume button to appear on fresh conversations.

https://claude.ai/code/session_01HqtD9R33oqfB14Gu1V5wHC

src/hooks/useChatSession.ts

@@ -106,12 +106,16 @@ export function useChatSession(
       usage: session?.usage,
       cost: session?.sessionCost ?? 0,
 
-      // Resume state
+      // Resume state - only show resume when there's actually something to continue
+      // tool_calls: model called tools, waiting for results
+      // length: response was truncated
+      // null: user aborted mid-stream (only if there's partial content)
       canResume: Boolean(
         session &&
         !session.isLoading &&
-        session.finishReason !== "stop" &&
-        session.finishReason !== "error",
+        (session.finishReason === "tool_calls" ||
+          session.finishReason === "length" ||
+          (session.finishReason === null && session.streamingContent)),
       ),
       finishReason: session?.finishReason,
     }),

src/services/llm/session-manager.ts

@@ -116,6 +116,7 @@ class ChatSessionManager {
       sessionCost: 0,
       subscriberCount: 1,
       lastActivity: Date.now(),
+      finishReason: "stop", // Nothing to resume initially
     };
 
     this.updateSession(conversationId, session);