feat(tui): fork slash command for keyboard-friendly session forking (resolves #5599) (#5610)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

packages/opencode/src/cli/cmd/tui/routes/session/index.tsx

@@ -53,6 +53,7 @@ import { iife } from "@/util/iife"
 import { DialogConfirm } from "@tui/ui/dialog-confirm"
 import { DialogPrompt } from "@tui/ui/dialog-prompt"
 import { DialogTimeline } from "./dialog-timeline"
+import { DialogForkFromTimeline } from "./dialog-fork-from-timeline"
 import { DialogSessionRename } from "../../component/dialog-session-rename"
 import { Sidebar } from "./sidebar"
 import { LANGUAGE_EXTENSIONS } from "@/lsp/language"
@@ -295,6 +296,25 @@ export function Session() {
         ))
       },
     },
+    {
+      title: "Fork from message",
+      value: "session.fork",
+      keybind: "session_fork",
+      category: "Session",
+      onSelect: (dialog) => {
+        dialog.replace(() => (
+          <DialogForkFromTimeline
+            onMove={(messageID) => {
+              const child = scroll.getChildren().find((child) => {
+                return child.id === messageID
+              })
+              if (child) scroll.scrollBy(child.y - scroll.y - 1)
+            }}
+            sessionID={route.sessionID}
+          />
+        ))
+      },
+    },
     {
       title: "Compact session",
       value: "session.compact",