fix wrongly remove reset nodes

[zalcit]

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Summary

Screenshots

Before	After
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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

reproduce:


expect: the final answer node print streamly

truth:

1. when first chat. first ifelse node execute.
2. _fetch_node_ids_in_reachable_branch can not fetch all node when the second ifelse's branch_identify is not match.
   for the ifelse2 node' branch_identify is a uuid but the ifelse1 node's branch_identify is true. so the node link break.
   
3. then _remove_node_ids_in_unreachable_branch with a 'wrong' reachable_node_ids. this method will remove all nodes
   
4. cause the wrong rest_node_ids, then cause the final answer node can not print stream. replaced with blocking answer.

[crazywoola]

It seems that we fixed in plugin daemon side

• refactor: using length-prefixed chunking for Backwards invocations dify-plugin-daemon#342
• https://github.com/langgenius/dify/pull/20903/files

[zalcit]

It seems that we fixed in plugin daemon side

• refactor: using length-prefixed chunking for Backwards invocations dify-plugin-daemon#342
• https://github.com/langgenius/dify/pull/20903/files

This is nothing todo with backwards invocations. It's just a normal call with ifelse branch. Maybe u can try the above method to reproduce.

[Nov1c444]

LGTM