ttulttul-ComfyUI-Modal/docs/LEARNINGS.md

Learnings

2026-04-17

• The workflow metadata already rides along in extra_data.extra_pnginfo.workflow, so the backend can discover node.properties.is_modal_remote without any extra frontend metadata channel.
• A single wildcard-output proxy node is not enough for server-side graph rewriting. ComfyUI validates downstream link indices and output arity against the replacement class, so the backend has to generate proxy node classes that mirror the original node’s output signature before validation runs.
• Keeping the sync engine content-addressable makes prompt rewrites cheap after the first upload. The route can block on sync safely as long as repeated requests collapse to a hash marker check.
• Hashing and zipping the entire custom_nodes/ tree inside the queue route is too expensive for COMFY_MODAL_EXECUTION_MODE=local. Local mode should skip custom-node bundle sync by default, with an explicit override when that path needs to be exercised.
• When rewriting a prompt node into a proxy, never reuse the same input dict for both prompt_node["inputs"] and original_node_data["inputs"]. Inserting original_node_data back into the live prompt inputs creates a recursive structure that breaks ComfyUI cache signature hashing with a RecursionError.
• Queue-time validation is necessary for remote nodes that still receive local Comfy runtime objects. Even if a node is marked remote, inputs like MODEL or CONDITIONING cannot be serialized across the current boundary, so the prompt should be rejected before execution rather than failing inside the serializer.