Fix gradient chain metadata sync for exposed Fill nodes

[YohYamasaki]

Closes #4314

This fix inserts a Transform node only when the Gradient tool is selected. The first try was inserting a Transform node when wiring Gradient Value -> Fill if no transform attribute exists. This kept the tool and node state synchronized best, but was not intuitive UX wise because of the sudden node insertion.

Screen.Recording.2026-07-07.at.18.02.55.mov

[gemini-code-assist]

Code Review

This pull request introduces changes to keep the rendered gradient and the Gradient tool state in sync. It adds a normalization step after input connections (NormalizeAfterInputConnection) to reset gradient metadata on a Fill node when a gradient value chain is connected, and inserts a Transform node for chain-backed gradients if one is missing. The review feedback points out an inconsistency in the graph traversal flow type, suggesting the use of FlowType::HorizontalFlow instead of FlowType::PrimaryFlow to align with other parts of the codebase.

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[cubic-dev-ai]

4 issues found across 6 files

Confidence score: 3/5

• editor/src/messages/portfolio/document/node_graph/node_graph_message_handler.rs now emits GraphOperationMessage::NormalizeAfterInputConnection from NodeGraphMessageHandler, which conflicts with the documented layering invariant and risks further cross-layer coupling/regressions in message flow as this path evolves — move the normalization trigger into the graph-operation layer (or update architecture boundaries explicitly) before merging.
• editor/src/messages/tool/tool_messages/gradient_tool.rs applies Transform insertion only in the fallback PointerDown path and may queue GradientTransformSet outside StartTransaction, so similar gradient interactions can behave inconsistently and leave changes outside expected undo/abort semantics — make all relevant PointerDown branches follow the same insertion path and wrap the transform mutation inside the transaction lifecycle.
• editor/src/messages/portfolio/document/graph_operation/graph_operation_message_handler.rs drops output_index when checking upstream metadata initialization, so multi-output nodes can resolve from the wrong port and initialize metadata from an unintended data flow — include the output port in upstream traversal/state lookup before merging.

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[YohYamasaki]

@cubic-dev-ai review

[cubic-dev-ai]

@cubic-dev-ai review

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[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

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[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}