Add in/out Flow attribute to every node and display them in the node header

[Copilot]

Add the a connection pin in the node's header, to force a flow evaluation, when nodes are not naturally connected by their attributes

Flow attributes are internal attributes:

• Rename FlowAttribute → Flow in desc/attribute.py and attribute.py (+ backward-compat alias)
• Update all imports, isinstance checks, comments, and QML type strings to use "Flow"
• Move flow input/output attrs from _attributes to _internalAttributes in node.py
• Update node.py _applyExpr() to also iterate over _internalAttributes
• Fix attribute.py _applyExpr() to search _internalAttributes when looking for source attr
• Update QML Node.qml to use internalAttribute()/hasInternalAttribute() for flowIn/flowOut
• Update nodeFactory.py compatibility checks to account for flow attrs in internalInputs
• Remove if v is not None filter from outputs in toDict()
• Update tests (test_flowAttribute.py, test_compatibility.py, test_pipeline.py)
• All 257 backend tests pass, CodeQL: 0 alerts

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[codecov]

Codecov Report

❌ Patch coverage is 96.74267% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.39%. Comparing base (3083c91) to head (e41541e).
⚠️ Report is 2 commits behind head on develop.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
meshroom/core/graph.py	76.47%	4 Missing ⚠️
meshroom/core/nodeFactory.py	87.50%	3 Missing ⚠️
meshroom/core/node.py	92.30%	2 Missing ⚠️
meshroom/core/attribute.py	94.44%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3048      +/-   ##
===========================================
+ Coverage    84.92%   85.39%   +0.47%     
===========================================
  Files           72       73       +1     
  Lines        11055    11403     +348     
===========================================
+ Hits          9388     9738     +350     
+ Misses        1667     1665       -2     

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[Copilot]

Pull request overview

This PR adds automatic flowIn/flowOut pins to nodes and moves those flow attributes into internalAttributes so they can be shown in the node header while remaining separate from normal data attributes.

Changes:

• Introduces Flow/FlowAttribute descriptor/runtime classes and auto-injects internal flow input/output attrs on nodes.
• Updates serialization, expression application, compatibility checks, and UI command lookup to account for internal flow attrs.
• Updates QML node rendering and backend tests for the new flow-pin behavior.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/test_pipeline.py	Adjusts pipeline test to ignore Flow outputs in attribute iteration.
tests/test_flowAttribute.py	Adds coverage for Flow descriptor behavior, linking, and graph serialization.
tests/test_compatibility.py	Extends compatibility expectations for internal flow attrs.
meshroom/ui/qml/GraphEditor/Node.qml	Moves flow pins into the node header and filters them from regular attribute lists.
meshroom/ui/qml/GraphEditor/AttributePin.qml	Adds compact pin mode for header rendering.
meshroom/ui/qml/GraphEditor/AttributeItemDelegate.qml	Handles Flow attrs as non-data UI elements.
meshroom/ui/commands.py	Resolves edge commands against regular or internal attributes.
meshroom/core/nodeFactory.py	Updates compatibility/name checks for internal flow serialization.
meshroom/core/node.py	Applies expressions to internal attrs and auto-creates internal flow pins.
meshroom/core/desc/node.py	Defines internal flow attrs on node descriptors.
meshroom/core/desc/attribute.py	Adds the Flow descriptor class and alias.
meshroom/core/desc/init.py	Re-exports Flow and FlowAttribute.
meshroom/core/attribute.py	Resolves link expressions against internal attrs and adds runtime Flow.

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[Alxiice]

yes indeed there's a problem here

[Alxiice]

but deleting these lines is even worse

[Alxiice]

Here is a gif a bit more detailed to show some functionnalities :

• the input flow can be connected to multiple outputs
• here the flow invalidates the node. Note that I finally decided remove it (because this would switch to compatibility mode all nodes in existing pipelines). This is up to discussion but I think it's better for the flow not to invalidate the node.
• the serialization works well, and the flow is only serialized if not empty