Fix simplified changes list on update operation

[konard]

🎯 Problem Description

Fixes issue #26: Wrong simplified changes list on update operation.

The issue occurred when update operations were showing intermediate transformation steps instead of simplified changes. For example, when running:

dotnet run -- '((($index: $source $target)) (($index: $target $source)))' --changes --after

Instead of showing clean transformations like:

(1: 1 2) (1: 2 1)  
(2: 2 1) (2: 1 2)

It was showing intermediate steps:

((1: 1 2)) ()
((1: 1 2)) ((1: 2 1))  
((2: 2 1)) ((2: 1 2))

🔧 Root Cause Analysis

The problem was in the ChangesSimplifier algorithm. When a link had multiple conflicting transformations from the same "before" state (e.g., both deletion (1: 1 2) -> (0: 0 0) and direct update (1: 1 2) -> (1: 2 1)), the simplifier's chain-building logic would fail.

This occurred because:

1. The same "before" state appeared in multiple transitions
2. The algorithm couldn't determine which transformation was the actual final one
3. All intermediate steps were returned instead of being simplified

✅ Solution

Added a preprocessing step RemoveDuplicateBeforeStates (C#) / remove_duplicate_before_states (Rust) that:

• Identifies conflicting transitions: When the same "before" state has multiple "after" states
• Handles null transitions intelligently: When one transition is to a null state (0: 0 0) and others are non-null, prefer the non-null transitions as they represent the actual final transformation
• Preserves legitimate multiple branches: Maintains scenarios where one initial state legitimately leads to multiple different final states

🧪 Testing

C# Tests

• ✅ All existing tests continue to pass (126 tests)
• ✅ SimplifyChanges_Issue26_UpdateOperationSimplification reproduces and verifies the fix
• ✅ SimplifyChanges_Issue26_AlternativeScenario_NoSimplificationOccurs tests the edge case

Rust Tests

• ✅ All existing tests continue to pass (34 tests)
• ✅ test_simplify_issue26_update_operation reproduces and verifies the fix
• ✅ test_simplify_issue26_alternative_scenario tests the edge case
• ✅ test_simplify_multiple_branches_from_same_initial tests legitimate branching
• ✅ test_simplify_specific_example_removes_intermediate_states tests chain simplification
• ✅ test_simplify_keeps_unchanged_states tests unchanged state preservation

🔍 Technical Details

Before the fix:

// These conflicting changes would cause the simplifier to fail:
(1: 1 2) -> (0: 0 0)    // deletion  
(1: 1 2) -> (1: 2 1)    // update
(2: 2 1) -> (2: 1 2)    // update
// Result: All 3 changes shown (no simplification)

After the fix:

// The preprocessing removes the conflicting null transition:
(1: 1 2) -> (1: 2 1)    // final transformation
(2: 2 1) -> (2: 1 2)    // final transformation  
// Result: Only 2 simplified changes shown

📋 Files Changed

C# (existing fix)

• csharp/Foundation.Data.Doublets.Cli/ChangesSimplifier.cs: Core fix implementation
• csharp/Foundation.Data.Doublets.Cli.Tests/ChangesSimplifier.cs: Test cases

Rust (new fix applied)

• rust/src/changes_simplifier.rs: Core fix implementation + comprehensive test cases

🔄 Symmetry

Both C# and Rust implementations now have:

1. Identical preprocessing logic (RemoveDuplicateBeforeStates / remove_duplicate_before_states)
2. Same algorithm structure (separate unchanged states, identify initial/final states, DFS traversal)
3. Matching test coverage for Issue Wrong simplified changes list on update operation #26 scenarios

🤖 Generated with Claude Code

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Resolves #26

[konard]

Resolve conflicts and ensure all changes are correct, consistent and fully meet the requirements. Check our logic for simplicity and simmetry.

Make sure we add tests and apply fix for both C# and Rust logic.

[konard]

🤖 AI Work Session Started

Starting automated work session at 2026-01-08T03:37:19.385Z

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[konard]

🤖 Solution Draft Log

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• Calculated by Anthropic: $1.949635 USD
• Difference: $-1.040523 (-34.80%)
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