Merge keys that normalize alike under one name instead of swapping them [patch]

[matt-edmondson]

Under Aggressive and Maximum merging, keys that normalize alike now merge. related: [a] and page_related: [b] become a single related holding both lists. Before this, each value was written under the other key's name and nothing was merged.

Cause

FindBasicCanonicalName mapped each key to another key in its equivalence class, so related went to page_related and page_related went to related. MergeSimilarProperties then saw two one-key groups, and MergeArrayValues wrote each list under the other key's name.

Change

• One name per equivalence class. Every key that normalizes alike maps to the same name, whatever the key order: a known property first, then the shortest key, then an ordinal tie-break. When the chosen key has a known mapping, that mapping is used.
• The partial-match pass chooses between a pair by the same rule, so two keys that contain each other can no longer swap either.
• Maximum no longer lets the semantic pass move the class's chosen key onto some other key after the basic pass has settled it.
• Safety net, as the triage suggested: a group with one original key keeps its own name rather than taking another existing key's. A lone known key such as keywords is still standardized when no other key is involved.

Tests

EquivalentKeyMergeTests adds nine cases:

• the list case and the scalar case, under Aggressive and Maximum, with the keys in both orders;

• the issue's end-to-end input through CombineFrontmatter(..., AsIs, AsIs, Aggressive).

• Without the fix: all nine fail. I checked by reverting PropertyMerger.cs.

• With the fix: all pass, and so does the full suite (206 tests).

Fixes #131

🤖 Generated with Claude Code

https://claude.ai/code/session_015BJVibRvmTotkqEGp3695R

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Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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