Previously, substring context matching required the pattern to be at least
30% of the line length to prevent ambiguous matches. This caused failures
when matching short identifiers like 'class EditTool' against long export
lines with generics and implements clauses.
Now, if exactly one substring match exists in the file, it is accepted
regardless of the ratio threshold - uniqueness alone is sufficient for
disambiguation. The ratio filter is only applied when multiple substring
matches exist.
Added regression tests for model edit attempts from session analysis.
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