Improve phenotype scaling and safeguarded line search

docs/FORMAT.md

@@ -150,6 +150,17 @@ numerical_error
 
 `converged_boundary` is a successful residual-only solution accepted after the one-sided variance-component score and likelihood checks.
 
+Phenotypes are scaled internally by their task-specific OLS residual RMS before
+optimization. Reported fixed effects, fixed-effect covariance, variance
+components, and restricted likelihood are transformed back to the original
+input phenotype units. Input binary files are never modified.
+
+The strong-Wolfe zoom uses safeguarded quadratic interpolation with a 2%
+endpoint margin and falls back to bisection. At an evaluation limit or a
+collapsed bracket, the last valid likelihood-improving point encountered is
+accepted. `line_search_failed` therefore means that the search found no valid
+point that improved the starting likelihood.
+
 ## Generic finalized output
 
 The Python CLI exports one TSV row per task. It includes the full summary plus: