Review coverage config and ratchet package coverage gates to 100%

Adopt the remaining useful patterns from covdefaults (exclude
`assert_never` lines, skip fully-covered files in reports) and raise
all package coverage thresholds to the current 100% baseline, making
the Codecov targets explicit in a new codecov.yml.

Closes #155

Author: tpvasconcelos

.coveragerc

@@ -17,7 +17,7 @@ src =
 [report]
 precision = 1
 show_missing = true
-skip_covered = false
+skip_covered = true
 fail_under = 50
 
 # Some of the patterns below were taken or adapted
@@ -36,6 +36,7 @@ exclude_lines =
     : \.\.\.(\s*#.*)?$
     ^ +\.\.\.$
     -> ['"]?NoReturn['"]?:
+    ^\s*assert_never\b
     # non-runnable code
     if __name__ == ['"]__main__['"]:$
 partial_branches =

AGENTS.md

@@ -209,7 +209,8 @@ def _coerce_to_densities(...):
 ## CI/CD Pipeline
 
 GitHub Actions runs tests on Python 3.10–3.14 across Ubuntu, macOS, and Windows.
-Codecov minimums are 98% overall and 100% diff coverage for new code.
+Codecov minimums are 100% overall and 100% diff coverage for new code.
+Intentionally-untested lines must carry an explicit `# pragma: no cover` comment.
 
 ## Notes for AI Assistants
 

codecov.yml

@@ -0,0 +1,15 @@
+# Codecov configuration
+# ref: https://docs.codecov.com/docs/codecov-yaml
+#
+# Note: CI only uploads the combined coverage report
+# (see the coverage-combine env in tox.ini), which omits
+# "cicd_utils/*" and "tests/*", so these targets apply
+# to the src/ridgeplot package only.
+coverage:
+  status:
+    project:
+      default:
+        target: 100%
+    patch:
+      default:
+        target: 100%

tox.ini

@@ -35,7 +35,7 @@ commands =
 
     pytest: pytest --no-cov {posargs}
 
-    tests-unit: pytest tests/unit --doctest-modules src {env:_COV_REPORT_XML} --cov-fail-under=95 {posargs:}
+    tests-unit: pytest tests/unit --doctest-modules src {env:_COV_REPORT_XML} --cov-fail-under=100 {posargs:}
     tests-unit: diff-cover {env:_DIFFCOVER_DFLT_ARGS} --fail-under=100
 
     tests-e2e: pytest tests/e2e --cov=cicd_utils/ridgeplot_examples {env:_COV_REPORT_XML} --cov-fail-under=74 {posargs:}
@@ -49,7 +49,7 @@ commands =
     coverage-combine: mv .coverage {env:COVERAGE_FILE}
     coverage-combine: coverage xml  --data-file={env:COVERAGE_FILE} --omit="cicd_utils/*,tests/*" -o {env:COVERAGE_XML_FILE}
     coverage-combine: coverage html --data-file={env:COVERAGE_FILE} --omit="cicd_utils/*,tests/*"
-    coverage-combine: coverage report --data-file={env:COVERAGE_FILE} --omit="cicd_utils/*,tests/*" --fail-under=98
+    coverage-combine: coverage report --data-file={env:COVERAGE_FILE} --omit="cicd_utils/*,tests/*" --fail-under=100
     coverage-combine: diff-cover {env:_DIFFCOVER_DFLT_ARGS} --fail-under=100
 
 [testenv:pre-commit-{all,quick,autoupgrade}]