ci: enforce coverage thresholds

.agents/project-standards.md

@@ -329,6 +329,10 @@ alias and constructor from the public package.
 - The project aims for complete coverage on core internal data-structure
   packages: `internal/list`, `internal/sortedlist`, `internal/deque`,
   `internal/heap`, and `internal/prioritymap`.
+- CI requires at least 95% coverage across library packages and 100% coverage
+  for changed lines. The cross-implementation benchmark harness under
+  `internal/benchmarks` remains part of build and test verification but is
+  excluded from the published coverage percentage.
 - Internal test files should mirror the implementation method order as much as
   practical. This makes coverage gaps easy to map back to code.
 - Prefer direct assertions over helper-heavy test DSLs.

README.md

@@ -165,6 +165,8 @@ CI builds and tests every package with the minimum supported Go release and the
 latest stable release. The published coverage report measures library packages;
 the cross-implementation benchmark harness under `internal/benchmarks` remains
 part of the build and test suite but is excluded from the coverage percentage.
+Codecov requires at least 95% project coverage and 100% coverage for changed
+lines.
 
 ## Status
 

codecov.yml

@@ -0,0 +1,10 @@
+coverage:
+  status:
+    project:
+      default:
+        target: 95%
+        threshold: 0%
+    patch:
+      default:
+        target: 100%
+        threshold: 0%