[Kanish2002]

Reports often need proportions rather than absolute counts. This adds required normalize overloads to the existing DataColumn and DataFrame selector/string operation families.

For ["a", "a", null, "b"], valueCounts(normalize = true) excludes the missing observation and returns counts [2/3, 1/3] as nonnullable Double. With dropNA = false, the denominator includes it and the result is [0.5, 0.25, 0.25].

Behavior and compatibility:

• Reuse existing counting, sort/ascending/dropNA rules and collision-safe result names. The default name remains count.
• Divide by the sum of retained counts. Empty/all-excluded input produces zero rows with a declared Double count column.
• Preserve every old signature and default. New overloads require normalize; false retains Int counts.
• Return DataFrame<*> for the new overloads because the existing ValueCount.count: Int schema cannot describe conditional Double output.
• Per dataframe-compiler-plugin-core/AGENTS.md, new overloads omit both refinement and interpreter annotations until supported Kotlin plugin versions understand the parameter. Name-based access works; generated result accessors are not implemented.
• Existing updateGroups composition supports normalization per group.

Related to #2165. Depends on #2168 for empty observed-column preservation. The branch contains that prerequisite commit followed by the normalization commit; it will need rebasing after the fix lands.

Validation:

• 55 isolated JUnit tests pass: 30 existing/empty-result value-count tests, 22 normalization tests (including 200 seeded nullable-input/policy cases), and three documentation examples.
• Compiles actual changed production sources plus unchanged current annotations/Plugin.kt with Kotlin 2.4.21 against published dataframe-core 1.0.0-rc01, using friend paths. Production targets JVM 8; tests target JVM 11. This is not a full current-repository build.
• Three exact sample tests also compile and pass with the actual DataFrame compiler plugin 2.4.21. A new-overload client compiles/runs with and without it; a stale Int count accessor is rejected.
• Legacy calls and bound callable references compile against both baseline/current classes. A client compiled against baseline runs with the changed classes. All 11 existing public ValueCountsKt JVM method descriptors remain; six overload/default methods are added.
• Standalone ktlint 1.8.0, git diff --check, and all three website sample references pass.

Draft for API-design review under the pre-1.0 freeze. Full debug build, repository tests, generated API dump/check, KoDEx and Korro rendering remain pending. The sample references are registered, but rendered snippet generation is not validated.

AI-assisted.