diff --git a/lib/core/base.sh b/lib/core/base.sh
index 3831732..e5a65ae 100644
--- a/lib/core/base.sh
+++ b/lib/core/base.sh
@@ -168,12 +168,14 @@ get_free_space() {
 }
 
 # Get Darwin kernel major version (e.g., 24 for 24.2.0)
+# Returns 999 on failure to adopt conservative behavior (assume modern system)
 get_darwin_major() {
     local kernel
     kernel=$(uname -r 2> /dev/null || true)
     local major="${kernel%%.*}"
     if [[ ! "$major" =~ ^[0-9]+$ ]]; then
-        major=0
+        # Return high number to skip potentially dangerous operations on unknown systems
+        major=999
     fi
     echo "$major"
 }
@@ -321,7 +323,17 @@ ensure_user_dir() {
 
     local dir="$target_path"
     while [[ -n "$dir" && "$dir" != "/" ]]; do
+        # Early stop: if ownership is already correct, no need to continue up the tree
+        if [[ -d "$dir" ]]; then
+            local current_uid
+            current_uid=$("$STAT_BSD" -f%u "$dir" 2> /dev/null || echo "")
+            if [[ "$current_uid" == "$owner_uid" ]]; then
+                break
+            fi
+        fi
+
         chown "$owner_uid:$owner_gid" "$dir" 2> /dev/null || true
+
         if [[ "$dir" == "$user_home" ]]; then
             break
         fi
diff --git a/tests/user_file_handling.bats b/tests/user_file_handling.bats
new file mode 100644
index 0000000..f1f2629
--- /dev/null
+++ b/tests/user_file_handling.bats
@@ -0,0 +1,252 @@
+#!/usr/bin/env bats
+
+# Tests for user file handling utilities in lib/core/base.sh
+# Covers: ensure_user_dir, ensure_user_file, get_invoking_user, etc.
+
+setup_file() {
+    PROJECT_ROOT="$(cd "${BATS_TEST_DIRNAME}/.." && pwd)"
+    export PROJECT_ROOT
+
+    ORIGINAL_HOME="${HOME:-}"
+    export ORIGINAL_HOME
+
+    HOME="$(mktemp -d "${BATS_TEST_DIRNAME}/tmp-userfile.XXXXXX")"
+    export HOME
+
+    mkdir -p "$HOME"
+}
+
+teardown_file() {
+    rm -rf "$HOME"
+    if [[ -n "${ORIGINAL_HOME:-}" ]]; then
+        export HOME="$ORIGINAL_HOME"
+    fi
+}
+
+setup() {
+    rm -rf "$HOME/.config" "$HOME/.cache"
+    mkdir -p "$HOME"
+}
+
+# ============================================================================
+# Darwin Version Detection Tests
+# ============================================================================
+
+@test "get_darwin_major returns numeric version on macOS" {
+    result=$(bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; get_darwin_major")
+    # Should be a number (e.g., 23, 24, etc.)
+    [[ "$result" =~ ^[0-9]+$ ]]
+}
+
+@test "get_darwin_major returns 999 on failure (mock uname failure)" {
+    # Mock uname to fail and verify fallback behavior
+    result=$(bash -c "
+        uname() { return 1; }
+        export -f uname
+        source '$PROJECT_ROOT/lib/core/base.sh'
+        get_darwin_major
+    ")
+    [ "$result" = "999" ]
+}
+
+@test "is_darwin_ge correctly compares versions" {
+    # Should return true for minimum <= current
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; is_darwin_ge 1"
+    [ $? -eq 0 ]
+
+    # Should return false for very high version requirement (unless on futuristic macOS)
+    # Note: With our 999 fallback, this will actually succeed on error, which is correct behavior
+    result=$(bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; is_darwin_ge 100 && echo 'yes' || echo 'no'")
+    # Just verify command runs without error
+    [[ -n "$result" ]]
+}
+
+# ============================================================================
+# User Context Detection Tests
+# ============================================================================
+
+@test "is_root_user detects non-root correctly" {
+    result=$(bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; is_root_user && echo 'root' || echo 'not-root'")
+    [ "$result" = "not-root" ]
+}
+
+@test "get_invoking_user returns current user when not sudo" {
+    result=$(bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; get_invoking_user")
+    [ -n "$result" ]
+    # Should be current user
+    [ "$result" = "${USER:-$(whoami)}" ]
+}
+
+@test "get_invoking_uid returns numeric UID" {
+    result=$(bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; get_invoking_uid")
+    [[ "$result" =~ ^[0-9]+$ ]]
+}
+
+@test "get_invoking_gid returns numeric GID" {
+    result=$(bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; get_invoking_gid")
+    [[ "$result" =~ ^[0-9]+$ ]]
+}
+
+@test "get_invoking_home returns home directory" {
+    result=$(bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; get_invoking_home")
+    [ -n "$result" ]
+    [ -d "$result" ]
+}
+
+@test "get_user_home returns home for valid user" {
+    current_user="${USER:-$(whoami)}"
+    result=$(bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; get_user_home '$current_user'")
+    [ -n "$result" ]
+    [ -d "$result" ]
+}
+
+@test "get_user_home returns empty for invalid user" {
+    result=$(bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; get_user_home 'nonexistent_user_12345'")
+    [ -z "$result" ] || [ "$result" = "~nonexistent_user_12345" ]
+}
+
+# ============================================================================
+# Directory Creation Tests
+# ============================================================================
+
+@test "ensure_user_dir creates simple directory" {
+    test_dir="$HOME/.cache/test"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_dir '$test_dir'"
+    [ -d "$test_dir" ]
+}
+
+@test "ensure_user_dir creates nested directory" {
+    test_dir="$HOME/.config/mole/deep/nested/path"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_dir '$test_dir'"
+    [ -d "$test_dir" ]
+}
+
+@test "ensure_user_dir handles tilde expansion" {
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_dir '~/.cache/tilde-test'"
+    [ -d "$HOME/.cache/tilde-test" ]
+}
+
+@test "ensure_user_dir is idempotent" {
+    test_dir="$HOME/.cache/idempotent"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_dir '$test_dir'"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_dir '$test_dir'"
+    [ -d "$test_dir" ]
+}
+
+@test "ensure_user_dir handles empty path gracefully" {
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_dir ''"
+    [ $? -eq 0 ]
+}
+
+@test "ensure_user_dir preserves ownership for non-root users" {
+    test_dir="$HOME/.cache/ownership-test"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_dir '$test_dir'"
+
+    current_uid=$(id -u)
+    dir_uid=$(/usr/bin/stat -f%u "$test_dir")
+    [ "$dir_uid" = "$current_uid" ]
+}
+
+# ============================================================================
+# File Creation Tests
+# ============================================================================
+
+@test "ensure_user_file creates file and parent directories" {
+    test_file="$HOME/.config/mole/test.log"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_file '$test_file'"
+    [ -f "$test_file" ]
+    [ -d "$(dirname "$test_file")" ]
+}
+
+@test "ensure_user_file handles tilde expansion" {
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_file '~/.cache/tilde-file.txt'"
+    [ -f "$HOME/.cache/tilde-file.txt" ]
+}
+
+@test "ensure_user_file is idempotent" {
+    test_file="$HOME/.cache/idempotent.txt"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_file '$test_file'"
+    echo "content" > "$test_file"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_file '$test_file'"
+    # Should preserve existing content
+    [ -f "$test_file" ]
+    [ "$(cat "$test_file")" = "content" ]
+}
+
+@test "ensure_user_file handles empty path gracefully" {
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_file ''"
+    [ $? -eq 0 ]
+}
+
+@test "ensure_user_file creates deeply nested files" {
+    test_file="$HOME/.config/deep/very/nested/structure/file.log"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_file '$test_file'"
+    [ -f "$test_file" ]
+}
+
+@test "ensure_user_file preserves ownership for non-root users" {
+    test_file="$HOME/.cache/file-ownership-test.txt"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_file '$test_file'"
+
+    current_uid=$(id -u)
+    file_uid=$(/usr/bin/stat -f%u "$test_file")
+    [ "$file_uid" = "$current_uid" ]
+}
+
+# ============================================================================
+# Performance Tests (Early Stop Optimization)
+# ============================================================================
+
+@test "ensure_user_dir early stop optimization works" {
+    # Create a nested structure
+    test_dir="$HOME/.cache/perf/test/nested"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_dir '$test_dir'"
+
+    # Call again - should detect correct ownership and stop early
+    # This is a behavioral test; we verify it doesn't fail
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_dir '$test_dir'"
+    [ -d "$test_dir" ]
+
+    # Verify ownership is still correct
+    current_uid=$(id -u)
+    dir_uid=$(/usr/bin/stat -f%u "$test_dir")
+    [ "$dir_uid" = "$current_uid" ]
+}
+
+# ============================================================================
+# Integration Tests
+# ============================================================================
+
+@test "ensure_user_dir and ensure_user_file work together" {
+    cache_dir="$HOME/.cache/mole"
+    cache_file="$cache_dir/integration_test.log"
+
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_dir '$cache_dir'"
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'; ensure_user_file '$cache_file'"
+
+    [ -d "$cache_dir" ]
+    [ -f "$cache_file" ]
+}
+
+@test "multiple ensure_user_file calls in same directory" {
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'
+        ensure_user_file '$HOME/.config/mole/file1.txt'
+        ensure_user_file '$HOME/.config/mole/file2.txt'
+        ensure_user_file '$HOME/.config/mole/file3.txt'
+    "
+
+    [ -f "$HOME/.config/mole/file1.txt" ]
+    [ -f "$HOME/.config/mole/file2.txt" ]
+    [ -f "$HOME/.config/mole/file3.txt" ]
+}
+
+@test "ensure functions handle concurrent calls safely" {
+    # Simulate concurrent directory creation
+    bash -c "source '$PROJECT_ROOT/lib/core/base.sh'
+        ensure_user_dir '$HOME/.cache/concurrent' &
+        ensure_user_dir '$HOME/.cache/concurrent' &
+        wait
+    "
+
+    [ -d "$HOME/.cache/concurrent" ]
+}