diff --git a/lib/validations.test.ts b/lib/validations.test.ts
index 1aa1b4e90..8d406b166 100644
--- a/lib/validations.test.ts
+++ b/lib/validations.test.ts
@@ -26,6 +26,7 @@ describe('streakParamsSchema — grace fallback behavior', () => {
     expect(parse({}).grace).toBe(1);
   });
 });
+
 describe('githubParamsSchema', () => {
   it('should pass when username is valid', () => {
     const result = githubParamsSchema.safeParse({
@@ -76,6 +77,7 @@ describe('githubParamsSchema', () => {
     }
   });
 });
+
 describe('streakParamsSchema user validation', () => {
   it('should pass when user is valid', () => {
     const result = streakParamsSchema.safeParse({
@@ -295,6 +297,7 @@ describe('streakParamsSchema', () => {
       expect(result.error.issues[0]?.message).toBe('Invalid GitHub username');
     }
   });
+
   it('should accept delta_format percent', () => {
     const result = streakParamsSchema.safeParse({
       user: 'octocat',
@@ -450,6 +453,7 @@ describe('streakParamsSchema — size fallback behavior', () => {
   it('falls back to "medium" for empty string', () => {
     expect(parse({ size: '' }).size).toBe('medium');
   });
+
   it('should accept org parameter when provided', () => {
     const result = streakParamsSchema.safeParse({
       user: 'octocat',
@@ -737,16 +741,23 @@ describe('streakParamsSchema — accent parameter HEX color validation', () => {
   });
 });
 
+/* ==========================================================================
+ * DATE RANGE BOUNDARY ROBUSTNESS (VARIATION 1)
+ * ========================================================================== */
+
 describe('streakParamsSchema — Date Range Boundary Robustness (Variation 1)', () => {
   it('should process validation safely and fallback when partial or missing year parameters are passed', () => {
+    // Arrange: Provide a mock payload missing a full YYYY format sequence
     const partialYearPayload = {
       user: 'octocat',
       from: '05-12',
       to: '05-30',
     };
 
+    // Act: Pass the object through the validator schema matrix
     const result = streakParamsSchema.safeParse(partialYearPayload);
 
+    // Assert: The validator handles it safely using implicit date engine fallbacks
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.data.from).toBeDefined();
@@ -755,12 +766,15 @@ describe('streakParamsSchema — Date Range Boundary Robustness (Variation 1)',
   });
 
   it('should pass cleanly and fallback to default ranges when date bounds are completely omitted', () => {
+    // Arrange: Pass only the bare minimum required parameters
     const minimalPayload = {
       user: 'octocat',
     };
 
+    // Act
     const result = streakParamsSchema.safeParse(minimalPayload);
 
+    // Assert: Verify that omitted range options return undefined to use downstream defaults smoothly
     expect(result.success).toBe(true);
     if (result.success) {
       expect(result.data.from).toBeUndefined();
diff --git a/utils/time.test.ts b/utils/time.test.ts
index 14e9bfb99..6505c7410 100644
--- a/utils/time.test.ts
+++ b/utils/time.test.ts
@@ -221,6 +221,38 @@ describe('getSecondsUntilMidnightInTimezone', () => {
     expect(secondsUTC).toBe(86400);
     expect(secondsLondon).toBe(86400);
   });
+
+  it('should handle extreme negative timezone offset boundary (-12:00)', () => {
+    // Arrange: Etc/GMT+12 is UTC-12 (Baker Island / Howland Island).
+    // When UTC is Jan 1, 11:59:50, Baker Island is Dec 31, 23:59:50 (10 seconds to midnight)
+    const boundaryTime = new Date(Date.UTC(2024, 0, 1, 11, 59, 50));
+    vi.setSystemTime(boundaryTime);
+
+    // Act
+    const seconds = getSecondsUntilMidnightInTimezone('Etc/GMT+12');
+
+    // Assert: Should correctly calculate 10 seconds without calendar shifting
+    expect(seconds).toBe(10);
+  });
+
+  it('should handle extreme timezone offsets without calendar date shifting', () => {
+    // Arrange: Test the most extreme offsets to ensure no calendar date shifting occurs
+    const extremeOffsets = [
+      { tz: 'Etc/GMT+12', offset: -12, utcHour: 12, expectedLocalHour: 0 }, // UTC-12
+      { tz: 'Etc/GMT-14', offset: 14, utcHour: 10, expectedLocalHour: 0 }, // UTC+14
+    ];
+
+    for (const { tz, utcHour, expectedLocalHour } of extremeOffsets) {
+      // Set UTC time such that local time is exactly midnight
+      vi.setSystemTime(new Date(Date.UTC(2024, 6, 15, utcHour, 0, 0)));
+
+      // Act: Get seconds until midnight in this timezone
+      const seconds = getSecondsUntilMidnightInTimezone(tz);
+
+      // Assert: At local midnight, should return exactly 86400 seconds (full day)
+      expect(seconds).toBe(86400);
+    }
+  });
 });
 
 describe('getSecondsUntilUTCMidnight — sliding window boundary robustness', () => {