diff --git a/packages/browser/src/sdk.ts b/packages/browser/src/sdk.ts
index 06e224e64006..11a8ccf19548 100644
--- a/packages/browser/src/sdk.ts
+++ b/packages/browser/src/sdk.ts
@@ -99,6 +99,7 @@ export function init(options: BrowserOptions = {}): Client | undefined {
   /* rollup-include-development-only */
   // Resolve Spotlight configuration with proper precedence
   const envSpotlight = getSpotlightConfig();
+  // resolveSpotlightOptions is the single source of truth that ensures empty strings are never used
   const spotlightValue = resolveSpotlightOptions(options.spotlight, envSpotlight);
 
   if (spotlightValue) {
diff --git a/packages/browser/src/utils/spotlightConfig.ts b/packages/browser/src/utils/spotlightConfig.ts
index 07393e28627c..d1efedc4e4d6 100644
--- a/packages/browser/src/utils/spotlightConfig.ts
+++ b/packages/browser/src/utils/spotlightConfig.ts
@@ -50,7 +50,9 @@ export function getSpotlightConfig(): boolean | string | undefined {
       }
 
       // Not a boolean, treat as custom URL string
-      // Note: empty/whitespace strings are filtered by resolveSpotlightOptions
+      // Note: Empty/whitespace strings are intentionally returned as-is. The resolveSpotlightOptions
+      // function is the single source of truth for filtering these and ensuring empty strings are
+      // NEVER used (returns undefined instead).
       if (DEBUG_BUILD) {
         debug.log(`[Spotlight] Found ${key}=${value} (custom URL) in environment variables`);
       }
diff --git a/packages/browser/test/utils/spotlightConfig.test.ts b/packages/browser/test/utils/spotlightConfig.test.ts
index eac34ea7de1f..a540c6be8ce6 100644
--- a/packages/browser/test/utils/spotlightConfig.test.ts
+++ b/packages/browser/test/utils/spotlightConfig.test.ts
@@ -59,24 +59,24 @@ describe('getSpotlightConfig', () => {
     expect(getSpotlightConfig()).toBe(customUrl);
   });
 
-  it('returns undefined when SENTRY_SPOTLIGHT is an empty string', () => {
+  it('returns empty string when SENTRY_SPOTLIGHT is an empty string (filtered by resolveSpotlightOptions)', () => {
     globalThis.process = {
       env: {
         SENTRY_SPOTLIGHT: '',
       } as Record<string, string>,
     } as NodeJS.Process;
 
-    expect(getSpotlightConfig()).toBeUndefined();
+    expect(getSpotlightConfig()).toBe('');
   });
 
-  it('returns undefined when SENTRY_SPOTLIGHT is whitespace only', () => {
+  it('returns whitespace string when SENTRY_SPOTLIGHT is whitespace only (filtered by resolveSpotlightOptions)', () => {
     globalThis.process = {
       env: {
         SENTRY_SPOTLIGHT: '   ',
       } as Record<string, string>,
     } as NodeJS.Process;
 
-    expect(getSpotlightConfig()).toBeUndefined();
+    expect(getSpotlightConfig()).toBe('   ');
   });
 
   it('parses various truthy values correctly', () => {
diff --git a/packages/core/src/utils/resolveSpotlightOptions.ts b/packages/core/src/utils/resolveSpotlightOptions.ts
index 01322956c2c8..520b1f4d6647 100644
--- a/packages/core/src/utils/resolveSpotlightOptions.ts
+++ b/packages/core/src/utils/resolveSpotlightOptions.ts
@@ -2,9 +2,13 @@
  * Resolves the final spotlight configuration based on options and environment variables.
  * Implements the precedence rules from the Spotlight spec.
  *
+ * This is the single source of truth for filtering empty/whitespace strings - it ensures that
+ * empty strings are NEVER returned (returns undefined instead). All callers can rely on this
+ * guarantee when handling spotlight configuration.
+ *
  * @param optionsSpotlight - The spotlight option from user config (false | true | string | undefined)
  * @param envSpotlight - The spotlight value from environment variables (false | true | string | undefined)
- * @returns The resolved spotlight configuration
+ * @returns The resolved spotlight configuration (false | true | string | undefined) - NEVER an empty string
  */
 export function resolveSpotlightOptions(
   optionsSpotlight: boolean | string | undefined,
diff --git a/packages/core/test/utils/resolveSpotlightOptions.test.ts b/packages/core/test/utils/resolveSpotlightOptions.test.ts
index 4232ffe2e989..27b1a61dddd5 100644
--- a/packages/core/test/utils/resolveSpotlightOptions.test.ts
+++ b/packages/core/test/utils/resolveSpotlightOptions.test.ts
@@ -55,36 +55,66 @@ describe('resolveSpotlightOptions', () => {
     expect(resolveSpotlightOptions(undefined, envUrl)).toBe(envUrl);
   });
 
-  describe('empty string handling', () => {
-    it('returns undefined when options.spotlight is an empty string', () => {
+  describe('empty string handling - NEVER returns empty strings', () => {
+    it('returns undefined (never empty string) when options.spotlight is an empty string', () => {
       expect(resolveSpotlightOptions('', undefined)).toBeUndefined();
       expect(resolveSpotlightOptions('', true)).toBeUndefined();
       expect(resolveSpotlightOptions('', 'http://env:8969')).toBeUndefined();
     });
 
-    it('returns undefined when options.spotlight is whitespace only', () => {
+    it('returns undefined (never empty string) when options.spotlight is whitespace only', () => {
       expect(resolveSpotlightOptions('   ', undefined)).toBeUndefined();
       expect(resolveSpotlightOptions('\t\n', true)).toBeUndefined();
     });
 
-    it('returns undefined when env is an empty string and options.spotlight is undefined', () => {
+    it('returns undefined (never empty string) when env is an empty string and options.spotlight is undefined', () => {
       expect(resolveSpotlightOptions(undefined, '')).toBeUndefined();
     });
 
-    it('returns undefined when env is whitespace only and options.spotlight is undefined', () => {
+    it('returns undefined (never empty string) when env is whitespace only and options.spotlight is undefined', () => {
       expect(resolveSpotlightOptions(undefined, '   ')).toBeUndefined();
       expect(resolveSpotlightOptions(undefined, '\t\n')).toBeUndefined();
     });
 
-    it('returns true when options.spotlight is true and env is empty string', () => {
+    it('returns true when options.spotlight is true and env is empty string (filters out empty env)', () => {
       expect(resolveSpotlightOptions(true, '')).toBe(true);
       expect(resolveSpotlightOptions(true, '   ')).toBe(true);
     });
 
-    it('returns valid URL when options.spotlight is valid URL even if env is empty', () => {
+    it('returns valid URL when options.spotlight is valid URL even if env is empty (filters out empty env)', () => {
       const validUrl = 'http://localhost:8969/stream';
       expect(resolveSpotlightOptions(validUrl, '')).toBe(validUrl);
       expect(resolveSpotlightOptions(validUrl, '   ')).toBe(validUrl);
     });
+
+    it('NEVER returns empty string - comprehensive check of all combinations', () => {
+      // Test all possible combinations to ensure empty strings are never returned
+      const emptyValues = ['', '   ', '\t\n', '  \t  \n  '];
+      const nonEmptyValues = [false, true, undefined, 'http://localhost:8969'];
+
+      // Empty options.spotlight with any env
+      for (const emptyOption of emptyValues) {
+        for (const env of [...emptyValues, ...nonEmptyValues]) {
+          const result = resolveSpotlightOptions(emptyOption, env);
+          expect(result).not.toBe('');
+          // Only test regex on strings
+          if (typeof result === 'string') {
+            expect(result).not.toMatch(/^\s+$/);
+          }
+        }
+      }
+
+      // Any options.spotlight with empty env
+      for (const option of [...emptyValues, ...nonEmptyValues]) {
+        for (const emptyEnv of emptyValues) {
+          const result = resolveSpotlightOptions(option, emptyEnv);
+          expect(result).not.toBe('');
+          // Only test regex on strings
+          if (typeof result === 'string') {
+            expect(result).not.toMatch(/^\s+$/);
+          }
+        }
+      }
+    });
   });
 });
diff --git a/packages/node-core/src/sdk/index.ts b/packages/node-core/src/sdk/index.ts
index 18df85c58e34..f8010e09b5c6 100644
--- a/packages/node-core/src/sdk/index.ts
+++ b/packages/node-core/src/sdk/index.ts
@@ -187,7 +187,8 @@ function getClientOptions(
   // Parse spotlight configuration with proper precedence per spec
   const envBool = envToBool(process.env.SENTRY_SPOTLIGHT, { strict: true });
   const envSpotlight = envBool !== null ? envBool : process.env.SENTRY_SPOTLIGHT;
-  // Note: resolveSpotlightOptions handles empty/whitespace string filtering
+  // Note: resolveSpotlightOptions is the single source of truth for filtering empty/whitespace strings
+  // and ensures that empty strings are NEVER returned (returns undefined instead)
   const spotlight = resolveSpotlightOptions(options.spotlight, envSpotlight);
 
   const tracesSampleRate = getTracesSampleRate(options.tracesSampleRate);
diff --git a/packages/replay-canvas/core b/packages/replay-canvas/core
new file mode 100644
index 000000000000..c0595c9682e7
Binary files /dev/null and b/packages/replay-canvas/core differ