memories: deny Snapchat-prefixed filenames from timestamp parsing

Snapchat assigns sequential IDs that happen to overlap real epoch
values, so the 10-16 digit timestamp regex matched and produced
2002-era dates for files actually saved in 2016/2021. The digits
themselves are indistinguishable from a unix timestamp, so we
dispatch on the source-app prefix instead. Case-insensitive,
extensible for future apps that exhibit the same pattern.

Reported cases:
  Snapchat-1021849065.mp4          → 2002-05-19 (actual 2021)
  Snapchat-1751031586660373917.jpg → 2002-09-09 (actual 2016)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/memories.rs

@@ -206,6 +206,20 @@ pub fn extract_date_from_filename(filename: &str) -> Option<DateTime<FixedOffset
         let timestamp_str = captures.get(1)?.as_str();
         let len = timestamp_str.len();
 
+        // Known apps whose filenames carry sequential IDs that happen to
+        // overlap real epoch values (e.g. `Snapchat-1021849065.mp4` parses
+        // as 2002-05-19, but the file was actually saved in 2021). The
+        // digits alone are indistinguishable from a unix timestamp, so we
+        // dispatch on the source-app prefix instead.
+        const NON_TIMESTAMP_PREFIXES: &[&str] = &["snapchat-"];
+        let lower = filename.to_ascii_lowercase();
+        if NON_TIMESTAMP_PREFIXES
+            .iter()
+            .any(|p| lower.starts_with(p))
+        {
+            return None;
+        }
+
         // Skip autogenerated filenames that start with "10000" (e.g., 1000004178.jpg)
         // These are not timestamps but auto-generated file IDs
         if timestamp_str.starts_with("10000") {
@@ -640,6 +654,22 @@ mod tests {
         assert!(extract_date_from_filename("IMG_21323906751390.jpeg").is_none());
     }
 
+    #[test]
+    fn test_extract_date_from_filename_snapchat_should_not_match() {
+        // Snapchat-prefixed filenames carry sequential app-assigned IDs
+        // that happen to fall inside plausible epoch ranges. The two
+        // reported cases:
+        //   Snapchat-1021849065.mp4         → 10 digits → 2002-05-19
+        //   Snapchat-1751031586660373917.jpg → 19 digits → 2002-09-09
+        // Real save dates are 2021 and 2016 respectively per
+        // FileModifyDate; the prefix denylist forces a fall-through to
+        // fs_time.
+        assert!(extract_date_from_filename("Snapchat-1021849065.mp4").is_none());
+        assert!(extract_date_from_filename("Snapchat-1751031586660373917.jpg").is_none());
+        // Case-insensitive match — lowercase variant should also reject.
+        assert!(extract_date_from_filename("snapchat-1021849065.mp4").is_none());
+    }
+
     // The obsolete `test_memory_date_priority_*` tests covered the old
     // request-time waterfall in `get_memory_date_with_priority`. Their
     // replacement lives in `crate::date_resolver::tests` (resolver