feat(js): Temporarily sample failing lookups with debug ids (#1607)

This captures 1 in 10_000 cases of a source or sourcemap lookup
failing even though a debug id is available as a Sentry error.
This is to gain some insight into how that can happen.

crates/symbolicator-js/Cargo.toml

@@ -12,6 +12,7 @@ futures = "0.3.12"
 humantime = "2.1.0"
 moka = { version = "0.12.8", features = ["future", "sync"] }
 once_cell = "1.17.1"
+rand = "0.9.0"
 regex = "1.5.5"
 reqwest = { workspace = true, features = [
     "gzip",

crates/symbolicator-js/src/lookup.rs

@@ -561,13 +561,28 @@ impl ArtifactFetcher {
         Option<CachedFileEntry<OwnedSourceMapCache>>,
     ) {
         // First, check if we have already cached / created the `SourceMapCache`.
-        let key = FileKey::MinifiedSource { abs_path, debug_id };
+        let key = FileKey::MinifiedSource {
+            abs_path: abs_path.clone(),
+            debug_id,
+        };
 
         // Fetch the minified file first
         let minified_source = self.get_file(&key).await;
         if minified_source.entry.is_err() {
             self.metrics
                 .record_not_found(SourceFileType::Source, debug_id.is_some());
+
+            // Temporarily sample cases of a file not being found even though it has a debug id.
+            if let Some(debug_id) = debug_id {
+                if rand::random::<f64>() < 0.0001 {
+                    tracing::error!(
+                        source_url = %self.source.url,
+                        abs_path,
+                        %debug_id,
+                        "Failed to fetch source with debug id"
+                    );
+                }
+            }
         }
 
         // Then fetch the corresponding sourcemap reference and debug_id
@@ -622,6 +637,18 @@ impl ArtifactFetcher {
         } else if sourcemap.entry.is_err() {
             self.metrics
                 .record_not_found(SourceFileType::SourceMap, debug_id.is_some());
+
+            // Temporarily sample cases of a file not being found even though it has a debug id.
+            if let Some(debug_id) = debug_id {
+                if rand::random::<f64>() < 0.0001 {
+                    tracing::error!(
+                        source_url = %self.source.url,
+                        abs_path,
+                        %debug_id,
+                        "Failed to fetch sourcemap with debug id"
+                    );
+                }
+            }
         }
 
         // Now that we (may) have both files, we can create a `SourceMapCache` for it