fix: sanitize TX_POOL_URL to ensure trailing slash

README.md

@@ -93,7 +93,7 @@ Key                           | Required | Description
 `ROLLUP_RPC_URL`              | Yes      | RPC endpoint for the rollup chain
 `QUINCEY_URL`                 | Yes      | Remote sequencer signing endpoint
 `SEQUENCER_KEY`               | No       | AWS Key ID _OR_ local private key for the Sequencer; set IFF using local Sequencer signing instead of remote (via `QUINCEY_URL`) Quincey signing
-`TX_POOL_URL`                 | Yes      | Transaction pool URL (must end with `/`)
+`TX_POOL_URL`                 | Yes      | Transaction pool URL
 `FLASHBOTS_ENDPOINT`          | No       | Flashbots API to submit blocks to
 `ROLLUP_BLOCK_GAS_LIMIT`      | No       | Override for rollup block gas limit
 `MAX_HOST_GAS_COEFFICIENT`    | No       | Optional maximum host gas coefficient, as a percentage, to use when building blocks

src/lib.rs

@@ -43,6 +43,16 @@ use std::sync::OnceLock;
 /// Global static configuration for the Builder binary.
 pub static CONFIG: OnceLock<config::BuilderConfig> = OnceLock::new();
 
+/// Ensures a URL has a trailing slash, which is required for correct behavior
+/// with `Url::join()`. Without a trailing slash, `join()` replaces the last
+/// path segment instead of appending to it.
+fn ensure_trailing_slash(url: &mut url::Url) {
+    let path = url.path();
+    if !path.ends_with('/') {
+        url.set_path(&format!("{}/", path));
+    }
+}
+
 /// Load the Builder configuration from the environment and store it in the
 /// global static CONFIG variable. Returns a reference to the configuration.
 ///
@@ -51,7 +61,13 @@ pub static CONFIG: OnceLock<config::BuilderConfig> = OnceLock::new();
 /// Panics if the configuration cannot be loaded from the environment AND no
 /// other configuration has been previously initialized.
 pub fn config_from_env() -> &'static config::BuilderConfig {
-    CONFIG.get_or_init(|| config::BuilderConfig::from_env().expect("Failed to load Builder config"))
+    CONFIG.get_or_init(|| {
+        let mut config =
+            config::BuilderConfig::from_env().expect("Failed to load Builder config");
+        // Sanitize tx_pool_url to ensure it ends with `/` for correct Url::join() behavior
+        ensure_trailing_slash(&mut config.tx_pool_url);
+        config
+    })
 }
 
 /// Get a reference to the global Builder configuration.