fix: close Chromium tabs on crawler fetch error paths

new_page() opened a tab that was only closed on the happy path; a `?` on
wait_for_nav / content() leaked it (chromiumoxide doesn't close on drop),
so errored fetches accumulated tabs in the shared browser. Add a generic,
unit-tested `close_after(close, body)` helper and wrap the three fetch
sites (chapter content, session probe, source navigate) so the tab is
closed on every exit path — including navigate's content()-read branch,
which previously leaked.

Bump to 0.124.5.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/crawler/nav.rs

@@ -85,6 +85,28 @@ pub async fn wait_for_selector(
 /// under a second.
 pub const SELECTOR_TIMEOUT: Duration = Duration::from_secs(10);
 
+/// Run `body` to completion, then run `close` — on *every* exit path,
+/// including an early `?` / `return` inside `body`. chromiumoxide's `Page`
+/// does **not** close its CDP target on drop, so a fetch helper that opens a
+/// page with `browser.new_page(...)` and then bails via `?` on a nav /
+/// content-read error would leak a browser tab for the process's lifetime.
+/// Wrapping the fallible work in `close_after` — with `close` built from a
+/// clone of the page — guarantees the tab is closed regardless of how `body`
+/// returns.
+///
+/// Both arguments are pre-built futures, so this stays generic over the
+/// body's return type (the anyhow and `PageError` fetch paths both use it)
+/// and references no browser types — which also lets it be unit-tested
+/// without standing up a real `Page`.
+pub(crate) async fn close_after<R>(
+    close: impl std::future::Future<Output = ()>,
+    body: impl std::future::Future<Output = R>,
+) -> R {
+    let result = body.await;
+    close.await;
+    result
+}
+
 impl NavError {
     /// Does this navigation error indicate the underlying Chromium
     /// process has died or its CDP connection has dropped? Used by the
@@ -150,6 +172,41 @@ mod tests {
         assert!(result.is_err(), "expected Elapsed on a hung future");
     }
 
+    #[tokio::test]
+    async fn close_after_runs_close_and_returns_value_on_ok() {
+        use std::sync::atomic::{AtomicBool, Ordering};
+        use std::sync::Arc;
+        let closed = Arc::new(AtomicBool::new(false));
+        let c = closed.clone();
+        let out: anyhow::Result<i32> = close_after(
+            async move { c.store(true, Ordering::SeqCst) },
+            async { Ok(7) },
+        )
+        .await;
+        assert_eq!(out.unwrap(), 7);
+        assert!(closed.load(Ordering::SeqCst), "close must run on the happy path");
+    }
+
+    #[tokio::test]
+    async fn close_after_runs_close_even_when_body_errs() {
+        use std::sync::atomic::{AtomicBool, Ordering};
+        use std::sync::Arc;
+        let closed = Arc::new(AtomicBool::new(false));
+        let c = closed.clone();
+        // This is the leak the fix targets: the body bails before it could
+        // close the page itself, and `close_after` must still close it.
+        let out: anyhow::Result<()> =
+            close_after(async move { c.store(true, Ordering::SeqCst) }, async {
+                anyhow::bail!("nav failed")
+            })
+            .await;
+        assert!(out.is_err());
+        assert!(
+            closed.load(Ordering::SeqCst),
+            "the page must be closed even when the body returns Err"
+        );
+    }
+
     #[test]
     fn nav_error_timeout_message_includes_duration() {
         let e = NavError::Timeout(Duration::from_secs(30));