feat(crawler): recircuit TOR on transient pages and unauthenticated probes

- target.rs swaps retry_on_transient → retry_on_transient_with_hook,
  signaling NEWNYM via ctx.tor between attempts when configured.
- session.rs gains verify_session_with_recircuit; the bare
  verify_session is now a one-line wrapper passing tor=None,
  unauth_max_recircuit=0. The inner run_session_probe_loop is
  pure-over-IO and unit-tested with closure-based fakes.
- content.rs extracts fetch_chapter_html_once + the closure-driven
  fetch_chapter_html_with_recircuit, used by sync_chapter_content to
  retry on Transient or Unauthenticated up to a recircuit_budget.
  Budget = 0 (no TOR) preserves original behavior bit-for-bit.
- app.rs and bin/crawler.rs construct the controller before on_launch
  and pass it into verify_session_with_recircuit, so a transient
  hiccup at startup no longer requires PHPSESSID rotation.

Recircuit budget defaults to CRAWLER_TOR_RECIRCUIT_MAX_ATTEMPTS (3).
Errors from NEWNYM are logged and swallowed — failing to recircuit
should not take down the crawl.

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

backend/src/crawler/source/target.rs

@@ -18,7 +18,7 @@ use super::{
     SourceMangaRef,
 };
 use crate::crawler::detect::{
-    has_logo_sentinel, is_broken_page_body, retry_on_transient, PageError,
+    has_logo_sentinel, is_broken_page_body, retry_on_transient_with_hook, PageError,
 };
 use crate::crawler::nav::{wait_for_nav, wait_for_selector, NavError, SELECTOR_TIMEOUT};
 
@@ -79,12 +79,13 @@ impl Source for TargetSource {
         // and the HTML is handed straight to the first `next_batch` call
         // so the walker doesn't re-fetch it. Page count is discovered
         // incrementally — see `TargetSourceWalker::next_batch`.
-        let first_html = retry_on_transient(
+        let first_html = retry_on_transient_with_hook(
             || async {
                 navigate(ctx, self.base_url.as_str(), LIST_PAGE_MARKER).await
             },
             PAGE_TRANSIENT_RETRY_ATTEMPTS,
             PAGE_TRANSIENT_RETRY_DELAY,
+            || async { recircuit_if_configured(ctx.tor).await },
         )
         .await?;
 
@@ -169,7 +170,7 @@ impl DiscoverWalk for TargetSourceWalker {
                     parse_manga_list_from(&doc)?
                 }
                 None => {
-                    retry_on_transient(
+                    retry_on_transient_with_hook(
                         || async {
                             let html = navigate(
                                 ctx,
@@ -182,12 +183,13 @@ impl DiscoverWalk for TargetSourceWalker {
                         },
                         PAGE_TRANSIENT_RETRY_ATTEMPTS,
                         PAGE_TRANSIENT_RETRY_DELAY,
+                        || async { recircuit_if_configured(ctx.tor).await },
                     )
                     .await?
                 }
             }
         } else {
-            retry_on_transient(
+            retry_on_transient_with_hook(
                 || async {
                     let url = page_url(&self.base_url, page_num);
                     let html = navigate(ctx, &url, LIST_PAGE_MARKER).await?;
@@ -196,6 +198,7 @@ impl DiscoverWalk for TargetSourceWalker {
                 },
                 PAGE_TRANSIENT_RETRY_ATTEMPTS,
                 PAGE_TRANSIENT_RETRY_DELAY,
+                || async { recircuit_if_configured(ctx.tor).await },
             )
             .await?
         };
@@ -274,6 +277,20 @@ fn classify_navigate_html(html: String) -> Result<String, PageError> {
     Ok(html)
 }
 
+/// Hook for [`retry_on_transient_with_hook`]: when TOR is configured,
+/// signal `NEWNYM` so the next navigation draws a fresh exit. Errors
+/// from the controller are logged and swallowed — failing to recircuit
+/// shouldn't take down the crawl, the next attempt just runs on the
+/// same circuit as before.
+async fn recircuit_if_configured(tor: Option<&crate::crawler::tor::TorController>) {
+    if let Some(t) = tor {
+        if let Err(e) = t.new_identity().await {
+            tracing::warn!(error = %e, "TOR NEWNYM failed; retrying on same circuit");
+        }
+    }
+}
+
+
 /// Substitutes the first `/N/` path segment with the target page
 /// number. Source impls that paginate via a different URL shape can
 /// override this — for the modeled site the segment is always present.