fix(crawler): redact TorAuth::Password in Debug, drop NEWNYM info→debug

The startup log line in app.rs and bin/crawler.rs `?t`-debug-formats
the TorController, which through the derived Debug on TorAuth would
expand TorAuth::Password(p) and leak the plaintext password to logs.
Implement Debug manually on TorAuth — None / Password(<redacted>) /
Cookie(<path>) — and lock the redaction with a regression test.

Drop the per-NEWNYM success log from info to debug: a busy crawl
rotates circuits many times per minute. Failed NEWNYMs already log
at warn — those stay loud.

Tightens the closed_connection_mid_reply_is_an_error assertion which
was tautological (`closed connection` OR `AUTHENTICATE`) by driving
the mock to read the AUTH line then drop, exercising only the
EOF-mid-reply path.

Audit ref: #7, #9, nit on tautological test.

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

backend/src/crawler/tor.rs

@@ -44,13 +44,28 @@ const READ_TIMEOUT: Duration = Duration::from_secs(5);
 /// reachable (different gid, no shared volume, etc.). `None` matches a
 /// torrc with no `CookieAuthentication 1` and no `HashedControlPassword`
 /// — useful for local experimentation, not for production.
-#[derive(Debug, Clone)]
+///
+/// `Debug` is implemented manually to redact the password (and the
+/// cookie path, which is non-sensitive but uninteresting in logs).
+/// Don't add `#[derive(Debug)]` — the controller is `?`-logged at
+/// startup and a derive would expand the password into the trace.
+#[derive(Clone)]
 pub enum TorAuth {
     None,
     Password(String),
     Cookie(PathBuf),
 }
 
+impl std::fmt::Debug for TorAuth {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            TorAuth::None => f.write_str("None"),
+            TorAuth::Password(_) => f.write_str("Password(<redacted>)"),
+            TorAuth::Cookie(_) => f.write_str("Cookie(<path>)"),
+        }
+    }
+}
+
 #[derive(Debug, Clone)]
 pub struct TorController {
     /// `host:port` string. Kept as a string (not a `SocketAddr`) so
@@ -114,7 +129,9 @@ impl TorController {
         // QUIT is courtesy; ignore errors — the daemon may close the
         // socket before our QUIT lands and that's perfectly fine.
         let _ = write_line(&mut write, "QUIT").await;
-        tracing::info!(addr = %self.addr, "TOR NEWNYM signaled");
+        // Debug-level: a busy crawl can rotate circuits many times per
+        // minute, INFO is too chatty. Failures still log at WARN.
+        tracing::debug!(addr = %self.addr, "TOR NEWNYM signaled");
         Ok(())
     }
 
@@ -313,19 +330,27 @@ mod tests {
 
     #[tokio::test]
     async fn closed_connection_mid_reply_is_an_error() {
-        // Listener accepts and immediately drops without replying.
+        // Listener accepts the AUTH line then drops without replying —
+        // this exercises the EOF-mid-reply path in expect_250 (rather
+        // than tor's own error replies which are covered elsewhere).
         let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
         let addr = listener.local_addr().unwrap().to_string();
         tokio::spawn(async move {
-            let _ = listener.accept().await;
+            if let Ok((sock, _)) = listener.accept().await {
-            // Drop the accepted socket immediately.
+                let (r, _w) = sock.into_split();
+                let mut r = BufReader::new(r);
+                let mut line = String::new();
+                let _ = r.read_line(&mut line).await; // read AUTH, ignore
+                // Drop _w (and the read half via scope exit) so the
+                // peer sees an immediate EOF on the next read.
+            }
         });
         let controller = TorController::new(addr, TorAuth::None);
         let err = controller.new_identity().await.expect_err("should fail");
         let msg = format!("{err:#}");
         assert!(
-            msg.contains("closed connection") || msg.contains("AUTHENTICATE"),
+            msg.contains("closed connection"),
-            "expected close-or-AUTH error, got: {msg}"
+            "expected EOF-mid-reply error, got: {msg}"
         );
     }
 
@@ -395,6 +420,25 @@ mod tests {
         assert_eq!(escape_quoted(r#"a"b\c"#), r#"a\"b\\c"#);
     }
 
+    #[test]
+    fn debug_format_redacts_password_and_cookie_path() {
+        // Regression: app.rs / bin/crawler.rs log the controller at
+        // startup via `tracing::info!(?t, ...)`. A derived Debug on
+        // TorAuth would expand TorAuth::Password(p) and leak the
+        // plaintext into logs.
+        let c = TorController::new("tor:9051", TorAuth::Password("super-secret".into()));
+        let dbg = format!("{c:?}");
+        assert!(!dbg.contains("super-secret"), "password leaked: {dbg}");
+        assert!(dbg.contains("<redacted>"), "expected <redacted>, got: {dbg}");
+
+        let c = TorController::new(
+            "tor:9051",
+            TorAuth::Cookie("/var/lib/tor/control_auth_cookie".into()),
+        );
+        let dbg = format!("{c:?}");
+        assert!(!dbg.contains("control_auth_cookie"), "cookie path leaked: {dbg}");
+    }
+
     #[test]
     fn hex_encode_zero_pads_low_bytes() {
         assert_eq!(hex_encode(&[0x00, 0x0f, 0xff]), "000fff");