From f5dc97b131446d3448f0aeb1bb8ef86916ce735c Mon Sep 17 00:00:00 2001
From: "Jim Zhang @ wonderhoi" <dqzhw@126.com>
Date: Thu, 16 Jul 2026 18:43:13 +0800
Subject: [PATCH] fix(net): scope passive callbacks to the registering page
 (#414)

The on_request/on_response Vec lived on the ObscuraHttpClient shared by
every page in the context, so a callback registered on one page fired for
all pages (#408 cross-page bleed) and outlived its page.

Callbacks now live in a per-page CallbackRegistry (Arc shared with the
page's JS runtime state). Page-driven fetch paths (navigation, POST,
scripts, stylesheets, robots.txt, module loads, JS fetch/XHR in both
plain and stealth modes) pass the registry through; the HTTP client
itself is callback-free.

Adds callbacks_do_not_bleed_across_pages: page A's callback stays silent
for page B's requests and stops firing after page A is dropped.
---
 crates/obscura-browser/src/page.rs   |  56 +++++---
 crates/obscura-js/src/ops.rs         |  42 +++---
 crates/obscura-js/src/runtime.rs     |  13 +-
 crates/obscura-net/src/client.rs     | 186 ++++++++++++++++++---------
 crates/obscura-net/src/lib.rs        |   5 +-
 crates/obscura/src/page.rs           |   6 +-
 crates/obscura/tests/interception.rs |  47 +++++++
 docs/Use-as-a-Rust-library.md        |   2 +-
 8 files changed, 249 insertions(+), 108 deletions(-)

diff --git a/crates/obscura-browser/src/page.rs b/crates/obscura-browser/src/page.rs
index 24e278e..a7176f0 100644
--- a/crates/obscura-browser/src/page.rs
+++ b/crates/obscura-browser/src/page.rs
@@ -3,7 +3,7 @@ use std::sync::Arc;
 use base64::{engine::general_purpose::STANDARD as BASE64, Engine as _};
 use obscura_dom::{parse_html, DomTree};
 use obscura_js::runtime::ObscuraJsRuntime;
-use obscura_net::{ObscuraHttpClient, ObscuraNetError, RequestCallback, Response, ResponseCallback};
+use obscura_net::{CallbackRegistry, ObscuraHttpClient, ObscuraNetError, RequestCallback, Response, ResponseCallback};
 use url::Url;
 
 use crate::context::BrowserContext;
@@ -194,6 +194,10 @@ pub struct Page {
     // contract. Includes `Runtime.addBinding` shims so puppeteer's
     // `exposeFunction` bindings exist before inline `<script>` tags execute.
     preload_scripts: Vec<String>,
+    /// Passive on_request/on_response callbacks, scoped to this page (issue
+    /// #408): they fire only for requests this page drives and die with it.
+    /// Arc because the JS runtime state holds a second handle for fetch()/XHR.
+    callbacks: Arc<CallbackRegistry>,
     #[cfg(feature = "stealth")]
     pub stealth_client: Option<Arc<StealthHttpClient>>,
 }
@@ -245,6 +249,7 @@ impl Page {
             blocked_url_patterns: Vec::new(),
             intercept_tx: None,
             preload_scripts: Vec::new(),
+            callbacks: Arc::new(CallbackRegistry::new()),
             #[cfg(feature = "stealth")]
             stealth_client,
         }
@@ -271,7 +276,9 @@ impl Page {
         if let Some(ref stealth) = self.stealth_client {
             return stealth.fetch(url).await;
         }
-        self.http_client.fetch(url).await
+        self.http_client
+            .fetch_with_callbacks(url, Some(&self.callbacks))
+            .await
     }
     fn init_js(&mut self) {
         // Drop any existing runtime so the JS realm starts clean on
@@ -333,6 +340,7 @@ impl Page {
 
         rt.set_cookie_jar(self.context.cookie_jar.clone());
         rt.set_http_client(self.http_client.clone());
+        rt.set_callbacks(self.callbacks.clone());
         rt.set_blocked_urls(self.blocked_url_patterns.clone());
         #[cfg(feature = "stealth")]
         if let Some(ref stealth) = self.stealth_client {
@@ -533,8 +541,10 @@ impl Page {
         }
 
         let client = self.http_client.clone();
+        let page_callbacks = self.callbacks.clone();
         let fetch_futures: Vec<_> = fetch_tasks.iter().map(|(idx, url)| {
             let client = client.clone();
+            let cbs = page_callbacks.clone();
             let url = url.clone();
             let idx = *idx;
             async move {
@@ -563,7 +573,7 @@ impl Page {
                     };
                     return Some((idx, url, resp));
                 }
-                match client.fetch(&parsed).await {
+                match client.fetch_with_callbacks(&parsed, Some(&cbs)).await {
                     Ok(resp) => Some((idx, url, resp)),
                     Err(e) => {
                         tracing::warn!("Failed to fetch script {}: {}", url, e);
@@ -947,7 +957,11 @@ impl Page {
                 if self.context.robots_cache.is_allowed(domain, "/robots.txt") {
                     let robots_url = format!("{}://{}/robots.txt", url.scheme(), domain);
                     if let Ok(robots_url) = Url::parse(&robots_url) {
-                        if let Ok(resp) = self.http_client.fetch(&robots_url).await {
+                        if let Ok(resp) = self
+                            .http_client
+                            .fetch_with_callbacks(&robots_url, Some(&self.callbacks))
+                            .await
+                        {
                             if resp.status == 200 {
                                 let body = String::from_utf8_lossy(&resp.body);
                                 self.context.robots_cache.parse_and_store(
@@ -1000,7 +1014,9 @@ impl Page {
             headers.insert("content-type".to_string(), content_type);
             Ok(obscura_net::Response { url: url.clone(), status: 200, headers, body: body_bytes, redirected_from: Vec::new() })
         } else if method == "POST" {
-            self.http_client.post_form(&url, body).await
+            self.http_client
+                .post_form_with_callbacks(&url, body, Some(&self.callbacks))
+                .await
         } else {
             self.do_fetch(&url).await
         }.map_err(|e| {
@@ -1086,12 +1102,14 @@ impl Page {
         }
 
         let client = self.http_client.clone();
+        let page_callbacks = self.callbacks.clone();
         let css_futures: Vec<_> = css_fetch_urls.iter().map(|full_url| {
             let client = client.clone();
+            let cbs = page_callbacks.clone();
             let url_str = full_url.clone();
             async move {
                 let parsed = Url::parse(&url_str).unwrap_or_else(|_| Url::parse("about:blank").unwrap());
-                match client.fetch(&parsed).await {
+                match client.fetch_with_callbacks(&parsed, Some(&cbs)).await {
                     Ok(resp) => Some((url_str, resp)),
                     Err(e) => {
                         tracing::debug!("Failed to fetch stylesheet {}: {}", url_str, e);
@@ -1650,34 +1668,34 @@ impl Page {
     }
 
     /// Register a passive callback fired for every JS `fetch()`/XHR (and
-    /// navigation) request, once the method/headers/body are known and before it
-    /// is sent. Non-blocking; use `enable_interception` to mutate or block.
-    /// Register a passive request observer, returning a stable id. Pass the id
-    /// to `off_request` to detach it (issue #408). Note the observer lives on
-    /// the context's shared http client, so it also sees requests from sibling
-    /// pages in the same context; detach it when the capturing phase ends.
+    /// navigation) request this page makes, once the method/headers/body are
+    /// known and before it is sent. Non-blocking; use `enable_interception` to
+    /// mutate or block. Returns a stable id; pass it to `off_request` to
+    /// detach (issue #408). Scoped to this page: it never sees sibling pages'
+    /// requests and dies with the page.
     pub fn on_request(&mut self, cb: RequestCallback) -> u64 {
-        self.http_client.register_on_request(cb)
+        self.callbacks.add_request(cb)
     }
 
     /// Register a passive callback fired with every JS `fetch()`/XHR (and
-    /// navigation) response, including its body. Non-blocking. Returns a stable
-    /// id for `off_response`. The main path for crawlers that need to capture
-    /// API response payloads. Shared across the context like `on_request`.
+    /// navigation) response this page receives, including its body.
+    /// Non-blocking. The main path for crawlers that need to capture API
+    /// response payloads. Returns a stable id for `off_response`. Page-scoped
+    /// like `on_request`.
     pub fn on_response(&mut self, cb: ResponseCallback) -> u64 {
-        self.http_client.register_on_response(cb)
+        self.callbacks.add_response(cb)
     }
 
     /// Detach a request observer registered with `on_request`. Returns true if
     /// one was removed.
     pub fn off_request(&mut self, id: u64) -> bool {
-        self.http_client.remove_on_request(id)
+        self.callbacks.remove_request(id)
     }
 
     /// Detach a response observer registered with `on_response`. Returns true if
     /// one was removed.
     pub fn off_response(&mut self, id: u64) -> bool {
-        self.http_client.remove_on_response(id)
+        self.callbacks.remove_response(id)
     }
 
     pub async fn process_pending_navigation(&mut self) -> Result<bool, PageError> {
diff --git a/crates/obscura-js/src/ops.rs b/crates/obscura-js/src/ops.rs
index b0834ae..4815d18 100644
--- a/crates/obscura-js/src/ops.rs
+++ b/crates/obscura-js/src/ops.rs
@@ -8,7 +8,7 @@ use deno_core::OpState;
 use deno_core::Extension;
 use base64::{engine::general_purpose::STANDARD as BASE64, Engine as _};
 use obscura_dom::{DomTree, NodeData, NodeId};
-use obscura_net::{CookieJar, ObscuraHttpClient, RequestInfo, ResourceType, Response};
+use obscura_net::{CallbackRegistry, CookieJar, ObscuraHttpClient, RequestInfo, ResourceType, Response};
 #[cfg(feature = "stealth")]
 use obscura_net::StealthHttpClient;
 use tokio::sync::Mutex;
@@ -75,6 +75,10 @@ pub struct ObscuraState {
     pub blocked_urls: Vec<String>,
     pub cookie_jar: Option<Arc<CookieJar>>,
     pub http_client: Option<Arc<ObscuraHttpClient>>,
+    /// The owning page's passive on_request/on_response callbacks (issue
+    /// #408). Page-scoped, so scripted fetch()/XHR observation stays local to
+    /// the page that registered it.
+    pub callbacks: Option<Arc<CallbackRegistry>>,
     /// When set (stealth mode), scripted fetch()/XHR is routed through the wreq
     /// client so the request carries the Chrome TLS fingerprint and client
     /// hints instead of the rustls ClientHello op_fetch_url would otherwise send.
@@ -111,6 +115,7 @@ impl ObscuraState {
             blocked_urls: Vec::new(),
             cookie_jar: None,
             http_client: None,
+            callbacks: None,
             #[cfg(feature = "stealth")]
             stealth_client: None,
             pending_navigation: None,
@@ -642,7 +647,7 @@ async fn op_fetch_url(
         }
     }
 
-    let (cookie_jar, in_flight, intercept_tx, proxy_url, http_client) = {
+    let (cookie_jar, in_flight, intercept_tx, proxy_url, callbacks) = {
         let state_borrow = state.borrow();
         let gs = state_borrow.borrow::<SharedState>().clone();
         let mut gs = gs.borrow_mut();
@@ -674,7 +679,7 @@ async fn op_fetch_url(
         } else {
             None
         };
-        (jar, in_flight, itx, proxy_url, gs.http_client.clone())
+        (jar, in_flight, itx, proxy_url, gs.callbacks.clone())
     };
 
     // Slots the interception channel can override via Continue so a consumer
@@ -782,9 +787,8 @@ async fn op_fetch_url(
     // reaches the network (Fulfill/Fail from the interception channel short-
     // circuit earlier). on_request/on_response previously fired only for
     // navigation; this wires them for JS fetch()/XHR too.
-    if let Some(ref hc) = http_client {
-        let cbs = hc.on_request.read().await;
-        if !cbs.is_empty() {
+    if let Some(ref cbs) = callbacks {
+        if cbs.has_request_callbacks().await {
             if let Ok(parsed) = url::Url::parse(&url) {
                 let info = RequestInfo {
                     url: parsed,
@@ -792,9 +796,7 @@ async fn op_fetch_url(
                     headers: custom_headers.clone(),
                     resource_type: ResourceType::Fetch,
                 };
-                for (_, cb) in cbs.iter() {
-                    cb(&info);
-                }
+                cbs.fire_request(&info).await;
             }
         }
     }
@@ -822,7 +824,7 @@ async fn op_fetch_url(
                 page_origin.clone(),
                 is_cross_origin,
                 mode.clone(),
-                http_client.clone(),
+                callbacks.clone(),
             )
             .await;
         }
@@ -1028,9 +1030,8 @@ async fn op_fetch_url(
         .map_err(|e| deno_error::JsErrorBox::generic(e.to_string()))?;
     let resp_body = String::from_utf8_lossy(&resp_bytes).to_string();
     let resp_body_base64 = BASE64.encode(&resp_bytes);
-    if let Some(ref hc) = http_client {
-        let cbs = hc.on_response.read().await;
-        if !cbs.is_empty() {
+    if let Some(ref cbs) = callbacks {
+        if cbs.has_response_callbacks().await {
             let resp = fetch_response(&url, status, resp_headers.clone(), resp_bytes.to_vec());
             let info = RequestInfo {
                 url: resp.url.clone(),
@@ -1038,9 +1039,7 @@ async fn op_fetch_url(
                 headers: resp_headers.clone(),
                 resource_type: ResourceType::Fetch,
             };
-            for (_, cb) in cbs.iter() {
-                cb(&info, &resp);
-            }
+            cbs.fire_response(&info, &resp).await;
         }
     }
     let response_request_id = {
@@ -1133,7 +1132,7 @@ async fn stealth_fetch_all(
     page_origin: String,
     is_cross_origin: bool,
     mode: String,
-    http_client: Option<Arc<ObscuraHttpClient>>,
+    callbacks: Option<Arc<CallbackRegistry>>,
 ) -> Result<String, deno_error::JsErrorBox> {
     let mut current_url = url.clone();
     let mut current_method = method;
@@ -1221,9 +1220,8 @@ async fn stealth_fetch_all(
 
     let resp_body = String::from_utf8_lossy(&resp_bytes).to_string();
     let resp_body_base64 = BASE64.encode(&resp_bytes);
-    if let Some(ref hc) = http_client {
-        let cbs = hc.on_response.read().await;
-        if !cbs.is_empty() {
+    if let Some(ref cbs) = callbacks {
+        if cbs.has_response_callbacks().await {
             let resp = fetch_response(&url, status, resp_headers.clone(), resp_bytes.clone());
             let info = RequestInfo {
                 url: resp.url.clone(),
@@ -1231,9 +1229,7 @@ async fn stealth_fetch_all(
                 headers: resp_headers.clone(),
                 resource_type: ResourceType::Fetch,
             };
-            for (_, cb) in cbs.iter() {
-                cb(&info, &resp);
-            }
+            cbs.fire_response(&info, &resp).await;
         }
     }
 
diff --git a/crates/obscura-js/src/runtime.rs b/crates/obscura-js/src/runtime.rs
index e558105..b1ee845 100644
--- a/crates/obscura-js/src/runtime.rs
+++ b/crates/obscura-js/src/runtime.rs
@@ -153,6 +153,12 @@ impl ObscuraJsRuntime {
         self.state.borrow_mut().http_client = Some(client);
     }
 
+    /// Install the owning page's passive on_request/on_response callback
+    /// registry so scripted fetch()/XHR observation is page-scoped (issue #408).
+    pub fn set_callbacks(&self, callbacks: std::sync::Arc<obscura_net::CallbackRegistry>) {
+        self.state.borrow_mut().callbacks = Some(callbacks);
+    }
+
     /// Install the stealth (wreq) HTTP client so scripted fetch()/XHR is routed
     /// through it in stealth mode (see op_fetch_url / stealth_fetch_all).
     #[cfg(feature = "stealth")]
@@ -631,9 +637,12 @@ impl ObscuraJsRuntime {
         // Fetch the module source. The old impl registered an empty string
         // and called it loaded, so every Vite / Next module bundle "loaded"
         // in 1ms with zero code and the SPA never mounted (issue #205).
-        let client = self.state.borrow().http_client.clone();
+        let (client, callbacks) = {
+            let st = self.state.borrow();
+            (st.http_client.clone(), st.callbacks.clone())
+        };
         let source_code = match client {
-            Some(c) => match c.fetch(&specifier).await {
+            Some(c) => match c.fetch_with_callbacks(&specifier, callbacks.as_deref()).await {
                 Ok(resp) => obscura_net::decode_non_html(&resp.body, resp.content_type()),
                 Err(e) => {
                     tracing::warn!("Module fetch failed ({}): {}", url, e);
diff --git a/crates/obscura-net/src/client.rs b/crates/obscura-net/src/client.rs
index d78f963..f259872 100644
--- a/crates/obscura-net/src/client.rs
+++ b/crates/obscura-net/src/client.rs
@@ -75,6 +75,107 @@ pub enum ResourceType {
 pub type RequestCallback = Arc<dyn Fn(&RequestInfo) + Send + Sync>;
 pub type ResponseCallback = Arc<dyn Fn(&RequestInfo, &Response) + Send + Sync>;
 
+/// Page-scoped store for the passive on_request/on_response callbacks (issue
+/// #408). Each `Page` owns one, so a callback never fires for another page's
+/// requests and dies with its page. The HTTP client itself stays
+/// callback-free; page-driven fetches pass the page's registry in. Ids keep
+/// the `u64` shape #416 established on `Page::on_request`/`on_response`.
+pub struct CallbackRegistry {
+    on_request: RwLock<Vec<(u64, RequestCallback)>>,
+    on_response: RwLock<Vec<(u64, ResponseCallback)>>,
+    id_counter: std::sync::atomic::AtomicU64,
+}
+
+impl CallbackRegistry {
+    pub fn new() -> Self {
+        CallbackRegistry {
+            on_request: RwLock::new(Vec::new()),
+            on_response: RwLock::new(Vec::new()),
+            id_counter: std::sync::atomic::AtomicU64::new(1),
+        }
+    }
+
+    fn next_id(&self) -> u64 {
+        self.id_counter
+            .fetch_add(1, std::sync::atomic::Ordering::Relaxed)
+    }
+
+    /// Register a request callback; the returned id detaches it via
+    /// `remove_request`. Sync like the pre-registry push path: registration
+    /// happens from `Page` setup where no reader holds the lock, so
+    /// `try_write` cannot fail there.
+    pub fn add_request(&self, cb: RequestCallback) -> u64 {
+        let id = self.next_id();
+        if let Ok(mut v) = self.on_request.try_write() {
+            v.push((id, cb));
+        }
+        id
+    }
+
+    /// Register a response callback; see `add_request`.
+    pub fn add_response(&self, cb: ResponseCallback) -> u64 {
+        let id = self.next_id();
+        if let Ok(mut v) = self.on_response.try_write() {
+            v.push((id, cb));
+        }
+        id
+    }
+
+    /// Detach a request callback. Returns true when the id was found and
+    /// removed, so a double detach is a visible no-op.
+    pub fn remove_request(&self, id: u64) -> bool {
+        match self.on_request.try_write() {
+            Ok(mut v) => {
+                let before = v.len();
+                v.retain(|(cid, _)| *cid != id);
+                v.len() != before
+            }
+            Err(_) => false,
+        }
+    }
+
+    /// Detach a response callback; see `remove_request`.
+    pub fn remove_response(&self, id: u64) -> bool {
+        match self.on_response.try_write() {
+            Ok(mut v) => {
+                let before = v.len();
+                v.retain(|(cid, _)| *cid != id);
+                v.len() != before
+            }
+            Err(_) => false,
+        }
+    }
+
+    /// True when at least one request callback is registered. Lets fire sites
+    /// skip building a `RequestInfo` when nobody listens.
+    pub async fn has_request_callbacks(&self) -> bool {
+        !self.on_request.read().await.is_empty()
+    }
+
+    /// True when at least one response callback is registered.
+    pub async fn has_response_callbacks(&self) -> bool {
+        !self.on_response.read().await.is_empty()
+    }
+
+    pub async fn fire_request(&self, info: &RequestInfo) {
+        for (_, cb) in self.on_request.read().await.iter() {
+            cb(info);
+        }
+    }
+
+    pub async fn fire_response(&self, info: &RequestInfo, resp: &Response) {
+        for (_, cb) in self.on_response.read().await.iter() {
+            cb(info, resp);
+        }
+    }
+}
+
+impl Default for CallbackRegistry {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /// Process-wide opt-in via env var. Older flow that issue #4 introduced. The
 /// new `--allow-private-network` CLI flag (issue #33) sets a per-client field
 /// that is OR'd with this so existing scripts and Docker setups that pin the
@@ -262,13 +363,6 @@ pub struct ObscuraHttpClient {
     pub user_agent: RwLock<String>,
     pub extra_headers: RwLock<HashMap<String, String>>,
     pub interceptor: RwLock<Option<Box<dyn RequestInterceptor + Send + Sync>>>,
-    /// Passive request/response observers, each tagged with a stable id so a
-    /// specific one can be detached via `remove_on_request`/`remove_on_response`
-    /// (issue #408). Without ids the vecs were append-only: no detach, and
-    /// re-registering across navigations piled up duplicates.
-    pub on_request: RwLock<Vec<(u64, RequestCallback)>>,
-    pub on_response: RwLock<Vec<(u64, ResponseCallback)>>,
-    callback_id_counter: std::sync::atomic::AtomicU64,
     pub timeout: Duration,
     pub in_flight: Arc<std::sync::atomic::AtomicU32>,
     pub block_trackers: bool,
@@ -345,9 +439,6 @@ impl ObscuraHttpClient {
             ),
             extra_headers: RwLock::new(HashMap::new()),
             interceptor: RwLock::new(None),
-            on_request: RwLock::new(Vec::new()),
-            on_response: RwLock::new(Vec::new()),
-            callback_id_counter: std::sync::atomic::AtomicU64::new(1),
             in_flight: Arc::new(std::sync::atomic::AtomicU32::new(0)),
             timeout: Duration::from_secs(30),
             block_trackers: false,
@@ -384,55 +475,33 @@ impl ObscuraHttpClient {
     }
 
     pub async fn fetch(&self, url: &Url) -> Result<Response, ObscuraNetError> {
-        self.fetch_with_method(Method::GET, url, None).await
+        self.fetch_with_method(Method::GET, url, None, None).await
     }
 
-    /// Register a passive request observer, returning a stable id. Pass the id
-    /// to `remove_on_request` to detach it (issue #408).
-    pub fn register_on_request(&self, cb: RequestCallback) -> u64 {
-        let id = self
-            .callback_id_counter
-            .fetch_add(1, std::sync::atomic::Ordering::Relaxed);
-        if let Ok(mut v) = self.on_request.try_write() {
-            v.push((id, cb));
-        }
-        id
-    }
-
-    /// Register a passive response observer, returning a stable id. Pass the id
-    /// to `remove_on_response` to detach it (issue #408).
-    pub fn register_on_response(&self, cb: ResponseCallback) -> u64 {
-        let id = self
-            .callback_id_counter
-            .fetch_add(1, std::sync::atomic::Ordering::Relaxed);
-        if let Ok(mut v) = self.on_response.try_write() {
-            v.push((id, cb));
-        }
-        id
-    }
-
-    /// Detach a request observer by its id. Returns true if one was removed.
-    pub fn remove_on_request(&self, id: u64) -> bool {
-        if let Ok(mut v) = self.on_request.try_write() {
-            let before = v.len();
-            v.retain(|(cid, _)| *cid != id);
-            return v.len() != before;
-        }
-        false
-    }
-
-    /// Detach a response observer by its id. Returns true if one was removed.
-    pub fn remove_on_response(&self, id: u64) -> bool {
-        if let Ok(mut v) = self.on_response.try_write() {
-            let before = v.len();
-            v.retain(|(cid, _)| *cid != id);
-            return v.len() != before;
-        }
-        false
+    /// `fetch` that also fires the page's passive on_request/on_response
+    /// callbacks (issue #408: callbacks are page-scoped, so the page-driven
+    /// fetch paths pass their registry in).
+    pub async fn fetch_with_callbacks(
+        &self,
+        url: &Url,
+        callbacks: Option<&CallbackRegistry>,
+    ) -> Result<Response, ObscuraNetError> {
+        self.fetch_with_method(Method::GET, url, None, callbacks).await
     }
 
     pub async fn post_form(&self, url: &Url, body: &str) -> Result<Response, ObscuraNetError> {
-        self.fetch_with_method(Method::POST, url, Some(body.as_bytes().to_vec())).await
+        self.fetch_with_method(Method::POST, url, Some(body.as_bytes().to_vec()), None).await
+    }
+
+    /// `post_form` variant of `fetch_with_callbacks`.
+    pub async fn post_form_with_callbacks(
+        &self,
+        url: &Url,
+        body: &str,
+        callbacks: Option<&CallbackRegistry>,
+    ) -> Result<Response, ObscuraNetError> {
+        self.fetch_with_method(Method::POST, url, Some(body.as_bytes().to_vec()), callbacks)
+            .await
     }
 
     pub async fn fetch_with_method(
@@ -440,6 +509,7 @@ impl ObscuraHttpClient {
         initial_method: Method,
         url: &Url,
         initial_body: Option<Vec<u8>>,
+        callbacks: Option<&CallbackRegistry>,
     ) -> Result<Response, ObscuraNetError> {
         validate_url(url, self.allow_private_network)?;
 
@@ -492,8 +562,8 @@ impl ObscuraHttpClient {
                 }
             }
 
-            for (_, cb) in self.on_request.read().await.iter() {
-                cb(&request_info);
+            if let Some(cbs) = callbacks {
+                cbs.fire_request(&request_info).await;
             }
 
             let ua = self.user_agent.read().await.clone();
@@ -638,8 +708,8 @@ impl ObscuraHttpClient {
                 redirected_from: redirects,
             };
 
-            for (_, cb) in self.on_response.read().await.iter() {
-                cb(&request_info, &response);
+            if let Some(cbs) = callbacks {
+                cbs.fire_response(&request_info, &response).await;
             }
 
             return Ok(response);
diff --git a/crates/obscura-net/src/lib.rs b/crates/obscura-net/src/lib.rs
index 0e6050d..0f790f2 100644
--- a/crates/obscura-net/src/lib.rs
+++ b/crates/obscura-net/src/lib.rs
@@ -8,8 +8,9 @@ pub mod blocklist;
 pub mod wreq_client;
 
 pub use client::{
-    env_allows_private_network, is_forbidden_ip, ObscuraHttpClient, ObscuraNetError, RequestCallback,
-    RequestInfo, ResourceType, Response, ResponseCallback, SsrfGuardResolver,
+    env_allows_private_network, is_forbidden_ip, CallbackRegistry, ObscuraHttpClient,
+    ObscuraNetError, RequestCallback, RequestInfo, ResourceType, Response, ResponseCallback,
+    SsrfGuardResolver,
 };
 pub use cookies::{default_cookie_path, CookieInfo, CookieJar};
 pub use encoding::{
diff --git a/crates/obscura/src/page.rs b/crates/obscura/src/page.rs
index 5859f4d..38fb2d2 100644
--- a/crates/obscura/src/page.rs
+++ b/crates/obscura/src/page.rs
@@ -128,9 +128,9 @@ impl Page {
     }
 
     /// Detach a request callback previously registered with `on_request`.
-    /// Returns true if a callback with that id was removed. Callbacks live on
-    /// the context's shared HTTP client, so detach them when a page or capture
-    /// phase ends to avoid firing for sibling pages (issue #408).
+    /// Returns true if a callback with that id was removed. Callbacks are
+    /// scoped to this page — they never fire for sibling pages and are
+    /// dropped with the page (issue #408).
     pub fn off_request(&mut self, id: u64) -> bool {
         self.inner.off_request(id)
     }
diff --git a/crates/obscura/tests/interception.rs b/crates/obscura/tests/interception.rs
index 4c72603..4bbe054 100644
--- a/crates/obscura/tests/interception.rs
+++ b/crates/obscura/tests/interception.rs
@@ -108,6 +108,53 @@ async fn page_intercepts_and_observes_js_fetch() {
     );
 }
 
+/// Issue #408 follow-up: callbacks are page-scoped. A callback registered on
+/// page A must not fire for requests made by page B in the same browser
+/// context, and must not survive page A being dropped.
+#[tokio::test]
+async fn callbacks_do_not_bleed_across_pages() {
+    std::env::set_var("OBSCURA_ALLOW_PRIVATE_NETWORK", "1");
+    let base = spawn_echo_server();
+
+    let browser = Browser::new().unwrap();
+    let mut page_a = browser.new_page().await.unwrap();
+    let mut page_b = browser.new_page().await.unwrap();
+
+    let a_hits = Arc::new(AtomicU32::new(0));
+    let a = a_hits.clone();
+    page_a.on_request(Arc::new(move |_info| {
+        a.fetch_add(1, Ordering::SeqCst);
+    }));
+
+    // Page B navigates (navigation + inline fetch('/api')); page A's callback
+    // must stay silent.
+    page_b.goto(&base).await.unwrap();
+    page_b.settle(500).await;
+    assert_eq!(
+        a_hits.load(Ordering::SeqCst),
+        0,
+        "page A's on_request fired for page B's requests"
+    );
+
+    // Page A navigates; its own callback fires.
+    page_a.goto(&base).await.unwrap();
+    assert!(
+        a_hits.load(Ordering::SeqCst) >= 1,
+        "page A's on_request did not fire for its own navigation"
+    );
+
+    // Dropping page A must not leave its callback firing for page B.
+    let before_drop = a_hits.load(Ordering::SeqCst);
+    drop(page_a);
+    page_b.goto(&base).await.unwrap();
+    page_b.settle(500).await;
+    assert_eq!(
+        a_hits.load(Ordering::SeqCst),
+        before_drop,
+        "dropped page A's on_request still fired for page B's requests"
+    );
+}
+
 #[tokio::test]
 async fn page_rewrites_request_url_via_interception() {
     std::env::set_var("OBSCURA_ALLOW_PRIVATE_NETWORK", "1");
diff --git a/docs/Use-as-a-Rust-library.md b/docs/Use-as-a-Rust-library.md
index 54017d2..97df3f3 100644
--- a/docs/Use-as-a-Rust-library.md
+++ b/docs/Use-as-a-Rust-library.md
@@ -69,7 +69,7 @@ The interception API observes, blocks, mocks, and rewrites the requests a page m
 
 ### Passive callbacks
 
-`on_request` and `on_response` fire for every request and response (navigation and JS `fetch()`/XHR) and are non-blocking. `on_response` is the main path for capturing the JSON an SPA loads asynchronously.
+`on_request` and `on_response` fire for every request and response (navigation and JS `fetch()`/XHR) and are non-blocking. `on_response` is the main path for capturing the JSON an SPA loads asynchronously. Both return a stable id; pass it to `off_request` / `off_response` to detach the callback when a crawl phase is done. Callbacks are scoped to the page that registered them: they never fire for another page's requests and are dropped with the page.
 
 ```rust
 use obscura::{Browser, ResourceType};