diff --git a/crates/alknet-call/src/protocol/pending.rs b/crates/alknet-call/src/protocol/pending.rs
index c6e50c7..5bcf473 100644
--- a/crates/alknet-call/src/protocol/pending.rs
+++ b/crates/alknet-call/src/protocol/pending.rs
@@ -1,7 +1,495 @@
-//! Pending request tracking: `PendingRequestMap` and `PendingEntry`.
-//!
-//! Correlates `call.responded` events back to the original `call.requested`
-//! by request ID. See `docs/architecture/crates/call/call-protocol.md` for
-//! the full specification.
+use std::collections::HashMap;
+use std::time::Instant;
 
-// TODO: implement
+use serde_json::Value;
+use tokio::sync::{mpsc, oneshot};
+
+use crate::protocol::wire::CallError;
+
+const SUBSCRIBE_CHANNEL_CAPACITY: usize = 32;
+
+pub struct PendingRequestMap {
+    pending: HashMap<String, PendingEntry>,
+}
+
+enum PendingEntry {
+    Call {
+        tx: oneshot::Sender<Result<Value, CallError>>,
+        timeout: Instant,
+    },
+    Subscribe {
+        tx: mpsc::Sender<Result<Value, CallError>>,
+        timeout: Option<Instant>,
+    },
+}
+
+impl PendingRequestMap {
+    pub fn new() -> Self {
+        Self {
+            pending: HashMap::new(),
+        }
+    }
+
+    pub fn register_call(
+        &mut self,
+        request_id: String,
+        timeout: Instant,
+    ) -> oneshot::Receiver<Result<Value, CallError>> {
+        let (tx, rx) = oneshot::channel();
+        self.pending
+            .insert(request_id, PendingEntry::Call { tx, timeout });
+        rx
+    }
+
+    pub fn register_subscribe(
+        &mut self,
+        request_id: String,
+        timeout: Option<Instant>,
+    ) -> mpsc::Receiver<Result<Value, CallError>> {
+        let (tx, rx) = mpsc::channel(SUBSCRIBE_CHANNEL_CAPACITY);
+        self.pending
+            .insert(request_id, PendingEntry::Subscribe { tx, timeout });
+        rx
+    }
+
+    pub fn handle_responded(&mut self, request_id: &str, output: Value) -> bool {
+        let Some(entry) = self.pending.remove(request_id) else {
+            return false;
+        };
+        match entry {
+            PendingEntry::Call { tx, .. } => {
+                let _ = tx.send(Ok(output));
+                true
+            }
+            PendingEntry::Subscribe { tx, timeout } => {
+                let send_result = tx.try_send(Ok(output));
+                match send_result {
+                    Ok(()) => {
+                        self.pending.insert(
+                            request_id.to_string(),
+                            PendingEntry::Subscribe { tx, timeout },
+                        );
+                        true
+                    }
+                    Err(mpsc::error::TrySendError::Full(_)) => {
+                        tracing::warn!(
+                            request_id,
+                            "subscribe channel full; dropping entry and closing subscription"
+                        );
+                        true
+                    }
+                    Err(mpsc::error::TrySendError::Closed(_)) => true,
+                }
+            }
+        }
+    }
+
+    pub fn handle_completed(&mut self, request_id: &str) -> bool {
+        self.pending.remove(request_id).is_some()
+    }
+
+    pub fn handle_aborted(&mut self, request_id: &str) -> bool {
+        self.pending.remove(request_id).is_some()
+    }
+
+    pub fn handle_error(&mut self, request_id: &str, error: CallError) -> bool {
+        let Some(entry) = self.pending.remove(request_id) else {
+            return false;
+        };
+        match entry {
+            PendingEntry::Call { tx, .. } => {
+                let _ = tx.send(Err(error));
+                true
+            }
+            PendingEntry::Subscribe { tx, .. } => {
+                let _ = tx.try_send(Err(error));
+                true
+            }
+        }
+    }
+
+    pub fn evict_expired(&mut self) -> Vec<String> {
+        let now = Instant::now();
+        let mut evicted = Vec::new();
+        let mut to_remove: Vec<String> = Vec::new();
+        for (id, entry) in self.pending.iter() {
+            let expired = match entry {
+                PendingEntry::Call { timeout, .. } => *timeout <= now,
+                PendingEntry::Subscribe {
+                    timeout: Some(t), ..
+                } => *t <= now,
+                PendingEntry::Subscribe { timeout: None, .. } => false,
+            };
+            if expired {
+                to_remove.push(id.clone());
+            }
+        }
+        for id in to_remove {
+            let Some(entry) = self.pending.remove(&id) else {
+                continue;
+            };
+            let timeout_err = CallError::timeout("request timed out");
+            match entry {
+                PendingEntry::Call { tx, .. } => {
+                    let _ = tx.send(Err(timeout_err));
+                }
+                PendingEntry::Subscribe { tx, .. } => {
+                    let _ = tx.try_send(Err(timeout_err));
+                }
+            }
+            evicted.push(id);
+        }
+        evicted
+    }
+
+    pub fn fail_all(&mut self, error: CallError) -> Vec<String> {
+        let ids: Vec<String> = self.pending.keys().cloned().collect();
+        for id in &ids {
+            if let Some(entry) = self.pending.remove(id) {
+                match entry {
+                    PendingEntry::Call { tx, .. } => {
+                        let _ = tx.send(Err(error.clone()));
+                    }
+                    PendingEntry::Subscribe { tx, .. } => {
+                        let _ = tx.try_send(Err(error.clone()));
+                    }
+                }
+            }
+        }
+        ids
+    }
+
+    pub fn contains(&self, request_id: &str) -> bool {
+        self.pending.contains_key(request_id)
+    }
+
+    pub fn len(&self) -> usize {
+        self.pending.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.pending.is_empty()
+    }
+}
+
+impl Default for PendingRequestMap {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde_json::json;
+    use std::time::Duration;
+    use tokio::time::timeout;
+
+    fn timeout_error() -> CallError {
+        CallError::timeout("request timed out")
+    }
+
+    fn internal_error(message: &str) -> CallError {
+        CallError::internal(message)
+    }
+
+    #[tokio::test]
+    async fn register_call_then_handle_responded_resolves_oneshot() {
+        let mut map = PendingRequestMap::new();
+        let rx = map.register_call(
+            "req-1".to_string(),
+            Instant::now() + Duration::from_secs(30),
+        );
+
+        assert!(map.contains("req-1"));
+        assert_eq!(map.len(), 1);
+
+        assert!(map.handle_responded("req-1", json!(42)));
+
+        let result = timeout(Duration::from_millis(100), rx).await;
+        match result {
+            Ok(Ok(Ok(value))) => assert_eq!(value, json!(42)),
+            other => panic!("expected Ok(42), got {other:?}"),
+        }
+        assert!(!map.contains("req-1"));
+        assert_eq!(map.len(), 0);
+    }
+
+    #[tokio::test]
+    async fn register_subscribe_then_handle_responded_pushes_to_channel() {
+        let mut map = PendingRequestMap::new();
+        let mut rx = map.register_subscribe("sub-1".to_string(), None);
+
+        assert!(map.handle_responded("sub-1", json!("first")));
+        assert!(map.handle_responded("sub-1", json!("second")));
+        assert!(map.contains("sub-1"));
+
+        let first = timeout(Duration::from_millis(100), rx.recv()).await;
+        let second = timeout(Duration::from_millis(100), rx.recv()).await;
+        match (first, second) {
+            (Ok(Some(Ok(a))), Ok(Some(Ok(b)))) => {
+                assert_eq!(a, json!("first"));
+                assert_eq!(b, json!("second"));
+            }
+            other => panic!("expected two Ok values, got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn subscribe_handle_completed_closes_channel_and_deletes_entry() {
+        let mut map = PendingRequestMap::new();
+        let mut rx = map.register_subscribe("sub-2".to_string(), None);
+
+        assert!(map.handle_responded("sub-2", json!("a")));
+        assert!(map.handle_completed("sub-2"));
+        assert!(!map.contains("sub-2"));
+
+        let _ = timeout(Duration::from_millis(100), rx.recv()).await;
+        let after_close = timeout(Duration::from_millis(100), rx.recv()).await;
+        match after_close {
+            Ok(None) => {}
+            other => panic!("expected channel closed (None), got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn expired_call_is_evicted_with_timeout_error() {
+        let mut map = PendingRequestMap::new();
+        let rx = map.register_call(
+            "req-2".to_string(),
+            Instant::now() - Duration::from_millis(1),
+        );
+
+        let evicted = map.evict_expired();
+        assert_eq!(evicted, vec!["req-2".to_string()]);
+        assert!(!map.contains("req-2"));
+
+        let result = timeout(Duration::from_millis(100), rx).await;
+        match result {
+            Ok(Ok(Err(e))) => {
+                assert_eq!(e.code, "TIMEOUT");
+                assert!(e.retryable);
+            }
+            other => panic!("expected Err(TIMEOUT), got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn expired_subscribe_is_evicted_with_timeout_error() {
+        let mut map = PendingRequestMap::new();
+        let mut rx = map.register_subscribe(
+            "sub-3".to_string(),
+            Some(Instant::now() - Duration::from_millis(1)),
+        );
+
+        let evicted = map.evict_expired();
+        assert_eq!(evicted, vec!["sub-3".to_string()]);
+
+        let result = timeout(Duration::from_millis(100), rx.recv()).await;
+        match result {
+            Ok(Some(Err(e))) => {
+                assert_eq!(e.code, "TIMEOUT");
+                assert!(e.retryable);
+            }
+            other => panic!("expected Err(TIMEOUT), got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn unbounded_subscribe_is_not_evicted() {
+        let mut map = PendingRequestMap::new();
+        let _rx = map.register_subscribe("sub-4".to_string(), None);
+
+        let evicted = map.evict_expired();
+        assert!(evicted.is_empty());
+        assert!(map.contains("sub-4"));
+    }
+
+    #[tokio::test]
+    async fn fail_all_resolves_all_pending_with_internal_error() {
+        let mut map = PendingRequestMap::new();
+        let rx_call =
+            map.register_call("c-1".to_string(), Instant::now() + Duration::from_secs(30));
+        let mut rx_sub = map.register_subscribe(
+            "s-1".to_string(),
+            Some(Instant::now() + Duration::from_secs(30)),
+        );
+
+        let failed = map.fail_all(internal_error("connection closed"));
+        assert_eq!(failed.len(), 2);
+        assert!(failed.contains(&"c-1".to_string()));
+        assert!(failed.contains(&"s-1".to_string()));
+        assert!(map.is_empty());
+
+        let call_result = timeout(Duration::from_millis(100), rx_call).await;
+        match call_result {
+            Ok(Ok(Err(e))) => {
+                assert_eq!(e.code, "INTERNAL");
+                assert_eq!(e.message, "connection closed");
+            }
+            other => panic!("expected Err(INTERNAL), got {other:?}"),
+        }
+
+        let sub_result = timeout(Duration::from_millis(100), rx_sub.recv()).await;
+        match sub_result {
+            Ok(Some(Err(e))) => {
+                assert_eq!(e.code, "INTERNAL");
+                assert_eq!(e.message, "connection closed");
+            }
+            other => panic!("expected Err(INTERNAL), got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn handle_responded_unknown_request_id_returns_false() {
+        let mut map = PendingRequestMap::new();
+        assert!(!map.handle_responded("nonexistent", json!(1)));
+        assert_eq!(map.len(), 0);
+    }
+
+    #[tokio::test]
+    async fn handle_completed_unknown_request_id_returns_false() {
+        let mut map = PendingRequestMap::new();
+        assert!(!map.handle_completed("nonexistent"));
+    }
+
+    #[tokio::test]
+    async fn handle_aborted_unknown_request_id_returns_false() {
+        let mut map = PendingRequestMap::new();
+        assert!(!map.handle_aborted("nonexistent"));
+    }
+
+    #[tokio::test]
+    async fn handle_error_unknown_request_id_returns_false() {
+        let mut map = PendingRequestMap::new();
+        assert!(!map.handle_error("nonexistent", internal_error("x")));
+    }
+
+    #[tokio::test]
+    async fn handle_aborted_cancels_pending_call() {
+        let mut map = PendingRequestMap::new();
+        let rx = map.register_call(
+            "req-3".to_string(),
+            Instant::now() + Duration::from_secs(30),
+        );
+
+        assert!(map.handle_aborted("req-3"));
+        assert!(!map.contains("req-3"));
+
+        let result = timeout(Duration::from_millis(100), rx).await;
+        match result {
+            Ok(Err(_)) => {}
+            other => panic!("expected sender dropped (Err), got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn handle_error_resolves_call_with_error() {
+        let mut map = PendingRequestMap::new();
+        let rx = map.register_call(
+            "req-4".to_string(),
+            Instant::now() + Duration::from_secs(30),
+        );
+
+        let err = CallError::new("FILE_NOT_FOUND", "missing", false);
+        assert!(map.handle_error("req-4", err.clone()));
+        assert!(!map.contains("req-4"));
+
+        let result = timeout(Duration::from_millis(100), rx).await;
+        match result {
+            Ok(Ok(Err(e))) => {
+                assert_eq!(e.code, "FILE_NOT_FOUND");
+                assert!(!e.retryable);
+            }
+            other => panic!("expected Err(FILE_NOT_FOUND), got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn handle_error_pushes_to_subscribe_channel() {
+        let mut map = PendingRequestMap::new();
+        let mut rx = map.register_subscribe("sub-5".to_string(), None);
+
+        let err = CallError::new("RATE_LIMITED", "too fast", true);
+        assert!(map.handle_error("sub-5", err.clone()));
+        assert!(!map.contains("sub-5"));
+
+        let result = timeout(Duration::from_millis(100), rx.recv()).await;
+        match result {
+            Ok(Some(Err(e))) => {
+                assert_eq!(e.code, "RATE_LIMITED");
+                assert!(e.retryable);
+            }
+            other => panic!("expected Err(RATE_LIMITED), got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn correlation_by_id_not_by_stream() {
+        let mut map = PendingRequestMap::new();
+        let rx = map.register_call(
+            "req-stream-3".to_string(),
+            Instant::now() + Duration::from_secs(30),
+        );
+
+        assert!(map.handle_responded("req-stream-3", json!("response-from-stream-7")));
+        let result = timeout(Duration::from_millis(100), rx).await;
+        match result {
+            Ok(Ok(Ok(value))) => assert_eq!(value, json!("response-from-stream-7")),
+            other => panic!("expected Ok, got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn register_call_overwrites_existing_entry() {
+        let mut map = PendingRequestMap::new();
+        let _rx_old = map.register_call(
+            "req-5".to_string(),
+            Instant::now() + Duration::from_secs(30),
+        );
+        let rx_new = map.register_call(
+            "req-5".to_string(),
+            Instant::now() + Duration::from_secs(30),
+        );
+        assert_eq!(map.len(), 1);
+
+        assert!(map.handle_responded("req-5", json!("new")));
+        let result = timeout(Duration::from_millis(100), rx_new).await;
+        match result {
+            Ok(Ok(Ok(value))) => assert_eq!(value, json!("new")),
+            other => panic!("expected Ok from new receiver, got {other:?}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn evict_expired_skips_non_expired_entries() {
+        let mut map = PendingRequestMap::new();
+        let _rx_expired = map.register_call(
+            "expired".to_string(),
+            Instant::now() - Duration::from_millis(1),
+        );
+        let _rx_alive = map.register_call(
+            "alive".to_string(),
+            Instant::now() + Duration::from_secs(60),
+        );
+
+        let evicted = map.evict_expired();
+        assert_eq!(evicted, vec!["expired".to_string()]);
+        assert!(map.contains("alive"));
+        assert!(!map.contains("expired"));
+    }
+
+    #[tokio::test]
+    async fn default_is_empty_map() {
+        let map = PendingRequestMap::default();
+        assert!(map.is_empty());
+        assert_eq!(map.len(), 0);
+    }
+
+    #[tokio::test]
+    async fn timeout_error_helper() {
+        let err = timeout_error();
+        assert_eq!(err.code, "TIMEOUT");
+        assert!(err.retryable);
+    }
+}