diff --git a/CHANGELOG.md b/CHANGELOG.md
index 998859dc..b70c0da5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,22 @@ All notable changes to the tines crates. Versions follow
 [Semantic Versioning](https://semver.org/); before 1.0, a minor bump may break
 the API.
 
+## 0.3.0 — 2026-10-18
+
+### Breaking
+
+- `Store` now requires `release(&mut self, id)` and
+  `is_released(&self, id) -> bool`. Implementations of `Store` — including test
+  doubles and future backends — must provide them.
+
+### Added
+
+- `Store::release` marks an observation as sent, so it is no longer offered for
+  exchange. `MemStore` tracks a per-entry `released` flag, and its
+  `for_each_addressed_id` skips released ids as an optimization (the exchange
+  predicate remains the load-bearing check). Releasing an id that is not stored
+  is a no-op.
+
 ## 0.2.1 — 2026-10-18
 
 ### Changed
diff --git a/Cargo.lock b/Cargo.lock
index 0adbfc8e..dc69b524 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -548,7 +548,7 @@ dependencies = [
 
 [[package]]
 name = "tines-core"
-version = "0.2.1"
+version = "0.3.0"
 dependencies = [
  "blake2",
  "heapless",
@@ -558,7 +558,7 @@ dependencies = [
 
 [[package]]
 name = "tines-sim"
-version = "0.2.1"
+version = "0.3.0"
 dependencies = [
  "proptest",
  "rand 0.8.8",
diff --git a/Cargo.toml b/Cargo.toml
index 43377637..1af11d4d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,7 +3,7 @@ members = ["tines-core", "tines-sim"]
 resolver = "2"
 
 [workspace.package]
-version = "0.2.1"
+version = "0.3.0"
 edition = "2021"
 license = "Apache-2.0"
 authors = ["K. Isom"]
diff --git a/tines-core/src/exchange.rs b/tines-core/src/exchange.rs
index fde08400..39604dbd 100644
--- a/tines-core/src/exchange.rs
+++ b/tines-core/src/exchange.rs
@@ -1820,6 +1820,12 @@ mod tests {
         fn for_each_addressed_id(&self, f: &mut dyn FnMut(&ObservationId)) {
             self.inner.for_each_addressed_id(f)
         }
+        fn release(&mut self, id: &ObservationId) {
+            self.inner.release(id)
+        }
+        fn is_released(&self, id: &ObservationId) -> bool {
+            self.inner.is_released(id)
+        }
         fn for_each_topic(&self, prefix: &[u8], now: Tick, f: &mut dyn FnMut(&Observation)) {
             self.inner.for_each_topic(prefix, now, f)
         }
diff --git a/tines-core/src/mem_store.rs b/tines-core/src/mem_store.rs
index 0034558b..a73d786d 100644
--- a/tines-core/src/mem_store.rs
+++ b/tines-core/src/mem_store.rs
@@ -21,6 +21,7 @@ use alloc::vec::Vec;
 struct Held {
     obs: Observation,
     stored_at: Tick,
+    released: bool,
 }
 
 /// An unbounded [`Store`] backed by a `BTreeMap` keyed by content-derived
@@ -77,6 +78,7 @@ impl Store for MemStore {
             Held {
                 obs,
                 stored_at: now,
+                released: false,
             },
         );
         Ok(true)
@@ -112,12 +114,24 @@ impl Store for MemStore {
 
     fn for_each_addressed_id(&self, f: &mut dyn FnMut(&ObservationId)) {
         for (id, held) in self.map.iter() {
-            if held.obs.to.is_some() {
+            // Skipping released ids is an optimization; the exchange predicate
+            // is the load-bearing check.
+            if held.obs.to.is_some() && !held.released {
                 f(id);
             }
         }
     }
 
+    fn release(&mut self, id: &ObservationId) {
+        if let Some(held) = self.map.get_mut(id) {
+            held.released = true;
+        }
+    }
+
+    fn is_released(&self, id: &ObservationId) -> bool {
+        self.map.get(id).map(|held| held.released).unwrap_or(false)
+    }
+
     fn for_each_topic(&self, prefix: &[u8], now: Tick, f: &mut dyn FnMut(&Observation)) {
         for held in self.map.values() {
             if held.obs.topic.starts_with(prefix) {
@@ -438,4 +452,24 @@ mod tests {
             std::collections::BTreeSet::from_iter([0u64, 1, 2, 100])
         );
     }
+
+    #[test]
+    fn release_marks_and_is_released_reports() {
+        let mut s = MemStore::new();
+        let o = obs([1; 16], 1, 0, None, b"door/1");
+        let id = o.id();
+        assert!(s.insert(o, 1000).unwrap());
+        assert!(!s.is_released(&id));
+        s.release(&id);
+        assert!(s.is_released(&id));
+    }
+
+    #[test]
+    fn release_unknown_is_noop() {
+        let mut s = MemStore::new();
+        // Releasing an id that was never inserted must not panic...
+        s.release(&[0u8; 16]);
+        // ...and must not report anything as released.
+        assert!(!s.is_released(&[0u8; 16]));
+    }
 }
diff --git a/tines-core/src/store.rs b/tines-core/src/store.rs
index f93adce9..abc25b11 100644
--- a/tines-core/src/store.rs
+++ b/tines-core/src/store.rs
@@ -74,6 +74,17 @@ pub trait Store {
         self.for_each_id(f)
     }
 
+    /// Mark the observation with `id` as released: it has been sent and must
+    /// not be offered for exchange again.
+    ///
+    /// Releasing an id that is not currently stored is a no-op. The mark
+    /// persists for the lifetime of the entry (until it is trimmed); a
+    /// re-inserted observation starts un-released.
+    fn release(&mut self, id: &ObservationId);
+
+    /// Returns `true` if the observation with `id` has been released.
+    fn is_released(&self, id: &ObservationId) -> bool;
+
     /// Visit every stored observation whose topic starts with `prefix`
     /// (an empty prefix matches all), each age-adjusted to `now`.
     fn for_each_topic(&self, prefix: &[u8], now: Tick, f: &mut dyn FnMut(&Observation));
diff --git a/tines-sim/Cargo.toml b/tines-sim/Cargo.toml
index 7d00a44b..48cf75ee 100644
--- a/tines-sim/Cargo.toml
+++ b/tines-sim/Cargo.toml
@@ -12,7 +12,7 @@ keywords = ["robotics", "gossip", "simulation", "delay-tolerant"]
 categories = ["simulation", "science::robotics"]
 
 [dependencies]
-tines-core = { path = "../tines-core", version = "0.2.1" }
+tines-core = { path = "../tines-core", version = "0.3.0" }
 rand = "0.8"
 
 [dev-dependencies]