diff --git a/wasm/dist-repl/index.html b/wasm/dist-repl/index.html
index 1fcec62..9edf37c 100644
--- a/wasm/dist-repl/index.html
+++ b/wasm/dist-repl/index.html
@@ -84,6 +84,7 @@
     <span class="spacer"></span>
     <button id="reset-tier" class="ghost" title="reboot the worker for the current tab — state lost">↻ reboot tier</button>
     <button id="clear-log"  class="ghost" title="clear the transcript">clear log</button>
+    <button id="pause"      class="ghost" disabled title="pause the running eval and snapshot its state into the portal vault — resume via the chip">⏸ pause</button>
     <button id="cancel"     class="ghost" disabled>cancel</button>
     <button id="lock"       class="ghost" title="lock vault — passes back to lock screen">lock</button>
   </section>
diff --git a/wasm/dist-repl/repl.css b/wasm/dist-repl/repl.css
index 1bbce52..7f83941 100644
--- a/wasm/dist-repl/repl.css
+++ b/wasm/dist-repl/repl.css
@@ -121,10 +121,10 @@ body.repl {
   z-index: 40;
   display: grid;
   /* tabs · new-tab · spacer · heap-pressure (injected by repl.js) ·
-   * reboot · clear · cancel · lock — 8 cells. Extend if the toolbar
-   * grows; CSS Grid drops trailing children onto a new row, which is
-   * how lock used to wrap. */
-  grid-template-columns: auto auto 1fr auto auto auto auto auto;
+   * reboot · clear · pause · cancel · lock — 9 cells. Extend if the
+   * toolbar grows; CSS Grid drops trailing children onto a new row,
+   * which is how lock used to wrap. */
+  grid-template-columns: auto auto 1fr auto auto auto auto auto auto;
   gap: 0.3rem;
   align-items: center;
   padding: 0.4rem 0.4rem;
diff --git a/wasm/dist-repl/repl.js b/wasm/dist-repl/repl.js
index 0c2de3c..0391338 100644
--- a/wasm/dist-repl/repl.js
+++ b/wasm/dist-repl/repl.js
@@ -21,6 +21,7 @@ const newTabBtn = document.getElementById("new-tab");
 const resetTierBtn = document.getElementById("reset-tier");
 const clearLogBtn = document.getElementById("clear-log");
 const cancelBtn = document.getElementById("cancel");
+const pauseBtn = document.getElementById("pause");
 const lockBtn = document.getElementById("lock");
 
 const replStream = document.getElementById("repl-stream");
@@ -671,6 +672,34 @@ async function importCheckpoint(file) {
     saveSoon();
 }
 
+// Manual pause-and-snapshot — the user wants to inspect or save the
+// state of a long-running eval without leaving the tab. Signals the
+// SAB pause flag, waits for the in-flight eval to settle, then runs
+// saveCheckpoint so the snapshot lands in the visible chip strip
+// with a user-chosen name. Workers stay alive so the next input
+// runs immediately.
+async function pauseAndSnapshot() {
+    if (!pauseFlagView) {
+        alert("pause requires COOP/COEP headers — start with `make serve-repl`, or for production set Cross-Origin-Opener-Policy: same-origin + Cross-Origin-Embedder-Policy: require-corp on the deploy");
+        return;
+    }
+    const tab = activeTab();
+    if (!tab) return;
+    const tier = tab.tier === "all" ? "c" : tab.tier;
+    if (tier === "asm") {
+        alert("manual pause not supported on asm tier yet — use cancel + portal-save when the eval is idle");
+        return;
+    }
+    pauseBtn.disabled = true;
+    Atomics.store(pauseFlagView, 0, 1);
+    await waitForPending(tab.id, tier, 5000);
+    Atomics.store(pauseFlagView, 0, 0);
+    // Reset activeInput marker so a follow-up tab switch doesn't try
+    // to "auto-resume" what the user has now explicitly saved.
+    tab.activeInput = null;
+    await saveCheckpoint();
+}
+
 function deleteCheckpoint(name) {
     const tab = activeTab();
     if (!tab || !tab.checkpoints) return;
@@ -973,6 +1002,7 @@ async function sendInput() {
     resetHistory();
     sendBtn.disabled = true;
     cancelBtn.disabled = false;
+    pauseBtn.disabled = !pauseFlagView;
     renderAll();
     saveSoon();
 
@@ -1033,6 +1063,7 @@ async function sendInput() {
             if (remaining === 0) {
                 sendBtn.disabled = false;
                 cancelBtn.disabled = true;
+                pauseBtn.disabled = true;
                 inputEl.focus();
                 // Eval finished cleanly — drop the activeInput marker so
                 // a subsequent tab switch doesn't try to resume something
@@ -1102,6 +1133,7 @@ clearLogBtn.addEventListener("click", () => {
     if (tab) { tab.transcript = []; renderAll(); saveSoon(); }
 });
 cancelBtn.addEventListener("click", cancelAllPendingInActiveTab);
+pauseBtn.addEventListener("click", pauseAndSnapshot);
 portalSaveBtn.addEventListener("click", saveCheckpoint);
 portalImportBtn.addEventListener("click", () => portalImportFileEl.click());
 portalImportFileEl.addEventListener("change", async (e) => {
diff --git a/wasm/repl/index.html b/wasm/repl/index.html
index 1fcec62..9edf37c 100644
--- a/wasm/repl/index.html
+++ b/wasm/repl/index.html
@@ -84,6 +84,7 @@
     <span class="spacer"></span>
     <button id="reset-tier" class="ghost" title="reboot the worker for the current tab — state lost">↻ reboot tier</button>
     <button id="clear-log"  class="ghost" title="clear the transcript">clear log</button>
+    <button id="pause"      class="ghost" disabled title="pause the running eval and snapshot its state into the portal vault — resume via the chip">⏸ pause</button>
     <button id="cancel"     class="ghost" disabled>cancel</button>
     <button id="lock"       class="ghost" title="lock vault — passes back to lock screen">lock</button>
   </section>
diff --git a/wasm/repl/repl.css b/wasm/repl/repl.css
index 1bbce52..7f83941 100644
--- a/wasm/repl/repl.css
+++ b/wasm/repl/repl.css
@@ -121,10 +121,10 @@ body.repl {
   z-index: 40;
   display: grid;
   /* tabs · new-tab · spacer · heap-pressure (injected by repl.js) ·
-   * reboot · clear · cancel · lock — 8 cells. Extend if the toolbar
-   * grows; CSS Grid drops trailing children onto a new row, which is
-   * how lock used to wrap. */
-  grid-template-columns: auto auto 1fr auto auto auto auto auto;
+   * reboot · clear · pause · cancel · lock — 9 cells. Extend if the
+   * toolbar grows; CSS Grid drops trailing children onto a new row,
+   * which is how lock used to wrap. */
+  grid-template-columns: auto auto 1fr auto auto auto auto auto auto;
   gap: 0.3rem;
   align-items: center;
   padding: 0.4rem 0.4rem;
diff --git a/wasm/repl/repl.js b/wasm/repl/repl.js
index 0c2de3c..0391338 100644
--- a/wasm/repl/repl.js
+++ b/wasm/repl/repl.js
@@ -21,6 +21,7 @@ const newTabBtn = document.getElementById("new-tab");
 const resetTierBtn = document.getElementById("reset-tier");
 const clearLogBtn = document.getElementById("clear-log");
 const cancelBtn = document.getElementById("cancel");
+const pauseBtn = document.getElementById("pause");
 const lockBtn = document.getElementById("lock");
 
 const replStream = document.getElementById("repl-stream");
@@ -671,6 +672,34 @@ async function importCheckpoint(file) {
     saveSoon();
 }
 
+// Manual pause-and-snapshot — the user wants to inspect or save the
+// state of a long-running eval without leaving the tab. Signals the
+// SAB pause flag, waits for the in-flight eval to settle, then runs
+// saveCheckpoint so the snapshot lands in the visible chip strip
+// with a user-chosen name. Workers stay alive so the next input
+// runs immediately.
+async function pauseAndSnapshot() {
+    if (!pauseFlagView) {
+        alert("pause requires COOP/COEP headers — start with `make serve-repl`, or for production set Cross-Origin-Opener-Policy: same-origin + Cross-Origin-Embedder-Policy: require-corp on the deploy");
+        return;
+    }
+    const tab = activeTab();
+    if (!tab) return;
+    const tier = tab.tier === "all" ? "c" : tab.tier;
+    if (tier === "asm") {
+        alert("manual pause not supported on asm tier yet — use cancel + portal-save when the eval is idle");
+        return;
+    }
+    pauseBtn.disabled = true;
+    Atomics.store(pauseFlagView, 0, 1);
+    await waitForPending(tab.id, tier, 5000);
+    Atomics.store(pauseFlagView, 0, 0);
+    // Reset activeInput marker so a follow-up tab switch doesn't try
+    // to "auto-resume" what the user has now explicitly saved.
+    tab.activeInput = null;
+    await saveCheckpoint();
+}
+
 function deleteCheckpoint(name) {
     const tab = activeTab();
     if (!tab || !tab.checkpoints) return;
@@ -973,6 +1002,7 @@ async function sendInput() {
     resetHistory();
     sendBtn.disabled = true;
     cancelBtn.disabled = false;
+    pauseBtn.disabled = !pauseFlagView;
     renderAll();
     saveSoon();
 
@@ -1033,6 +1063,7 @@ async function sendInput() {
             if (remaining === 0) {
                 sendBtn.disabled = false;
                 cancelBtn.disabled = true;
+                pauseBtn.disabled = true;
                 inputEl.focus();
                 // Eval finished cleanly — drop the activeInput marker so
                 // a subsequent tab switch doesn't try to resume something
@@ -1102,6 +1133,7 @@ clearLogBtn.addEventListener("click", () => {
     if (tab) { tab.transcript = []; renderAll(); saveSoon(); }
 });
 cancelBtn.addEventListener("click", cancelAllPendingInActiveTab);
+pauseBtn.addEventListener("click", pauseAndSnapshot);
 portalSaveBtn.addEventListener("click", saveCheckpoint);
 portalImportBtn.addEventListener("click", () => portalImportFileEl.click());
 portalImportFileEl.addEventListener("change", async (e) => {
diff --git a/www/repl/index.html b/www/repl/index.html
index 1fcec62..9edf37c 100644
--- a/www/repl/index.html
+++ b/www/repl/index.html
@@ -84,6 +84,7 @@
     <span class="spacer"></span>
     <button id="reset-tier" class="ghost" title="reboot the worker for the current tab — state lost">↻ reboot tier</button>
     <button id="clear-log"  class="ghost" title="clear the transcript">clear log</button>
+    <button id="pause"      class="ghost" disabled title="pause the running eval and snapshot its state into the portal vault — resume via the chip">⏸ pause</button>
     <button id="cancel"     class="ghost" disabled>cancel</button>
     <button id="lock"       class="ghost" title="lock vault — passes back to lock screen">lock</button>
   </section>
diff --git a/www/repl/repl.css b/www/repl/repl.css
index 1bbce52..7f83941 100644
--- a/www/repl/repl.css
+++ b/www/repl/repl.css
@@ -121,10 +121,10 @@ body.repl {
   z-index: 40;
   display: grid;
   /* tabs · new-tab · spacer · heap-pressure (injected by repl.js) ·
-   * reboot · clear · cancel · lock — 8 cells. Extend if the toolbar
-   * grows; CSS Grid drops trailing children onto a new row, which is
-   * how lock used to wrap. */
-  grid-template-columns: auto auto 1fr auto auto auto auto auto;
+   * reboot · clear · pause · cancel · lock — 9 cells. Extend if the
+   * toolbar grows; CSS Grid drops trailing children onto a new row,
+   * which is how lock used to wrap. */
+  grid-template-columns: auto auto 1fr auto auto auto auto auto auto;
   gap: 0.3rem;
   align-items: center;
   padding: 0.4rem 0.4rem;
diff --git a/www/repl/repl.js b/www/repl/repl.js
index 0c2de3c..0391338 100644
--- a/www/repl/repl.js
+++ b/www/repl/repl.js
@@ -21,6 +21,7 @@ const newTabBtn = document.getElementById("new-tab");
 const resetTierBtn = document.getElementById("reset-tier");
 const clearLogBtn = document.getElementById("clear-log");
 const cancelBtn = document.getElementById("cancel");
+const pauseBtn = document.getElementById("pause");
 const lockBtn = document.getElementById("lock");
 
 const replStream = document.getElementById("repl-stream");
@@ -671,6 +672,34 @@ async function importCheckpoint(file) {
     saveSoon();
 }
 
+// Manual pause-and-snapshot — the user wants to inspect or save the
+// state of a long-running eval without leaving the tab. Signals the
+// SAB pause flag, waits for the in-flight eval to settle, then runs
+// saveCheckpoint so the snapshot lands in the visible chip strip
+// with a user-chosen name. Workers stay alive so the next input
+// runs immediately.
+async function pauseAndSnapshot() {
+    if (!pauseFlagView) {
+        alert("pause requires COOP/COEP headers — start with `make serve-repl`, or for production set Cross-Origin-Opener-Policy: same-origin + Cross-Origin-Embedder-Policy: require-corp on the deploy");
+        return;
+    }
+    const tab = activeTab();
+    if (!tab) return;
+    const tier = tab.tier === "all" ? "c" : tab.tier;
+    if (tier === "asm") {
+        alert("manual pause not supported on asm tier yet — use cancel + portal-save when the eval is idle");
+        return;
+    }
+    pauseBtn.disabled = true;
+    Atomics.store(pauseFlagView, 0, 1);
+    await waitForPending(tab.id, tier, 5000);
+    Atomics.store(pauseFlagView, 0, 0);
+    // Reset activeInput marker so a follow-up tab switch doesn't try
+    // to "auto-resume" what the user has now explicitly saved.
+    tab.activeInput = null;
+    await saveCheckpoint();
+}
+
 function deleteCheckpoint(name) {
     const tab = activeTab();
     if (!tab || !tab.checkpoints) return;
@@ -973,6 +1002,7 @@ async function sendInput() {
     resetHistory();
     sendBtn.disabled = true;
     cancelBtn.disabled = false;
+    pauseBtn.disabled = !pauseFlagView;
     renderAll();
     saveSoon();
 
@@ -1033,6 +1063,7 @@ async function sendInput() {
             if (remaining === 0) {
                 sendBtn.disabled = false;
                 cancelBtn.disabled = true;
+                pauseBtn.disabled = true;
                 inputEl.focus();
                 // Eval finished cleanly — drop the activeInput marker so
                 // a subsequent tab switch doesn't try to resume something
@@ -1102,6 +1133,7 @@ clearLogBtn.addEventListener("click", () => {
     if (tab) { tab.transcript = []; renderAll(); saveSoon(); }
 });
 cancelBtn.addEventListener("click", cancelAllPendingInActiveTab);
+pauseBtn.addEventListener("click", pauseAndSnapshot);
 portalSaveBtn.addEventListener("click", saveCheckpoint);
 portalImportBtn.addEventListener("click", () => portalImportFileEl.click());
 portalImportFileEl.addEventListener("change", async (e) => {