diff --git a/wasm/c/lumbda-c.loader.js b/wasm/c/lumbda-c.loader.js
index 1e2e8e2..1fccb21 100644
--- a/wasm/c/lumbda-c.loader.js
+++ b/wasm/c/lumbda-c.loader.js
@@ -99,7 +99,14 @@ async function _bootstrap() {
             // free path right now (LUMBDA_NO_BOEHM), so used = total —
             // every malloc accumulates until reload. Documented and
             // surfaced in the REPL so the user sees the pressure.
-            const total = module.HEAPU8.byteLength;
+            //
+            // HEAPU8 isn't always live: after a worker reboots, the
+            // heap poll can fire while the new Module is mid-init and
+            // HEAPU8 isn't yet wired. Return null so the REPL hides
+            // the pressure indicator for that tick instead of crashing.
+            const heap = module.HEAPU8;
+            if (!heap) return null;
+            const total = heap.byteLength;
             return { used: total, total };
         },
     };
diff --git a/wasm/dist-repl/c/lumbda-c.loader.js b/wasm/dist-repl/c/lumbda-c.loader.js
index 1e2e8e2..1fccb21 100644
--- a/wasm/dist-repl/c/lumbda-c.loader.js
+++ b/wasm/dist-repl/c/lumbda-c.loader.js
@@ -99,7 +99,14 @@ async function _bootstrap() {
             // free path right now (LUMBDA_NO_BOEHM), so used = total —
             // every malloc accumulates until reload. Documented and
             // surfaced in the REPL so the user sees the pressure.
-            const total = module.HEAPU8.byteLength;
+            //
+            // HEAPU8 isn't always live: after a worker reboots, the
+            // heap poll can fire while the new Module is mid-init and
+            // HEAPU8 isn't yet wired. Return null so the REPL hides
+            // the pressure indicator for that tick instead of crashing.
+            const heap = module.HEAPU8;
+            if (!heap) return null;
+            const total = heap.byteLength;
             return { used: total, total };
         },
     };
diff --git a/wasm/dist-repl/index.html b/wasm/dist-repl/index.html
index 5845a02..37ff31c 100644
--- a/wasm/dist-repl/index.html
+++ b/wasm/dist-repl/index.html
@@ -90,6 +90,9 @@
   <section class="portal-bar" id="portal-bar">
     <span class="portal-label" title="save the current tab's tier state to your encrypted vault. comes back exactly the same after a tab close + reopen.">portals:</span>
     <button id="portal-save" class="ghost" title="save tier state — names the snapshot by date+time">💾 save</button>
+    <button id="portal-import" class="ghost" title="import a .portal.json file">📁 import</button>
+    <button id="portal-scope" class="ghost" title="toggle between this tab's checkpoints and every tab's">📂 this tab</button>
+    <input id="portal-import-file" type="file" accept=".json,.portal,application/json" hidden>
     <div id="portal-chips" class="portal-chips"></div>
   </section>
   <div id="transcript" class="transcript"></div>
diff --git a/wasm/dist-repl/repl.css b/wasm/dist-repl/repl.css
index 2a37d53..244bf2f 100644
--- a/wasm/dist-repl/repl.css
+++ b/wasm/dist-repl/repl.css
@@ -190,7 +190,8 @@ body.repl {
  * (the asm-wat tier stays grey). */
 .portal-bar {
   display: grid;
-  grid-template-columns: auto auto 1fr;
+  /* label · save · import · scope · chips-row */
+  grid-template-columns: auto auto auto auto 1fr;
   gap: 0.4rem;
   align-items: center;
   padding: 0.2rem 0.5rem;
@@ -211,7 +212,8 @@ body.repl {
 }
 .portal-chips .chip {
   display: inline-grid;
-  grid-template-columns: auto auto;
+  /* label · ⇣ download · × delete */
+  grid-template-columns: auto auto auto;
   gap: 0.3rem;
   align-items: center;
   background: var(--pane-bg);
@@ -223,12 +225,20 @@ body.repl {
   white-space: nowrap;
 }
 .portal-chips .chip:hover { border-color: var(--green); }
+.portal-chips .chip-global {
+  /* Cross-tab snapshots get a muted accent so they read as "borrowed
+   * from another tab" rather than belonging here. */
+  border-style: dashed;
+  opacity: 0.85;
+}
+.portal-chips .chip .chip-export,
 .portal-chips .chip .chip-close {
   color: var(--muted);
   font-size: 0.85em;
   cursor: pointer;
   padding: 0 0.15rem;
 }
+.portal-chips .chip .chip-export:hover { color: var(--green); }
 .portal-chips .chip .chip-close:hover { color: var(--err); }
 
 /* ─── Transcript ───────────────────────────────────────────────── */
diff --git a/wasm/dist-repl/repl.js b/wasm/dist-repl/repl.js
index e72fc91..0cf89d4 100644
--- a/wasm/dist-repl/repl.js
+++ b/wasm/dist-repl/repl.js
@@ -30,7 +30,14 @@ const tierSelectEl = document.getElementById("tier-select");
 const sendBtn = document.getElementById("send");
 const portalBarEl = document.getElementById("portal-bar");
 const portalSaveBtn = document.getElementById("portal-save");
+const portalImportBtn = document.getElementById("portal-import");
+const portalImportFileEl = document.getElementById("portal-import-file");
+const portalScopeBtn = document.getElementById("portal-scope");
 const portalChipsEl = document.getElementById("portal-chips");
+// Whether the chip strip shows every tab's checkpoints (true) or just
+// the active tab's (false). UI-only — never persisted, so a fresh
+// session always starts in the focused per-tab view.
+let showGlobalCheckpoints = false;
 
 // ─── State ──────────────────────────────────────────────────────────
 const state = {
@@ -309,6 +316,14 @@ async function saveCheckpoint() {
                         `${ts.getSeconds().toString().padStart(2, "0")}`;
     const name = safePortalName(prompt("checkpoint name:", defaultName) || "");
     if (!name) return;
+    // Overwrite guard — saving with an existing name silently nuked
+    // the old blob, which has cost more than one "where did my snapshot
+    // go?" moment. Ask first.
+    if (tab.checkpoints && tab.checkpoints[name]) {
+        const old = tab.checkpoints[name];
+        const when = new Date(old.savedAt).toLocaleString();
+        if (!confirm(`'${name}' already exists (${old.tier}, saved ${when}). overwrite?`)) return;
+    }
 
     let entry;
     if (tier === "asm") {
@@ -340,10 +355,15 @@ async function saveCheckpoint() {
     saveSoon();
 }
 
-async function restoreCheckpoint(name) {
+// Restore a checkpoint into the active tab. The optional sourceCp
+// override lets the global-checkpoints view pass in a cp from a
+// different tab — the restore still operates on activeTab() so the
+// user lands on the tab they were working in, with that tab's tier
+// state reset to the snapshot.
+async function restoreCheckpoint(name, sourceCp) {
     const tab = activeTab();
     if (!tab) return;
-    const cp = tab.checkpoints && tab.checkpoints[name];
+    const cp = sourceCp || (tab.checkpoints && tab.checkpoints[name]);
     if (!cp) return;
     if (!confirm(`restore '${name}'? current ${cp.tier} state is replaced.`)) return;
     if (tab.tier !== cp.tier) {
@@ -383,6 +403,91 @@ async function restoreCheckpoint(name) {
     saveSoon();
 }
 
+function renameCheckpoint(oldName) {
+    const tab = activeTab();
+    if (!tab || !tab.checkpoints || !tab.checkpoints[oldName]) return;
+    const raw = prompt(`rename '${oldName}' to:`, oldName);
+    if (raw === null) return;
+    const newName = safePortalName(raw);
+    if (!newName || newName === oldName) return;
+    if (tab.checkpoints[newName]) {
+        const old = tab.checkpoints[newName];
+        const when = new Date(old.savedAt).toLocaleString();
+        if (!confirm(`'${newName}' already exists (${old.tier}, saved ${when}). overwrite?`)) return;
+    }
+    tab.checkpoints[newName] = tab.checkpoints[oldName];
+    delete tab.checkpoints[oldName];
+    renderAll();
+    saveSoon();
+}
+
+// Export a checkpoint to a downloadable .portal.json file. The blob
+// itself is opaque JSON for c/python (portal_save's wire format) and a
+// {tier, mode: "replay", inputs} object for asm. Either way the file
+// holds everything importCheckpoint needs to reconstruct the entry; no
+// vault-side metadata bleeds out.
+function exportCheckpoint(name) {
+    const tab = activeTab();
+    if (!tab || !tab.checkpoints || !tab.checkpoints[name]) return;
+    const entry = tab.checkpoints[name];
+    const payload = { __portal: 1, name, ...entry };
+    const data = new Blob([JSON.stringify(payload, null, 2)], { type: "application/json" });
+    const url = URL.createObjectURL(data);
+    const a = document.createElement("a");
+    a.href = url;
+    a.download = `${name}.portal.json`;
+    document.body.appendChild(a);
+    a.click();
+    document.body.removeChild(a);
+    setTimeout(() => URL.revokeObjectURL(url), 1000);
+}
+
+// Import a checkpoint File (from <input type="file">). Validates the
+// shape, prompts on name collision, lands the entry in the active
+// tab's checkpoints map. The imported entry lives on whatever tier it
+// was saved under — restoring it will switch the active tab to that
+// tier automatically (restoreCheckpoint already does the swap).
+async function importCheckpoint(file) {
+    const tab = activeTab();
+    if (!tab) return;
+    let payload;
+    try {
+        const text = await file.text();
+        payload = JSON.parse(text);
+    } catch (e) {
+        alert("import failed — not valid JSON: " + e.message);
+        return;
+    }
+    if (!payload || payload.__portal !== 1 || !payload.tier || !payload.savedAt) {
+        alert("import failed — file isn't a portal snapshot (missing __portal/tier/savedAt)");
+        return;
+    }
+    const baseName = safePortalName(payload.name || file.name.replace(/\.portal\.json$/i, "")) || "imported";
+    let name = baseName;
+    tab.checkpoints = tab.checkpoints || {};
+    if (tab.checkpoints[name]) {
+        const old = tab.checkpoints[name];
+        const when = new Date(old.savedAt).toLocaleString();
+        if (!confirm(`'${name}' already exists (${old.tier}, saved ${when}). overwrite?`)) {
+            // Auto-suffix on decline so the user gets to keep both.
+            let i = 2;
+            while (tab.checkpoints[`${baseName}-${i}`]) i++;
+            name = `${baseName}-${i}`;
+        }
+    }
+    const entry = { tier: payload.tier, savedAt: payload.savedAt };
+    if (payload.mode === "replay") {
+        entry.mode = "replay";
+        entry.inputs = Array.isArray(payload.inputs) ? payload.inputs : [];
+    } else {
+        entry.mode = "blob";
+        entry.blob = payload.blob || "";
+    }
+    tab.checkpoints[name] = entry;
+    renderAll();
+    saveSoon();
+}
+
 function deleteCheckpoint(name) {
     const tab = activeTab();
     if (!tab || !tab.checkpoints) return;
@@ -492,24 +597,63 @@ function renderAll() {
         transcriptEl.appendChild(block);
     }
 
-    // Portal chips — one per saved checkpoint in the active tab.
+    // Portal chips — when showGlobalCheckpoints is off, one per saved
+    // checkpoint in the active tab. When on, gather every checkpoint
+    // across every tab so the user can restore a snapshot saved on
+    // tab A into tab B. The label gains a "· tabName" suffix in
+    // global mode so it's clear where each chip came from.
     portalChipsEl.innerHTML = "";
-    const checkpoints = tab.checkpoints || {};
-    const names = Object.keys(checkpoints).sort();
-    for (const name of names) {
+    portalScopeBtn.textContent = showGlobalCheckpoints ? "🌐 all tabs" : "📂 this tab";
+    portalScopeBtn.title = showGlobalCheckpoints
+        ? "showing checkpoints from every tab — click for this tab only"
+        : "showing only this tab's checkpoints — click for every tab";
+    const chipRows = [];
+    if (showGlobalCheckpoints) {
+        for (const t of state.tabs) {
+            const cps = t.checkpoints || {};
+            for (const name of Object.keys(cps)) {
+                chipRows.push({ tab: t, name, cp: cps[name] });
+            }
+        }
+        chipRows.sort((a, b) => b.cp.savedAt - a.cp.savedAt);
+    } else {
+        const cps = tab.checkpoints || {};
+        for (const name of Object.keys(cps).sort()) {
+            chipRows.push({ tab, name, cp: cps[name] });
+        }
+    }
+    for (const { tab: cpTab, name, cp } of chipRows) {
         const chip = document.createElement("span");
         chip.className = "chip";
-        chip.title = `${name} · ${checkpoints[name].tier} · saved ${new Date(checkpoints[name].savedAt).toLocaleString()} — click to restore`;
+        const when = new Date(cp.savedAt).toLocaleString();
+        chip.title = showGlobalCheckpoints
+            ? `${name} · ${cp.tier} · saved ${when} on tab '${cpTab.name}' — click to restore into THIS tab`
+            : `${name} · ${cp.tier} · saved ${when} — click to restore, dbl-click to rename`;
         const label = document.createElement("span");
-        label.textContent = name;
-        label.addEventListener("click", () => restoreCheckpoint(name));
-        const close = document.createElement("span");
-        close.className = "chip-close";
-        close.textContent = "×";
-        close.title = "delete checkpoint";
-        close.addEventListener("click", (e) => { e.stopPropagation(); if (confirm(`delete '${name}'?`)) deleteCheckpoint(name); });
-        chip.appendChild(label);
-        chip.appendChild(close);
+        label.textContent = showGlobalCheckpoints ? `${name} · ${cpTab.name}` : name;
+        // Restore always operates on the active tab; in global mode
+        // the snapshot's cp object is passed so we don't depend on
+        // the active tab having a checkpoints[name] match.
+        label.addEventListener("click", () => restoreCheckpoint(name, cp));
+        if (!showGlobalCheckpoints) {
+            label.addEventListener("dblclick", (e) => { e.stopPropagation(); renameCheckpoint(name); });
+            const exportBtn = document.createElement("span");
+            exportBtn.className = "chip-export";
+            exportBtn.textContent = "⇣";
+            exportBtn.title = "download checkpoint as .portal.json";
+            exportBtn.addEventListener("click", (e) => { e.stopPropagation(); exportCheckpoint(name); });
+            const close = document.createElement("span");
+            close.className = "chip-close";
+            close.textContent = "×";
+            close.title = "delete checkpoint";
+            close.addEventListener("click", (e) => { e.stopPropagation(); if (confirm(`delete '${name}'?`)) deleteCheckpoint(name); });
+            chip.appendChild(label);
+            chip.appendChild(exportBtn);
+            chip.appendChild(close);
+        } else {
+            chip.classList.add("chip-global");
+            chip.appendChild(label);
+        }
         portalChipsEl.appendChild(chip);
     }
 
@@ -766,6 +910,17 @@ clearLogBtn.addEventListener("click", () => {
 });
 cancelBtn.addEventListener("click", cancelAllPendingInActiveTab);
 portalSaveBtn.addEventListener("click", saveCheckpoint);
+portalImportBtn.addEventListener("click", () => portalImportFileEl.click());
+portalImportFileEl.addEventListener("change", async (e) => {
+    const file = e.target.files && e.target.files[0];
+    if (!file) return;
+    await importCheckpoint(file);
+    e.target.value = "";
+});
+portalScopeBtn.addEventListener("click", () => {
+    showGlobalCheckpoints = !showGlobalCheckpoints;
+    renderAll();
+});
 lockBtn.addEventListener("click", relock);
 // Insert heap pressure indicator into the tabbar after the spacer.
 document.getElementById("tabbar").insertBefore(heapEl, resetTierBtn);
diff --git a/wasm/repl/index.html b/wasm/repl/index.html
index 5845a02..37ff31c 100644
--- a/wasm/repl/index.html
+++ b/wasm/repl/index.html
@@ -90,6 +90,9 @@
   <section class="portal-bar" id="portal-bar">
     <span class="portal-label" title="save the current tab's tier state to your encrypted vault. comes back exactly the same after a tab close + reopen.">portals:</span>
     <button id="portal-save" class="ghost" title="save tier state — names the snapshot by date+time">💾 save</button>
+    <button id="portal-import" class="ghost" title="import a .portal.json file">📁 import</button>
+    <button id="portal-scope" class="ghost" title="toggle between this tab's checkpoints and every tab's">📂 this tab</button>
+    <input id="portal-import-file" type="file" accept=".json,.portal,application/json" hidden>
     <div id="portal-chips" class="portal-chips"></div>
   </section>
   <div id="transcript" class="transcript"></div>
diff --git a/wasm/repl/repl.css b/wasm/repl/repl.css
index 2a37d53..244bf2f 100644
--- a/wasm/repl/repl.css
+++ b/wasm/repl/repl.css
@@ -190,7 +190,8 @@ body.repl {
  * (the asm-wat tier stays grey). */
 .portal-bar {
   display: grid;
-  grid-template-columns: auto auto 1fr;
+  /* label · save · import · scope · chips-row */
+  grid-template-columns: auto auto auto auto 1fr;
   gap: 0.4rem;
   align-items: center;
   padding: 0.2rem 0.5rem;
@@ -211,7 +212,8 @@ body.repl {
 }
 .portal-chips .chip {
   display: inline-grid;
-  grid-template-columns: auto auto;
+  /* label · ⇣ download · × delete */
+  grid-template-columns: auto auto auto;
   gap: 0.3rem;
   align-items: center;
   background: var(--pane-bg);
@@ -223,12 +225,20 @@ body.repl {
   white-space: nowrap;
 }
 .portal-chips .chip:hover { border-color: var(--green); }
+.portal-chips .chip-global {
+  /* Cross-tab snapshots get a muted accent so they read as "borrowed
+   * from another tab" rather than belonging here. */
+  border-style: dashed;
+  opacity: 0.85;
+}
+.portal-chips .chip .chip-export,
 .portal-chips .chip .chip-close {
   color: var(--muted);
   font-size: 0.85em;
   cursor: pointer;
   padding: 0 0.15rem;
 }
+.portal-chips .chip .chip-export:hover { color: var(--green); }
 .portal-chips .chip .chip-close:hover { color: var(--err); }
 
 /* ─── Transcript ───────────────────────────────────────────────── */
diff --git a/wasm/repl/repl.js b/wasm/repl/repl.js
index e72fc91..0cf89d4 100644
--- a/wasm/repl/repl.js
+++ b/wasm/repl/repl.js
@@ -30,7 +30,14 @@ const tierSelectEl = document.getElementById("tier-select");
 const sendBtn = document.getElementById("send");
 const portalBarEl = document.getElementById("portal-bar");
 const portalSaveBtn = document.getElementById("portal-save");
+const portalImportBtn = document.getElementById("portal-import");
+const portalImportFileEl = document.getElementById("portal-import-file");
+const portalScopeBtn = document.getElementById("portal-scope");
 const portalChipsEl = document.getElementById("portal-chips");
+// Whether the chip strip shows every tab's checkpoints (true) or just
+// the active tab's (false). UI-only — never persisted, so a fresh
+// session always starts in the focused per-tab view.
+let showGlobalCheckpoints = false;
 
 // ─── State ──────────────────────────────────────────────────────────
 const state = {
@@ -309,6 +316,14 @@ async function saveCheckpoint() {
                         `${ts.getSeconds().toString().padStart(2, "0")}`;
     const name = safePortalName(prompt("checkpoint name:", defaultName) || "");
     if (!name) return;
+    // Overwrite guard — saving with an existing name silently nuked
+    // the old blob, which has cost more than one "where did my snapshot
+    // go?" moment. Ask first.
+    if (tab.checkpoints && tab.checkpoints[name]) {
+        const old = tab.checkpoints[name];
+        const when = new Date(old.savedAt).toLocaleString();
+        if (!confirm(`'${name}' already exists (${old.tier}, saved ${when}). overwrite?`)) return;
+    }
 
     let entry;
     if (tier === "asm") {
@@ -340,10 +355,15 @@ async function saveCheckpoint() {
     saveSoon();
 }
 
-async function restoreCheckpoint(name) {
+// Restore a checkpoint into the active tab. The optional sourceCp
+// override lets the global-checkpoints view pass in a cp from a
+// different tab — the restore still operates on activeTab() so the
+// user lands on the tab they were working in, with that tab's tier
+// state reset to the snapshot.
+async function restoreCheckpoint(name, sourceCp) {
     const tab = activeTab();
     if (!tab) return;
-    const cp = tab.checkpoints && tab.checkpoints[name];
+    const cp = sourceCp || (tab.checkpoints && tab.checkpoints[name]);
     if (!cp) return;
     if (!confirm(`restore '${name}'? current ${cp.tier} state is replaced.`)) return;
     if (tab.tier !== cp.tier) {
@@ -383,6 +403,91 @@ async function restoreCheckpoint(name) {
     saveSoon();
 }
 
+function renameCheckpoint(oldName) {
+    const tab = activeTab();
+    if (!tab || !tab.checkpoints || !tab.checkpoints[oldName]) return;
+    const raw = prompt(`rename '${oldName}' to:`, oldName);
+    if (raw === null) return;
+    const newName = safePortalName(raw);
+    if (!newName || newName === oldName) return;
+    if (tab.checkpoints[newName]) {
+        const old = tab.checkpoints[newName];
+        const when = new Date(old.savedAt).toLocaleString();
+        if (!confirm(`'${newName}' already exists (${old.tier}, saved ${when}). overwrite?`)) return;
+    }
+    tab.checkpoints[newName] = tab.checkpoints[oldName];
+    delete tab.checkpoints[oldName];
+    renderAll();
+    saveSoon();
+}
+
+// Export a checkpoint to a downloadable .portal.json file. The blob
+// itself is opaque JSON for c/python (portal_save's wire format) and a
+// {tier, mode: "replay", inputs} object for asm. Either way the file
+// holds everything importCheckpoint needs to reconstruct the entry; no
+// vault-side metadata bleeds out.
+function exportCheckpoint(name) {
+    const tab = activeTab();
+    if (!tab || !tab.checkpoints || !tab.checkpoints[name]) return;
+    const entry = tab.checkpoints[name];
+    const payload = { __portal: 1, name, ...entry };
+    const data = new Blob([JSON.stringify(payload, null, 2)], { type: "application/json" });
+    const url = URL.createObjectURL(data);
+    const a = document.createElement("a");
+    a.href = url;
+    a.download = `${name}.portal.json`;
+    document.body.appendChild(a);
+    a.click();
+    document.body.removeChild(a);
+    setTimeout(() => URL.revokeObjectURL(url), 1000);
+}
+
+// Import a checkpoint File (from <input type="file">). Validates the
+// shape, prompts on name collision, lands the entry in the active
+// tab's checkpoints map. The imported entry lives on whatever tier it
+// was saved under — restoring it will switch the active tab to that
+// tier automatically (restoreCheckpoint already does the swap).
+async function importCheckpoint(file) {
+    const tab = activeTab();
+    if (!tab) return;
+    let payload;
+    try {
+        const text = await file.text();
+        payload = JSON.parse(text);
+    } catch (e) {
+        alert("import failed — not valid JSON: " + e.message);
+        return;
+    }
+    if (!payload || payload.__portal !== 1 || !payload.tier || !payload.savedAt) {
+        alert("import failed — file isn't a portal snapshot (missing __portal/tier/savedAt)");
+        return;
+    }
+    const baseName = safePortalName(payload.name || file.name.replace(/\.portal\.json$/i, "")) || "imported";
+    let name = baseName;
+    tab.checkpoints = tab.checkpoints || {};
+    if (tab.checkpoints[name]) {
+        const old = tab.checkpoints[name];
+        const when = new Date(old.savedAt).toLocaleString();
+        if (!confirm(`'${name}' already exists (${old.tier}, saved ${when}). overwrite?`)) {
+            // Auto-suffix on decline so the user gets to keep both.
+            let i = 2;
+            while (tab.checkpoints[`${baseName}-${i}`]) i++;
+            name = `${baseName}-${i}`;
+        }
+    }
+    const entry = { tier: payload.tier, savedAt: payload.savedAt };
+    if (payload.mode === "replay") {
+        entry.mode = "replay";
+        entry.inputs = Array.isArray(payload.inputs) ? payload.inputs : [];
+    } else {
+        entry.mode = "blob";
+        entry.blob = payload.blob || "";
+    }
+    tab.checkpoints[name] = entry;
+    renderAll();
+    saveSoon();
+}
+
 function deleteCheckpoint(name) {
     const tab = activeTab();
     if (!tab || !tab.checkpoints) return;
@@ -492,24 +597,63 @@ function renderAll() {
         transcriptEl.appendChild(block);
     }
 
-    // Portal chips — one per saved checkpoint in the active tab.
+    // Portal chips — when showGlobalCheckpoints is off, one per saved
+    // checkpoint in the active tab. When on, gather every checkpoint
+    // across every tab so the user can restore a snapshot saved on
+    // tab A into tab B. The label gains a "· tabName" suffix in
+    // global mode so it's clear where each chip came from.
     portalChipsEl.innerHTML = "";
-    const checkpoints = tab.checkpoints || {};
-    const names = Object.keys(checkpoints).sort();
-    for (const name of names) {
+    portalScopeBtn.textContent = showGlobalCheckpoints ? "🌐 all tabs" : "📂 this tab";
+    portalScopeBtn.title = showGlobalCheckpoints
+        ? "showing checkpoints from every tab — click for this tab only"
+        : "showing only this tab's checkpoints — click for every tab";
+    const chipRows = [];
+    if (showGlobalCheckpoints) {
+        for (const t of state.tabs) {
+            const cps = t.checkpoints || {};
+            for (const name of Object.keys(cps)) {
+                chipRows.push({ tab: t, name, cp: cps[name] });
+            }
+        }
+        chipRows.sort((a, b) => b.cp.savedAt - a.cp.savedAt);
+    } else {
+        const cps = tab.checkpoints || {};
+        for (const name of Object.keys(cps).sort()) {
+            chipRows.push({ tab, name, cp: cps[name] });
+        }
+    }
+    for (const { tab: cpTab, name, cp } of chipRows) {
         const chip = document.createElement("span");
         chip.className = "chip";
-        chip.title = `${name} · ${checkpoints[name].tier} · saved ${new Date(checkpoints[name].savedAt).toLocaleString()} — click to restore`;
+        const when = new Date(cp.savedAt).toLocaleString();
+        chip.title = showGlobalCheckpoints
+            ? `${name} · ${cp.tier} · saved ${when} on tab '${cpTab.name}' — click to restore into THIS tab`
+            : `${name} · ${cp.tier} · saved ${when} — click to restore, dbl-click to rename`;
         const label = document.createElement("span");
-        label.textContent = name;
-        label.addEventListener("click", () => restoreCheckpoint(name));
-        const close = document.createElement("span");
-        close.className = "chip-close";
-        close.textContent = "×";
-        close.title = "delete checkpoint";
-        close.addEventListener("click", (e) => { e.stopPropagation(); if (confirm(`delete '${name}'?`)) deleteCheckpoint(name); });
-        chip.appendChild(label);
-        chip.appendChild(close);
+        label.textContent = showGlobalCheckpoints ? `${name} · ${cpTab.name}` : name;
+        // Restore always operates on the active tab; in global mode
+        // the snapshot's cp object is passed so we don't depend on
+        // the active tab having a checkpoints[name] match.
+        label.addEventListener("click", () => restoreCheckpoint(name, cp));
+        if (!showGlobalCheckpoints) {
+            label.addEventListener("dblclick", (e) => { e.stopPropagation(); renameCheckpoint(name); });
+            const exportBtn = document.createElement("span");
+            exportBtn.className = "chip-export";
+            exportBtn.textContent = "⇣";
+            exportBtn.title = "download checkpoint as .portal.json";
+            exportBtn.addEventListener("click", (e) => { e.stopPropagation(); exportCheckpoint(name); });
+            const close = document.createElement("span");
+            close.className = "chip-close";
+            close.textContent = "×";
+            close.title = "delete checkpoint";
+            close.addEventListener("click", (e) => { e.stopPropagation(); if (confirm(`delete '${name}'?`)) deleteCheckpoint(name); });
+            chip.appendChild(label);
+            chip.appendChild(exportBtn);
+            chip.appendChild(close);
+        } else {
+            chip.classList.add("chip-global");
+            chip.appendChild(label);
+        }
         portalChipsEl.appendChild(chip);
     }
 
@@ -766,6 +910,17 @@ clearLogBtn.addEventListener("click", () => {
 });
 cancelBtn.addEventListener("click", cancelAllPendingInActiveTab);
 portalSaveBtn.addEventListener("click", saveCheckpoint);
+portalImportBtn.addEventListener("click", () => portalImportFileEl.click());
+portalImportFileEl.addEventListener("change", async (e) => {
+    const file = e.target.files && e.target.files[0];
+    if (!file) return;
+    await importCheckpoint(file);
+    e.target.value = "";
+});
+portalScopeBtn.addEventListener("click", () => {
+    showGlobalCheckpoints = !showGlobalCheckpoints;
+    renderAll();
+});
 lockBtn.addEventListener("click", relock);
 // Insert heap pressure indicator into the tabbar after the spacer.
 document.getElementById("tabbar").insertBefore(heapEl, resetTierBtn);
diff --git a/www/playground/c/lumbda-c.loader.js b/www/playground/c/lumbda-c.loader.js
index 1e2e8e2..1fccb21 100644
--- a/www/playground/c/lumbda-c.loader.js
+++ b/www/playground/c/lumbda-c.loader.js
@@ -99,7 +99,14 @@ async function _bootstrap() {
             // free path right now (LUMBDA_NO_BOEHM), so used = total —
             // every malloc accumulates until reload. Documented and
             // surfaced in the REPL so the user sees the pressure.
-            const total = module.HEAPU8.byteLength;
+            //
+            // HEAPU8 isn't always live: after a worker reboots, the
+            // heap poll can fire while the new Module is mid-init and
+            // HEAPU8 isn't yet wired. Return null so the REPL hides
+            // the pressure indicator for that tick instead of crashing.
+            const heap = module.HEAPU8;
+            if (!heap) return null;
+            const total = heap.byteLength;
             return { used: total, total };
         },
     };
diff --git a/www/repl/c/lumbda-c.loader.js b/www/repl/c/lumbda-c.loader.js
index 1e2e8e2..1fccb21 100644
--- a/www/repl/c/lumbda-c.loader.js
+++ b/www/repl/c/lumbda-c.loader.js
@@ -99,7 +99,14 @@ async function _bootstrap() {
             // free path right now (LUMBDA_NO_BOEHM), so used = total —
             // every malloc accumulates until reload. Documented and
             // surfaced in the REPL so the user sees the pressure.
-            const total = module.HEAPU8.byteLength;
+            //
+            // HEAPU8 isn't always live: after a worker reboots, the
+            // heap poll can fire while the new Module is mid-init and
+            // HEAPU8 isn't yet wired. Return null so the REPL hides
+            // the pressure indicator for that tick instead of crashing.
+            const heap = module.HEAPU8;
+            if (!heap) return null;
+            const total = heap.byteLength;
             return { used: total, total };
         },
     };
diff --git a/www/repl/index.html b/www/repl/index.html
index 5845a02..37ff31c 100644
--- a/www/repl/index.html
+++ b/www/repl/index.html
@@ -90,6 +90,9 @@
   <section class="portal-bar" id="portal-bar">
     <span class="portal-label" title="save the current tab's tier state to your encrypted vault. comes back exactly the same after a tab close + reopen.">portals:</span>
     <button id="portal-save" class="ghost" title="save tier state — names the snapshot by date+time">💾 save</button>
+    <button id="portal-import" class="ghost" title="import a .portal.json file">📁 import</button>
+    <button id="portal-scope" class="ghost" title="toggle between this tab's checkpoints and every tab's">📂 this tab</button>
+    <input id="portal-import-file" type="file" accept=".json,.portal,application/json" hidden>
     <div id="portal-chips" class="portal-chips"></div>
   </section>
   <div id="transcript" class="transcript"></div>
diff --git a/www/repl/repl.css b/www/repl/repl.css
index 2a37d53..244bf2f 100644
--- a/www/repl/repl.css
+++ b/www/repl/repl.css
@@ -190,7 +190,8 @@ body.repl {
  * (the asm-wat tier stays grey). */
 .portal-bar {
   display: grid;
-  grid-template-columns: auto auto 1fr;
+  /* label · save · import · scope · chips-row */
+  grid-template-columns: auto auto auto auto 1fr;
   gap: 0.4rem;
   align-items: center;
   padding: 0.2rem 0.5rem;
@@ -211,7 +212,8 @@ body.repl {
 }
 .portal-chips .chip {
   display: inline-grid;
-  grid-template-columns: auto auto;
+  /* label · ⇣ download · × delete */
+  grid-template-columns: auto auto auto;
   gap: 0.3rem;
   align-items: center;
   background: var(--pane-bg);
@@ -223,12 +225,20 @@ body.repl {
   white-space: nowrap;
 }
 .portal-chips .chip:hover { border-color: var(--green); }
+.portal-chips .chip-global {
+  /* Cross-tab snapshots get a muted accent so they read as "borrowed
+   * from another tab" rather than belonging here. */
+  border-style: dashed;
+  opacity: 0.85;
+}
+.portal-chips .chip .chip-export,
 .portal-chips .chip .chip-close {
   color: var(--muted);
   font-size: 0.85em;
   cursor: pointer;
   padding: 0 0.15rem;
 }
+.portal-chips .chip .chip-export:hover { color: var(--green); }
 .portal-chips .chip .chip-close:hover { color: var(--err); }
 
 /* ─── Transcript ───────────────────────────────────────────────── */
diff --git a/www/repl/repl.js b/www/repl/repl.js
index e72fc91..0cf89d4 100644
--- a/www/repl/repl.js
+++ b/www/repl/repl.js
@@ -30,7 +30,14 @@ const tierSelectEl = document.getElementById("tier-select");
 const sendBtn = document.getElementById("send");
 const portalBarEl = document.getElementById("portal-bar");
 const portalSaveBtn = document.getElementById("portal-save");
+const portalImportBtn = document.getElementById("portal-import");
+const portalImportFileEl = document.getElementById("portal-import-file");
+const portalScopeBtn = document.getElementById("portal-scope");
 const portalChipsEl = document.getElementById("portal-chips");
+// Whether the chip strip shows every tab's checkpoints (true) or just
+// the active tab's (false). UI-only — never persisted, so a fresh
+// session always starts in the focused per-tab view.
+let showGlobalCheckpoints = false;
 
 // ─── State ──────────────────────────────────────────────────────────
 const state = {
@@ -309,6 +316,14 @@ async function saveCheckpoint() {
                         `${ts.getSeconds().toString().padStart(2, "0")}`;
     const name = safePortalName(prompt("checkpoint name:", defaultName) || "");
     if (!name) return;
+    // Overwrite guard — saving with an existing name silently nuked
+    // the old blob, which has cost more than one "where did my snapshot
+    // go?" moment. Ask first.
+    if (tab.checkpoints && tab.checkpoints[name]) {
+        const old = tab.checkpoints[name];
+        const when = new Date(old.savedAt).toLocaleString();
+        if (!confirm(`'${name}' already exists (${old.tier}, saved ${when}). overwrite?`)) return;
+    }
 
     let entry;
     if (tier === "asm") {
@@ -340,10 +355,15 @@ async function saveCheckpoint() {
     saveSoon();
 }
 
-async function restoreCheckpoint(name) {
+// Restore a checkpoint into the active tab. The optional sourceCp
+// override lets the global-checkpoints view pass in a cp from a
+// different tab — the restore still operates on activeTab() so the
+// user lands on the tab they were working in, with that tab's tier
+// state reset to the snapshot.
+async function restoreCheckpoint(name, sourceCp) {
     const tab = activeTab();
     if (!tab) return;
-    const cp = tab.checkpoints && tab.checkpoints[name];
+    const cp = sourceCp || (tab.checkpoints && tab.checkpoints[name]);
     if (!cp) return;
     if (!confirm(`restore '${name}'? current ${cp.tier} state is replaced.`)) return;
     if (tab.tier !== cp.tier) {
@@ -383,6 +403,91 @@ async function restoreCheckpoint(name) {
     saveSoon();
 }
 
+function renameCheckpoint(oldName) {
+    const tab = activeTab();
+    if (!tab || !tab.checkpoints || !tab.checkpoints[oldName]) return;
+    const raw = prompt(`rename '${oldName}' to:`, oldName);
+    if (raw === null) return;
+    const newName = safePortalName(raw);
+    if (!newName || newName === oldName) return;
+    if (tab.checkpoints[newName]) {
+        const old = tab.checkpoints[newName];
+        const when = new Date(old.savedAt).toLocaleString();
+        if (!confirm(`'${newName}' already exists (${old.tier}, saved ${when}). overwrite?`)) return;
+    }
+    tab.checkpoints[newName] = tab.checkpoints[oldName];
+    delete tab.checkpoints[oldName];
+    renderAll();
+    saveSoon();
+}
+
+// Export a checkpoint to a downloadable .portal.json file. The blob
+// itself is opaque JSON for c/python (portal_save's wire format) and a
+// {tier, mode: "replay", inputs} object for asm. Either way the file
+// holds everything importCheckpoint needs to reconstruct the entry; no
+// vault-side metadata bleeds out.
+function exportCheckpoint(name) {
+    const tab = activeTab();
+    if (!tab || !tab.checkpoints || !tab.checkpoints[name]) return;
+    const entry = tab.checkpoints[name];
+    const payload = { __portal: 1, name, ...entry };
+    const data = new Blob([JSON.stringify(payload, null, 2)], { type: "application/json" });
+    const url = URL.createObjectURL(data);
+    const a = document.createElement("a");
+    a.href = url;
+    a.download = `${name}.portal.json`;
+    document.body.appendChild(a);
+    a.click();
+    document.body.removeChild(a);
+    setTimeout(() => URL.revokeObjectURL(url), 1000);
+}
+
+// Import a checkpoint File (from <input type="file">). Validates the
+// shape, prompts on name collision, lands the entry in the active
+// tab's checkpoints map. The imported entry lives on whatever tier it
+// was saved under — restoring it will switch the active tab to that
+// tier automatically (restoreCheckpoint already does the swap).
+async function importCheckpoint(file) {
+    const tab = activeTab();
+    if (!tab) return;
+    let payload;
+    try {
+        const text = await file.text();
+        payload = JSON.parse(text);
+    } catch (e) {
+        alert("import failed — not valid JSON: " + e.message);
+        return;
+    }
+    if (!payload || payload.__portal !== 1 || !payload.tier || !payload.savedAt) {
+        alert("import failed — file isn't a portal snapshot (missing __portal/tier/savedAt)");
+        return;
+    }
+    const baseName = safePortalName(payload.name || file.name.replace(/\.portal\.json$/i, "")) || "imported";
+    let name = baseName;
+    tab.checkpoints = tab.checkpoints || {};
+    if (tab.checkpoints[name]) {
+        const old = tab.checkpoints[name];
+        const when = new Date(old.savedAt).toLocaleString();
+        if (!confirm(`'${name}' already exists (${old.tier}, saved ${when}). overwrite?`)) {
+            // Auto-suffix on decline so the user gets to keep both.
+            let i = 2;
+            while (tab.checkpoints[`${baseName}-${i}`]) i++;
+            name = `${baseName}-${i}`;
+        }
+    }
+    const entry = { tier: payload.tier, savedAt: payload.savedAt };
+    if (payload.mode === "replay") {
+        entry.mode = "replay";
+        entry.inputs = Array.isArray(payload.inputs) ? payload.inputs : [];
+    } else {
+        entry.mode = "blob";
+        entry.blob = payload.blob || "";
+    }
+    tab.checkpoints[name] = entry;
+    renderAll();
+    saveSoon();
+}
+
 function deleteCheckpoint(name) {
     const tab = activeTab();
     if (!tab || !tab.checkpoints) return;
@@ -492,24 +597,63 @@ function renderAll() {
         transcriptEl.appendChild(block);
     }
 
-    // Portal chips — one per saved checkpoint in the active tab.
+    // Portal chips — when showGlobalCheckpoints is off, one per saved
+    // checkpoint in the active tab. When on, gather every checkpoint
+    // across every tab so the user can restore a snapshot saved on
+    // tab A into tab B. The label gains a "· tabName" suffix in
+    // global mode so it's clear where each chip came from.
     portalChipsEl.innerHTML = "";
-    const checkpoints = tab.checkpoints || {};
-    const names = Object.keys(checkpoints).sort();
-    for (const name of names) {
+    portalScopeBtn.textContent = showGlobalCheckpoints ? "🌐 all tabs" : "📂 this tab";
+    portalScopeBtn.title = showGlobalCheckpoints
+        ? "showing checkpoints from every tab — click for this tab only"
+        : "showing only this tab's checkpoints — click for every tab";
+    const chipRows = [];
+    if (showGlobalCheckpoints) {
+        for (const t of state.tabs) {
+            const cps = t.checkpoints || {};
+            for (const name of Object.keys(cps)) {
+                chipRows.push({ tab: t, name, cp: cps[name] });
+            }
+        }
+        chipRows.sort((a, b) => b.cp.savedAt - a.cp.savedAt);
+    } else {
+        const cps = tab.checkpoints || {};
+        for (const name of Object.keys(cps).sort()) {
+            chipRows.push({ tab, name, cp: cps[name] });
+        }
+    }
+    for (const { tab: cpTab, name, cp } of chipRows) {
         const chip = document.createElement("span");
         chip.className = "chip";
-        chip.title = `${name} · ${checkpoints[name].tier} · saved ${new Date(checkpoints[name].savedAt).toLocaleString()} — click to restore`;
+        const when = new Date(cp.savedAt).toLocaleString();
+        chip.title = showGlobalCheckpoints
+            ? `${name} · ${cp.tier} · saved ${when} on tab '${cpTab.name}' — click to restore into THIS tab`
+            : `${name} · ${cp.tier} · saved ${when} — click to restore, dbl-click to rename`;
         const label = document.createElement("span");
-        label.textContent = name;
-        label.addEventListener("click", () => restoreCheckpoint(name));
-        const close = document.createElement("span");
-        close.className = "chip-close";
-        close.textContent = "×";
-        close.title = "delete checkpoint";
-        close.addEventListener("click", (e) => { e.stopPropagation(); if (confirm(`delete '${name}'?`)) deleteCheckpoint(name); });
-        chip.appendChild(label);
-        chip.appendChild(close);
+        label.textContent = showGlobalCheckpoints ? `${name} · ${cpTab.name}` : name;
+        // Restore always operates on the active tab; in global mode
+        // the snapshot's cp object is passed so we don't depend on
+        // the active tab having a checkpoints[name] match.
+        label.addEventListener("click", () => restoreCheckpoint(name, cp));
+        if (!showGlobalCheckpoints) {
+            label.addEventListener("dblclick", (e) => { e.stopPropagation(); renameCheckpoint(name); });
+            const exportBtn = document.createElement("span");
+            exportBtn.className = "chip-export";
+            exportBtn.textContent = "⇣";
+            exportBtn.title = "download checkpoint as .portal.json";
+            exportBtn.addEventListener("click", (e) => { e.stopPropagation(); exportCheckpoint(name); });
+            const close = document.createElement("span");
+            close.className = "chip-close";
+            close.textContent = "×";
+            close.title = "delete checkpoint";
+            close.addEventListener("click", (e) => { e.stopPropagation(); if (confirm(`delete '${name}'?`)) deleteCheckpoint(name); });
+            chip.appendChild(label);
+            chip.appendChild(exportBtn);
+            chip.appendChild(close);
+        } else {
+            chip.classList.add("chip-global");
+            chip.appendChild(label);
+        }
         portalChipsEl.appendChild(chip);
     }
 
@@ -766,6 +910,17 @@ clearLogBtn.addEventListener("click", () => {
 });
 cancelBtn.addEventListener("click", cancelAllPendingInActiveTab);
 portalSaveBtn.addEventListener("click", saveCheckpoint);
+portalImportBtn.addEventListener("click", () => portalImportFileEl.click());
+portalImportFileEl.addEventListener("change", async (e) => {
+    const file = e.target.files && e.target.files[0];
+    if (!file) return;
+    await importCheckpoint(file);
+    e.target.value = "";
+});
+portalScopeBtn.addEventListener("click", () => {
+    showGlobalCheckpoints = !showGlobalCheckpoints;
+    renderAll();
+});
 lockBtn.addEventListener("click", relock);
 // Insert heap pressure indicator into the tabbar after the spacer.
 document.getElementById("tabbar").insertBefore(heapEl, resetTierBtn);