diff --git a/src/core/blob-cache.ts b/src/core/blob-cache.ts
index dfcb776..1ebdb46 100644
--- a/src/core/blob-cache.ts
+++ b/src/core/blob-cache.ts
@@ -279,6 +279,7 @@ export class BlobCache {
     if (sizeHint != null && sizeHint > this.options.maxObject) { this.metric("bypass", sizeHint); throw new CacheAdmissionError("object_too_large"); }
     const token = randomUUID(), reservation = this.options.maxObject * 3 + 1024;
     const deadline = Date.now() + 120000;
+    let leaseUntil = 0;
     for (;;) {
       const owned = this.transaction(() => {
         this.expire();
@@ -289,7 +290,8 @@ export class BlobCache {
         }
         // Eviction unlinks files: commit its metadata even if admission still fails.
         if (this.usage() + reserved + reservation > this.options.budget) return null;
-        this.db.prepare("INSERT INTO fills VALUES(?,?,?,?)").run(key, token, Date.now() + 120000, reservation); return true;
+        leaseUntil = Date.now() + 120000;
+        this.db.prepare("INSERT INTO fills VALUES(?,?,?,?)").run(key, token, leaseUntil, reservation); return true;
       }, true);
       if (owned === null) throw new CacheAdmissionError("cache_budget_busy");
       if (owned) break;
@@ -300,10 +302,23 @@ export class BlobCache {
     }
     const raw = join(this.options.root, "tmp", `${token}.raw`), gz = join(this.options.root, "tmp", `${token}.gz`);
     let input: Readable | undefined, file: string | undefined;
+    let renewAt = Date.now() + 30000, leaseLost = false;
+    const loseLease = () => { leaseLost = true; input?.destroy(new Error("cache_fill_lease_lost")); };
     const heartbeat = setInterval(() => {
-      try { if (!this.db.prepare("UPDATE fills SET expires=? WHERE key=? AND token=?").run(Date.now() + 120000, key, token).changes) input?.destroy(new Error("cache_fill_lease_lost")); }
-      catch { input?.destroy(new Error("cache_fill_lease_lost")); }
-    }, 30000); heartbeat.unref();
+      const now = Date.now();
+      if (leaseLost || now < renewAt) return;
+      if (now >= leaseUntil) { loseLease(); return; }
+      try {
+        const renewedUntil = now + 120000;
+        if (!this.db.prepare("UPDATE fills SET expires=? WHERE key=? AND token=? AND expires>?").run(renewedUntil, key, token, now).changes) {
+          loseLease(); return;
+        }
+        leaseUntil = renewedUntil; renewAt = now + 30000;
+      } catch (error) {
+        if (!isCacheContention(error)) loseLease();
+        // Retry contention on the next tick within the last confirmed lease.
+      }
+    }, 1000); heartbeat.unref();
     const timeout = setTimeout(() => input?.destroy(new Error("cache_fill_timeout")), 120000); timeout.unref();
     try {
       // The pool reservation is already durable before acquiring physical headroom.
@@ -314,6 +329,7 @@ export class BlobCache {
       // Recheck after ownership; another producer may have published between the initial lookup and lease acquisition.
       hit = await this.lookup(key); if (hit) return hit;
       input = await produce();
+      if (leaseLost || Date.now() >= leaseUntil) throw new Error("cache_fill_lease_lost");
       let size = 0; const sha256 = createHash("sha256");
       await pipeline(input, new Transform({ transform: (chunk, _encoding, done) => {
         size += chunk.length; sha256.update(chunk);
diff --git a/test/shared-blob-cache.test.js b/test/shared-blob-cache.test.js
index 1da7367..604df6b 100644
--- a/test/shared-blob-cache.test.js
+++ b/test/shared-blob-cache.test.js
@@ -212,6 +212,42 @@ describe("shared content-addressed blob pool", function () {
       assert.equal((await error).message, "cache_reader_lease_lost");
     } finally { Date.now = now; other.db.exec("ROLLBACK"); reader.destroy(); other.close(); }
   });
+  for (const outcome of ["recover", "expire", "replaced"]) {
+    it(`handles fill heartbeat contention and ${outcome}`, async () => {
+      const other = new BlobCache(cache.options), interval = global.setInterval, now = Date.now;
+      let tick, started;
+      const ready = new Promise(resolve => { started = resolve; });
+      const input = new Readable({ read() {} });
+      global.setInterval = fn => { tick = fn; return interval(fn, 10000000); };
+      const fill = cache.getOrFill("fill-heartbeat", async () => { started(); return input; });
+      // Attach rejection handling before deliberately terminating the producer.
+      const result = fill.then(read);
+      const checked = outcome === "recover" ? result : assert.rejects(result, /cache_fill_lease_lost/);
+      try {
+        await ready; global.setInterval = interval; await delay(10);
+        const base = now();
+        other.db.exec("BEGIN IMMEDIATE"); Date.now = () => base + 31000; tick();
+        assert.equal(input.destroyed, false);
+        other.db.exec("ROLLBACK");
+        if (outcome === "recover") {
+          Date.now = () => base + 32000; tick();
+          assert.ok(Number(cache.db.prepare("SELECT expires FROM fills WHERE key=?").get("fill-heartbeat").expires) >= base + 152000);
+          Date.now = now; input.push("completed after contention"); input.push(null);
+          assert.equal((await checked).toString(), "completed after contention");
+        } else {
+          if (outcome === "replaced") other.db.prepare("UPDATE fills SET token=? WHERE key=?").run("replacement", "fill-heartbeat");
+          Date.now = () => base + (outcome === "expire" ? 121000 : 32000); tick();
+          assert.equal(input.destroyed, true);
+          Date.now = now; await checked;
+          assert.equal(cache.stats().blobs, 0);
+        }
+      } finally {
+        global.setInterval = interval; Date.now = now;
+        if (other.db.isTransaction) other.db.exec("ROLLBACK");
+        input.destroy(); await checked.catch(() => {}); other.close();
+      }
+    });
+  }
   it("coordinates physical headroom between source and result pools", async () => {
     const native = require("node:fs"), statfs = native.statfsSync;
     const other = new BlobCache({ ...cache.options, root: join(root, "results"), reservationRoot: root, freeBytes: 1000 });