diff --git a/lib/agentic/execution_journal.rb b/lib/agentic/execution_journal.rb
index 5e96540..89c9ad9 100644
--- a/lib/agentic/execution_journal.rb
+++ b/lib/agentic/execution_journal.rb
@@ -133,7 +133,20 @@ def lifecycle_hooks(hooks = {})
     # @param payload [Hash] Event data (must be JSON-serializable)
     # @return [void]
     def record(event, payload = {})
-      line = JSON.generate({event: event, at: Time.now.utc.iso8601(3)}.merge(payload))
+      at = Time.now.utc.iso8601(3)
+      line = begin
+        JSON.generate({event: event, at: at}.merge(payload))
+      rescue JSON::GeneratorError => e
+        # A journal write is a side effect of a task that already
+        # finished; it must never be the thing that fails it. Keep the
+        # fields replay keys on (task_id, description) so the task still
+        # counts, and record what could not be serialized.
+        JSON.generate(
+          {event: event, at: at}
+            .merge(payload.slice(:task_id, :description).select { |_, v| v.is_a?(String) })
+            .merge(payload_error: e.class.name, payload_inspect: payload.inspect[0, 500].scrub("?"))
+        )
+      end
 
       @mutex.synchronize do
         File.open(@path, "a") do |file|
diff --git a/spec/agentic/execution_journal_spec.rb b/spec/agentic/execution_journal_spec.rb
index 9f564c0..104a50c 100644
--- a/spec/agentic/execution_journal_spec.rb
+++ b/spec/agentic/execution_journal_spec.rb
@@ -22,6 +22,30 @@
       expect(lines).to all(have_key("at"))
     end
 
+    it "still lands a line when the payload cannot be serialized" do
+      binary = (+"caf\xE9").force_encoding(Encoding::BINARY)
+      journal.record(:task_succeeded, task_id: "t-bin", description: "Fetch page", output: {body: binary})
+
+      lines = File.readlines(path)
+      expect(lines.size).to eq(1)
+      entry = JSON.parse(lines.first)
+      expect(entry).to include("event" => "task_succeeded", "task_id" => "t-bin", "description" => "Fetch page")
+      expect(entry).to have_key("at")
+      expect(entry["payload_error"]).to eq("JSON::GeneratorError")
+      expect(entry["payload_inspect"]).to include("t-bin")
+
+      state = described_class.replay(path: path, mode: :strict)
+      expect(state.completed_task_ids).to eq(["t-bin"])
+    end
+
+    it "survives a payload with a symbol and a string spelling of the same key" do
+      journal.record(:task_succeeded, task_id: "t-dup", output: {:k => 1, "k" => 2})
+
+      expect(File.readlines(path).size).to eq(1)
+      state = described_class.replay(path: path)
+      expect(state.completed_task_ids).to eq(["t-dup"])
+    end
+
     it "is safe under concurrent writers" do
       threads = 8.times.map do |i|
         Thread.new do