fix: make event_seq session-scoped, not job-scoped (§8.3)

Key the monotonic event_seq counter by the submitter session_id so every
job in a session shares one strictly-monotonic, gap-free stream. Two jobs
in the same session no longer each start at 1 and collide in that session's
replay window, restoring the resume gap-free guarantee. (#43)

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: nficano

lib/arcp/runtime/job_manager.rb

@@ -33,7 +33,7 @@ def initialize(runtime:, lease_manager:, subscription_manager:, event_log:, cloc
         @jobs = {}                      # job_id => JobRecord
         @order = []                     # insertion order of job_ids (oldest first)
         @next_seq = 0                   # monotonic counter assigned at submit
-        @event_seq = Hash.new(0)        # job_id => last emitted seq
+        @event_seq = Hash.new(0)        # submitter session_id => last emitted seq
         @idempotency = {}               # [principal, key] => job_id
         @accepted = {}                  # job_id => [resolved, lease, credentials, accepted_at]
         @mutex = Mutex.new
@@ -237,10 +237,17 @@ def record_created_after?(record, threshold)
       def lookup(job_id) = @mutex.synchronize { @jobs[job_id] }
 
       def publish_event(job_id, event)
-        seq = @mutex.synchronize { @event_seq[job_id] += 1 }
+        # Spec §8.3: event_seq is session-scoped, strictly monotonic, and
+        # gap-free. Key the counter by the submitter session so every job in
+        # a session shares one monotonic stream (two jobs no longer both
+        # start at 1 and collide in that session's replay window).
+        session_id, seq = @mutex.synchronize do
+          sid = @jobs[job_id]&.submitter_session_id || ''
+          [sid, @event_seq[sid] += 1]
+        end
         env = Arcp::Envelope.build(
           type: Arcp::MessageTypes::JOB_EVENT,
-          session_id: @mutex.synchronize { @jobs[job_id]&.submitter_session_id || '' },
+          session_id: session_id,
           job_id: job_id, event_seq: seq, payload: event.to_h
         )
         @event_log.append(env.session_id, env)

spec/integration/audit_findings_2026_05_28_spec.rb

@@ -47,6 +47,38 @@
     end
   end
 
+  describe 'event_seq is session-scoped across a session\'s jobs (#43)' do
+    it 'assigns strictly increasing, gap-free seqs across two jobs in one session' do
+      Sync do
+        runtime = build_runtime(
+          agents: { emitter: lambda { |ctx|
+            3.times { |i| ctx.log(level: 'info', message: "m#{i}") }
+            Async::Task.current.sleep(5)
+          } }
+        )
+        client, server_task = open_pair(runtime)
+
+        client.submit_job(agent: 'emitter')
+        client.submit_job(agent: 'emitter')
+        Async::Task.current.sleep(0.1)
+
+        session_id = client.session.id
+        seqs = runtime.event_log
+                      .replay(session_id)
+                      .select { |e| e.type == Arcp::MessageTypes::JOB_EVENT }
+                      .map(&:event_seq)
+
+        expect(seqs.size).to eq(6)
+        expect(seqs.uniq).to eq(seqs)        # no repeats across the two jobs
+        expect(seqs).to eq(seqs.sort)        # strictly monotonic
+        expect(seqs).to eq((1..6).to_a)      # gap-free from 1
+
+        client.close
+        server_task.stop
+      end
+    end
+  end
+
   describe 'cancellation emits job.cancelled then job.error (#47)' do
     it 'acknowledges with job.cancelled before the CANCELLED job.error' do
       Sync do