Fix streaming subscription race

CHANGELOG.md

@@ -1,5 +1,17 @@
 # Changelog
 
+## 0.0.1.alpha6 - 2026-07-18
+
+### Fixed
+
+- Make `Opencode::Client#stream` wait for OpenCode's initial
+  `server.connected` SSE readiness frame before submitting `prompt_async`,
+  closing the fast-response window where a turn could emit events before the
+  client was listening.
+- Keep prompt submission at-most-once across automatic SSE reconnects. A
+  reconnect now reopens only the event stream; it never posts the user prompt
+  again, and prompt transport failures remain visible to the caller.
+
 ## 0.0.1.alpha5 - 2026-07-15
 
 ### Added

README.md

@@ -86,6 +86,11 @@ reply.reasoning_text  # => the model's hidden reasoning, if any
 reply.parts_json      # => the full ordered parts array, ready for persistence
 ```
 
+`stream` waits for OpenCode's initial `server.connected` SSE readiness frame
+before it submits the asynchronous prompt. If the event connection drops
+afterward, the client reconnects only the subscription; it never reposts the
+prompt. This prevents both missed fast responses and duplicate turns.
+
 ### Synchronous send (no streaming)
 
 ```ruby
@@ -187,7 +192,9 @@ bundle install
 bundle exec rake test
 ```
 
-The smoke suite covers Client end-to-end against WebMock-stubbed OpenCode endpoints.
+The smoke suite covers Client end-to-end against WebMock-stubbed OpenCode
+endpoints, including subscription-before-prompt ordering and
+reconnect-without-repost.
 
 ## License
 

lib/opencode/client.rb

@@ -131,21 +131,35 @@ module Opencode
       on_activity_tick: nil,
       &block
     )
-      send_message_async(
-        session_id, text,
-        model: model, agent: agent, system: system, message_id: message_id
-      )
-
       reply = Opencode::Reply.new
       reply.add_observer(StreamBlockObserver.new(&block)) if block_given?
 
-      stream_events(
+      # Opening the event stream after prompt_async leaves a race where a fast
+      # turn can emit (and finish) before the client is subscribed. Wait for
+      # OpenCode's initial server.connected SSE frame, then submit the prompt
+      # exactly once. Reconnects invoke on_subscribed again, so mark the attempt
+      # before the POST: an ambiguous prompt response must never cause the same
+      # turn to be submitted twice.
+      prompt_attempted = false
+      on_subscribed = lambda do
+        next false if prompt_attempted
+
+        prompt_attempted = true
+        send_message_async(
+          session_id, text,
+          model: model, agent: agent, system: system, message_id: message_id
+        )
+        true
+      end
+
+      consume_event_stream(
         session_id: session_id,
         timeout: stream_timeout,
         first_event_timeout: first_event_timeout,
         idle_stream_timeout: idle_stream_timeout,
         reply: reply,
-        on_activity_tick: on_activity_tick
+        on_activity_tick: on_activity_tick,
+        on_subscribed: on_subscribed
       ) do |event|
         reply.apply(event)
       end
@@ -285,6 +299,20 @@ module Opencode
     def stream_events(session_id:, timeout: 600, first_event_timeout: 120,
                        idle_stream_timeout: nil,
                        reply: nil, on_activity_tick: nil, &block)
+      consume_event_stream(
+        session_id: session_id,
+        timeout: timeout,
+        first_event_timeout: first_event_timeout,
+        idle_stream_timeout: idle_stream_timeout,
+        reply: reply,
+        on_activity_tick: on_activity_tick,
+        &block
+      )
+    end
+
+    private def consume_event_stream(session_id:, timeout:, first_event_timeout:,
+                                     idle_stream_timeout:, reply:, on_activity_tick:,
+                                     on_subscribed: nil, &block)
       uri = build_uri("/event")
       deadline = Process.clock_gettime(Process::CLOCK_MONOTONIC) + timeout
       first_event_deadline = Process.clock_gettime(Process::CLOCK_MONOTONIC) + first_event_timeout
@@ -319,6 +347,8 @@ module Opencode
         http.open_timeout = 10
         http.read_timeout = 30
 
+        subscription_callback_error = nil
+        subscription_ready = on_subscribed.nil?
         begin
           buffer = String.new
 
@@ -352,6 +382,36 @@ module Opencode
                 event = parse_sse_event(raw_event, session_id)
                 next unless event
 
+                unless subscription_ready
+                  # Every supported OpenCode server starts /event with this
+                  # frame. Receiving it proves the stream body is flowing; on
+                  # current servers the bus listener is registered eagerly,
+                  # and on older lazy-stream servers it is the strongest
+                  # available readiness handshake before prompting.
+                  next unless event[:type] == "server.connected"
+
+                  begin
+                    turn_started = on_subscribed.call
+                  rescue StandardError => error
+                    # Prompt submission happens inside the open SSE response.
+                    # Do not mistake its transport failure for an SSE disconnect
+                    # and hide it behind a reconnect/first-event timeout.
+                    subscription_callback_error = error
+                    raise
+                  end
+                  if turn_started
+                    # Before this fix stream_events began only after the prompt
+                    # POST returned. Preserve those timeout semantics: the turn
+                    # and first-session-event windows begin after prompt_async
+                    # succeeds, not while establishing the readiness handshake.
+                    started_at = Process.clock_gettime(Process::CLOCK_MONOTONIC)
+                    deadline = started_at + timeout
+                    first_event_deadline = started_at + first_event_timeout
+                    last_meaningful_event_at = started_at
+                  end
+                  subscription_ready = true
+                end
+
                 unless event[:type]&.start_with?("server.")
                   received_session_event = true
                   last_meaningful_event_at = Process.clock_gettime(Process::CLOCK_MONOTONIC)
@@ -368,6 +428,8 @@ module Opencode
             end
           end
         rescue *TRANSIENT_SSE_ERRORS
+          raise if subscription_callback_error
+
           # Treat transport-level SSE disconnects like clean EOF: reconnect
           # until an idle session event, the overall timeout, or first-event
           # timeout.

lib/opencode/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Opencode
-  VERSION = "0.0.1.alpha5"
+  VERSION = "0.0.1.alpha6"
 end

test/opencode/smoke_test.rb

@@ -11,6 +11,7 @@ class SmokeTest < Minitest::Test
   BASE = "http://opencode.test"
   PASSWORD = "test-secret"
   SESSION_ID = "ses_smoke_1"
+  CONNECTED_EVENT = { type: "server.connected", properties: {} }.freeze
 
   def setup
     @client = Opencode::Client.new(
@@ -130,6 +131,7 @@ class SmokeTest < Minitest::Test
       .to_return(status: 204, body: "")
 
     sse = [
+      CONNECTED_EVENT,
       { type: "message.part.delta",
         properties: { sessionID: SESSION_ID, partID: "p1", field: "text", delta: "hello " } },
       { type: "message.part.delta",
@@ -157,11 +159,164 @@ class SmokeTest < Minitest::Test
     refute_empty parts_yielded
   end
 
+  def test_stream_waits_for_server_connected_before_posting_the_prompt
+    request_order = []
+    connection_count = 0
+    terminal_event = {
+      type: "session.status",
+      properties: { sessionID: SESSION_ID, status: { type: "idle" } }
+    }
+
+    stub_request(:get, %r{#{Regexp.escape(BASE)}/event(\?.*)?\z})
+      .to_return do
+        connection_count += 1
+        request_order << :sse_accepted
+        events = if connection_count == 1
+          [ { type: "server.heartbeat", properties: {} } ]
+        else
+          [ CONNECTED_EVENT, terminal_event ]
+        end
+        {
+          status: 200,
+          body: events.map { |event| "data: #{event.to_json}\n\n" }.join,
+          headers: { "Content-Type" => "text/event-stream" }
+        }
+      end
+
+    stub_request(:post, "#{BASE}/session/#{SESSION_ID}/prompt_async")
+      .to_return do
+        request_order << :prompt
+        { status: 204, body: "" }
+      end
+
+    stub_request(:get, "#{BASE}/session/#{SESSION_ID}/message")
+      .to_return(status: 200, body: [].to_json,
+                 headers: { "Content-Type" => "application/json" })
+
+    @client.stream(SESSION_ID, "ping", stream_timeout: 1, first_event_timeout: 1)
+
+    assert_equal [ :sse_accepted, :sse_accepted, :prompt ], request_order
+  end
+
+  def test_stream_does_not_post_when_sse_subscription_is_rejected
+    stub_request(:get, %r{#{Regexp.escape(BASE)}/event(\?.*)?\z})
+      .to_return(status: 503, body: "unavailable")
+    prompt = stub_request(:post, "#{BASE}/session/#{SESSION_ID}/prompt_async")
+      .to_return(status: 204, body: "")
+
+    error = assert_raises(Opencode::ServerError) do
+      @client.stream(SESSION_ID, "ping", stream_timeout: 1, first_event_timeout: 1)
+    end
+
+    assert_match "SSE connection failed: HTTP 503", error.message
+    assert_not_requested prompt
+  end
+
+  def test_stream_surfaces_prompt_timeout_without_reconnecting
+    event_stream = stub_request(:get, %r{#{Regexp.escape(BASE)}/event(\?.*)?\z})
+      .to_return(status: 200, body: "data: #{CONNECTED_EVENT.to_json}\n\n",
+                 headers: { "Content-Type" => "text/event-stream" })
+    prompt = stub_request(:post, "#{BASE}/session/#{SESSION_ID}/prompt_async")
+      .to_raise(Net::ReadTimeout.new("prompt timed out"))
+
+    error = assert_raises(Opencode::TimeoutError) do
+      @client.stream(SESSION_ID, "ping", stream_timeout: 1, first_event_timeout: 1)
+    end
+
+    assert_match "OpenCode timeout after 5s", error.message
+    assert_requested event_stream, times: 1
+    assert_requested prompt, times: 1
+  end
+
+  def test_stream_reconnects_without_reposting_the_prompt
+    first_connection = [
+      CONNECTED_EVENT,
+      { type: "server.heartbeat", properties: {} }
+    ]
+    second_connection = [
+      CONNECTED_EVENT,
+      {
+        type: "message.part.delta",
+        properties: { sessionID: SESSION_ID, partID: "p1", field: "text", delta: "once" }
+      },
+      {
+        type: "session.status",
+        properties: { sessionID: SESSION_ID, status: { type: "idle" } }
+      }
+    ]
+
+    event_stream = stub_request(:get, %r{#{Regexp.escape(BASE)}/event(\?.*)?\z})
+      .to_return(
+        {
+          status: 200,
+          body: first_connection.map { |event| "data: #{event.to_json}\n\n" }.join,
+          headers: { "Content-Type" => "text/event-stream" }
+        },
+        {
+          status: 200,
+          body: second_connection.map { |event| "data: #{event.to_json}\n\n" }.join,
+          headers: { "Content-Type" => "text/event-stream" }
+        }
+      )
+    prompt = stub_request(:post, "#{BASE}/session/#{SESSION_ID}/prompt_async")
+      .to_return(status: 204, body: "")
+    stub_request(:get, "#{BASE}/session/#{SESSION_ID}/message")
+      .to_return(status: 200, body: [].to_json,
+                 headers: { "Content-Type" => "application/json" })
+
+    reply = @client.stream(SESSION_ID, "ping", stream_timeout: 1, first_event_timeout: 1)
+
+    assert_equal "once", reply.full_text
+    assert_requested event_stream, times: 2
+    assert_requested prompt, times: 1
+  end
+
+  def test_stream_events_preserves_question_and_permission_wait_state
+    events = [
+      {
+        type: "question.asked",
+        properties: { id: "que_1", sessionID: SESSION_ID, questions: [] }
+      },
+      {
+        type: "question.replied",
+        properties: { requestID: "que_1", sessionID: SESSION_ID, answers: [ [ "yes" ] ] }
+      },
+      {
+        type: "permission.asked",
+        properties: { id: "per_1", sessionID: SESSION_ID, permission: "bash" }
+      },
+      {
+        type: "permission.replied",
+        properties: { requestID: "per_1", sessionID: SESSION_ID, reply: "once" }
+      },
+      {
+        type: "session.status",
+        properties: { sessionID: SESSION_ID, status: { type: "idle" } }
+      }
+    ]
+    stub_request(:get, %r{#{Regexp.escape(BASE)}/event(\?.*)?\z})
+      .to_return(
+        status: 200,
+        body: events.map { |event| "data: #{event.to_json}\n\n" }.join,
+        headers: { "Content-Type" => "text/event-stream" }
+      )
+
+    reply = Opencode::Reply.new
+    wait_states = []
+    @client.stream_events(session_id: SESSION_ID, reply: reply) do |event|
+      reply.apply(event)
+      wait_states << reply.prompt_blocked?
+    end
+
+    assert_equal [ true, false, true, false, false ], wait_states
+  end
+
   def test_stream_block_is_optional
     stub_request(:post, "#{BASE}/session/#{SESSION_ID}/prompt_async")
       .to_return(status: 204, body: "")
 
     sse = [
+      CONNECTED_EVENT,
       { type: "message.part.delta",
         properties: { sessionID: SESSION_ID, partID: "p1", field: "text", delta: "ack" } },
       { type: "session.idle", properties: { sessionID: SESSION_ID } }
@@ -199,6 +354,7 @@ class SmokeTest < Minitest::Test
       }
     }
     sse = [
+      CONNECTED_EVENT,
       { type: "todo.updated", properties: { sessionID: SESSION_ID, todos: [] } },
       { type: "message.part.updated", properties: { sessionID: SESSION_ID, part: skill_part } },
       { type: "message.part.updated", properties: { sessionID: SESSION_ID, part: task_part } },