diff --git a/surfsense_backend/app/services/streaming/__init__.py b/surfsense_backend/app/services/streaming/__init__.py
new file mode 100644
index 000000000..287d48a7a
--- /dev/null
+++ b/surfsense_backend/app/services/streaming/__init__.py
@@ -0,0 +1,20 @@
+"""Single-responsibility split of the streaming SSE protocol.
+
+Layout:
+* ``envelope/`` - SSE wire framing + ID generators
+* ``emitter/`` - identity of the agent that emitted an event + runtime registry
+* ``events/`` - one module per SSE event family
+* ``service.py`` - composition root used by the orchestrator
+* ``interrupt_correlation.py`` - id-aware lookup over LangGraph state
+
+Naming on the wire:
+* AI SDK protocol fields keep their existing camelCase
+  (``toolCallId``, ``messageId``, ``inputTextDelta``, ``langchainToolCallId``).
+* Every SurfSense-added field uses ``snake_case``, including the
+  top-level ``emitted_by`` envelope and all inner ``data`` payloads.
+
+Production keeps using ``app.services.new_streaming_service`` and
+``app.tasks.chat.stream_new_chat`` until the cutover phase.
+"""
+
+from __future__ import annotations
diff --git a/surfsense_backend/app/services/streaming/interrupt_correlation.py b/surfsense_backend/app/services/streaming/interrupt_correlation.py
new file mode 100644
index 000000000..3045dfb6a
--- /dev/null
+++ b/surfsense_backend/app/services/streaming/interrupt_correlation.py
@@ -0,0 +1,84 @@
+"""Id-aware lookup of pending LangGraph interrupts (replaces first-wins)."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any
+
+
+@dataclass(frozen=True)
+class PendingInterrupt:
+    interrupt_id: str | None
+    value: dict[str, Any]
+    source_task_id: str | None = None
+
+
+def list_pending_interrupts(state: Any) -> list[PendingInterrupt]:
+    out: list[PendingInterrupt] = []
+
+    for task in getattr(state, "tasks", None) or ():
+        task_id = _safe_str(getattr(task, "id", None))
+        for it in getattr(task, "interrupts", None) or ():
+            value = _coerce_interrupt_value(it)
+            if value is None:
+                continue
+            interrupt_id = _safe_str(getattr(it, "id", None))
+            out.append(
+                PendingInterrupt(
+                    interrupt_id=interrupt_id,
+                    value=value,
+                    source_task_id=task_id,
+                )
+            )
+
+    for it in getattr(state, "interrupts", None) or ():
+        value = _coerce_interrupt_value(it)
+        if value is None:
+            continue
+        interrupt_id = _safe_str(getattr(it, "id", None))
+        out.append(PendingInterrupt(interrupt_id=interrupt_id, value=value))
+
+    return out
+
+
+def get_pending_interrupt_by_id(
+    state: Any, interrupt_id: str
+) -> PendingInterrupt | None:
+    for pending in list_pending_interrupts(state):
+        if pending.interrupt_id == interrupt_id:
+            return pending
+    return None
+
+
+def get_pending_interrupt_for_tool_call(
+    state: Any, tool_call_id: str
+) -> PendingInterrupt | None:
+    for pending in list_pending_interrupts(state):
+        actions = pending.value.get("action_requests")
+        if not isinstance(actions, list):
+            continue
+        for action in actions:
+            if not isinstance(action, dict):
+                continue
+            if action.get("tool_call_id") == tool_call_id:
+                return pending
+    return None
+
+
+def first_pending_interrupt(state: Any) -> PendingInterrupt | None:
+    """Explicit opt-in to legacy first-wins; prefer the id-aware helpers above."""
+    pending = list_pending_interrupts(state)
+    return pending[0] if pending else None
+
+
+def _coerce_interrupt_value(item: Any) -> dict[str, Any] | None:
+    if isinstance(item, dict):
+        return item if item else None
+    value = getattr(item, "value", None)
+    if isinstance(value, dict):
+        return value if value else None
+    return None
+
+
+def _safe_str(value: Any) -> str | None:
+    return value if isinstance(value, str) and value else None
diff --git a/surfsense_backend/app/services/streaming/service.py b/surfsense_backend/app/services/streaming/service.py
new file mode 100644
index 000000000..5a75a1b2d
--- /dev/null
+++ b/surfsense_backend/app/services/streaming/service.py
@@ -0,0 +1,414 @@
+"""Composition root: bundles every formatter + a per-invocation emitter registry."""
+
+from __future__ import annotations
+
+from collections.abc import Iterable
+from typing import Any
+
+from . import envelope
+from .emitter import Emitter, EmitterRegistry
+from .events import (
+    action_log,
+    data,
+    error,
+    interrupt,
+    lifecycle,
+    reasoning,
+    source,
+    subagent_lifecycle,
+    text,
+    tool,
+)
+
+
+class StreamingService:
+    def __init__(self) -> None:
+        self._message_id: str | None = None
+        self.emitter_registry = EmitterRegistry()
+
+    @property
+    def message_id(self) -> str | None:
+        return self._message_id
+
+    def begin_message(self, message_id: str | None = None) -> str:
+        self._message_id = message_id or envelope.generate_message_id()
+        return self._message_id
+
+    @staticmethod
+    def generate_text_id() -> str:
+        return envelope.generate_text_id()
+
+    @staticmethod
+    def generate_reasoning_id() -> str:
+        return envelope.generate_reasoning_id()
+
+    @staticmethod
+    def generate_tool_call_id() -> str:
+        return envelope.generate_tool_call_id()
+
+    @staticmethod
+    def generate_subagent_run_id() -> str:
+        return envelope.generate_subagent_run_id()
+
+    @staticmethod
+    def get_response_headers() -> dict[str, str]:
+        return envelope.get_response_headers()
+
+    @staticmethod
+    def format_done() -> str:
+        return envelope.format_done()
+
+    def resolve_emitter(
+        self,
+        *,
+        run_id: str | None,
+        parent_ids: Iterable[str] | None,
+    ) -> Emitter:
+        return self.emitter_registry.resolve(run_id=run_id, parent_ids=parent_ids)
+
+    def format_message_start(
+        self,
+        message_id: str | None = None,
+        *,
+        emitter: Emitter | None = None,
+    ) -> str:
+        chosen = self.begin_message(message_id)
+        return lifecycle.format_message_start(chosen, emitter=emitter)
+
+    def format_message_finish(self, *, emitter: Emitter | None = None) -> str:
+        return lifecycle.format_message_finish(emitter=emitter)
+
+    def format_step_start(self, *, emitter: Emitter | None = None) -> str:
+        return lifecycle.format_step_start(emitter=emitter)
+
+    def format_step_finish(self, *, emitter: Emitter | None = None) -> str:
+        return lifecycle.format_step_finish(emitter=emitter)
+
+    def format_text_start(
+        self, text_id: str, *, emitter: Emitter | None = None
+    ) -> str:
+        return text.format_text_start(text_id, emitter=emitter)
+
+    def format_text_delta(
+        self, text_id: str, delta: str, *, emitter: Emitter | None = None
+    ) -> str:
+        return text.format_text_delta(text_id, delta, emitter=emitter)
+
+    def format_text_end(
+        self, text_id: str, *, emitter: Emitter | None = None
+    ) -> str:
+        return text.format_text_end(text_id, emitter=emitter)
+
+    def format_reasoning_start(
+        self, reasoning_id: str, *, emitter: Emitter | None = None
+    ) -> str:
+        return reasoning.format_reasoning_start(reasoning_id, emitter=emitter)
+
+    def format_reasoning_delta(
+        self,
+        reasoning_id: str,
+        delta: str,
+        *,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return reasoning.format_reasoning_delta(reasoning_id, delta, emitter=emitter)
+
+    def format_reasoning_end(
+        self, reasoning_id: str, *, emitter: Emitter | None = None
+    ) -> str:
+        return reasoning.format_reasoning_end(reasoning_id, emitter=emitter)
+
+    def format_tool_input_start(
+        self,
+        tool_call_id: str,
+        tool_name: str,
+        *,
+        langchain_tool_call_id: str | None = None,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return tool.format_tool_input_start(
+            tool_call_id,
+            tool_name,
+            langchain_tool_call_id=langchain_tool_call_id,
+            emitter=emitter,
+        )
+
+    def format_tool_input_delta(
+        self,
+        tool_call_id: str,
+        input_text_delta: str,
+        *,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return tool.format_tool_input_delta(
+            tool_call_id, input_text_delta, emitter=emitter
+        )
+
+    def format_tool_input_available(
+        self,
+        tool_call_id: str,
+        tool_name: str,
+        input_data: dict[str, Any],
+        *,
+        langchain_tool_call_id: str | None = None,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return tool.format_tool_input_available(
+            tool_call_id,
+            tool_name,
+            input_data,
+            langchain_tool_call_id=langchain_tool_call_id,
+            emitter=emitter,
+        )
+
+    def format_tool_output_available(
+        self,
+        tool_call_id: str,
+        output: Any,
+        *,
+        langchain_tool_call_id: str | None = None,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return tool.format_tool_output_available(
+            tool_call_id,
+            output,
+            langchain_tool_call_id=langchain_tool_call_id,
+            emitter=emitter,
+        )
+
+    def format_source_url(
+        self,
+        url: str,
+        *,
+        source_id: str | None = None,
+        title: str | None = None,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return source.format_source_url(
+            url, source_id=source_id, title=title, emitter=emitter
+        )
+
+    def format_source_document(
+        self,
+        source_id: str,
+        *,
+        media_type: str = "file",
+        title: str | None = None,
+        description: str | None = None,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return source.format_source_document(
+            source_id,
+            media_type=media_type,
+            title=title,
+            description=description,
+            emitter=emitter,
+        )
+
+    def format_file(
+        self, url: str, media_type: str, *, emitter: Emitter | None = None
+    ) -> str:
+        return source.format_file(url, media_type, emitter=emitter)
+
+    def format_data(
+        self, data_type: str, payload: Any, *, emitter: Emitter | None = None
+    ) -> str:
+        return data.format_data(data_type, payload, emitter=emitter)
+
+    def format_terminal_info(
+        self,
+        text_value: str,
+        *,
+        message_type: str = "info",
+        emitter: Emitter | None = None,
+    ) -> str:
+        return data.format_terminal_info(
+            text_value, message_type=message_type, emitter=emitter
+        )
+
+    def format_further_questions(
+        self,
+        questions: list[str],
+        *,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return data.format_further_questions(questions, emitter=emitter)
+
+    def format_thinking_step(
+        self,
+        *,
+        step_id: str,
+        title: str,
+        status: str = "in_progress",
+        items: list[str] | None = None,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return data.format_thinking_step(
+            step_id=step_id,
+            title=title,
+            status=status,
+            items=items,
+            emitter=emitter,
+        )
+
+    def format_thread_title_update(
+        self,
+        *,
+        thread_id: int,
+        title: str,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return data.format_thread_title_update(
+            thread_id=thread_id, title=title, emitter=emitter
+        )
+
+    def format_turn_info(
+        self,
+        *,
+        chat_turn_id: str,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return data.format_turn_info(chat_turn_id=chat_turn_id, emitter=emitter)
+
+    def format_turn_status(
+        self,
+        *,
+        status: str,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return data.format_turn_status(status=status, emitter=emitter)
+
+    def format_user_message_id(
+        self,
+        *,
+        message_id: str,
+        turn_id: str,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return data.format_user_message_id(
+            message_id=message_id, turn_id=turn_id, emitter=emitter
+        )
+
+    def format_assistant_message_id(
+        self,
+        *,
+        message_id: str,
+        turn_id: str,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return data.format_assistant_message_id(
+            message_id=message_id, turn_id=turn_id, emitter=emitter
+        )
+
+    def format_error(
+        self,
+        error_text: str,
+        *,
+        error_code: str | None = None,
+        extra: dict[str, Any] | None = None,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return error.format_error(
+            error_text,
+            error_code=error_code,
+            extra=extra,
+            emitter=emitter,
+        )
+
+    def format_interrupt_request(
+        self,
+        interrupt_value: dict[str, Any],
+        *,
+        interrupt_id: str | None = None,
+        pending_interrupt_count: int | None = None,
+        chat_turn_id: str | None = None,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return interrupt.format_interrupt_request(
+            interrupt_value,
+            interrupt_id=interrupt_id,
+            pending_interrupt_count=pending_interrupt_count,
+            chat_turn_id=chat_turn_id,
+            emitter=emitter,
+        )
+
+    def format_subagent_start(
+        self,
+        *,
+        subagent_run_id: str,
+        subagent_type: str,
+        parent_tool_call_id: str,
+        chat_turn_id: str | None = None,
+        description: str | None = None,
+        started_at: str | None = None,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return subagent_lifecycle.format_subagent_start(
+            subagent_run_id=subagent_run_id,
+            subagent_type=subagent_type,
+            parent_tool_call_id=parent_tool_call_id,
+            chat_turn_id=chat_turn_id,
+            description=description,
+            started_at=started_at,
+            emitter=emitter,
+        )
+
+    def format_subagent_finish(
+        self,
+        *,
+        subagent_run_id: str,
+        subagent_type: str,
+        parent_tool_call_id: str,
+        status: str = "completed",
+        ended_at: str | None = None,
+        duration_ms: int | None = None,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return subagent_lifecycle.format_subagent_finish(
+            subagent_run_id=subagent_run_id,
+            subagent_type=subagent_type,
+            parent_tool_call_id=parent_tool_call_id,
+            status=status,
+            ended_at=ended_at,
+            duration_ms=duration_ms,
+            emitter=emitter,
+        )
+
+    def format_subagent_error(
+        self,
+        *,
+        subagent_run_id: str,
+        subagent_type: str,
+        parent_tool_call_id: str,
+        error_text: str,
+        error_type: str | None = None,
+        ended_at: str | None = None,
+        duration_ms: int | None = None,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return subagent_lifecycle.format_subagent_error(
+            subagent_run_id=subagent_run_id,
+            subagent_type=subagent_type,
+            parent_tool_call_id=parent_tool_call_id,
+            error_text=error_text,
+            error_type=error_type,
+            ended_at=ended_at,
+            duration_ms=duration_ms,
+            emitter=emitter,
+        )
+
+    def format_action_log(
+        self,
+        payload: dict[str, Any],
+        *,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return action_log.format_action_log(payload, emitter=emitter)
+
+    def format_action_log_updated(
+        self,
+        payload: dict[str, Any],
+        *,
+        emitter: Emitter | None = None,
+    ) -> str:
+        return action_log.format_action_log_updated(payload, emitter=emitter)