feat: add streaming responses to API and CLI

Add real-time streaming support for agent responses using Server-Sent
Events (SSE). Responses now appear as they're generated instead of
waiting for completion.

- Add run_stream method to BaseAgent and ExploreAgentImpl
- Add /agents/stream SSE endpoint to API router
- Add run_agent_stream method to CLI client
- Add --stream flag to chat and explore commands (enabled by default)
- Use --no-stream for batch mode with spinner

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

webber-api/src/domains/agents/base.py

@@ -4,6 +4,7 @@ Base classes and registry for agent implementations.
 All agents are built on PydanticAI and registered in a central registry.
 """
 from abc import ABC, abstractmethod
+from collections.abc import AsyncIterator
 from dataclasses import dataclass, field
 from typing import Any, Protocol, runtime_checkable
 
@@ -112,6 +113,22 @@ class BaseAgent(ABC):
         """Execute the agent."""
         pass
 
+    async def run_stream(
+        self, prompt: str, **kwargs: Any
+    ) -> AsyncIterator[str]:
+        """
+        Execute the agent with streaming output.
+
+        Default implementation falls back to non-streaming run().
+        Override this for true streaming support.
+
+        Yields:
+            Text chunks as they become available
+        """
+        # Default: fall back to non-streaming
+        result = await self.run(prompt, **kwargs)
+        yield result
+
 
 # === Agent Registry ===
 

webber-api/src/domains/agents/explore/agent.py

@@ -5,6 +5,7 @@ Fast codebase exploration with read-only tools.
 Uses sanitized Ollama provider for reliable tool calling.
 """
 import os
+from collections.abc import AsyncIterator
 from dataclasses import dataclass
 from typing import Any
 
@@ -113,6 +114,34 @@ class ExploreAgentImpl(BaseAgent):
                 raise
 
 
+    async def run_stream(
+        self,
+        prompt: str,
+        working_dir: str | None = None,
+        allowed_paths: list[str] | None = None,
+        **kwargs: Any
+    ) -> AsyncIterator[str]:
+        """
+        Run the explore agent with streaming output.
+
+        Yields text chunks as they become available.
+        """
+        ctx = ExploreContext(
+            working_dir=working_dir or os.getcwd(),
+            allowed_paths=allowed_paths or self._settings.effective_allowed_paths,
+            timeout_seconds=self._settings.tool_timeout_seconds,
+        )
+
+        async with trace_span("explore_agent_stream"):
+            try:
+                async with self.agent.run_stream(prompt, deps=ctx) as result:
+                    async for chunk in result.stream_text():
+                        yield chunk
+            except Exception as e:
+                logger.exception(f"Explore agent stream error: {e}")
+                raise
+
+
 # Create and register the singleton instance
 explore_agent = ExploreAgentImpl()
 register_agent(explore_agent)
@@ -125,3 +154,13 @@ async def explore(
 ) -> str:
     """Run exploration query."""
     return await explore_agent.run(prompt, working_dir=working_dir, **kwargs)
+
+
+async def explore_stream(
+    prompt: str,
+    working_dir: str | None = None,
+    **kwargs: Any
+) -> AsyncIterator[str]:
+    """Run exploration query with streaming."""
+    async for chunk in explore_agent.run_stream(prompt, working_dir=working_dir, **kwargs):
+        yield chunk

webber-api/src/domains/agents/router.py

@@ -1,7 +1,9 @@
 """
 REST API routes for agents.
 """
+import json
 from fastapi import APIRouter, HTTPException
+from fastapi.responses import StreamingResponse
 
 from src.domains.agents.base import get_agent, list_agents
 
@@ -68,6 +70,53 @@ async def run_agent(request: AgentRunRequest) -> AgentRunResponse:
         )
 
 
+@router.post("/stream")
+@logged()
+async def stream_agent(request: AgentRunRequest) -> StreamingResponse:
+    """
+    Run an agent with streaming response.
+
+    Returns Server-Sent Events (SSE) with text chunks.
+    Event types:
+    - "chunk": Text chunk from the agent
+    - "done": Stream complete
+    - "error": Error occurred
+    """
+    agent = get_agent(request.agent_type)
+    if not agent:
+        raise HTTPException(
+            status_code=400,
+            detail=f"Unknown agent type: {request.agent_type}"
+        )
+
+    async def generate():
+        try:
+            async for chunk in agent.run_stream(
+                request.prompt,
+                working_dir=request.working_dir,
+            ):
+                # SSE format: data: {json}\n\n
+                event = {"event": "chunk", "data": chunk}
+                yield f"data: {json.dumps(event)}\n\n"
+
+            # Signal completion
+            yield f"data: {json.dumps({'event': 'done'})}\n\n"
+
+        except Exception as e:
+            logger.exception(f"Stream error: {e}")
+            error_event = {"event": "error", "data": str(e)}
+            yield f"data: {json.dumps(error_event)}\n\n"
+
+    return StreamingResponse(
+        generate(),
+        media_type="text/event-stream",
+        headers={
+            "Cache-Control": "no-cache",
+            "Connection": "keep-alive",
+        }
+    )
+
+
 @router.get("/{agent_type}", response_model=AgentInfo)
 async def get_agent_info(agent_type: str) -> AgentInfo:
     """Get information about a specific agent."""

webber-cli/webber_cli/client.py

@@ -3,7 +3,9 @@ Webber API client.
 
 Communicates with the Webber API backend for agent execution.
 """
+import json
 import httpx
+from collections.abc import AsyncIterator
 from dataclasses import dataclass
 from typing import Any
 
@@ -132,6 +134,52 @@ class WebberClient:
             error=data.get("error"),
         )
 
+    async def run_agent_stream(
+        self,
+        agent_type: str,
+        prompt: str,
+        working_dir: str = ".",
+    ) -> AsyncIterator[str]:
+        """
+        Run an agent with streaming response.
+
+        Args:
+            agent_type: Type of agent (e.g., "explore")
+            prompt: User prompt/query
+            working_dir: Working directory for the agent
+
+        Yields:
+            Text chunks as they arrive
+        """
+        # Use a fresh client for streaming with longer timeout
+        async with httpx.AsyncClient(
+            base_url=self.base_url,
+            timeout=httpx.Timeout(300.0, connect=10.0),
+        ) as client:
+            async with client.stream(
+                "POST",
+                "/agents/stream",
+                json={
+                    "agent_type": agent_type,
+                    "prompt": prompt,
+                    "working_dir": working_dir,
+                },
+            ) as response:
+                response.raise_for_status()
+                async for line in response.aiter_lines():
+                    if line.startswith("data: "):
+                        try:
+                            data = json.loads(line[6:])
+                            event = data.get("event")
+                            if event == "chunk":
+                                yield data.get("data", "")
+                            elif event == "error":
+                                raise Exception(data.get("data", "Unknown error"))
+                            elif event == "done":
+                                break
+                        except json.JSONDecodeError:
+                            continue
+
     async def __aenter__(self) -> "WebberClient":
         """Async context manager entry."""
         return self

webber-cli/webber_cli/main.py

@@ -9,9 +9,11 @@ Usage:
 """
 import asyncio
 import os
+import sys
 from pathlib import Path
 
 import typer
+from rich.live import Live
 from rich.markdown import Markdown
 from rich.panel import Panel
 
@@ -74,6 +76,12 @@ def chat(
         "--agent",
         help="Agent to use",
     ),
+    stream: bool = typer.Option(
+        True,
+        "--stream/--no-stream",
+        "-s",
+        help="Stream responses in real-time",
+    ),
 ) -> None:
     """
     Start interactive chat session.
@@ -87,12 +95,14 @@ def chat(
         raise typer.Exit(1)
 
     try:
-        asyncio.run(_chat_loop(api_url, agent, working_dir))
+        asyncio.run(_chat_loop(api_url, agent, working_dir, stream))
     except KeyboardInterrupt:
         console.print("\n[dim]Goodbye![/]")
 
 
-async def _chat_loop(api_url: str, agent_type: str, working_dir: str) -> None:
+async def _chat_loop(
+    api_url: str, agent_type: str, working_dir: str, stream: bool = True
+) -> None:
     """Interactive chat loop."""
     theme = get_theme()
 
@@ -118,6 +128,8 @@ async def _chat_loop(api_url: str, agent_type: str, working_dir: str) -> None:
         console.print(f"[title]Webber CLI[/] [dim]→ {api_url}[/]")
         console.print(f"[dim]Working in:[/] [path]{working_dir}[/]")
         console.print(f"[dim]Agent:[/] {agent_info.name} - {agent_info.description}")
+        mode = "streaming" if stream else "batch"
+        console.print(f"[dim]Mode:[/] {mode}")
         console.print()
         console.print("[dim]Type 'exit' to quit, 'clear' to clear screen.[/]")
         console.print()
@@ -148,15 +160,31 @@ async def _chat_loop(api_url: str, agent_type: str, working_dir: str) -> None:
                         console.print(f"[error]Directory not found:[/] {new_dir}")
                     continue
 
-                # Call the API
-                with console.status("[info]Thinking...[/]", spinner=theme.spinner):
-                    result = await client.run_agent(agent_type, user_input, working_dir)
-
                 console.print()
-                if result.success:
-                    console.print(Markdown(result.response))
+
+                if stream:
+                    # Stream response in real-time
+                    full_response = ""
+                    try:
+                        async for chunk in client.run_agent_stream(
+                            agent_type, user_input, working_dir
+                        ):
+                            sys.stdout.write(chunk)
+                            sys.stdout.flush()
+                            full_response += chunk
+                        console.print()  # Newline after streaming
+                    except Exception as e:
+                        console.print(f"\n[error]Stream error:[/] {e}")
                 else:
-                    console.print(f"[error]Error:[/] {result.error}")
+                    # Batch mode with spinner
+                    with console.status("[info]Thinking...[/]", spinner=theme.spinner):
+                        result = await client.run_agent(agent_type, user_input, working_dir)
+
+                    if result.success:
+                        console.print(Markdown(result.response))
+                    else:
+                        console.print(f"[error]Error:[/] {result.error}")
+
                 console.print()
 
             except KeyboardInterrupt:
@@ -181,6 +209,12 @@ def explore(
         "-a",
         help="Webber API URL",
     ),
+    stream: bool = typer.Option(
+        True,
+        "--stream/--no-stream",
+        "-s",
+        help="Stream responses in real-time",
+    ),
 ) -> None:
     """
     One-shot codebase exploration.
@@ -193,10 +227,12 @@ def explore(
         console.print(f"[error]Error:[/] Directory not found: {working_dir}")
         raise typer.Exit(1)
 
-    asyncio.run(_explore(api_url, query, working_dir))
+    asyncio.run(_explore(api_url, query, working_dir, stream))
 
 
-async def _explore(api_url: str, query: str, working_dir: str) -> None:
+async def _explore(
+    api_url: str, query: str, working_dir: str, stream: bool = True
+) -> None:
     """Execute exploration query."""
     theme = get_theme()
 
@@ -211,21 +247,32 @@ async def _explore(api_url: str, query: str, working_dir: str) -> None:
         console.print(f"[dim]Query:[/] {query}")
         console.print()
 
-        with console.status("[info]Searching...[/]", spinner=theme.spinner):
-            result = await client.run_agent("explore", query, working_dir)
-
-        if result.success:
-            console.print(Panel(
-                Markdown(result.response),
-                title="[success]Findings[/]",
-                border_style=theme.colors.border_success,
-            ))
+        if stream:
+            # Stream response in real-time
+            try:
+                async for chunk in client.run_agent_stream("explore", query, working_dir):
+                    sys.stdout.write(chunk)
+                    sys.stdout.flush()
+                console.print()  # Newline after streaming
+            except Exception as e:
+                console.print(f"\n[error]Stream error:[/] {e}")
         else:
-            console.print(Panel(
-                f"[error]{result.error}[/]",
-                title="[error]Error[/]",
-                border_style=theme.colors.border_error,
-            ))
+            # Batch mode with spinner
+            with console.status("[info]Searching...[/]", spinner=theme.spinner):
+                result = await client.run_agent("explore", query, working_dir)
+
+            if result.success:
+                console.print(Panel(
+                    Markdown(result.response),
+                    title="[success]Findings[/]",
+                    border_style=theme.colors.border_success,
+                ))
+            else:
+                console.print(Panel(
+                    f"[error]{result.error}[/]",
+                    title="[error]Error[/]",
+                    border_style=theme.colors.border_error,
+                ))
 
 
 @app.command()