feat(api): WS index_session frames + handlers

Add six v7 WsFrameType enum members (index_session_start/cancel/batch,
index_file_result/progress/done), wire dispatch in device_ws message loop,
and implement _handle_index_session_start/cancel/file_batch with per-file
summarisation, token accounting, and quota enforcement.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/api/routes/device_ws.py

@@ -57,6 +57,10 @@ logger = logging.getLogger(__name__)
 
 router = APIRouter(prefix="/ws", tags=["device-ws"])
 
+# ── v7 folder index session state ─────────────────────────────────────
+# Keyed by sessionId; value: { user_id, project_id, processed, total, cancelled }
+_index_sessions: dict[str, dict] = {}
+
 _HEARTBEAT_INTERVAL = 30  # seconds
 _PONG_TIMEOUT = 10  # seconds — grace window after a ping
 
@@ -180,6 +184,19 @@ async def _message_loop(websocket: WebSocket, user_id: str) -> None:
                 _handle_journey_message(websocket, user_id, frame)
             )
 
+        elif frame_type == WsFrameType.index_session_start:
+            asyncio.create_task(
+                _handle_index_session_start(websocket, user_id, frame)
+            )
+
+        elif frame_type == WsFrameType.index_file_batch:
+            asyncio.create_task(
+                _handle_index_file_batch(websocket, user_id, frame)
+            )
+
+        elif frame_type == WsFrameType.index_session_cancel:
+            await _handle_index_session_cancel(websocket, frame)
+
         elif frame_type == "pong":
             # Heartbeat ack — nothing to do, connection is alive.
             pass
@@ -569,6 +586,173 @@ async def _handle_journey_message(
         clear_client_executor()
 
 
+# ── v7 Folder Index Handlers ──────────────────────────────────────────
+
+
+async def _handle_index_session_start(
+    websocket: WebSocket,
+    user_id: str,
+    frame: dict,
+) -> None:
+    """Register a new folder index session.  No response sent — client is declaring intent."""
+    session_id: str = frame.get("sessionId") or frame.get("session_id", "")
+    project_id: str | None = frame.get("projectId") or frame.get("project_id")
+    total: int = int(frame.get("totalFiles", 0))
+
+    if not session_id:
+        logger.warning("device_ws: index_session_start missing sessionId user=%s", user_id)
+        return
+
+    _index_sessions[session_id] = {
+        "user_id": user_id,
+        "project_id": project_id,
+        "processed": 0,
+        "total": total,
+        "cancelled": False,
+    }
+    logger.info(
+        "device_ws: index_session_start user=%s session=%s project=%s total=%d",
+        user_id, session_id, project_id, total,
+    )
+
+
+async def _handle_index_session_cancel(
+    websocket: WebSocket,
+    frame: dict,
+) -> None:
+    """Mark a session as cancelled and emit index_session_done(cancelled)."""
+    session_id: str = frame.get("sessionId") or frame.get("session_id", "")
+    session = _index_sessions.get(session_id)
+    if session:
+        session["cancelled"] = True
+
+    await websocket.send_text(json.dumps({
+        "type": WsFrameType.index_session_done,
+        "sessionId": session_id,
+        "status": "cancelled",
+    }))
+    _index_sessions.pop(session_id, None)
+    logger.info("device_ws: index_session_cancel session=%s", session_id)
+
+
+async def _handle_index_file_batch(
+    websocket: WebSocket,
+    user_id: str,
+    frame: dict,
+) -> None:
+    """Process a batch of files for an index session, streaming results back."""
+    # Lazy imports to avoid heavy load at module startup.
+    from app.core.folder_indexer import (  # noqa: PLC0415
+        summarize_image,
+        summarize_pdf,
+        summarize_docx,
+        summarize_text,
+    )
+    from app.billing.tier_manager import tier_manager  # noqa: PLC0415
+    from app.billing.quota import add_token_usage  # noqa: PLC0415
+
+    session_id: str = frame.get("sessionId") or frame.get("session_id", "")
+    files: list[dict] = frame.get("files", [])
+
+    session = _index_sessions.get(session_id)
+    if not session or session.get("cancelled"):
+        return
+
+    async with async_session() as db:
+        tier = await tier_manager.get_tier(user_id, db)
+        raw_cap = tier_manager.get_feature_value(tier, "folder_monthly_tokens")
+        cap: int | None = None if raw_cap == -1 else raw_cap
+
+        for file_info in files:
+            if session.get("cancelled"):
+                return
+
+            rel_path: str = file_info.get("relPath", "")
+            kind: str = file_info.get("kind", "text")
+            content: str = file_info.get("content", "")
+            ext: str = file_info.get("ext", "")
+            mime: str = file_info.get("mime", "application/octet-stream")
+            name: str = rel_path.split("/")[-1] or rel_path
+
+            try:
+                if kind == "image":
+                    res = await summarize_image(image_b64=content, mime=mime)
+                elif kind == "pdf":
+                    res = await summarize_pdf(pdf_b64=content, name=name)
+                elif kind == "docx":
+                    res = await summarize_docx(docx_b64=content, name=name)
+                else:
+                    res = await summarize_text(content=content, ext=ext, name=name)
+            except Exception as exc:
+                logger.warning(
+                    "device_ws: index_file_batch summarize failed session=%s path=%s: %s",
+                    session_id, rel_path, exc,
+                )
+                await websocket.send_text(json.dumps({
+                    "type": WsFrameType.index_file_result,
+                    "sessionId": session_id,
+                    "relPath": rel_path,
+                    "summary": None,
+                    "tokensUsed": 0,
+                    "error": str(exc),
+                }))
+                session["processed"] += 1
+                continue
+
+            # Account for token usage and check cap.
+            usage = await add_token_usage(
+                user_id=user_id,
+                feature="folder_index",
+                tokens=res.tokens_used,
+                db=db,
+                cap=cap,
+            )
+
+            await websocket.send_text(json.dumps({
+                "type": WsFrameType.index_file_result,
+                "sessionId": session_id,
+                "relPath": rel_path,
+                "summary": res.summary,
+                "tokensUsed": res.tokens_used,
+            }))
+            session["processed"] += 1
+
+            if usage.exhausted:
+                await websocket.send_text(json.dumps({
+                    "type": WsFrameType.index_session_done,
+                    "sessionId": session_id,
+                    "status": "quota_exceeded",
+                }))
+                _index_sessions.pop(session_id, None)
+                logger.info(
+                    "device_ws: index_session quota_exceeded user=%s session=%s",
+                    user_id, session_id,
+                )
+                return
+
+        # After processing the batch, emit progress.
+        processed = session["processed"]
+        total = session["total"]
+        await websocket.send_text(json.dumps({
+            "type": WsFrameType.index_session_progress,
+            "sessionId": session_id,
+            "processed": processed,
+            "total": total,
+        }))
+
+        if processed >= total:
+            await websocket.send_text(json.dumps({
+                "type": WsFrameType.index_session_done,
+                "sessionId": session_id,
+                "status": "completed",
+            }))
+            _index_sessions.pop(session_id, None)
+            logger.info(
+                "device_ws: index_session_done completed user=%s session=%s processed=%d",
+                user_id, session_id, processed,
+            )
+
+
 # ── Heartbeat ─────────────────────────────────────────────────────────
 
 async def _heartbeat_loop(websocket: WebSocket) -> None: