## Problem
Convex backend RSS grew to 7.7G due to ~17 HTTP POST /api/query/min
(32K+ in 32h) from the SSE polling loop in /api/tree/events?pollMs=1000.
Each poll triggered a Convex query even when nothing changed.
## Root Cause
The tree live EventSource client polled every 1s via SSE, calling
load_stream_overview() → execute_runtime_query_via_convex() → Convex
POST /api/query on every cycle, regardless of workspace state.
## Solution
Replace polling with push: add a `stream_delta_tx` broadcast channel
that publishes after every Convex mutation, consumed by WebSocket and
SSE endpoints for push-only delivery.
### Server-side
- **app.rs**: Add `stream_delta_tx: broadcast::Sender<Value>` to AppState
- **command_support.rs**: `execute_runtime_command_via_convex_with_artifacts`
now takes `&AppState` (was `&AppConfig`) and pushes `{"kind":"command_committed",...}`
to `stream_delta_tx` after every successful mutation
- **ws.rs**: Rewrite `handle_socket` with `tokio::select!` subscribing to
`stream_delta_tx`; pushes delta events to WS clients on mutation, handles
client `resync` requests for fresh snapshots
- **sse.rs**: `tree_events` endpoint now subscribes to both `block_delta_tx`
and `stream_delta_tx`; when broadcast channels are available, runs in
push-only mode (250ms heartbeat, no Convex query). Polling degrades to
60s safety net. Keeps backward compatibility for non-WS clients.
### Client-side
- **layout.rs**: Bootstrap JSON now defaults to `transport: "convex-command-log-ws"`
with `wsEndpoint: "/api/realtime/ws"`. TREE_LIVE_CONTROLLER_JS extended
with `startWithWebSocket()` supporting snapshot/delta/resync/lagged-hint
events; auto-fallback to SSE on WS failure after 2s.
### Caller updates (17 call sites)
- documents.rs, mindmap_api.rs, resource_trash.rs, tree.rs
- hermes_tools/{artifact,block,page}.rs
All updated from `state.config()` to `&state` for the new signature.
## Verification
- `cargo build` + `cargo test`: 295/298 passed (3 pre-existing failures)
- Browser smoke: page loaded → transport=convex-command-log-ws, status=connected
- Convex logs: 0 POST /api/query in 2min with page idle (vs ~17/min before)
- Initial burst: 8 queries on page load (normal), then silence
lix-2026