fix(gateway): preserve chat.history context under hard caps

docs/web/control-ui.md

@@ -92,6 +92,7 @@ Cron jobs panel notes:
 
 - `chat.send` is **non-blocking**: it acks immediately with `{ runId, status: "started" }` and the response streams via `chat` events.
 - Re-sending with the same `idempotencyKey` returns `{ status: "in_flight" }` while running, and `{ status: "ok" }` after completion.
+- `chat.history` responses are size-bounded for UI safety. When transcript entries are too large, Gateway may truncate long text fields, omit heavy metadata blocks, and replace oversized messages with a placeholder (`[chat.history omitted: message too large]`).
 - `chat.inject` appends an assistant note to the session transcript and broadcasts a `chat` event for UI-only updates (no agent run, no channel delivery).
 - Stop:
   - Click **Stop** (calls `chat.abort`)

docs/web/webchat.md

@@ -24,6 +24,7 @@ Status: the macOS/iOS SwiftUI chat UI talks directly to the Gateway WebSocket.
 ## How it works (behavior)
 
 - The UI connects to the Gateway WebSocket and uses `chat.history`, `chat.send`, and `chat.inject`.
+- `chat.history` is bounded for stability: Gateway may truncate long text fields, omit heavy metadata, and replace oversized entries with `[chat.history omitted: message too large]`.
 - `chat.inject` appends an assistant note directly to the transcript and broadcasts it to the UI (no agent run).
 - Aborted runs can keep partial assistant output visible in the UI.
 - Gateway persists aborted partial assistant text into transcript history when buffered output exists, and marks those entries with abort metadata.