fix(control-ui): allow configured chat message width

Adds validated gateway.controlUi.chatMessageMaxWidth support for grouped Control UI chat messages, carries it through the Gateway bootstrap payload into UI state, applies it as a CSS custom property, and documents the setting while preserving the existing default width.

Fixes #67935.

Validation:
- Targeted config, gateway, and Control UI tests passed locally.
- Config schema/docs checks passed.
- Testbox changed-file gate passed.
- GitHub CI and security checks are green on cea25a4ca9.

docs/.generated/config-baseline.sha256

@@ -1,4 +1,4 @@
-f3a0cf57605c6c25ce162080d2631c0256018c2ec128383d521153f65e69a699  config-baseline.json
-711b933e8748fe220d4be1bcc7df74503ab9c5973e967839302b8c5c773ecebf  config-baseline.core.json
+cf956c5e58ec0e36cf47708b0cd42fa34b1f39d0da951de343be0ba6e5b28168  config-baseline.json
+057e444dfc78472bac172d9d8a7bd9c9a40f9ca4755268307cfcbd7e87a4d932  config-baseline.core.json
 a2a949a99f5cc5960d4d7ae0159b6b48c4d6b1f813be67cda196457ab2f88034  config-baseline.channel.json
 fffe0e74eab92a88c3c57952a70bc932438ce3a7f5f9982688437f2cdaee0bcb  config-baseline.plugin.json

docs/gateway/configuration-reference.md

@@ -366,6 +366,7 @@ See [Plugins](/tools/plugin).
       // root: "dist/control-ui",
       // embedSandbox: "scripts", // strict | scripts | trusted
       // allowExternalEmbedUrls: false, // dangerous: allow absolute external http(s) embed URLs
+      // chatMessageMaxWidth: "min(1280px, 82%)", // optional grouped chat message max-width
       // allowedOrigins: ["https://control.example.com"], // required for non-loopback Control UI
       // dangerouslyAllowHostHeaderOriginFallback: false, // dangerous Host-header origin fallback mode
       // allowInsecureAuth: false,
@@ -427,6 +428,7 @@ See [Plugins](/tools/plugin).
   lock out a different origin.
 - `tailscale.mode`: `serve` (tailnet only, loopback bind) or `funnel` (public, requires auth).
 - `controlUi.allowedOrigins`: explicit browser-origin allowlist for Gateway WebSocket connects. Required when browser clients are expected from non-loopback origins.
+- `controlUi.chatMessageMaxWidth`: optional max-width for grouped Control UI chat messages. Accepts constrained CSS width values such as `960px`, `82%`, `min(1280px, 82%)`, and `calc(100% - 2rem)`.
 - `controlUi.dangerouslyAllowHostHeaderOriginFallback`: dangerous mode that enables Host-header origin fallback for deployments that intentionally rely on Host-header origin policy.
 - `remote.transport`: `ssh` (default) or `direct` (ws/wss). For `direct`, `remote.url` must be `ws://` or `wss://`.
 - `OPENCLAW_ALLOW_INSECURE_PRIVATE_WS=1`: client-side process-environment

docs/web/control-ui.md

@@ -247,6 +247,22 @@ Use `trusted` only when the embedded document genuinely needs same-origin behavi
 
 Absolute external `http(s)` embed URLs stay blocked by default. If you intentionally want `[embed url="https://..."]` to load third-party pages, set `gateway.controlUi.allowExternalEmbedUrls: true`.
 
+## Chat message width
+
+Grouped chat messages use a readable default max-width. Wide-monitor deployments can override it without patching bundled CSS by setting `gateway.controlUi.chatMessageMaxWidth`:
+
+```json5
+{
+  gateway: {
+    controlUi: {
+      chatMessageMaxWidth: "min(1280px, 82%)",
+    },
+  },
+}
+```
+
+The value is validated before it reaches the browser. Supported values include plain lengths and percentages such as `960px` or `82%`, plus constrained `min(...)`, `max(...)`, `clamp(...)`, `calc(...)`, and `fit-content(...)` width expressions.
+
 ## Tailnet access (recommended)
 
 <Tabs>