feat(chat): view context — tell the assistant what you're looking at

An eye next to the paperclip shares what the user has open with their next
message: the page, the folder being browsed, the file open in the viewer and
any highlighted passage (line numbers where a source view exists), plus which
entity a detail page is about. The bag is client-authored {label, value} pairs
in English — the backend only clamps (chars, never bytes), neutralizes the
harness tag and renders one <system-extra> block per message, deduped
consecutively so it appears exactly when the view changed. On by default,
per-device toggle, hover/tap to preview, a chip on every sent message;
docs/view-context.md for users, an updated harness.md clause for the model.

web/components/copilot.js

@@ -1,7 +1,8 @@
 import { html, nothing } from 'lit';
 import { ChatSession }   from '../lib/chat-session.js';
 import { t, I18nMixin }  from '../lib/i18n.js';
-import { renderMsg, renderAttachmentChips } from './copilot-render.js';
+import { pageFromHash }  from '../lib/routes.js';
+import { renderMsg, renderAttachmentChips, renderViewContextPill } from './copilot-render.js';
 import { renderTaskStrip } from './shared/agent-tasks.js';
 
 // Built-in (server-handled) slash commands shown at the top of the composer
@@ -138,11 +139,13 @@ export class AppCopilot extends I18nMixin(ChatSession) {
     window.addEventListener('llm-page-change',   this._onPageChange);
   }
 
+  // Shared with the sidebar and the view-context store (`lib/routes.js`). It used
+  // to be a third copy of the same list, and had already drifted: `files`,
+  // `plugins`, `shared-folders` and the plugin routes were missing, so a deep
+  // link to one of those opened the chat full-screen over the page it should
+  // have docked beside.
   _pageFromHash() {
-    const m = location.hash.slice(1).match(/^([^/?]+)/);
-    const seg = m ? m[1] : '';
-    const known = ['inbox', 'dashboard', 'tasks', 'projects', 'models', 'providers', 'approval', 'agents', 'users', 'roles', 'connectors', 'connector', 'marketplace', 'profile', 'config', 'llm-requests', 'session', 'system-agents', 'file_viewer', 'tool_detail'];
-    return known.includes(seg) ? seg : 'home';
+    return pageFromHash();
   }
 
   _onPageChange(e) {
@@ -738,6 +741,7 @@ export class AppCopilot extends I18nMixin(ChatSession) {
                 title=${t('chat.attach')}
                 @click=${() => this.querySelector('.copilot-file-input')?.click()}
               ><i class="bi bi-paperclip"></i></button>
+              ${renderViewContextPill(this)}
               ${this._providers.length > 1 ? html`
                 <div class="copilot-model-wrap">
                   ${this._modelOpen ? html`