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/projects/project-board.js

@@ -1,8 +1,14 @@
 import { html, nothing } from 'lit';
 import { LightElement } from '../../lib/base.js';
 import { t }            from '../../lib/i18n.js';
+import { setSlice, clearSlice } from '../../lib/view-context.js';
 import '../shared/file-explorer.js';
 
+/// The view-context slice this board owns (see `lib/view-context.js`). The
+/// board element is dropped by the host whenever the page closes or returns to
+/// the list, so `disconnectedCallback` is the whole cleanup story.
+const VIEW_SLICE = 'entity@projects';
+
 /// A project's detail page: header + description, then two tabs — **Files** (the
 /// shared `<file-explorer>`, pointed at the project folder) and **Sharing**
 /// (member picker with read/write, mirroring the shared-folders UI).
@@ -33,9 +39,23 @@ export class ProjectBoardSection extends LightElement {
 
   disconnectedCallback() {
     window.removeEventListener('locale-changed', this.__onLocaleChanged);
+    clearSlice(VIEW_SLICE);
     super.disconnectedCallback();
   }
 
+  // Say which project this is, and which tab is showing. The tab matters because
+  // the explorer keeps its `path` slice standing while hidden behind *Sharing*:
+  // without this, the context would describe a folder and not that the user is
+  // looking at the member list.
+  _publishViewContext() {
+    const p = this._project;
+    if (!p) return;
+    setSlice(VIEW_SLICE, [
+      { label: 'Open project', value: p.root_path ? `${p.name} — folder ${p.root_path}` : String(p.name) },
+      { label: 'Open tab',     value: this._tab === 'sharing' ? 'Sharing' : 'Files' },
+    ]);
+  }
+
   async load(projectId, tab) {
     this._projectId = projectId;
     this._project   = null;
@@ -49,6 +69,7 @@ export class ProjectBoardSection extends LightElement {
       if (!projRes.ok) throw new Error(`HTTP ${projRes.status}`);
       this._project = await projRes.json();
       if (usersRes.ok) this._users = await usersRes.json();
+      this._publishViewContext();
     } catch (e) {
       this._error = e.message;
     }
@@ -57,7 +78,10 @@ export class ProjectBoardSection extends LightElement {
   async _reload() {
     try {
       const res = await fetch(`/api/projects/${this._projectId}`);
-      if (res.ok) this._project = await res.json();
+      if (res.ok) {
+        this._project = await res.json();
+        this._publishViewContext();
+      }
     } catch { /* transient */ }
   }
 
@@ -121,11 +145,13 @@ export class ProjectBoardSection extends LightElement {
   // Switch the visible tab without reloading (host back/forward sync).
   setTab(tab) {
     this._tab = tab === 'sharing' ? 'sharing' : 'files';
+    this._publishViewContext();
   }
 
   _selectTab(tab) {
     if (tab === this._tab) return;
     this._tab = tab;
+    this._publishViewContext();
     this.dispatchEvent(new CustomEvent('project-tab-change', {
       detail: { tab }, bubbles: true, composed: true,
     }));