fix(web): address the late review batch on context bodies

- Content blocks render in the order the model received them. Partitioning
  hoisted every unknown block past the text around it, so an interleaved log
  read back in an order the model never saw.
- A delta distinguishes a newly reconciled file from a rewritten one; `set`
  and `replace` already separate them at the producer, and collapsing both to
  "updated" misread a new file.
- The superseded note states current fact in its consequences and testing
  rather than keeping claims the implementation now contradicts, per
  implemented/AGENTS.md; the decision itself stays as the record of that
  change, with the supersession pointer above it.

packages/client/ui-conversation/tests/chat-branch-tails.spec.tsx

@@ -288,6 +288,52 @@ describe('MessageItem arms', () => {
       .toContain('<system-reminder>')
   })
 
+  it('a delta distinguishes a newly reconciled file from a rewritten one', () => {
+    const view = render(
+      <MessageItem t={t} node={{
+        kind: 'context',
+        seq: 3,
+        content: [{ type: 'text', text: 'delta' }],
+        source: {
+          kind: 'workspace-instructions',
+          form: 'instructions',
+          changes: [
+            { action: 'set', scope: 'a', path: 'new/AGENTS.md' },
+            { action: 'replace', scope: 'b', path: 'old/AGENTS.md' },
+          ],
+        },
+        provenance: { role: 'inject', label: 'new/AGENTS.md, old/AGENTS.md' },
+        form: 'instructions',
+      } as never}
+      />,
+    )
+    fireEvent.click(view.getByRole('button', { name: /^上下文注入\s*new\/AGENTS\.md, old\/AGENTS\.md$/ }))
+    const files = [...view.container.querySelectorAll('[data-context-files] li')].map(node => node.textContent)
+    expect(files).toEqual(['new/AGENTS.md已新增', 'old/AGENTS.md已更新'])
+  })
+
+  it('keeps an interleaved unknown block in the order the model received it', () => {
+    const view = render(
+      <MessageItem t={t} node={{
+        kind: 'context',
+        seq: 3,
+        content: [
+          { type: 'text', text: 'before' },
+          { type: 'future-block', payload: 1 },
+          { type: 'text', text: 'after' },
+        ],
+        source: null,
+        provenance: { role: 'inject', label: null },
+        form: null,
+      } as never}
+      />,
+    )
+    fireEvent.click(view.getByRole('button', { name: '上下文注入' }))
+    const texts = [...view.container.querySelectorAll('[data-context-text]')].map(node => node.textContent)
+    expect(texts).toEqual(['before', 'after'])
+    expect(view.getByText(/未知内容块/)).toBeTruthy()
+  })
+
   it('the catalog form lists its durable entries instead of the model-facing prose', () => {
     const view = render(
       <MessageItem t={t} node={{