Merge commit 'ecbf75a5e70f662b6420375140cf12eb6bac7860' into worktree/retarget-pr885-20260729

# Conflicts:
#	docs/development.i18n.yaml
#	packages/client/ui-conversation/src/client/chat/MessageItem.tsx
#	packages/client/ui-primitives/src/markdown/CodeBlock.tsx
#	scripts/snapshots/translation-prompt-v4/request-response.expected.json

packages/client/ui-primitives/src/clipboard.ts

@@ -0,0 +1,48 @@
+// Package-internal clipboard write, shared by every copy control in this
+// package (CodeBlock's code copy, TerminalBlock's output copy). Not part of the
+// public surface: consumers get the components, not the host detection.
+
+/**
+ * Write text to the host clipboard, preferring the async Clipboard API and
+ * falling back to `execCommand('copy')` on hosts (jsdom, insecure contexts)
+ * that omit it.
+ * @param text - the exact text to place on the clipboard.
+ * @returns true only when the host accepted the write.
+ */
+export async function writeClipboard(text: string): Promise<boolean> {
+  // lib.dom types clipboard non-optional, but insecure contexts omit it —
+  // that runtime gap is exactly what this guard detects.
+  /* oxlint-disable-next-line typescript/no-unnecessary-condition */
+  if (navigator.clipboard?.writeText) {
+    try {
+      await navigator.clipboard.writeText(text)
+      return true
+    } catch {
+      // Denied permissions / iframe policy — do not claim success.
+      return false
+    }
+  }
+  // jsdom and older hosts: best-effort execCommand path when present.
+  // execCommand('copy') is the only clipboard fallback where the async API
+  // is missing; deprecated but deliberately retained.
+  /* oxlint-disable typescript/no-deprecated */
+  const exec = typeof document.execCommand === 'function'
+    ? document.execCommand.bind(document)
+    : undefined
+  if (exec === undefined) return false
+  const el = document.createElement('textarea')
+  el.value = text
+  el.setAttribute('readonly', '')
+  el.style.position = 'fixed'
+  el.style.left = '-9999px'
+  document.body.appendChild(el)
+  el.select()
+  try {
+    return exec('copy')
+  } catch {
+    return false
+  } finally {
+    el.remove()
+  }
+  /* oxlint-enable typescript/no-deprecated */
+}