feat(desktop): add assistant message actions

.qwen/e2e-tests/electron-desktop/assistant-message-actions.md

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+# Assistant Message Actions and File Reference Chips
+
+- Slice date: 2026-04-26
+- Executable harness: `packages/desktop/scripts/e2e-cdp-smoke.mjs`
+- Command:
+  `cd packages/desktop && npm run e2e:cdp`
+- Result: pass
+- Artifact directory:
+  `.qwen/e2e-tests/electron-desktop/artifacts/2026-04-25T18-10-35-606Z/`
+
+## Scenario
+
+1. Launch the real Electron app with isolated HOME, runtime, user-data, and a
+   fake dirty Git workspace.
+2. Open the fake project through the desktop directory picker path.
+3. Send the first composer prompt and approve the fake command request.
+4. Wait for the fake ACP assistant response that references `README.md:1`.
+5. Assert the assistant message renders compact Copy, Retry last prompt, and
+   Open Changes actions plus a file-reference chip.
+6. Click Copy and verify visible composer feedback.
+7. Click Retry and verify the previous user prompt is restored into the
+   composer without sending a new request, then clear the retry draft.
+8. Continue the existing changed-files, review, settings, terminal, and final
+   layout smoke path.
+
+## Assertions
+
+- The assistant action row is inside the chat timeline and stays above the
+  composer without overlap.
+- The assistant action row exposes `Copy Response`, `Retry Last Prompt`, and
+  `Open Changes` as accessible button labels.
+- The assistant file chip shows `README.md:1` and exposes `Open README.md:1`.
+- Copy produces `Copied response.` feedback.
+- Retry restores `Please exercise command approval.` to the composer and does
+  not auto-send a new approval request.
+- The assistant message does not show fake tool call IDs or session IDs.
+- Console errors: 0.
+- Failed local network requests: 0.
+
+## Artifacts
+
+- `assistant-message-actions.json`
+- `assistant-message-actions.png`
+- `assistant-retry-draft.json`
+- `resolved-tool-activity.json`
+- `conversation-changes-summary.json`
+- `completed-workspace.png`
+- `electron.log`
+- `summary.json`
+
+## Known Uncovered Risk
+
+The harness covers one deterministic assistant response with one file
+reference. Live assistant prose with many repeated paths, uncommon file
+extensions, or markdown-wrapped references still needs broader coverage.