fix(desktop): lighten conversation timeline surfaces

.qwen/e2e-tests/electron-desktop/conversation-surface-fidelity.md

@@ -0,0 +1,69 @@
+# Conversation Surface Prototype Fidelity
+
+- 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/2026-04-26T01-26-44-948Z/`
+
+## 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 dense fake ACP assistant response, file-reference chips,
+   assistant actions, and changed-files summary.
+5. Capture computed styles and geometry for the assistant message, user prompt,
+   changed-files summary, action buttons, timeline, and document width.
+6. Save `conversation-surface-fidelity.json` and
+   `conversation-surface-fidelity.png`, then continue the compact conversation,
+   compact review, review safety, commit, settings, and terminal workflows.
+
+## Assertions
+
+- Assistant message border widths are all `0`.
+- Assistant message background alpha is `0`, so assistant prose is not a
+  framed card.
+- User prompt remains a compact right-aligned bubble with a visible border and
+  background alpha of `0.1`.
+- Changed-files summary remains an inline supporting surface with background
+  alpha `0.024`, border alpha `0.11`, and height `153.5` px.
+- Changed-file rows do not render as nested cards.
+- Changed-files `Review Changes` action height is `30` px.
+- Assistant action buttons remain compact at `28x28` px.
+- Document scroll width stayed equal to the `1240` px viewport.
+- Console errors: 0.
+- Failed local network requests: 0.
+
+## Artifacts
+
+- `conversation-surface-fidelity.json`
+- `conversation-surface-fidelity.png`
+- `assistant-message-actions.json`
+- `assistant-message-actions.png`
+- `compact-dense-conversation.json`
+- `compact-dense-conversation.png`
+- `compact-review-drawer.json`
+- `compact-review-drawer.png`
+- `review-drawer-layout.json`
+- `terminal-expanded-layout.json`
+- `electron.log`
+- `summary.json`
+
+## Failed Run Fixed
+
+Iteration 15 produced a partial artifact directory at
+`.qwen/e2e-tests/electron-desktop/artifacts/2026-04-26T01-19-16-242Z/`.
+That run stopped before `conversation-surface-fidelity.json` or `summary.json`
+were written. Iteration 16 reran the full CDP smoke successfully with the same
+slice changes and produced the passing artifact directory above.
+
+## Known Uncovered Risk
+
+The harness validates deterministic fake ACP content at the default and compact
+desktop sizes. Long branch names, long model names, and unusually long project
+names with the review drawer open still need a focused truncation and overflow
+assertion.