The previous fix moved the hover group onto the message shell, but the action row still occupied layout space while invisible. That invisible row kept expanding the shell hit area, so moving the pointer into the empty metadata strip could still reveal copy and timestamp controls.
Collapse the action row to zero height by default and expand it only while the message shell is hovered or focused. Keep message content spacing separate from the action row so hidden controls do not create a hover target.
Constraint: Copy/fork controls must remain reachable after the bubble reveals them.
Rejected: Use display:none for the action row | would remove the keyboard focus path entirely.
Confidence: high
Scope-risk: narrow
Directive: Keep hidden message metadata rows out of normal hover hit-testing; do not reintroduce invisible layout space around chat bubbles.
Tested: cd desktop && bun run test src/components/chat/MessageList.test.tsx --run -t "keeps user actions anchored"
Tested: cd desktop && bun run test src/components/chat/MessageList.test.tsx --run
Tested: cd desktop && bun run test src/components/chat/UserMessage.test.tsx --run
Tested: bun run check:desktop
Tested: git diff --check
Not-tested: Live Tauri native hover smoke
Related: #642
0ab624bff4