"Keep addressed agents active" should insert a space after the agent mentions

[hutchisr]

Describe the bug

When "Keep addressed agents active" is enabled, a mention for the agent(s) is inserted into the chat input, but no space is inserted after, so if the user starts typing the mention will be undone and converted to part of the user's input instead of the intended mention. The user will have to manually hit spacebar to avoid this which undermines the convenience of this feature

Steps to reproduce

1. In Settings -> Agents, enable Keep addressed agents active
2. Message an agent
3. Follow up with the agent

Expected behavior
What did you expect to happen?

Version and platform
Find your version at the bottom of the Settings sidebar. Write "unknown" if you can't determine it.

• Buzz version: 0.5.5
• OS: macOS 26.6

Logs / additional context

[VaibhavJain2609]

Claiming this issue — working on a fix so "Keep addressed agents active" inserts a trailing space after restored agent mentions so typing doesn't collapse the mention chips.

Couldn't self-assign (permission). Branch: `fix/4979-keep-agents-active-trailing-space`

[VaibhavJain2609]

Opened PR: #5021

Root cause: TipTap markdown `setContent` strips trailing whitespace, so post-send restore via `setContentAndFocusEnd` dropped the space that `resolvePostSendContent` adds. Fix re-attaches the space with `insertText` after parse.