Fixes https://github.com/coder/coder/issues/22375
Updates `stringutil.Truncate` to properly handle multi-byte UTF-8
characters.
Adds tests for multi-byte truncation with word boundary.
Created by Mux using Opus 4.6
## Problem
Tasks currently only expose a machine-friendly name field (e.g.
`task-python-debug-a1b2`), but this value is primarily an identifier
rather than a clean, descriptive label. We need a separate
display-friendly name for use in the UI.
This PR introduces a new `display_name` field and updates the task-name
generation flow. The Claude system prompt was updated to return valid
JSON with both `name` and `display_name`. The name generation logic
follows a fallback chain (Anthropic > prompt sanitization > random
fallback). To make task names more closely resemble their display names,
the legacy `task-` prefix has been removed. For context, PR
https://github.com/coder/coder/pull/20834 introduced a small Task icon
to the workspace list to help identify workspaces associated to tasks.
## Changes
- Database migration: Added `display_name` column to tasks table
- Updated system prompt to generate both task name and display name as
valid JSON
- Task name generation now follows a fallback chain: Anthropic > prompt
sanitization > random fallback
- Removed `task-` prefix from task names to allow more descriptive names
- Note: PR https://github.com/coder/coder/pull/20834 adds a Task icon to
workspaces in the workspace list to distinguish task-created workspaces
**Note:** UI changes will be addressed in a follow-up PR
Related to: https://github.com/coder/coder/issues/20801
Closes https://github.com/coder/coder/issues/18159
If an Anthropic API key is available, we call out to Claude to generate
a task name based on the user-provided prompt instead of our random name
generator.
Cian Johnston