Skill autocomplete only triggers at start of input, not mid-line

Bug

The skill/slash-command autocomplete dropdown only appears when /<text> is the first and only content in the input. If there is any text before it, typing /<text> does not trigger the autocomplete picker.

Reproduction

1. Type /com — autocomplete dropdown appears ✅
2. Type fix the tests then /com — no autocomplete dropdown ❌
3. Type on a new line after other text: fix the tests\n/com — no autocomplete dropdown ❌

Expected behavior

The autocomplete picker should activate whenever the cursor is at the end of a /<text> token, regardless of surrounding text. This matches how Slack, Notion, and Discord handle command completion.

Why this matters

Users with custom skills/commands (especially 10+) rely on the autocomplete picker to discover and select the right command. Having to clear the input, pick the command, then re-type context is a friction point — especially when composing prompts that combine instructions with a skill invocation (e.g., review the changes then /commit).

Prior issues

• #6956 (closed NOT_PLANNED) and #29752 (closed as duplicate) covered broader slash command usability. This issue is narrowed to just the autocomplete trigger position — the smallest, most targeted fix.

Environment

• Claude Code 2.1.78
• macOS (arm64)