[FEATURE] claude agents dispatch input: @ should also autocomplete file paths, not only repos/subagents

Feature request

In the claude agents view (docs), the dispatch input's @ autocomplete only suggests repositories (and subagents) — there is no way to autocomplete file paths into the prompt, unlike the in-session @ file/folder mention picker in a normal Claude Code conversation.

Repro

1. Run claude agents inside a git repository (or a parent directory containing repos).
2. Press n (or focus the dispatch input) to compose a new session prompt.
3. Type @ — the picker lists sibling repos / subagents only.
4. Continue typing a path that exists in the repo, e.g. @src/app/foo.service.ts — no file suggestions ever appear.

Expected (desired): once the dispatch target repo is unambiguous — the view was opened inside a single repo, or the prompt already contains a @<repo> mention — the @ picker should fall through to the normal file/folder suggestion source scoped to that repo, like the in-session prompt does.

Why it matters

Prompts dispatched from the agents view very often need to point the agent at specific files. Current workarounds all defeat the purpose of dispatching directly from the view:

• typing file paths by hand (error-prone, slow in deep trees)
• composing the prompt in a normal REPL session (where @ file autocomplete works) and dispatching with /bg instead
• spawning with a minimal prompt, attaching to the session, then sending a follow-up with @ file mentions

Related (but distinct) issues

• #61407 — fuzzy match for the existing @<repo> / @<subagent> picker (improves the repo picker; doesn't add file mentions)
• #58738 — expand dispatch @ autocomplete to non-git folders (still directory-level, not files)
• #60499 — IDE file references not working in agents mode (IDE integration, not the TUI dispatch picker)

Environment

• Claude Code 2.1.168 (terminal CLI)
• Platform: Linux