[Feature]: Slash-command autocomplete should trigger mid-input, not only at the start of the composer

[Sumstead72]

Before submitting

• I searched existing issues and did not find a duplicate.
• I am describing a concrete problem or use case, not just a vague idea.

Area

apps/web

Problem or use case

The slash-command picker only appears when / is the first character in the composer.
Typing / anywhere later in the input inserts a bare slash with no command list, so
there is no way to discover or complete a second command in the same message.

I frequently invoke multiple skills/commands in one prompt. Today that means either
typing the later command names from memory (no completion, no validation), or writing
the second command first and editing around it.

Repro

1. Focus the composer.
2. Type / — the command list appears. Pick a command.
3. Continue typing, then type / again mid-input.
4. No command list appears.

Proposed solution

Trigger the command picker on any / that begins a token — i.e. / at the start of the
input or preceded by whitespace/newline — not only at offset 0. Same trigger and
completion behavior as the first one, inserting at the cursor.

Suggested guards so this does not fire on paths or URLs:

• Only trigger when the / is preceded by start-of-input or whitespace.
• Do not trigger inside a fenced code block or an in-progress @file mention.

Why this matters

Chaining commands in one message is a normal workflow, and it is currently the only
composer affordance that is position-locked. @file mentions already work mid-prompt
(#922 fixed exactly this for @), so / is the odd one out — the inconsistency is what
makes it surprising rather than just limiting.

Smallest useful scope

Whitespace-preceded / triggers the picker and inserts at the cursor. No change to
ranking, fuzzy matching, or multi-command execution semantics.

Alternatives considered

Typing later commands from memory, or composing the message out of order. Both work but
lose discovery and typo-catching for every command after the first.

Examples or references

• Composer @file autocomplete should work in the middle of an existing prompt #922 — "Composer @file autocomplete should work in the middle of an existing prompt"
  (closed as completed); this is the / parity case.

Environment

T3 Code 0.0.34 (nightly), Windows 11.