[FEATURE]: Desktop client: intercept built-in slash commands (/new, /clear) in the input

Environment

• T3 Code desktop client (Electron, Alpha channel), macOS arm64
• opencode CLI 1.18.29 (in the terminal TUI, /clear and /new both work)
• Provider: OpenRouter (GLM), i.e. a non-Claude, provider-agnostic session

Expected

The docs list /clear as an alias of /new ("Start a new session", ctrl+x n). Typing /clear or /new in the desktop app input should start a new session.

Actual

The desktop input passes slash commands through to the model as plain user messages: nothing is intercepted, and the session keeps its full context. Verified against the shipped app bundle (app.asar, ~194MB):

• Zero occurrences of "/clear", "/help", "/compact", name:"clear", name:"new"; the single "/new" string is a doc-comment example
• All aliases:[...] arrays in the bundle are syntax-highlighting language tags
• The only slash-related schema is ServerProviderSlashCommand (provider-advertised commands); an OpenRouter provider registers none
• The server dist has no slash command registry at all

So the built-in commands documented for the TUI have no desktop-input equivalent, and config-defined custom commands (command/*.md) cannot fill the gap, because the client never executes commands.

Request

Intercept built-in commands in the desktop input, at minimum /new and /clear. Longer term, surfacing custom commands (command/*.md) the way the TUI does would make the clients feature-equal.

Note

The current passthrough is genuinely useful and worth preserving: typing /skill-name reaches the agent, which loads and runs that skill. Suggested rule: registered command names intercept; anything else falls through to the agent as a prompt.

Related closed issues (same-session /clear semantics, shipped for the TUI): #19499, #1368