[Bug] Built-in slash commands ignored when sent from Remote Control due to system-reminder prefix

Bug Description
Title: /clear (and other built-in commands) silently ignored when sent from phone/Remote Control — <system-reminder> prefix defeats start-of-message recognition Summary: Built-in slash commands sent from the mobile/web Remote Control interface are not intercepted by the CLI and instead get forwarded to the model as literal user text. The session is never cleared. Repro: 1. Connect to an active CLI session from the phone (Remote Control). 2. Type /clear and send. 3. Observe the message rendered as: ❯ <system-reminder>Message sent at Sun 2026-06-14 22:46:01 UTC.</system-reminder> /clear 4. Context is not cleared; the conversation continues unchanged. Expected: /clear is intercepted by the CLI, context is wiped, prior session preserved in /resume. (Per the Remote Control docs, /clear is listed as a command that should work from mobile/web.) Actual: Nothing clears. The command reaches the model as a normal message. Likely root cause: The Remote Control relay prepends a <system-reminder>Message sent at …</system-reminder> timestamp to forwarded messages. The CLI only recognizes a slash command when it is at the start of the message. Because the system-reminder now occupies the start, the start-of-command check fails and the command is treated as literal text. Suggested fix: Strip/normalize the injected <system-reminder> preamble (or run the start-of-command check against the user-typed payload, not the wrapped transport message) before command dispatch, so built-in commands from Remote Control are intercepted correctly. Impact: Affects all built-in commands sent remotely (/clear, /compact, /context, etc.) — users on phone cannot reset/compact context and may not realize the command was no-op'd. Environment: Claude Code via phone Remote Control driving a local terminal session (macOS).

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.173
• Feedback ID: d6c1121a-02a1-4051-9a85-08f1c456316d

Errors

[{"error":"Error: 404 {\"type\":\"error\",\"error\":{\"type\":\"not_found_error\",\"message\":\"Claude Fable 5 is not available. Please use Opus 4.8. Learn more: https://www.anthropic.com/news/fable-mythos-access\"},\"request_id\":\"req_011CbzvmeMAgcgQukJRp5YY6\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:12:66126)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:52:7694)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-06-13T08:16:34.325Z"}]