Default Studio host to 127.0.0.1 and prompt before auto-start

[rolandtannous]

Summary

Resolves #4684 and supersedes #4864.

Credit to @Bedrovelsen for initially raising the issue and writing the original fix in #4864. This PR carries the same goals forward and is rebased onto current main to clear the studio/backend/run.py conflict that #4864 picked up as main evolved (notably the addition of --api-only and llama_parallel_slots to run.py's argparse handling).

Studio previously bound to 0.0.0.0 (all interfaces) by default, and the installer silently auto-started a server at the end of install — exposing the service on the network without user consent and contradicting the documented privacy-first / 100% local guarantee.

Changes

• studio/backend/run.py: run_server() and argparse --host default to 127.0.0.1. (No _make_argument_parser() extraction, since main has since added --api-only/llama_parallel_slots to that block — the default-value change alone meets the security goal.)
• unsloth_cli/commands/studio.py: typer --host default to 127.0.0.1 in both studio_default() and run() (the unsloth studio run one-liner). security: default Studio host to 127.0.0.1 and prompt before auto-start #4864 only touched the first.
• install.sh: drop -H 0.0.0.0 from the generated ~/.local/share/unsloth/launch-studio.sh template; replace silent auto-start with a [Y/n] prompt; add a (add -H 0.0.0.0 to allow network / cloud access) note in the manual hint.
• install.ps1: drop -H 0.0.0.0 from the PowerShell launcher template; replace silent auto-start with a Read-Host [Y/n] prompt; same note.
• studio/setup.sh: drop -H 0.0.0.0 from the post-setup launch: hint and add the cloud/network note. (Not in security: default Studio host to 127.0.0.1 and prompt before auto-start #4864 — without this, the post-setup hint contradicted the new default.)
• README.md: simplify Launch examples to unsloth studio -p 8888; add a note that -H 0.0.0.0 is available for cloud/LAN use. -p 8888 is kept in user-visible hints since it documents the default port (only -H 0.0.0.0 is the security concern being removed).

Users who need all-interfaces binding (cloud VMs, LAN sharing) can still pass -H 0.0.0.0 explicitly.

Tauri impact

None. Both installers exit on the --tauri early-return well before the auto-start prompt block, and the Tauri runtime path uses --api-only (Tauri parses the TAURI_PORT={port} line and connects via 127.0.0.1 regardless of bind host). Desktop shortcuts (.desktop / .lnk / .app) now invoke unsloth studio and bind loopback by default — correct desktop behaviour.

Tests (TDD)

• studio/backend/tests/test_host_defaults.py — AST inspection of run_server() parameter default and argparse --host default. Walks the whole module so the assertions hold whether the parser lives in __main__ or a helper.
• tests/studio/test_cli_studio_defaults.py — AST inspection of the typer Option default for both studio_default() and run().
• tests/sh/test_install_host_defaults.sh — static analysis of install.sh, install.ps1, studio/setup.sh, and README.md.

Test plan

• Linux interactive: ./install.sh --local → prompt appears, Enter launches Studio bound to 127.0.0.1:8888, n prints manual hint and exits cleanly.
• unsloth studio (no flags) binds to 127.0.0.1:8888.
• unsloth studio -H 0.0.0.0 -p 8888 still binds to all interfaces.
• Tauri install (--tauri) skips the prompt and finishes as before. Notified Mugi. Mugi to adjust
• pytest studio/backend/tests/test_host_defaults.py tests/studio/test_cli_studio_defaults.py passes.
• bash tests/sh/test_install_host_defaults.sh passes.

[gemini-code-assist]

Code Review

This pull request changes the default host binding for Unsloth Studio from 0.0.0.0 to 127.0.0.1 across the backend, CLI, and installation scripts to ensure a "privacy-first" local experience. Documentation and setup scripts have been updated to reflect this change, including new interactive prompts in the installers and instructions for users who require network access. Additionally, new tests using AST parsing have been added to verify these defaults. I have no feedback to provide.

[rolandtannous]

tests

colab.test.mp4

local.test.mp4

merging