fix(server): bind to localhost by default

[aaronjmars]

Summary\n\n- Change the standalone switchyard-server default bind address from 0.0.0.0 to 127.0.0.1.\n- Keep all-interface exposure available through an explicit --host value.\n\nThis is a project-improvement contribution following NVIDIA PSIRT ticket 6648053. It is intentionally separate from the closed security report and does not claim that the documented demo server is a security bug.\n\n## Testing\n\n- git diff --check\n- Cargo tests unavailable because Cargo is not installed in this environment.

Summary by CodeRabbit

• Security
  • The server now binds to localhost by default, reducing unintended external exposure.
  • External access requires explicitly configuring a host address.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: c3ab0d50-277f-4093-996e-4d5dee9f5ac6

📥 Commits

Reviewing files that changed from the base of the PR and between c597bfd and 949be12.

📒 Files selected for processing (1)

• crates/switchyard-server/src/cli.rs

Included review availability: Your plan provides up to 12 included reviews per hour; 11 remain after this review.

---

Walkthrough

The server CLI now binds to IPv4 localhost by default. Comments state that external exposure requires an explicit --host value.

Changes

Server bind configuration

Layer / File(s)	Summary
Local-only server default crates/switchyard-server/src/cli.rs	The default host changed from 0.0.0.0 to IPv4 localhost. Comments document the explicit --host requirement for external exposure.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to 949be

The server will bind to localhost by default, reducing unintended remote exposure while preserving external access through an explicit --host value. No actionable merge-blocking risk remains after normal checks and review.

Poem

A rabbit guards the localhost gate
The server binds close, not wide open in wait
A host flag leads the way
For journeys beyond the tray
Safe defaults now hop into place

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: the server now binds to localhost by default.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1 files.

---

_{Comment @coderabbitai help to get the list of available commands.}

[afourniernv]

Thanks for raising this. This changes the deployment behavior of switchyard-server, not just the bind address. It would also affect the checked-in systemd service and normal Docker port publishing.

I've opened #596 so we can decide what the default should be and account for those paths together. I'm going to close this PR for now.