fix(rivetkit): warn when manager port falls back to a different port

[NathanFlurry]

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[railway-app]

🚅 Deployed to the rivet-pr-4489 environment in rivet-frontend

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[NathanFlurry]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• fix(rivetkit): remove drizzle-orm peer dep and add runtime version check #4492
• chore(skill): add version check to rivetkit skill #4491
• fix(rivetkit): prevent Turbopack from tracing sqlite-vfs dynamic import #4490
• fix(rivetkit): warn when manager port falls back to a different port #4489 👈 (View in Graphite)
• fix(rivetkit): clear connectableTs on actor sleep #4488
• fix(rivetkit): gate node:sqlite behind RIVETKIT_NODE_SQLITE env var #4487
• main

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[claude]

PR Review: fix(rivetkit): warn when manager port falls back to a different port

This is a small, focused change that adds a warning log when findFreePort returns a different port than the configured one. The change is sensible and helps developers identify port conflicts during development.

Feedback

Logging format

The warning uses a template string inside the msg field:

logger().warn({
    msg: `port ${configuredManagerPort} is in use, using ${managerPort}`,
});

Per the project's structured logging conventions in CLAUDE.md:

Do not format parameters into the main message, instead use structured logging fields.

The same principle should apply to the TypeScript logger. The structured data (ports) should be separate fields rather than interpolated into the message string:

logger().warn({
    msg: "manager port is in use, falling back to a different port",
    configuredPort: configuredManagerPort,
    actualPort: managerPort,
});

This makes the log easier to query/filter programmatically in log aggregation tools.

Message casing

The message is already lowercase, consistent with the project's convention. No issues here.

Summary

The change is correct and addresses a real UX gap — previously, port fallback happened silently. The only suggested improvement is to follow the project's structured logging style by separating port values into named fields rather than interpolating them into the message string.