chore: publish mailtrap-local to NUR via goreleaser

[leonid-shevtsov]

What & why

Add a nix: publisher to goreleaser so each tag opens a PR in mailtrap/mailtrap-nur, keeping the Nix package in sync with releases the same way we already do for Homebrew.

• Wire release workflow to install Nix (for nix-hash) and pass the renamed cross-repo secret GORELEASER_TOKEN.
• Fail the release job if the expected Homebrew or NUR package PR is missing (goreleaser soft-fails those errors).
• Add Nix install docs and release-pipeline notes to README so the new distribution channel is discoverable.

How to test

No QA needed — non-user-facing release-pipeline and docs changes only.

[coderabbitai]

📝 Walkthrough

Walkthrough

The release workflow now installs Nix, uses GORELEASER_TOKEN for cross-repository publishing, and verifies the expected mailtrap-nur pull request. GoReleaser adds Nix package updates and installation output. The README documents Nix distribution and release destinations.

Changes

Release distribution

Layer / File(s)	Summary
Release workflow setup .github/workflows/release.yml	The release job targets the release environment, installs Nix, passes GORELEASER_TOKEN alongside GITHUB_TOKEN, and verifies the expected version-specific mailtrap-nur pull request.
GoReleaser publishing configuration .goreleaser.yaml	Homebrew authentication uses GORELEASER_TOKEN. A Nix publisher updates mailtrap-nur, creates the mailtrap-sendmail symlink, and adds Nix installation output.
Distribution documentation README.md	Documents Nix commands, the mailtrap-nur package, automated pull requests, and updated release repository locations.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• mailtrap/mailtrap-local#43: The PR also modifies GoReleaser Homebrew publishing and authentication configuration.

Sequence Diagram(s)

sequenceDiagram
  participant GitHubActions
  participant Nix
  participant GoReleaser
  participant mailtrapNur
  GitHubActions->>Nix: install Nix
  GitHubActions->>GoReleaser: run with GITHUB_TOKEN and GORELEASER_TOKEN
  GoReleaser->>mailtrapNur: open version-specific package update PR
  GitHubActions->>mailtrapNur: verify the expected PR

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Suggested reviewers: sergeykorolev, mklocek, piobeny

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.
Title check	✅ Passed	The title clearly identifies the main change: publishing mailtrap-local to NUR through GoReleaser.
Description check	✅ Passed	The description explains the motivation, key changes, and testing approach, but it omits the template's Images and GIFs section.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In @.goreleaser.yaml:
- Around line 170-171: Update the GoReleaser configuration around the NUR
pull_request setting to add a post-release verification or alert that confirms
the expected mailtrap-nur pull request was created successfully. Ensure the
release flow detects and surfaces a missing NUR PR even when GoReleaser reports
the creation error non-fatally, without changing the existing release behavior
for successful PR creation.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 38186dae-7995-49d5-8464-66e7bfc0bff4

📥 Commits

Reviewing files that changed from the base of the PR and between 23653a6 and 1d44829.

📒 Files selected for processing (3)

• .github/workflows/release.yml
• .goreleaser.yaml
• README.md

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In @.github/workflows/release.yml:
- Around line 85-87: Update the NUR PR lookup in the release workflow to accept
only valid OPEN or MERGED pull requests, rather than any result from --state
all. Ensure the jq selection evaluates matching PRs for the
mailtrap-local-${version} head and does not accept a closed or unrelated PR;
preserve the existing URL output for an accepted result.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 040035be-441b-46ac-a5cd-89df752a23c5

📥 Commits

Reviewing files that changed from the base of the PR and between 1d44829 and ac80426.

📒 Files selected for processing (1)

• .github/workflows/release.yml