Prepare release v0.13.1

[robzolkos]

Summary

Release metadata generated by GOWORK=off make release VERSION=0.13.1:

• set the Nix package version to 0.13.1 and verify the Nix build (dependencies changed since 0.13.0; vendorHash verified unchanged)
• stamp the Claude and Codex plugin manifests as 0.13.1

The full release preflight (make release-check: check, replace-check, govulncheck, race tests, surface compatibility) passed before branch protection rejected the script's direct main push. No release tag has been created. After this PR merges, rerunning the release command from main creates and pushes the tag without another metadata change.

What 0.13.1 ships (since v0.13.0)

• Connect an agent in one flow: versions first, one approval, watcher included (Connect an agent in one flow: versions first, one approval, watcher included #875), with the post-upgrade notice naming which side of a plugin/CLI mismatch to update
• OAuth reaches Basecamp's own hosts through fake-IP DNS (Let OAuth reach Basecamp's own hosts through fake-IP DNS #889)
• Go 1.26.9 for eleven standard-library advisories, and golang.org/x/net v0.60.0 (Fix Security CI: golang.org/x/net v0.60.0 and Go toolchain 1.26.9 #886)
• The skill tells agents rich-text fields support Mermaid diagrams (Tell agents that rich-text fields support Mermaid diagrams #878)

No command or flag was added or removed (.surface unchanged), so this is a patch release.

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Summary by cubic

Prepares release v0.13.1 by bumping the version to 0.13.1 in the Nix package and the Claude and Codex plugin manifests. The release preflight passed; no tag has been created, so rerunning the release command after merge creates and pushes the v0.13.1 tag.

^{Written for commit c687059. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 3 files

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[Copilot]

🟢 Approved

The three generated metadata updates are consistent with the v0.13.1 release and existing release scripts.

0 open findings

What changed in this PR

Prepares the v0.13.1 release by synchronizing release metadata across Nix and both agent plugins.

Changes:

• Bumps the Nix package version to 0.13.1.
• Bumps Claude and Codex plugin manifests to 0.13.1.

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File	Description
nix/​package.nix	Updates the packaged CLI version.
.codex-plugin/​plugin.json	Updates Codex plugin metadata.
.claude-plugin/​plugin.json	Updates Claude plugin metadata.

🧠 Review effort: Balanced

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