[Task] Expand release agent and workflow tests

[ashleyshaw]

Summary

Replace placeholder release-path checks with behavioural tests that prove the agent and workflow stop at the right time.

Action

• Action Type: Create
• Target File: scripts/agents/__tests__/release.agent.mcp.test.js and scripts/workflows/__tests__/release-workflow-scripts.test.js

Proposed Test Content

Add tests for:

• run() happy path and guard failures
• preflight failures for existing tag or release
• tag creation and release creation mutation calls
• GitHub API retry and failure handling
• workflow argument composition and invalid input rejection
• dry-run vs live-path sequencing
• release-notes preview ref resolution

Scope & Applicability

• Type: Main test files and workflow scripts
• Affected Areas: release agent, workflow runner, notes preview, MCP provider, shell provider
• Audience: Developers and maintainers

Acceptance Criteria

• Test covers all required scenarios and edge cases
• Test is properly structured and follows conventions
• Change is documented in the project change log
• Test has been run and passes as expected
• PR uses correct branch prefix
• Approved by at least one maintainer

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Definition of Ready (DoR)

• Purpose, scope, and audience defined
• Target file and action type specified
• Acceptance criteria listed
• Estimate added (if applicable)

Definition of Done (DoD)

• All acceptance criteria met and verified
• Changelog entry prepared for PR
• Test passes all required scenarios and environments
• Documentation updated (if needed)
• PR uses correct branch prefix (test/)
• Approved by at least one maintainer

[linear-code]

LS-924