Declare the Node, gh, and OS support policy #19

Goal

Declare the supported Node, gh CLI, and OS matrix, including a Node 20 legacy/EOL review, without inventing updates.

Observations

• CI currently runs a 3-OS Node 20 matrix; B01 only checks basic pass and reports declared skips.
• Node 20 legacy/EOL status needs review and a recorded decision; no version bump is implied now.
• Native-unassessable cases are treated as high risk.

Decision gate

Approve the declared support policy and the Node 20 legacy review outcome before extending native coverage.

Acceptance criteria

• Supported Node, gh, and OS versions are documented with rationale.
• Node 20 legacy/EOL status has a recorded decision (keep or plan migration).
• Unsupported combinations are explicit, not silently skipped.

Verification

• Docs review -> every supported combination is listed and testable.
• Matrix run -> declared combinations execute; undeclared ones report as unsupported.

Release checkpoint

Remaining risk: policy without native runs stays unverified. B03-02 extends coverage beyond the basic matrix.

Tracking

Roadmap item: B03-01. All acceptance criteria remain pending; publication does not grant approval or release authority.