Migration tool must preserve up-next lane instead of promoting to asap

[flyingrobots]

Problem

The backlog migration tooling collapsed Echo docs/method/backlog/up-next/** cards into the lane:asap label during the Echo migration.

Concrete evidence:

• Echo PR #527 initially created issues #468 through #505 from docs/method/backlog/up-next/**.
• Those issues were labeled lane:asap instead of lane:up-next.
• The archive mapping initially recorded the same wrong lane.
• The defect had to be corrected manually in Echo commit af1bf7b0 by creating lane:up-next, relabeling issues #468 through #505, and fixing the archive README.

This is a migration correctness bug. It changes scheduling semantics while claiming to preserve backlog lanes.

Desired outcome

The Method migration script preserves all supported backlog lanes exactly, including up-next.

Acceptance criteria

• Migrating docs/method/backlog/up-next/foo.md creates an issue labeled lane:up-next.
• The script creates lane:up-next when missing, with the canonical Method label description/color.
• The generated archive/mapping output records lane:up-next, not lane:asap.
• A regression fixture covers every canonical lane: asap, up-next, v0.1.0/release, inbox, cool-ideas, and bad-code.
• The script fails loudly on an unknown lane instead of silently remapping it.

References

• Echo PR #527
• Echo fix commit af1bf7b0

[coderabbitai]

🔗 Related PRs

#20 - Add backlog notes for agent-first planning and review workflow [merged]
#21 - Align test taxonomy fixtures with live legends [merged]
#64 - Make GitHub Issues the Method work tracker [closed]

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