Self-host Route A: harden v1 emitter — drive v1-emitted v2 crate to cargo-check-green via RC1-4 root-cause fixes (regen seed)

[gunbai-bot]

Auto-opened by session-dashboard for session warm-cat-908.
Pushing to session/warm-cat-908 advances this PR.

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[briansrls]

Closing as stale/superseded: "harden v1 emitter (Route A)" is from 2026-06-18 and CONFLICTING; the self-host front-end effort has since moved to the active self-parse closure lane (#5406 merged, #5404 cont.). Branch retained — reopen if Route A emitter-hardening is still the plan.