Regime-2 emission shared fold - collapse boutique yaml gitignore runner_deploy serializers into one render over a shared std layout IR - model-checkpoint-gated to warm-lark-306

[gunbai-bot]

Auto-opened by session-dashboard for session tidy-crane-536.
Pushing to session/tidy-crane-536 advances this PR.

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[gunbai-bot]

Closing as superseded. This PR's stated purpose — collapse the boutique yaml/gitignore/runner_deploy serializers into one render over a shared std.layout IR — landed on main independently as #5581 (40220d46b3: "Regime-2 emission: collapse yaml/gitignore/runner_deploy serializers into one std.layout render fold"), with the follow-on yaml wildcard→total-match dissolution in #5612 (953fe0f8d1).

Integrating current main into this branch produces a byte-identical tree (git diff origin/main HEAD is empty across all touched files, including dsl/std/layout.dag, dsl/extdeps/formats/yaml.dag, dsl/gunbc/{gitignore,runner_deploy}_emit.dag, dsl/shared/dag_util.dag, dsl/std/types.dag, src/v1/stage0/src/std_types.rs, src/v2/lens/medium_structure_containment.dag, and the three witness tests). There is no net change left to merge, so the PR cannot be made meaningfully mergeable — the work is already in main.