ROADMAP slice-2 step-2: emit a section from the work-DAG model + §2 delete redundant box enum

[gunbai-bot]

Slice-2 step-2: emit a ROADMAP section from the work-DAG model

Third slice of inverting the hand-maintained ROADMAP (docs/plans/invert-hand-maintained.md).
Builds the roadmap-specific projection emit(roadmap_work_model, Markdown) on top of the
authorities that already landed:

• gunbc.roadmap_model (roadmap_model (slice-2 step 1): work-DAG authority model for a ROADMAP line #5498) — the work-DAG line model;
• gunbc.roadmap_status (Invert hand-maintained docs - generate ROADMAP from .dag authority plus drift-gate, starting with the PR-to-checkbox status slice #5491) — the PR→completion binding;
• std.markdown + extdeps.languages.markdown.serialize_markdown_source (Add Markdown as an emit medium: row-driven serialize_markdown_source (medium rows) #5501, deep-newt) — the
  row-driven Markdown medium.

gunbc.roadmap_emit.project_roadmap_section(title, nodes, edges, merged) -> MarkdownDocument composes
these into an H2 section whose task-list items render each line's box. The checkbox is the
DONE-authority decision (plan §6.1): a CompletesIff line's box is derived from the merged-PR
set (the inversion — generated, never hand-toggled); a HandChecked line renders its authored box
(the honest DecodeFidelity residue, §5). Children nest one indent level (fuel-bounded, §4).

SCAFFOLD-marked: the dsl serializer fold on the v1 seed, in the same shape as
expected_ci_yml = serialize_yaml(project_workflow_to_yaml(…)). Dissolution trigger = the eventual v2
Markdown TargetModel (§4 one-grammar-both-ways), at which point the projection emits v2 Nodes.

§2: deleted the redundant box enum (not just renamed it)

roadmap_status previously modeled the box as a 2-variant enum (Done | Todo), which collided with
std.markdown.CheckboxState = Checked | Unchecked (two same-named types → the resolver drops both
constructor sets). The enum was only ever consumed as a Bool by the projection, so it was a redundant
second representation. Deleted it (net concepts shrink > rename): completion is now a plain
Bool (RoadmapStatusEntry.claimed_done; predicate prs_all_merged), std.markdown.CheckboxState
is the project's sole checkbox type, and the Bool→glyph map lives in the emit layer
(task_item_with) so roadmap_status stays medium-agnostic. Deleted: CompletionState,
derive_checkbox, checkbox_done, test checkbox_is_done. claimed_done is kept on the entry so
slice-1's drift gate still works for CompletesIff lines (it dissolves into the emit wall later, plan §7).

Proof by execution

dsl/test/claim/roadmap_emit_test.dag (auto-enrolled in the CI floor) is discriminating: the H2
heading renders, a HandChecked parent renders its authored box + plan-doc link, and a CompletesIff
child renders a derived [x] when its PR is in the merged set / [ ] when not — flip the merged set
and the box flips. All three roadmap witness suites (status / model / emit) run green.

🤖 Generated with Claude Code