giles e12e314bc3 host: factor the shared composition CORE — one fold, N domains (composition step 8) ...

The roadmap's capstone: now that two folds exist (render, execute), extract the machinery
they share. host/comp-fold (compose.sx) is the reusable core — the seq/alt/each combinator
dispatch + the `when` predicate set (host/comp--pred?) + the context-environment + the `each`
source (host/comp--source) + recursion + the depth guard, ALL in one place. A domain plugs in
via a small dict {:empty :combine :leaf :overflow}; only its leaves and how results combine
differ:
  render  = {:empty ""     :combine str    …}  leaf -> markup (+ row/grid layout combinators)
  execute = {:empty (list) :combine concat …}  leaf -> effect

host/comp-render and host/exec-run are now one-liners over host/comp-fold with their domain.
execute.sx shed its own seq/alt/each dispatch — it's just a dict + a leaf. A THIRD domain
(eval/reduce/extent over the same algebra) is now only a new dict + leaf, no new control flow.

Both folds went through the core with ZERO behaviour change: new tests/compose.sx exercises
the core + render domain directly (17/17 — leaves, seq, row, alt+when (has/eq/not), each
(items/query/empty), tmpl recursion over a (children) tree + depth guard, ref transclude, one
object two contexts); execute 13/13; blog 162/164 (2 pre-existing relate-picker fails). Full
host conformance 388/390. Wired tests/compose.sx into conformance.

plans/composition-objects.md roadmap steps 1-8 COMPLETE.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

2026-06-30 23:53:56 +00:00

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