roadmap: heap-Str ABI as P1 milestone, blocker for Show + print rewire

Names the runtime infrastructure prerequisite (malloc-backed refcounted
Str alongside static @.str_* globals) as its own milestone. Show + print
rewire now carries an explicit depends-on link. Existing Eq/Ord [x]
entry removed (shipped milestone 23; mirrored in WhatsNew + journal).

docs/roadmap.md

@@ -41,23 +41,34 @@ context. Pick the next milestone from P1.)_
 
 ## P1 — Next
 
-- [x] **\[milestone\]** Post-22 Prelude — Eq/Ord — shipped milestone
-  23 (2026-05-12). `Ordering` ADT, `Eq`/`Ord` classes, primitive
-  instances on Int / Bool / Str, polymorphic free fns
-  `ne`/`lt`/`le`/`gt`/`ge`, runtime `ail_str_eq` + `ail_str_compare`,
-  end-to-end coverage including user-ADT-instance integration. Float
-  has neither instance by design; polymorphic helpers at Float fire
-  Float-aware `NoInstance` per DESIGN.md §"Float semantics".
+- [ ] **\[milestone\]** Heap-`Str` ABI — runtime infrastructure for
+  malloc-backed, refcounted `Str` values alongside the existing
+  static `@.str_*` globals. Today the `Str` path is static-only
+  (DESIGN.md §"Float semantics" notes this explicitly), so any
+  primitive that needs to produce a `Str` at runtime — `int_to_str`,
+  `float_to_str` (currently type-installed but `CodegenError::Internal`
+  on call), eventual `Show.show`, future `++` on strings — cannot
+  ship. Scope: pick the representation (likely a `{rc_header, len,
+  bytes…}` slab consistent with the rest of the RC runtime), teach
+  codegen to accept both static and heap `Str` at the same ABI slot,
+  wire RC `inc`/`drop`/`clone`/`compare`/`eq` on the heap form, and
+  ship `int_to_str` + `float_to_str` as the first two callers so the
+  ABI gets exercised end-to-end. Unblocks Show + print rewire below.
+  - context: DESIGN.md §"Float semantics" (`float_to_str` is type-
+    installed, codegen-deferred); spec 2026-05-11-23-eq-ord-prelude
+    §"Show. Defers behind a heap-Str-ABI milestone"; spec
+    2026-05-10-fieldtest-floats §F4 ("dynamic Str allocation in the
+    runtime"); spec 2026-05-09-22-typeclasses §22b.4b ("Show#Int
+    needs an `int_to_str` primitive returning heap-allocated Str").
 
 - [ ] **\[milestone\]** Post-22 Prelude — Show + print rewire — ship
   `Show` typeclass with `Show Int/Bool/Str/Float` instances; rewire
-  `print` through `Show.show`. Gated on heap-`Str` ABI runtime work
-  (`int_to_str` needs to allocate). Originally queued as 22b.4 in
-  the typeclass milestone, kept on hold pending demand and the
+  `print` through `Show.show`. Originally queued as 22b.4 in the
+  typeclass milestone, kept on hold pending demand and the
   heap-`Str` prerequisite.
-  - context: brainstorm 2026-05-12 (iter 23.5 wrap). Heap-`Str` ABI
-    is the load-bearing prerequisite; until it ships, `Show Int`
+  - depends on: Heap-`Str` ABI (above). Without it, `Show Int`
     cannot allocate a `Str` to return.
+  - context: brainstorm 2026-05-12 (iter 23.5 wrap).
 
 ## P2 — Medium-term