lang: opt-in UFCS — ufcs-marked fns + alias dot-dispatch, generic binding via receiver; one binding builder for plan-side generic returns

issues/0119-ufcs-generic-free-function-unresolved.md

@@ -1,20 +1,24 @@
 # 0119 — UFCS dot-call on a GENERIC free function: "unresolved '<name>'"
 
-> **RESOLVED — not a bug** (2026-06-11, Agra language ruling, same
-> session). Dot-form UFCS on generic free functions is NOT the language
-> contract: UFCS free-function dot-dispatch is the annotated mechanism
-> (`name :: ufcs target;`, concrete targets), and the FLUENT spelling
-> for free functions is the pipe operator — `xs |> first_of()` desugars
-> at parse time to `first_of(xs)`, which dispatches generics through
-> the normal monomorphization machinery (verified:
-> `context.allocator |> create(Session)` works). specs.md §UFCS
-> corrected (it overstated "works with ... generic functions" for the
-> dot form). No compiler change. MEM Phase 2.2 unblocked — helpers
-> shipped as free functions with the direct + `|>` contract
-> (examples/0838-memory-helpers.sx pins both spellings).
-> Residual corner (not contracted, unfiled): a `ufcs` ALIAS naming a
-> generic target also doesn't dot-dispatch; file separately if ever
-> wanted.
+> **RESOLVED** (2026-06-11, same session — Agra language ruling + the
+> opt-in implementation). Final model: free-function dot-calls are
+> OPT-IN. `name :: ufcs (params) { body }` (new declaration form) and
+> `name :: ufcs target;` (alias) both opt in; a PLAIN fn never
+> dot-dispatches (tailored diagnostic steers to direct / `|>` /
+> marking it ufcs). Generic ufcs fns dispatch via dot with the
+> receiver participating in `$T` binding; a protocol-typed receiver
+> dispatches its own methods first and falls through to ufcs fns
+> (`context.allocator.create(Session)` works). Bonus root-cause fix:
+> plan-side `inferGenericReturnType` now delegates to the SAME
+> `buildTypeBindings` the monomorphizer uses, so structured generic
+> params (`[]$T`) type direct calls correctly too (was a `T{}` stub
+> through print's Any boxing — pre-existing). The previously-implicit
+> unannotated dot-dispatch was REMOVED (inverted vs the model);
+> in-tree reliance was 6 example files (audited; migrated to marked
+> form), zero in m3te/game. specs.md §UFCS rewritten around the
+> opt-in matrix. Regression: examples/0053-basic-ufcs-opt-in.sx +
+> 1166-diagnostics-ufcs-not-opted-in.sx; mem helpers marked ufcs
+> (0838 pins dot + pipe + direct). Suite 585/585.
 
 ## Symptom