iter mq.3: retire MethodNameCollision + multi-class E2E + DESIGN.md sync

Closes the module-qualified-class-names milestone. Deletes the
workspace-load workaround; the two-libraries case now resolves via
type-driven dispatch at the call site with explicit qualifier as the
LLM-author's disambiguation tool. Resolves both mq.2 known-debt items
(active_declared_constraints plumbing, (class,method) re-key). New
synth warnings channel emits class-method-shadowed-by-fn at all three
fn-precedence branches per spec section Class-fn collisions. Three new
E2E fixtures + integration tests cover the ambiguous, qualified, and
class-fn-shadow trajectories. DESIGN.md class-names paragraph rewritten,
new section Method dispatch added. Roadmap P2 marked done, milestone-24
unblocked for re-brainstorm.

9/9 tasks. 545 tests green. bench/compile_check.py + cross_lang.py
exit 0; bench/check.py exit 1 (2 noise-class regressions, runtime
uncoupled to typecheck iter).

docs/roadmap.md

@@ -80,9 +80,10 @@ context. Pick the next milestone from P1.)_
   - context: brainstorm 2026-05-12 (iter 23.5 wrap); deferral
     2026-05-13 (user-direction Option C after plan-recon flagged the
     collision; iter 24.1 retained as standalone runtime infrastructure).
-  - depends on: P2 milestone "Module-qualified class names +
-    type-driven method dispatch" (retires the `MethodNameCollision`
-    workaround that drives the collision).
+  - ready for re-brainstorm — the `MethodNameCollision` workaround
+    that blocked the original spec retired in mq.3 (2026-05-13).
+    Fresh brainstorm re-derives the spec against the post-retirement
+    architecture (type-driven dispatch, class-ref canonical form).
 
 ## P2 — Medium-term
 
@@ -123,24 +124,22 @@ context. Pick the next milestone from P1.)_
   classes beyond the prelude four; multi-parameter classes; superclass
   chains; richer instance bodies. Deferred from milestone 22.
   - context: JOURNAL 2026-05-09
-- [ ] **\[milestone\]** Module-qualified class names + type-driven
-  method dispatch — retire the `MethodNameCollision` workaround
-  (`crates/ailang-core/src/workspace.rs:472`) that today keeps bare
-  class names viable by enforcing workspace-global method-name
-  uniqueness. Replaces name-driven method resolution
-  (`ModuleGlobals::class_methods: IndexMap<String, ClassMethodEntry>`,
-  `crates/ailang-check/src/lib.rs:983`; consumed by
-  `mono::rewrite_class_method_calls`, `crates/ailang-check/src/mono.rs:657`)
-  with type-driven dispatch — look up `eq` candidates by argument
-  type, pick the unique class instance, fail closed on ambiguity.
-  Once shipped, two libraries can each declare `class Eq` with their
-  own `eq`. Carries its own DESIGN spec: inference rules, ambiguity
-  diagnostics, and the canonical-form extension for class-reference
-  fields (`InstanceDef.class`, `SuperclassRef.class`, `Constraint.class`)
-  that the canonical-type-names milestone explicitly out-of-scoped.
+- [x] **\[milestone\]** Module-qualified class names + type-driven
+  method dispatch — retired the `MethodNameCollision` workaround;
+  shipped 2026-05-13 as iters mq.1 (canonical-form extension for
+  class-ref fields + workspace-internal qualification), mq.2 (type-
+  driven dispatch mechanism installed: `method_to_candidate_classes`
+  inverse index, multi-candidate `ResidualConstraint`,
+  `resolve_method_dispatch` 5-step rule, `AmbiguousMethodResolution` +
+  `UnknownClass` diagnostics), and mq.3 (retirement + multi-class E2E
+  + `class-method-shadowed-by-fn` warning + DESIGN.md sync). Two
+  libraries can now each declare `class Eq` with their own `eq`;
+  cross-class method ambiguity is resolved at the call site via
+  type-driven dispatch with `<module>.<Class>.<method>` as the
+  disambiguation form.
   - context: `docs/specs/2026-05-10-canonical-type-names.md` "Out of
-    scope: Class names" — the workaround is named there so it stays
-    visible until this milestone retires it.
+    scope: Class names" — the workaround was named there so it
+    stayed visible until this milestone retired it.
 - [ ] **\[todo\]** Boehm full retirement — remove the transitional
   Boehm GC path now that RC + uniqueness is the canonical memory
   story.