fix(resolve): infer expression-body method returns; keep generic receivers typed through field/method hops

[Hessesian]

Problem

Moneta's getTexts().title and loadScreenData(..).text.scenes chains missed. Three linked gaps:

1. find_method_return_type read only a declared : Type, so fun f() = <expr> had no return type. Callers fell through to a bare-name scan that picked an arbitrary same-named function (149 getTexts in the corpus) — a silent wrong target, not just a Gap. The type is now inferred from the expression body behind the existing resolution-cycle guard.
2. cst_symbol's known-type gate looked the whole inferred string up as a type name, so any generic call-result receiver (Box<out Texts>) lost its receiver_type. It now gates on, and records, the type's own name.
3. infer_navigation_expr_type returned a member's raw declared type (T) without substituting the receiver's type arguments, and build_type_arg_subst kept out/in projections. Field and method hops now share resolve_field_type_on / resolve_method_return_type_on with the chain strategies; StrExt::strip_variance is the one canonical projection strip.

Tests (each red before the fix)

• method_return_type_is_inferred_from_an_expression_body (with a decoy getTexts)
• expression_body_return_inference_terminates_on_a_self_referential_method
• generic_call_result_receiver_keeps_its_base_type_as_receiver_type
• property_of_a_type_parameter_resolves_to_the_receivers_type_argument
• strip_variance_removes_only_a_leading_projection
• cargo test (2019), clippy -D warnings, fmt clean

Measurement (Moneta, resolution-accuracy, 13,325 files)

Member recall flat at 92.0%, but absolute resolved +14.5k (746.9k → 761.4k); member refs 166k → 209k because many references now carry a receiver type (previously untyped → counted as bare/NameScan). text/title/scenes Gaps stay high for that reason plus a separate root cause (the inferred receiver type loses its origin file) being fixed in the follow-up stack — see the design in docs/superpowers/specs/2026-08-24-qualified-resolution-unification-design.md (deferred declaring_uri note).

Does not fix: bare-name collisions on inferred receiver types, T from firstOrNull, TransformedText.

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🟡 Changes recommended

Generic method lookup, projection semantics, qualified-type validation, and implicit Unit returns can currently produce incorrect resolution.

Review effort: Balanced
Findings: 1 · 4

Open (5)

• Respect contravariant projection types in member reads · New
• Normalize covariant type arguments for unindexed classes · New
• Validate complete qualified type paths · New
• Normalize generic receiver types before method lookup · New
• Infer Unit for functions without explicit return types · New

What changed in this PR

Adds expression-body return inference and preserves generic receiver typing through member chains.

Changes:

• Infers undeclared expression-body method return types with cycle protection.
• Adds variance stripping and generic type substitution across field/method hops.
• Retains normalized receiver types during CST symbol classification.

File	Description
src/​str_ext.rs	Adds variance projection stripping.
src/​str_ext_tests.rs	Tests variance stripping.
src/​resolver/​infer.rs	Infers expression-body returns.
src/​resolver/​infer_tests.rs	Tests inference and cycles.
src/​indexer/​node_ext.rs	Reuses variance normalization.
src/​indexer/​infer/​type_subst.rs	Normalizes projected type arguments.
src/​indexer/​infer/​expr_type.rs	Applies generic-aware member resolution.
src/​indexer/​infer/​cst_symbol.rs	Normalizes classified receiver types.
src/​indexer/​infer/​cst_symbol_tests.rs	Tests generic receiver chains.
src/​indexer/​infer/​chain.rs	Shares substituted field/method resolution.

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