refactor(infer): delete receiver.rs — the CST path is the only resolution path

[Hessesian]

Summary

Task 8, the finale of the CST lambda-triad collapse: receiver.rs (518 lines) is deleted. Net −783 lines. Every lambda-typing question — it, this, named params, completion scope — now resolves through one CST path; the text-expression inference module and all of its helpers are gone. Task 9's sweep (lambda_receiver_type_named_arg_ml, dead helpers/constants) is fully absorbed.

The two problems that gated the deletion

• Walk scopes on nodes (commit 1): Task 7's ancestor walk resolved each enclosing lambda's it_type by slicing before-brace text into lambda_receiver_type_from_context. lambda_scope_info now resolves from the lambda_literal node via the same cst_lambda_param_type_at the innermost path uses; before_brace survives only to build the display label.
• Inner-call callee gap: the reason it_type_at_lambda kept a text heuristic was that the node path didn't unwrap a one-level inner call_expression callee. Two minimal unwraps (NodeExt::call_fn_and_qualifier, resolve_callee_chain) close it at root — and subsumed a pre-existing hand-rolled unwrap in lambda_this_ctx, which is deleted. Decoys (trailing_lambda_it_infer_at_cursor, it_element_type_with_call_args) verified RED without the heuristic, GREEN via the node path, assertions untouched.

Also in here

• EOF-cursor fix (Copilot finding on refactor(completion): rewrite lambda scope-context onto the CST ancestor-walk #202): cursor_node_at used str::lines(), which drops the final empty line of \n-terminated content — a cursor at EOF returned None and emptied the completion scope stack. Fixed with a pinning test (it_resolves_on_trailing_empty_line_at_eof).
• A nullability truth-telling: stdlib_let_generic_param_not_leaked now expects Long? — the receiver is a plain .let on Long?, so it genuinely is Long?; the old Long was the text heuristic silently stripping nullability. Reviewed and ruled correct per Kotlin semantics.
• Moves, not rewrites: uppercase_dotted_type_prefix → chain.rs, resolve_call_params + fun_trailing_lambda_this_type → cst_lambda.rs (bodies byte-identical). ItTypeAtLambda and LambdaParamKind::This deleted — the collapse removed type ceremony too, not just text.
• Test policy: 25 text-heuristic unit tests converted to prove the production CST path; 10 deleted with per-test reasons (each left an in-place pointer to its surviving CST twin).

Verification

• cargo test --bin kmp-lsp — 1433 passed, 0 failed (1442 − 10 converted-away + 1 new). cargo clippy -- -D warnings clean.
• Every deleted function verified at zero live references (Serena find_referencing_symbols + -D dead-code gate).
• Task-scoped review: Approved, no Critical/Important; the assertion change adjudicated against Kotlin semantics.

Stacked on #204. With this, the lambda-triad collapse (Tasks 1–9) is complete.

🤖 Generated with Claude Code

https://claude.ai/code/session_01EJsyQ1UgF8uJYR4HgpxEBB

[Copilot]

Pull request overview

This PR completes the “CST lambda-triad collapse” by removing the text-based lambda receiver inference module and routing it/this/named-param typing and completion scope exclusively through CST-backed resolution, including fixes for trailing-lambda call nesting and EOF cursor positioning.

Changes:

• Delete src/indexer/infer/receiver.rs and remove its exports/usages, consolidating lambda parameter inference through cst_lambda_param_type_at / CST ancestor-walk paths.
• Improve callee/receiver-chain unwrapping for f(args) { ... } nesting in both NodeExt and CST chain resolution so call-site inference works without text heuristics.
• Fix CST cursor lookup at EOF on \n-terminated documents and add a pinning regression test.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/indexer/node_ext.rs	Unwrap nested call_expression to recover callee/qualifier for trailing-lambda-with-args shapes.
src/indexer/infer/type_subst.rs	Simplify type-arg extraction helpers after receiver.rs deletion.
src/indexer/infer/receiver.rs	Deleted: former text-based lambda receiver/type inference path.
src/indexer/infer/mod.rs	Remove receiver module from infer module surface.
src/indexer/infer/lambda.rs	Remove lambda_type_first_input helper; rely on remaining nth/receiver helpers.
src/indexer/infer/lambda_tests.rs	Drop tests tied to removed lambda_type_first_input; adjust to remaining API.
src/indexer/infer/it_this.rs	Route it inference through CST-only cst_it_element_type; keep brace-repair flow.
src/indexer/infer/it_this_tests.rs	Add EOF trailing-empty-line regression test; convert many tests to CST param typing seam.
src/indexer/infer/cst_lambda.rs	Remove text-heuristic fallback plumbing; unify it resolution and fix cursor_node_at EOF handling.
src/indexer/infer/chain.rs	Unwrap nested call-expression callee chains; relocate uppercase_dotted_type_prefix.
src/indexer/infer/args.rs	Remove dead named-arg text extraction helper previously only used by receiver.rs.
src/indexer/infer/args_tests.rs	Remove tests for deleted named-arg text helper.
src/indexer.rs	Remove re-exports of deleted receiver/text helpers.
src/indexer_tests.rs	Replace text-heuristic direct tests with CST-based cursor-positioned inference assertions.