Proposal: Generalized generic type inference

[MadsTorgersen]

Summary

• add a construct-neutral model for generic type inference inputs and outputs
• add target-derived upper bounds for by-value results and exact bounds for by-reference results
• define adapters for method invocation and method-group conversion, including return-type inference
• document mixed argument/target inference, compatibility risks, alternatives, and unresolved ref/target questions
• establish this proposal as the intended successor to target-typed-generic-type-inference.md under champion issue [Proposal]: Target-typed generic type inference #9626, without editing that earlier draft

Shared proposal series

Layer	Generalized inference	Type groups	Constructor inference
csharplang proposal	#10311 — generalized foundation	#10310	#10312
csharpstandard specification	#1	#2	#3

The csharplang proposal PRs are independent siblings based directly on main. The csharpstandard PRs are mechanically stacked in order: #2 on #1, then #3 on #2. This PR is the generalized foundation; constructor candidate construction and type-group lookup remain in their sibling proposals.

The older proposals/target-typed-generic-type-inference.md needs a later superseded banner or redirect. That cleanup is intentionally out of scope for this PR.

Compatibility and open design

This is not purely additive: target-derived bounds and method-group return inference can change inference success, candidate sets, ambiguities, overload selection, and failures. The proposal leaves the precise source of invocation target/ref-kind information, by-ref compatibility boundaries, method-group staging, and the split between user-facing behavior and standards refactoring as explicit open questions.

Validation

• git diff --check
• required proposal sections and repository-relative links checked
• sibling proposal links checked against live PR URLs
• design reviewed against the current csharpstandard Async Streams #1 diff
• branch ancestry verified directly against origin/main