fix: correct Sym.node and getSymNode types to include undefined

[Copilot]

Sym.node was typed as Node but is always undefined for declaration symbols (where nodes are stored in declarations[] instead). createSymbol() accepts undefined as node, yet the type hid this, masking bugs at call sites that never checked for undefined.

Type fixes

• Sym.node: Node → Node | undefined
• getSymNode(): return type Node → Node | undefined

Caller fixes

checker.ts

• Added compilerAssert where nodes are guaranteed by invariants (member containers, member symbols, template parameters, alias symbols) — documents the invariant and fails fast if violated
• isTemplatedNode(node): accepts Node | undefined, returns false for undefined
• getMemberKindName(node): accepts Node | undefined, returns "Type" for undefined

name-resolver.ts

• resolveMetaMemberByName: returns NotFound early if symbol has no node
• createMetaTypePrototypes model property handler: was using baseSym.node (always undefined for declaration symbols) — fixed to use getSymNode(baseSym) with a compilerAssert

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/compiler@10613

commit: 6a1b498