mcpx: --runtime node rejects TypeScript that Node runs, because of one flag (strip-types) #263

Problem

mcpx's node runtime is invoked with --experimental-strip-types, whose strip-only mode rejects non-erasable TypeScript (enum, value namespaces, parameter properties) that Node itself runs fine once types are transformed. On machines without deno or bun, auto-resolution lands on node, so such scripts fail with a raw SyntaxError that looks like the author's mistake.

This is the same defect as dezren39/darwin-nix#108 (approach B), fixed there by dezren39/nix PR #387. This repo's pkgs/mcpx copy still has the old flag — internal/runner/runtimes.go differs from the fixed nix copy only in this hunk.

Evidence (verified 2026-10-18 on main 2b46689)

• pkgs/mcpx/internal/runner/runtimes.go:425: a := []string{"--no-warnings", "--experimental-strip-types"}

• pkgs/mcpx/docs/runtimes.md:49 documents the same strip-types invocation.

• Repro on Node v24.20.0 (the sandbox node):

  $ cat t.ts
  enum Color { Red, Green }
  const c: Color = Color.Green;
  console.log("enum value:", c);
  namespace NS { export const x = 42; }
  console.log("ns:", NS.x);
  
  $ node --no-warnings --experimental-strip-types t.ts
  SyntaxError [ERR_UNSUPPORTED_TYPESCRIPT_SYNTAX]: TypeScript enum is not supported in strip-only mode
  
  $ node --no-warnings --experimental-transform-types t.ts
  enum value: 1
  ns: 42
  

• Strip-types is also a no-op default on Node 24, so the flag buys nothing there.

Fix (mirrors dezren39/nix PR #387)

• internal/runner/runtimes.go: swap --experimental-strip-types → --experimental-transform-types, with the explanatory comment from the nix fix.
• docs/runtimes.md: update the node row to match.
• Add internal/runner/runtimes_test.go (the package currently has no such test file): an argv assertion (transform present, strip absent, via the existing fakeRuntimes helper in permissions_test.go) and an end-to-end test that an enum script actually runs under the resolved node (skipping on nodes too old for the flag).

Out of scope: approach C from dezren39/darwin-nix#108 (runtime capability probe + actionable parse-failure diagnostics) — that remains tracked there.

Acceptance criteria

• mcpx run / mcpx exec scripts using enum or value namespaces run successfully when node is the resolved runtime.
• New regression tests fail without the flag change and pass with it (ablation).
• go test ./internal/runner/ green; docs row matches the actual argv.