fix(emit): normalize extra-extension declaration paths (issue #63)

[Copilot]

vue-tsc declaration emit produces Button.vue.d.vue.ts instead of Button.vue.d.ts when backed by TNB. tsgo uses the {name}.d.{ext}.ts convention for allowArbitraryExtensions sources, but the host (stock TypeScript + Volar) expects {name}.d.ts.

Changes

• patches/typescript/overlay/src/compiler/tsgoChecker.ts — adds fixExtraExtDeclarationPath and applies it in the Program.emit output loop. For each registered extra file extension, strips the redundant .{ext} from .d.{ext}.ts output paths before handing the name to the host's writeFile:

  Button.vue.d.vue.ts  →  Button.vue.d.ts
  

  Keyed on programCtx.pendingExtraFileExtensions — no framework name literals; covers any registered extra extension (.vue, .svelte, .astro, …).

• tools/triage-vue-tsc-decl-emit.mjs — new witness: registers .vue via supportedTSExtensionsFlat, runs createProgram + emit on a minimal .vue fixture, asserts output is Button.vue.d.ts not Button.vue.d.vue.ts. Added to wg5 in ci-witness-groups.mjs (TOTAL 72 → 73).

• Fixes vue-tsc emits Button.vue.d.vue.ts instead of Button.vue.d.ts #63

[johnsoncodehk]

Closing this — the root cause is an upstream tsgo bug, not a bridge divergence, so this would be a stopgap that papers over the engine rather than fixing it.

GetDeclarationEmitExtensionForPath in typescript-go/internal/tspath/extension.go (pristine — no TNB patch touches it) puts the resolution convention .d.<ext>.ts into the emit function:

default:
    ext := GetAnyExtensionFromPath(path, nil, false)
    if ext != "" {
        return ".d" + ext + ".ts"  // Button.vue → ".d.vue.ts"
    }
    return ExtensionDts

Stock's emitter default is .d.ts. The real fix belongs upstream: change that default to .d.ts (keeping the .json → .d.json.ts case). I'll file the upstream issue.

fixExtraExtDeclarationPath is a clean mechanism (keys on registered extra extensions, no framework literals), but it's still a host-boundary workaround for an upstream bug. If we want it as a stopgap, AGENTS.md requires a README tsgo-behavior-changes entry, a Ledger() annotation, and the upstream issue link — none of which is present.