Remove vercel from the default scaffolded target list

[mike-north]

Summary

vercel shipped in the DEFAULT scaffolded target list but is a silent no-op: it is accepted by
scaffold, build, validate, and check-support, and appears in list-targets, yet emits ZERO
build artifacts. A user who keeps the default config believes they have a working vercel target
that in fact produces nothing.

This PR removes vercel from the default scaffold set. vercel remains fully supported
elsewhere in the toolkit — it's still addable via core.scaffold(name, { targets: [...] }) or
aipm add-target <plugin> vercel — this only changes what a bare aipm scaffold <name> declares.

Changes

• packages/core/src/pipeline/types.ts: adds DEFAULT_SCAFFOLD_TARGETS, TARGET_IDS minus
  vercel.
• packages/core/src/pipeline/scaffold.ts: runScaffold now defaults to
  DEFAULT_SCAFFOLD_TARGETS instead of TARGET_IDS when opts.targets is omitted.
• packages/core/src/pipeline/scaffold.test.ts: updates the existing "canonical file set"
  default-scaffold test (vercel's skills/*/SKILL.md is no longer part of the default set) and
  adds the regression + guard coverage below.
• .changeset/remove-vercel-from-default-scaffold.md: minor bump for core + cli (user-visible
  default-scaffold behavior change).

Acceptance criteria → tests

1. Remove vercel from the DEFAULT scaffolded targets list → runScaffold > does not declare vercel among the default targets (issue #94) (packages/core/src/pipeline/scaffold.test.ts).
   Confirmed to fail against pre-fix code (reverting the one-line default in scaffold.ts makes it
   fail with expected [...] to not include 'vercel').
2. Add a test asserting every default-scaffolded target emits at least one artifact on build →
   every default-scaffolded target emits a build artifact (issue #94) > produces at least one build artifact per target for a freshly scaffolded plugin with default targets
   (packages/core/src/pipeline/scaffold.test.ts). This test reads back the targets runScaffold
   actually declared (not the DEFAULT_SCAFFOLD_TARGETS constant directly), so it independently
   catches any future default target that ships with zero build artifacts — confirmed by
   temporarily reintroducing vercel into the default set, which makes this test fail with
   expected an artifact for default target 'vercel'. A companion negative test
   (vercel (excluded from defaults) emits zero build artifacts on a bare scaffold) documents why
   vercel specifically is excluded.

Both scaffold+build tests run against a workspace-mode repo (a hand-written aipm.workspace.ts),
matching the issue's real repro shape (aipm scaffold + aipm build in a repo that has opted into
marketplace-registry generation) — registry-backed targets (claude/cursor/codex/open-plugins) only
produce build artifacts in that mode; gemini/kiro's dist bundles are unconditional.

Note: exercising this combination surfaced a separate, pre-existing gap — runScaffold
hand-writes the repo-root Open Plugins marketplace.json unconditionally, which collides with
runBuild's generated version of the same path on a workspace-mode repo's first build
(root-artifact-collision). This is orthogonal to #94 (a build-failure/collision issue, not a
no-op-target issue) and reproduces identically on main before this change — the new tests work
around it exactly as the build's own finding documents (remove the hand-authored file before
building). Flagging here since it may warrant its own issue, but it's out of scope for this PR.

Non-goals (per issue)

• The broader "declared-but-unsupported target state" UX is out of scope.
• vercel support itself is untouched — still fully buildable/validatable/addable, just no longer a
  default.

Refs #94

[Copilot]

Pull request overview

This PR adjusts the core scaffolding defaults so a bare aipm scaffold <name> no longer declares vercel, preventing a freshly scaffolded plugin from including a target that produces no build artifacts out of the box. It also adds regression/guard tests to ensure the default scaffold target set remains “non-no-op” over time.

Changes:

• Introduces DEFAULT_SCAFFOLD_TARGETS (all known targets except vercel) and uses it as the default in runScaffold when opts.targets is omitted.
• Updates scaffold tests to reflect the new default set and adds a guard test ensuring every default-scaffolded target emits at least one build artifact (in workspace-mode builds).
• Adds a changeset to bump @ai-plugin-marketplace/core and @ai-plugin-marketplace/cli for the user-visible default behavior change.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
packages/core/src/pipeline/types.ts	Adds DEFAULT_SCAFFOLD_TARGETS as the new default scaffold target list (excluding vercel).
packages/core/src/pipeline/scaffold.ts	Switches runScaffold default targets from TARGET_IDS to DEFAULT_SCAFFOLD_TARGETS.
packages/core/src/pipeline/scaffold.test.ts	Updates default scaffold expectations and adds regression + build-artifact guard coverage for issue #94.
.changeset/remove-vercel-from-default-scaffold.md	Declares minor bumps for core + cli due to the default scaffold behavior change.

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