Fix aipm lint silent for a plugin-shaped dir missing aipm.config.ts

[mike-north]

Summary

#91 made aipm validate (hard envelope-invalid finding) and aipm build (thrown
ConfigLoadError) catch a plugin-shaped directory missing aipm.config.ts. aipm lint stayed
silent for the identical tree, so the three surfaces disagreed on a real defect: a user relying on
lint got a clean bill of health for a directory validate/build correctly flagged.

• schema/envelope-shape (packages/core/src/lint/rules/legacy-envelope-shape.ts) no longer
  short-circuits with [] on a failed envelope load. It has no fs.existsSync pre-check at all;
  it always calls loadPluginConfig() and derives every diagnostic from the thrown error,
  mirroring runValidate()'s envelope-load catch in pipeline/validate.ts — a ConfigLoadError
  with a ZodError cause expands into per-issue diagnostics, and anything else becomes a single
  hard envelope-invalid carrying err.message verbatim. Agreement with validate is therefore
  structural rather than a duplicated message string, and it covers both a missing
  aipm.config.ts and one that exists but cannot be imported (syntax error, no usable default
  export) — the latter previously left lint silent while validate/build flagged it.
• packages/core/src/lint/engine.ts's comment on its envelope short-circuit is corrected; it
  claimed the config loader explained an unusable envelope on its own, which was not true for the
  import-failure path.
• No change to validate/build behavior (unchanged since plugin dir without aipm.config.ts silently drops out of discovery: validate AND build exit 0 green ('Built 0 plugin(s)') #91) or to the envelope-invalid →
  schema/envelope-shape mapping in the reconciled docs/specs/lint-engine.md §3.6 migration
  table (Reconcile docs/specs/lint-engine.md with the shipped engine/CLI (spec drifted behind implementation) #88) — the rule id/category/severity were already correct; only the missing-config case
  needed to actually fire it.
• docs/specs/lint-engine.md §3.1 updated to describe schema/envelope-shape as firing on any
  failure to resolve the envelope — missing, unimportable, or schema-violating — not only a
  malformed one.

Acceptance criteria mapping

1. "For a plugin-shaped directory missing aipm.config.ts, aipm lint emits a diagnostic
   equivalent in severity and meaning to validate's hard envelope-invalid finding for the same
   tree." — covered by
   packages/core/src/lint/engine.test.ts's lint() — plugin-shaped repo-root subdirectory missing aipm.config.ts (#91, #101) > agrees with runValidate(): both report the equivalent envelope-invalid finding for the same tree, which asserts the lint diagnostic's ruleId
   (schema/envelope-shape), category (schema), severity (error), legacyCode
   (envelope-invalid), and message (byte-identical to validate's).

2. "A test asserts that lint and validate AGREE on this case ... not one silent while the other
   flags it." — the same test runs lint() and runValidate() against the identical temp tree
   (the plugin dir without aipm.config.ts silently drops out of discovery: validate AND build exit 0 green ('Built 0 plugin(s)') #91 repro shape: a plugins/* dir with a target manifest but no aipm.config.ts) and
   asserts both surface the equivalent finding. It fails against pre-fix code (lint returns [])
   and passes with the fix.

3. Follow-on from the same defect class: lint() — plugin whose aipm.config.ts exists but fails to import (#101) asserts the same agreement for a config with a deliberate syntax error, where
   lint previously emitted zero diagnostics; a sibling test pins the schema-violation path to
   its per-issue expansion so the two error shapes stay distinct. Confirmed end-to-end: against a
   plugin with an unparseable aipm.config.ts, aipm lint and aipm validate both exit 1 with
   Failed to import aipm.config.ts: ParseError: Unexpected token; pre-fix, lint exited 0
   silently.

A second test in the first describe block (emits nothing further beyond the envelope-invalid diagnostic for the config-less plugin) confirms the engine's existing short-circuit (continue
after the failed loadPluginConfig call) still holds — no other rule spuriously runs against an
unresolved envelope.

Test plan

• pnpm --filter @ai-plugin-marketplace/core exec vitest run src/lint/engine.test.ts (new
  agreement tests + existing suite)
• pnpm run check (typecheck, lint, api-report, full test suite, format, deps, knip) — green
• pnpm run fix:format run before push

Refs #101

[Copilot]

Pull request overview

Aligns aipm lint with aipm validate/aipm build by ensuring a plugin-shaped directory missing aipm.config.ts is surfaced as an envelope-invalid-backed diagnostic instead of being silently ignored, and documents + tests the agreement.

Changes:

• Update schema/envelope-shape to emit an envelope-invalid diagnostic when aipm.config.ts is missing.
• Add regression tests asserting lint() and runValidate() agree on the missing-config plugin-shaped directory case.
• Update the lint engine spec and add a patch changeset documenting the behavior change.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
packages/core/src/lint/rules/legacy-envelope-shape.ts	Emit envelope-invalid diagnostic for missing aipm.config.ts in plugin-shaped dirs.
packages/core/src/lint/engine.test.ts	Add agreement regression tests for lint() vs runValidate() on missing-config plugins.
docs/specs/lint-engine.md	Document that schema/envelope-shape also fires on missing aipm.config.ts.
.changeset/lint-missing-config-envelope-invalid.md	Patch changeset describing the lint behavior fix.

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