BundleManifest.from_dict guarded 'requires' and 'provides' with
"must be a mapping when present", but a present-but-non-mapping 'integration'
(e.g. a bare string "copilot") silently failed the isinstance(dict) check and
was dropped — leaving the bundle wrongly integration-agnostic (is_agnostic()
True) instead of surfacing the authoring mistake. Add the same guard so
'integration' is consistent with its sibling mapping fields.
Test: integration='copilot' now raises BundlerError (fails before: silently
dropped, no raise).
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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