fix: register union member types from query return types

[JacobCutts13]

What to review

The only code change is 3 lines in packages/graphql/src/generate-documents.ts. Everything else (_generated_documents.graphql, _generated_documents.ts, _generated_sdk.ts) is regenerated output — don't review those files, just verify the query and model look right (see test plan below).

Root cause

searchKnowledgeSources returns [KnowledgeSourceSearchResult!]! — a union of HelpCenterArticleSearchResult | IndexedDocumentSearchResult.

The query scan loop in generate-documents.ts registered fragment types for object types and connection node types, but had no branch for union/interface return types. So neither union member was ever registered in fragmentTypes. At codegen time, the fallback path (generateInlineScalarSelection) only selected scalars — hence the generated query only contained content for each member, and helpCenterArticle, helpCenter, and indexedDocument were silently dropped from both the query and the TypeScript types.

Fix

Add an else if (isUnionType || isInterfaceType) branch that calls registerUnionMembers. This causes the members to be registered, their fragments to be generated, and the query to use those fragments — so all expected fields are fetched at runtime and present in the TypeScript types.

The fix also corrects the same bug for other union-returning queries (CustomerCardInstance, IndexingStatus, etc.) that had the same issue.

Fixes T-29052: https://app.plain.com/workspace/w_01G0EZ1XTM37C5X11SQTDNCTM1/thread/th_01KVVHH239N7D7YCG9WWAF8E4H

Test plan

• In _generated_documents.graphql, SearchKnowledgeSources uses ...HelpCenterArticleSearchResultFields and ...IndexedDocumentSearchResultFields (not just content)
• HelpCenterArticleSearchResultModel in _generated_sdk.ts exposes helpCenterArticle and helpCenter as lazy-loaded getters
• IndexedDocumentSearchResultModel exposes indexedDocument
• pnpm typecheck passes

🤖 Generated with Claude Code

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Note

Low Risk
Behavior change is limited to build-time GraphQL document generation and regenerated SDK queries; no runtime server or auth logic.

Overview
Fixes searchKnowledgeSources (and other union-returning queries) so generated operations fetch full union member fields instead of only scalar fallbacks like content.

generate-documents.ts now treats query fields whose return type is a union or interface like other discoverable types: it calls registerUnionMembers, so members such as HelpCenterArticleSearchResult and IndexedDocumentSearchResult get fragments and appear in SearchKnowledgeSources with helpCenterArticle, helpCenter, and indexedDocument (not just content). The same regeneration updates customer card instance, knowledge source, and indexing-status selections.

Adds a @team-plain/graphql patch changeset and renames contributor agent docs from CLAUDE.md to AGENTS.md (with CLAUDE.md pointing at it).

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[JacobCutts13]

Non-regression proof

Ran a field-path comparison between `main` and this branch. The script parses both `_generated_documents.graphql` files, fully resolves all fragment spreads, and checks that every field path selected on `main` still exists on this branch.

```
Checked 461 operations.
✓ All fields present on main are also present on branch. No regressions.

+720 field paths added across all operations (additive only).
```

Zero fields removed. 720 new field paths — the SDK now fetches the full set of fields for union-returning queries (including the fixed `searchKnowledgeSources`, plus `customerCardInstances` and others that had the same latent bug).