[core] fix: skip files without a document and narrow validate/hash types under strict mode (#4683)

[eddeee888]

Description

Part of the strict: true tracker #10985. This fixes the 4 errors in graphql-codegen-core that appear when strict is on.

• codegen.ts (TS2345, twice): transformedDocuments.flatMap(d => d.document) has type (DocumentNode | undefined)[]. It now filters out files without a document using an inline guard (d.document ? [d.document] : []), so validateGraphQlDocuments no longer gets undefined. This skips files without a document the same way document-nodes does ([document-nodes] fix: skip files without a document and annotate filter param under strict mode (#4683) #10990).
• codegen.ts (TS2769): the validation cache key concatenated doc.hash, which is string | null | undefined, even though an earlier .some(...) check had already returned early for non-string hashes. The hashes are now collected once into documentHashes and checked with documentHashes.every(hash => typeof hash === 'string'). TypeScript 5.5+ infers that callback as a type guard, so documentHashes is known to be string[] where the key is built. The result is the same as the old .some(...) check.
• execute-plugin.ts (TS2722): TypeScript lost the plugin.validate narrowing inside the profiler.run callback. It is now saved to a local const validate = plugin.validate before the check, and the callback calls validate(...). The function is no longer called as a method on plugin, so a validate that relied on this would lose it. None of the plugins in this repo do.

I used type guards instead of ! assertions. There are two runtime changes: files without a document are skipped during validation, and validate is no longer called with the plugin as this. The CLI always passes files that have a document, and no in-repo plugin uses this in validate, so generated output is unchanged. There is a patch changeset for @graphql-codegen/core.

Related #4683

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• tsc --noEmit -p tsconfig.json with the tracker's strict: true config applied locally: 0 errors in graphql-codegen-core (4 before). With the repo's normal config it still passes with 0 errors.
• Unit tests (graphql-codegen-core)
• Unit tests (graphql-codegen-cli): 72 fail in this environment, but the same 72 fail on unmodified master, so this change doesn't cause them. CI is the source of truth for these.

🤖 Generated with Claude Code

https://claude.ai/code/session_01AKWv2u4brsoCsbLcCkiwcZ

[changeset-bot]

🦋 Changeset detected

Latest commit: 5109cc4

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@graphql-codegen/core	Patch

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[github-actions]

🚀 Snapshot Release (alpha)

The latest changes of this PR are available as alpha on npm (based on the declared changesets):

Package	Version	Info
@graphql-codegen/core	6.2.1-alpha-20260926075408-5109cc46d1b5058cdc796ba8baf625025d380af2	npm ↗︎ unpkg ↗︎
@graphql-codegen/add	7.1.1-alpha-20260926075408-5109cc46d1b5058cdc796ba8baf625025d380af2	npm ↗︎ unpkg ↗︎
@graphql-codegen/typescript-document-nodes	6.1.1-alpha-20260926075408-5109cc46d1b5058cdc796ba8baf625025d380af2	npm ↗︎ unpkg ↗︎