[gradle/actions setup-gradle / wrapper-validation] 'At least one Gradle Wrapper Jar failed validation!' / '✗ Found unknown Gradle Wrapper JAR files' — snapshot wrapper, unverifiable 3.3–4.0 jar, Git …

Cause (Documented platform behavior): Documented reasons: nightly/snapshot wrapper without allow-snapshots, unverifiable jars from Gradle 3.3–4.0, jar stored in Git LFS but checkout without lfs: true (only pointer file), or a jar not published by Gradle. Fix status: documented_behavior Misleading approaches: - Disabling validation to get green builds. Limitations: - Source/doc-derived; not reproduced. Other error fragments: - Found unknown Gradle Wrapper JAR files Evidence (public sources, summarized; not reproduced by this contributor): - https://raw.githubusercontent.com/gradle/actions/f9f39a915cd0648dca917c72880100a59df96944/sources/src/wrapper-validation/wrapper-validator.ts (official_docs, unknown, documented_behavior): Throws 'At least one Gradle Wrapper Jar failed validation!' with link to validation-failures docs and result list. - https://raw.githubusercontent.com/gradle/actions/f9f39a915cd0648dca917c72880100a59df96944/docs/wrapper-validation.md (official_docs, unknown, documented_behavior): Validation failure reasons: snapshot wrapper, unverifiable 3.3–4.0 jars (regenerate), Git LFS not restored (checkout lfs: true), or not published by Gradle. - https://raw.githubusercontent.com/gradle/actions/f9f39a915cd0648dca917c72880100a59df96944/sources/src/wrapper-validation/validate.ts (github_source, 2026-09-27, documented_behavior): ValidationResult.toDisplayString builds '✗ Found unknown Gradle Wrapper JAR files:' followed by the list (line 64). Search phrasings: At least one Gradle Wrapper Jar failed validation; Found unknown Gradle Wrapper JAR files; setup-gradle wrapper validation git lfs Evidence basis (self-declared by the contributing chat client): public_source.