[nmcc24]

Fixes from the full-codebase review of 3.0.0-beta.3: all eight Tier 1 items, the release workflow's ordering and gates, and a stricter fixture matrix. Each fix comes with a fixture or test that fails without it.

Changelog

• afce031 Check the release notes before tagging. New scripts/release-notes.sh <version> prints the version's CHANGELOG section and fails if it's missing or holds only whitespace. The check job runs it first, dry runs included, and the publish step uses it for the notes. Before, a missing section was found only after the tag was pushed, leaving a tag whose release a re-run couldn't publish.
• 67ffbb5 Report XCTest failures at the full path of the failing line. SourceLocation is now (fileID:, filePath: StaticString, line:, column:), and file: is dropped from verify (both), verifyNoMoreInteractions (both), inOrder, enableDefaultStubImplementation and refuseActorDefaultImplementation. XCTFail gets the full #filePath: #file is the short Module/File.swift form in Swift 6, so Xcode couldn't place the failure. New XCTestFailureTest.testFailureIsReportedAtTheVerifyLine asserts the issue's file and line (it fails on master).
• f2411bb Add hasLength(in:) and give hasLength(inRange:) back its Cuckoo 2 meaning. hasLength(in:) takes any range with its standard meaning. hasLength(inRange: Range<Int>, inclusive: Bool = true) matches as in Cuckoo 2 (1..<3 matches 3) and is deprecated with a migration message, so migrated tests keep passing and warn instead of silently matching differently. The migration guide also gains the review's missing deprecations and behaviour changes.
• b2b504f Release: require master's CI, and tag on Ubuntu. The first job checks that CI passed succeeded on the commit being released (a dry run only warns). "Tag and publish" runs on Ubuntu with sha256sum, which gives SwiftPM's checksum, instead of waiting for a macOS runner.
• c8aeaa2 Dependabot leaves swift-syntax majors alone; CLAUDE.md fixes. A new swift-syntax major needs its own CI pin, so its upper bound is raised by hand.
• 8f04359 Fail the fixture matrix on a silent swiftc failure or a warning in a mock. It caught fixture 05's mock writing a bare Error (9 ExistentialAny warnings with upcoming features on), fixed to any Error.
• 271a8cb Say what to do when a release's verify job fails. Releases are immutable, so: note the problem on the release and ship the next version.
• f43ffd0 Answer an unstubbed rethrows call with a default value. Called with a non-throwing closure, it threw into a call site with no try and crashed the test process (signal 5). It now records the failure and returns the default value, sync and async. RethrowsTest (5 tests).
• f4bee8a Keep associated types' where clauses in the mock. An associatedtype's where requirements join the protocol's, and requirements on nested types (Items.Element == Int, which were dropped or written as an invalid typealias) become a where clause on the mock and stub. Fixture 34 and a runtime test.
• ed35612 Mock variadic parameters. The mock keeps the ..., and records and matches the arguments as an array, as the function receives them. Swift can't pass that array on as separate arguments, so forwarding to the real or default implementation crashes with a message, as for ~Copyable arguments. Fixture 33 covers methods, generic, async, static and closure variadics, subscripts, actors, main-actor and associated-type protocols, and a class.
• 86c2fa1 Test, document and snapshot variadic parameters. VariadicTest (4 tests), Matching.md, CHANGELOG.
• 550dd7c Give a protocol's mock the isolation it inherits. A protocol refining a @MainActor, global-actor, Actor or Sendable protocol got a nonisolated mock that didn't compile. Isolation now propagates from parents through any number of levels, unless the protocol states its own. Fixture 35 and InheritedIsolationTests (4). Every existing snapshot is unchanged.
• 8ff9fb6 Leave the generator's dependencies out of a release's manifest. With a prebuilt generator (release tags only), the generator targets, its executable product, swift-syntax, ArgumentParser and TOMLDecoder are left out, so a project whose macro packages pin swift-syntax below 602 can add Cuckoo. Master is unchanged. The release smoke test adds a consumer pinned to swift-syntax 600.0.0..<602.0.0, which fails on the old manifest with the resolution error and passes now.

Verified

• macOS (Xcode 27.2): swift test (466 runtime + 92 generator tests, 13 known issues, 0 warnings); CuckooTests on the iOS simulator; tvOS and watchOS arm64 build-for-testing.
• Linux Swift 6.2, 6.3 (native) and 6.4 (swiftbuild): swift test with features off and on (558 tests, 13 known issues, 0 warnings), and the fixture matrix in all four CI modes.
• scripts/build-docs.sh (Swift 6.3): no warnings.
• The old-swift-syntax smoke consumer, with the 3.0.0-beta.3 bundle: passes on macOS and Linux (swift:6.3-jammy).

[nmcc24]

CI passed failed on afce031 only because the two macos-26 legs never got a runner (runner id 0) and were cancelled; every job that ran passed. More commits for this PR are about to be pushed, which re-runs CI, so no re-run is needed for this one.

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