Fix temp directories leaked by the update-gh-pages task (#240)

[alexander-yevsyukov]

What

The updateGitHubPages task created the javadoc, html, and repoTemp temporary
directories (via LazyTempPath) directly under the system temp directory, with cleanup
performed only eagerly — UpdateGitHubPages.cleanup() (in a finally) and
Repository.close() (via use {}). When a build fails, or the Gradle daemon is killed,
before that cleanup runs, the directories leak permanently. File.deleteOnExit() cannot
help here: it does not delete non-empty directories, and these always are.

Fixes #240.

How

Group every such directory under one recognizable base directory
(<java.io.tmpdir>/io.spine.gradle.fs) and remove that base directory recursively via a
single JVM shutdown hook — mirroring the approach of
SpineEventEngine/base#671.

• New SpineTempDir lazily creates the base directory and registers the shutdown hook
  exactly once (by lazy, synchronized). The hook logs to stderr if the recursive
  delete does not fully succeed, so a failed cleanup is visible rather than silent.
• LazyTempPath now creates its directory under SpineTempDir.path
  (createTempDirectory(SpineTempDir.path, prefix)); the javadoc/html/repoTemp
  call sites are unchanged.
• The existing eager cleanup stays the primary mechanism (it frees disk promptly in a
  long-lived daemon); the shutdown hook is the safety net.

The issue's note about "migrating it to Kotlin" is already satisfied — this code is Kotlin.
(The legacy scripts/publish-documentation/publish.sh creates a different workspace
directory and is out of scope.)

Tests

• LazyTempPathSpec (4 tests) — directories are created on first use, under the system
  temp dir, under the io.spine.gradle.fs base dir, and all instances share one parent.
• SpineTempDirSpec (2 tests) — SpineTempDir.path resolves to
  <java.io.tmpdir>/io.spine.gradle.fs and exists after access.

Verification

• ./gradlew -p buildSrc build — green (whole buildSrc suite; 6/6 new fs tests pass)
  under JDK 17. (The repo root has no build task; all code lives in buildSrc.)
• Pre-PR reviewers kotlin-engineer, spine-code-review, and review-docs — all APPROVE.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR addresses leaked temporary directories created by the updateGitHubPages pipeline by routing all LazyTempPath directories under a shared base temp directory and ensuring a JVM-shutdown cleanup safety net.

Changes:

• Introduces SpineTempDir as a shared parent directory under java.io.tmpdir, with recursive deletion via a JVM shutdown hook.
• Updates LazyTempPath to create its temp directories under SpineTempDir.path.
• Adds unit tests covering the new temp directory layout and lazy creation behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
buildSrc/src/main/kotlin/io/spine/gradle/fs/SpineTempDir.kt	Adds shared base temp directory and shutdown-hook cleanup logic.
buildSrc/src/main/kotlin/io/spine/gradle/fs/LazyTempPath.kt	Routes temp directory creation through SpineTempDir and updates KDoc.
buildSrc/src/test/kotlin/io/spine/gradle/fs/LazyTempPathSpec.kt	Verifies LazyTempPath creates directories under the shared base dir.
buildSrc/src/test/kotlin/io/spine/gradle/fs/SpineTempDirSpec.kt	Verifies SpineTempDir.path location and lazy directory creation.
.agents/tasks/fix-temp-dirs-update-gh-pages.md	Adds the task record describing the approach, plan, and verification.