Raise test coverage: instrument context-tests and add tests

[alexander-yevsyukov]

Summary

Raises JVM test coverage for the validation compiler. Production-code coverage
improves from 301 → 166 missed lines (−135, ~45%) and 104 → 68 missed
branches, via a mix of a coverage-measurement fix and new tests.

What changed

Credit context-tests coverage (the main lever)

context-tests ran its in-process compilation tests (66 RangeReaction cases,
Min/Max, and the other reaction/option specs) without the Kover plugin,
so the coverage they produce for :context production classes was never
credited to the aggregated report — those classes showed large false gaps.

• context-tests/build.gradle.kts now applies org.jetbrains.kotlinx.kover, so
  KoverConfig folds the module into the root rollup.
• build.gradle.kts excludes the module's generated Protobuf test fixtures
  (io.spine.tools.validation.given.**) from the aggregated report. KoverConfig
  only excludes generated classes discovered under main source sets, not
  testFixtures, so without this the generated fixtures would flood the report.

This credits ~105 previously-uncounted production lines and ~34 branches with
no new tests.

New tests

• ValidationSdkSpec — the ValidationSdk artifact coordinates / compiler-plugin FQN.
• ValidateOptionSpec (+ validate_option_spec.proto) — the previously
  untested (validate)-on-a-non-message-field error path.
• DeprecatedOptionsSpec (+ deprecated_options_spec.proto) — the
  deprecation warnings for (is_required) and (if_invalid), captured via
  tapConsole.
• ValidationGradlePluginSpec — applies the plugin to a ProjectBuilder
  project and verifies the extension registration, transitive plugin
  application, and the runtime dependency. Requires testImplementation(gradleKotlinDsl())
  because the transitively-applied Spine Compiler plugin references
  org.gradle.kotlin.dsl extensions.

Version + reports

• version.gradle.kts bumped 2.0.0-SNAPSHOT.448 → .449 (also migrated the
  deprecated by extra(...) delegate to extra.set(...)).
• docs/dependencies/{pom.xml,dependencies.md} regenerated — applying Kover to
  context-tests brings its JaCoCo-engine dependencies into the aggregated graph.

Follow-up (not in this PR)

While raising coverage, ValidatorGenerator / ApplyValidator
(java/.../generate/ValidatorGenerator.kt, ~49 lines) were found to be dead
code — never instantiated anywhere; the nested-message validation they were
meant to generate is handled at runtime by ValidatorRegistry. They show as
100% uncovered because they are unreachable. Removal is a separate production
change needing its own review.

The remaining gaps are the SetOnceRenderer-style view-query renderers (not
populated under PipelineSetup), the gradle plugin's afterEvaluate/doFirst
paths (need a real build / TestKit), and non-actionable guards/throw-helpers.

Reviewer notes

• Pre-PR gate ran green: clean build dokkaGenerate passed; spine-code-review,
  kotlin-engineer, and review-docs all returned APPROVE.
• The Kover exclude only drops generated fixtures (given.**); no main source
  declares that package, so no production coverage is masked.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Raises JVM test coverage and improves coverage accounting by ensuring :context-tests contributes to the aggregated Kover report (while excluding generated Protobuf test fixtures), and by adding targeted tests for the Validation Gradle plugin and option reactions.

Changes:

• Apply Kover to :context-tests and exclude io.spine.tools.validation.given.** from aggregated coverage to avoid generated-fixture noise.
• Add new compilation/Gradle-plugin tests covering (validate) misuse and deprecated-option warnings, plus Gradle plugin wiring expectations.
• Bump snapshot version to 2.0.0-SNAPSHOT.449 and regenerate dependency reports.

Reviewed changes

Copilot reviewed 22 out of 24 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
version.gradle.kts	Bumps the published snapshot version.
build.gradle.kts	Adds root Kover report filter to exclude generated test fixtures.
context-tests/build.gradle.kts	Applies Kover so :context-tests coverage is included in aggregation.
context-tests/src/testFixtures/proto/spine/validation/validate_option_spec.proto	Adds fixture for (validate) option misuse case.
context-tests/src/testFixtures/proto/spine/validation/deprecated_options_spec.proto	Adds fixtures for deprecated option warning cases.
context-tests/src/test/kotlin/io/spine/tools/validation/ValidateOptionSpec.kt	Adds compilation-failure test for (validate) on non-message fields.
context-tests/src/test/kotlin/io/spine/tools/validation/DeprecatedOptionsSpec.kt	Adds tests asserting deprecation warnings are emitted.
gradle-plugin/src/test/kotlin/io/spine/tools/validation/gradle/ValidationSdkSpec.kt	Adds tests for exposed artifact coordinates and compiler-plugin FQN.
gradle-plugin/src/test/kotlin/io/spine/tools/validation/gradle/ValidationGradlePluginSpec.kt	Adds tests for plugin application behavior (extensions, plugins, deps).
gradle-plugin/build.gradle.kts	Adds gradleKotlinDsl() to test runtime to support ProjectBuilder-based tests.
docs/dependencies/pom.xml	Regenerates dependency POM with updated version and dependency graph changes.
docs/dependencies/dependencies.md	Regenerates dependency/license report with updated version and new deps.
.agents/tasks/spine-task-group-constant.md	Removes an obsolete agent task document.
.agents/tasks/gradle-caching-plan.md	Removes an obsolete agent task document.
.agents/tasks/enforce-max-line-length.md	Removes an obsolete agent task document.
.agents/tasks/cross-agent-skill-best-practices.md	Removes an obsolete agent task document.
.agents/tasks/buildsrc-gradle-review-findings.md	Removes an obsolete agent task document.
.agents/tasks/archive/validating-builder-validate.md	Adds an archived task note document.
.agents/tasks/archive/setup-cross-tool-agent-instructions.md	Removes an obsolete archived agent task document.
.agents/tasks/archive/raise-coverage.md	Removes an obsolete archived agent task document.
.agents/tasks/archive/raise-coverage-kover-migration.md	Removes an obsolete archived agent task document.
.agents/tasks/archive/prompt-caching-org.md	Removes an obsolete archived agent task document.
.agents/tasks/archive/prohibit-automatic-commits.md	Removes an obsolete archived agent task document.
.agents/tasks/archive/api-discovery.md	Removes an obsolete archived agent task document.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.55%. Comparing base (ec8c202) to head (bd0a068).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #318      +/-   ##
============================================
+ Coverage     82.64%   90.55%   +7.90%     
- Complexity      332      363      +31     
============================================
  Files            82       85       +3     
  Lines          2040     2138      +98     
  Branches        161      161              
============================================
+ Hits           1686     1936     +250     
+ Misses          289      158     -131     
+ Partials         65       44      -21     

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• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[alexander-yevsyukov]

Fixed in bd0a068.

The version bump migrated version.gradle.kts from val validationVersion by extra(...) to extra.set("validationVersion", ...), which removed the line that build-and-release.md embedded via start/end="val validationVersion".

Rather than keep a val form just for the anchor, I re-anchored the embed on validationVersion (unique in the file and stable across version bumps, so it won't need touching on future bumps) and regenerated the snippet with :docs:embedCode. :docs:checkSamples now passes locally.