feat/v2-logging: Name outcome and situation on every summary log line

[vedanthvdev]

Summary

Closes the last open Phase 1 follow-up from docs/DESIGN-v2.md §0 — the summary log format now names the outcome (SELECTED / FULL_SUITE / SKIPPED) and the situation on every run, so CI dashboards and operators can bucket runs without parsing the tail of the line.

Before

Affected Tests: 3 changed file(s), 2 production class(es), 5 test class(es) affected
Affected Tests: 1 changed file(s); running full suite (runAllOnNonJavaChange=true / onUnmappedFile=FULL_SUITE — non-Java or unmapped file in diff).
Affected Tests: 1 changed file(s), 0 production class(es), 0 test class(es) affected
Skipping test execution (ALL_FILES_IGNORED: SKIPPED).

Two summary shapes, no outcome name on the SELECTED branch, and SKIPPED was a follow-up line with different vocabulary.

After

Affected Tests: SELECTED (DISCOVERY_SUCCESS) — 3 changed file(s), 2 production class(es), 5 test class(es) affected
Affected Tests: FULL_SUITE (UNMAPPED_FILE) — 1 changed file(s); running full suite (runAllOnNonJavaChange=true / onUnmappedFile=FULL_SUITE — non-Java or unmapped file in diff).
Affected Tests: SKIPPED (ALL_FILES_IGNORED) — 1 changed file(s); every changed file matched ignorePaths.

One unified shape — Affected Tests: <OUTCOME> (<SITUATION>) — <details> — across all three branches.

What changed

• AffectedTestTask.renderSummary rewritten to three explicit branches (runAll / skipped / selected), each prefixed with <OUTCOME> (<SITUATION>) —.
• New describeSkipReason(Situation) helper mirrors the existing describeEscalation so every SKIPPED situation has a distinct phrase:
  • EMPTY_DIFF → no changed files detected
  • ALL_FILES_IGNORED → every changed file matched ignorePaths
  • ALL_FILES_OUT_OF_SCOPE → every changed file sat under out-of-scope dirs
  • UNMAPPED_FILE → onUnmappedFile=SKIPPED — non-Java or unmapped file in diff
  • DISCOVERY_EMPTY → no affected tests discovered
  • DISCOVERY_SUCCESS → throws (engine contract violation)
• Redundant follow-up log removed: the "Skipping test execution ({}: {})." side-line was duplicating what the new summary now carries, so it's gone. The defensive "No affected tests to run. Skipping test execution." fallback is also silenced — the engine should already route that through DISCOVERY_EMPTY/SKIPPED, and the summary line above covers it.
• README.md grows a Summary log format section with concrete samples for all three branches and a note on which pre-v2 phrases are preserved.

Backward compatibility

Every pre-v2 CI-grep phrase still appears verbatim in the reason segment:

• running full suite ✓
• runAllIfNoMatches=true ✓
• runAllOnNonJavaChange=true ✓
• no affected tests discovered ✓
• no changed files ✓
• production class(es) / test class(es) / changed file(s) ✓

This change is purely additive on the log string — it prefixes every line with OUTCOME (SITUATION) — and expands the SKIPPED branch from a follow-up line into the summary. No existing grep should break.

Tests

• AffectedTestTaskLogFormatTest gains four new cases:
  • summaryPrefixNamesOutcomeAndSituationOnEveryBranch — pins the new prefix for SELECTED / FULL_SUITE / SKIPPED.
  • skippedBranchNamesReasonPhraseForEachSituation — iterates every non-DISCOVERY_SUCCESS situation and asserts the matching phrase is present.
  • describeSkipReasonRejectsDiscoverySuccess / describeSkipReasonRejectsNull — enforce the engine contract at the helper level.
• The existing formatPlaceholderCountMatchesArgsLength… guard is generalised to cover all three branches so the SLF4J placeholder/arg contract is validated for the new SKIPPED format too.

Test plan

• ./gradlew check (core + gradle test + functionalTest + validatePlugins) passes locally.
• CI run on this branch stays green.
• Spot-check that the existing Modulr security-service pipeline log (which greps running full suite + runAllOnNonJavaChange=true) still matches.