Parallelize critical CI test workloads

[jamesfredley]

Summary

• add deterministic SHA-256 sharding for Gradle Test tasks while preserving existing onlyIf predicates
• split Groovy Joint validation into three shards and Windows JDK 25 main CI into two shards
• retain one complete build in shard zero and restore dependency-only caches in every shard

No workflow, OS/JDK matrix leg, validation task, or test task is removed.

Verification

• build-logic: full test suite passes
• validateActions: all 23 workflows pass
• Groovy Joint: 401 test-task candidates split 132/129/140 with zero overlap
• Windows: 401 candidates split 200/201 with zero overlap and no missing baseline tasks
• Windows sibling graph: 2,811 scheduled tasks versus 6,963 in the current full leg
• unsharded builds emit no shard manifest and retain existing behavior

Performance Gate

This is a draft measurement PR. The current aggregate pull-request wall-clock baseline is approximately 117 minutes, with Groovy Joint and Windows main CI as the measured limiters. Keep this change only if aggregate completion improves by at least 15% and 10 minutes without reducing coverage.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.3497%. Comparing base (a1e526f) to head (7ebf2fb).
⚠️ Report is 19 commits behind head on 8.0.x.

Additional details and impacted files

@@                Coverage Diff                 @@
##                8.0.x     #16116        +/-   ##
==================================================
+ Coverage     52.3431%   52.3497%   +0.0066%     
- Complexity      18296      18302         +6     
==================================================
  Files            2036       2036                
  Lines           96347      96373        +26     
  Branches        16829      16836         +7     
==================================================
+ Hits            50431      50451        +20     
- Misses          38492      38498         +6     
  Partials         7424       7424                

see 4 files with indirect coverage changes

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[jamesfredley]

First-run measurement

The acceptance gate passes on the unchanged PR SHA.

Critical path	Baseline	PR #16116	Improvement
Aggregate PR completion	117m24s	86m32s	30m52s / 26.3%
Groovy Joint workflow	117m24s	60m07s	57m17s / 48.8%
Main CI workflow	106m35s	86m32s	20m03s / 18.8%

Shard timings:

• Groovy Joint: 56m03s, 41m03s, 37m51s after the 3m57s Groovy build
• Windows JDK 25: 83m55s and 51m00s
• all sharded jobs passed

The initial Main CI attempt had one unrelated failure in unsharded Spring Security Tests (21): ExtendedSecurityInfoSpec.testLogoutHandlers. The same JDK 25 job passed, the preceding 30 captured JDK 21 runs were green, and the unchanged failed-job rerun passed in 56m51s. No source change was made for that intermittent failure.

The next aggregate limiter is now the unchanged Build Grails-Core Rerunning all Tasks job at 86m27s, narrowly ahead of Windows shard 0.

[jamesfredley]

Iteration 2 hosted measurement

All checks passed on cd4490aea5.

Metric	Historical baseline	Iteration 1	Iteration 2	Total improvement
Aggregate PR wall-clock	117m24s	86m32s	62m09s	55m15s / 47.1%
Main CI workflow	106m35s	86m32s	62m09s	44m26s / 41.7%
Groovy Joint workflow	117m24s	60m07s	26m28s	90m56s / 77.5%

Iteration 2 alone reduced aggregate completion by another 24m23s / 28.2%.

The two former critical jobs moved well below the new floor:

Job	Iteration 1	Iteration 2
Rerun all tasks, shard 0	86m27s	46m59s
Windows JDK 25, shard 0	83m55s	33m06s
Windows JDK 25, shard 1	51m00s	27m51s
Windows JDK 25, shard 2	-	30m37s

The critical path is now unchanged functional validation: Functional Tests (Java 21, indy=true) at 62m04s, followed by Java 25 functional tests at 61m46s and Hibernate 7 Java 21 indy tests at 59m52s.

Coverage proof remains exhaustive and disjoint:

• JDK 21 rerun topology: 401 candidates split 132/129/140, zero overlap.
• Hosted JDK 25 topology: 416 candidates split 136/132/148, zero overlap.
• Aggregate report facade remains shard-0-only.

No validation, task, test, platform leg, or rerun flag was removed.

Run: https://github.com/apache/grails-core/actions/runs/31267347078

[testlens-app]

✅ All tests passed ✅

🏷️ Commit: 7ebf2fb
▶️ Tests: 46925 executed
🟡 Checks: 59/66 completed

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