Add per-process array scheduling hints for Google Batch

[fraser-combe]

Summary

closes #6825

Adds two per-process array task-group scheduling hints for the Google Batch executor, exposed through the hints process directive (#7034): scheduling.policy and scheduling.parallelism. They let a pipeline control how an array process's tasks are scheduled on Batch - run sequentially on a single VM, and/or with a concurrency cap - per process, which isn't possible today. The keys follow the scheduling.* namespace convention from the hints-process-directive ADR (20260323-hints-process-directive.md); the ADR catalogs scheduling.provisioningModel (#7343) and scheduling.priority, and these two array-scheduling keys extend that same namespace.

What it adds

• A scheduling.policy hint (a String) on the Google Batch executor, mapping to the Batch TaskGroup.SchedulingPolicy:
  • in_order > IN_ORDER: the array's tasks run sequentially by index on a single VM. Batch requires parallelism = 1 for IN_ORDER, so it is set automatically.
  • as_soon_as_possible > the default; the policy is left unset (today's behaviour).
  • values are case-insensitive and trimmed (in-order is accepted as in_order).
• A scheduling.parallelism hint (a positive integer) that caps how many of an array's tasks run concurrently, clamped to the array size. Ignored under in_order (which pins parallelism to 1).
• Array-only. Both hints apply only to array (TaskArrayRun) tasks. A non-array process that sets them gets a warning and no effect.
• Strict value validation. An unknown scheduling.policy value, or a non-integer / non-positive scheduling.parallelism, throws IllegalArgumentException - no silent fallback, so a typo fails fast.
• Unknown-key validation. An unrecognized google-batch/-prefixed hint key throws, per the ADR (unrecognized prefixed hints are errors); all unknown prefixed keys are reported together in one exception. Bare and foreign-executor keys are left untouched.
• Resolution. Each hint resolves both the bare key (scheduling.policy) and the executor-prefixed key (google-batch/scheduling.policy); the prefixed form is prioritized. This mirrors the AWS Batch executor's existing hint resolution (get(prefix+key) ?: get(key)).
• Fallback. When the hints are unset, task-group construction is unchanged from today.

process BIG_ARRAY {
  array 100
  hints 'scheduling.policy': 'in_order'
  // or
  hints 'scheduling.parallelism': '8'
}

Tests

Unit tests added in nf-google (GoogleBatchTaskHandlerTest):

1. should apply array scheduling from hints - policy mapping (in_order, the in-order spelling, as_soon_as_possible), the parallelism cap, clamping to the array size, string and integer values, and the google-batch/-prefixed form.
2. should throw on invalid array scheduling hint - an unknown policy value and a non-integer / zero / negative parallelism all throw.
3. should accept known and unprefixed google-batch hints - null/empty maps, a known prefixed key, a bare key, and a foreign-executor key are all left untouched (no throw).
4. should reject unknown prefixed google-batch hints - an unrecognized google-batch/-prefixed key throws, per the ADR's prefixed-error rule.

Validation

The unit tests above assert the resulting TaskGroup (schedulingPolicy and parallelism) for each case. I have not run this against a live Google Batch project yet.

Related

• Key names. I followed the ADR's scheduling.* namespace (scheduling.policy, scheduling.parallelism)
• Closes Feature Request: add option to change default scheduling policy with nf-google #6825
• Built on the hints process directive (Add hints process directive for executor-specific scheduling hints #7034 / ADR 20260323-hints-process-directive.md)
• Related to#7343 (scheduling.provisioningModel) targets the same executor, the same handler, and the same scheduling.* namespace, and uses the same get(prefix+key) ?: get(key) resolution and unknown-google-batch/*-key validation. This PR carries the minimal shared plumbing itself so it stands alone; either can merge first.

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