fix(task-create): handle WorkflowAlreadyStartedError gracefully

[alvinkam2001]

Summary

Makes task/create idempotent in the Temporal ACP path. Duplicate submits for the same task ID (e.g. load-balanced agentex-agent replicas racing on the same notification) no longer surface WorkflowAlreadyStartedError, Temporal returns the existing workflow handle instead.

Change

• TemporalTaskService.submit_task now passes id_conflict_policy=WorkflowIDConflictPolicy.USE_EXISTING.
• TemporalClient.start_workflow accepts an id_conflict_policy param (defaults to UNSPECIFIED, preserving current behavior for any other caller).

Why

WorkflowIDReusePolicy.ALLOW_DUPLICATE (already set) only governs reuse after a run closes — it doesn't help when a run is currently open. Workflows are mainly just noise as the workflow still runs

Test plan

• New unit tests in tests/lib/core/services/test_temporal_task_service.py:
  • submit_task passes USE_EXISTING to the client
  • TemporalClient.start_workflow forwards id_conflict_policy when set
  • TemporalClient.start_workflow defaults to UNSPECIFIED (backwards-compat)
• Existing TemporalTaskService tests still pass
• Sanity check in staging: fire two task/create calls with the same task ID, confirm both return 200 with the same workflow ID and no error log

Greptile Summary

The PR makes Temporal-backed task/create submissions idempotent while preserving the existing default behavior for other workflow starts.

• Adds a local conflict-policy enum and maps it to Temporal SDK policies.
• Uses USE_EXISTING when submitting task workflows.
• Adds unit coverage for service forwarding, default behavior, and invalid policy combinations.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
src/agentex/lib/core/clients/temporal/temporal_client.py	Adds conflict-policy mapping and forwarding while retaining an unspecified default for existing callers.
src/agentex/lib/core/clients/temporal/types.py	Introduces a wrapper enum corresponding to Temporal workflow-ID conflict policies.
src/agentex/lib/core/temporal/services/temporal_task_service.py	Configures task workflow starts to return an existing handle when the workflow ID is already active.
tests/lib/core/services/test_temporal_task_service.py	Covers task-service idempotency configuration, policy mapping, defaults, and invalid combinations.

Sequence Diagram

sequenceDiagram
    participant Caller
    participant TaskService as TemporalTaskService
    participant Wrapper as TemporalClient
    participant Temporal
    Caller->>TaskService: submit_task(task ID)
    TaskService->>Wrapper: start_workflow(USE_EXISTING)
    Wrapper->>Temporal: "start_workflow(id_conflict_policy=USE_EXISTING)"
    alt Workflow ID is already running
        Temporal-->>Wrapper: Existing workflow handle
    else Workflow ID is available
        Temporal-->>Wrapper: New workflow handle
    end
    Wrapper-->>TaskService: Workflow ID
    TaskService-->>Caller: Workflow ID

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_{Reviews (3): Last reviewed commit: "address comments" | Re-trigger Greptile}

[jromualdez-scale]

Took a look — the change itself makes sense to me. The reuse vs conflict policy distinction is the right diagnosis and USE_EXISTING is literally what temporalio documents for this ("Set to USE_EXISTING for idempotent deduplication on workflow ID"), so no concerns there.

Couple of non-blocking comments on the wrapper API below.