Windows: workflow agent handoff rejects successful result artifacts due to path separators

[yxr-2025]

Problem

On Windows, a workflow child agent can complete successfully and persist the correct structured result, but the DSL agent() call receives ok: false with:

Workflow handoff result artifact is invalid

This breaks successful schema-based workflow agents on Windows: the child execution and audit artifact are correct, but the handoff fails, no result ref is produced, and downstream inputs: chains are interrupted.

Environment

• OS: Windows
• OpenPI: current upstream main at a15a0d8
• Node.js: v24.12.0

Reproduction

node --test --experimental-strip-types --test-name-pattern "agent calls run through the injected session factory" tests/extensions/workflows/execute.e2e.test.ts

The test deterministically fails in about 2.6 seconds. The workflow reports the child agent as successful, but its DSL result is:

{
  "ok": false,
  "output": ""
}

A direct boundary probe shows the mismatch:

artifact=agent-results\agent-0001.json
handoff=Workflow handoff result artifact is invalid

Root cause

persistWorkflowAgentResult() creates a persisted protocol identity with the platform-dependent path.join():

https://github.com/openpi-dev/openpi/blob/a15a0d8/extensions/workflows/artifacts.ts#L130-L133

On Windows this returns:

agent-results\agent-0001.json

The handoff registry correctly accepts only the canonical POSIX grammar:

https://github.com/openpi-dev/openpi/blob/a15a0d8/extensions/workflows/handoff.ts#L190-L197

agent-results/agent-0001.json

The dashboard projection also assumes the canonical / prefix:

https://github.com/openpi-dev/openpi/blob/a15a0d8/extensions/workflows/dashboard.ts#L352-L355

The current artifact unit test verifies that the returned value can be used as a local filesystem path, but does not assert that the persisted artifact identity is platform-independent.

Expected behavior

Persisted workflow artifact identities should always use canonical POSIX / separators on every host. Filesystem access can continue resolving that run-relative identity with the platform path APIs.

A successful child agent with structured output should remain ok: true, produce a handoff ref, and remain usable by downstream workflow inputs on Windows.

Suggested fix

Generate the identity with a POSIX join or an explicit canonical join at the producer boundary, for example:

const artifact = path.posix.join(
  "agent-results",
  `agent-${String(index).padStart(4, "0")}.json`,
);

Prefer keeping the consumer strict instead of accepting both slash formats, so persisted artifact identities remain canonical.

Regression coverage

• Assert persistWorkflowAgentResult() returns agent-results/agent-0001.json on Windows and other platforms.
• Keep the existing execute E2E green on Windows and verify the successful DSL result includes the expected output/ref.
• Verify the persisted workflow.json uses / in resultArtifact.

[yxr-2025]

I'll take this one. I plan to keep the handoff/dashboard consumers strict, canonicalize the artifact identity at the producer boundary, and add unit plus execute E2E regression coverage for Windows before opening a PR.