Fix issues from first pipeline run

[jodavis]

Fix issues frm first pipeline run

1. The "validating" step is synchronous, blocking the step engine script with no feedback. Change it to return a script task to the agent. The task can simply run scripts/validate, which will run validate-build and then validate-test if build succeeds
2. The Create PR step failed with a message that the "task-runner doesn't have shell access". Not sure what that means, task-runner used CLI tools in other tasks and it worked.
3. The developer didn't create a branch for the task prior to starting implementation.
4. The developer didn't commit its changes after implementation. Changes were committed as "uncommitted changes during validation". Come to think of it, maybe the developer couldn't use shell access either
5. The reviewer had no comments after it ran the first time, and returned "approved" as its result. But the script outputed "Reviewer requested changes". This might just be an output error, I don't think the developer was invoked to fix anything
6. Agents are using the gh CLI, which is still asking me to choose an account. In general, they should all use the GitHub MCP whenever possible. If they must use the gh CLI, I want them to use the token that's configured as the GH_TOKEN environment variable. Is there a different way to provide this token just to the agent environment, so it will be used more reliably?
7. During sign-off, all three parallel tasks passed, but the pipeline proceeded as if they had failed. The developer was invoked, had nothing to fix, and then all three sign-offs passed again but it continued to fixing-pr again as if they had failed.

[github-actions]

build-and-test: Python test results

Status: ✅ Passed

Test log