Fix weekly upstream sync agentic workflow prompt

[Copilot]

Resolves #41

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Before the change?

• The weekly-upstream-sync.md prompt was written as documentation ("This document describes the workflow..."), not as agent instructions. The agent misinterpreted it, invoked the agentic-merge-upstream skill, attempted to actually merge upstream changes, failed to push from the AWF sandbox (no git credentials), and never called any safe-output tools — causing the workflow to fail with no output.

After the change?

• Prompt rewritten as clear imperative instructions: clone upstream, compare commits against .lastmerge, use safe-output tools (create_issue, close_issue, assign_to_agent, noop) to report results.
• Explicit constraints added: do not invoke skills, do not edit files, do not push code.
• Concrete bash commands provided for each detection step.
• Frontmatter unchanged — no lock file recompilation needed (prompt content is runtime-imported via {{#runtime-import}}).

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• mvn spotless:apply has been run to format the code
• mvn clean verify passes locally

Does this introduce a breaking change?

• Yes
• No

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[Copilot]

Pull request overview

Updates the agentic workflow prompt for weekly upstream sync checks so the automation agent reliably detects upstream changes and reports results via safe-output tools (without attempting merges).

Changes:

• Rewrites the prompt from descriptive documentation into imperative agent instructions.
• Adds explicit constraints to prevent invoking skills, editing files, or pushing code.
• Specifies concrete commands/steps for comparing .lastmerge to upstream and creating/closing issues via safe outputs.

Show a summary per file

File	Description
.github/workflows/weekly-upstream-sync.md	Reworks the workflow prompt into actionable instructions and adds guardrails for safe-output-only reporting.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 2

[Copilot]

The link target (.github/prompts/agentic-merge-upstream.prompt.md) is relative to this file’s directory, so on GitHub it resolves to .github/workflows/.github/prompts/... and is broken. Use a correct relative path (e.g., ../prompts/agentic-merge-upstream.prompt.md) or an absolute GitHub URL so the referenced prompt can be opened reliably from the created issue body/instructions.

Suggested change

	Follow the [agentic-merge-upstream](.github/prompts/agentic-merge-upstream.prompt.md) prompt to port these changes to the Java SDK.
	Follow the [agentic-merge-upstream](../prompts/agentic-merge-upstream.prompt.md) prompt to port these changes to the Java SDK.

[Copilot]

Step 3b instructs calling assign_to_agent but doesn’t specify which identifier to pass. The safe-output assign_to_agent tool requires one of issue_number or pull_number (no default in this workflow), so the instructions should explicitly say to use the created issue’s number (from create_issue output) or to set a temporary_id on create_issue and pass that to assign_to_agent.

Suggested change

	4. After creating the issue, use the `assign_to_agent` safe-output tool to assign Copilot to the newly created issue.
	4. After creating the issue, use the `assign_to_agent` safe-output tool to assign Copilot to the newly created issue, passing the created issue's number from the `create_issue` output as `issue_number`.

[edburns]

Net effect
No code, tests, or build behavior changes. This is purely a prompt engineering fix for the weekly upstream sync GitHub Actions workflow. The workflow's YAML definition and frontmatter are untouched — only the markdown body (which gets runtime-imported as the agent's instructions) was rewritten so the agent stays in its lane: detect changes → create/close issues → stop.

@brunoborges you are clear to merge this.