fix(ci): use tree-hash anchor for accurate promotion commit list

[castrojo]

... and of course I messed it up, one more. :)

Solution

Find the most-recent commit on main whose tree hash matches the current lts tree. Since squash-merges preserve content exactly, this is always the main commit that was squash-merged into lts. git log is anchored from that point, showing only genuinely new commits regardless of squash-merge history.

If no match is found within 500 commits (first-ever promotion), falls back to git diff --name-status.

Also fixed

• Removed || true from gh pr edit — failures now surface visibly instead of silently leaving the PR body stale
• Added guard: if git diff detects a difference but origin/lts..origin/main is empty (lts is ahead/diverged), skip rather than open a misleading empty PR

Addresses Copilot review comments from #1195.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com
Assisted-by: Claude Sonnet 4.6 via GitHub Copilot

[Copilot]

Pull request overview

This PR updates the main → lts promotion mechanism by replacing the manual workflow_dispatch-based squash-push workflow with an automated, human-gated draft PR flow, and refreshes the CI/CD documentation accordingly.

Changes:

• Document the PR-gated main → lts promotion flow and update release schedule references in AGENTS.md.
• Remove the legacy .github/workflows/promote-to-lts.yml workflow.
• Add .github/workflows/create-lts-pr.yml to auto-create/update a draft PR from main to lts when content differs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
AGENTS.md	Updates the authoritative CI/CD reference to describe PR-gated promotion and the Tuesday release schedule.
.github/workflows/promote-to-lts.yml	Removes the old manual squash-push promotion workflow.
.github/workflows/create-lts-pr.yml	Adds automation to create/update the main → lts promotion PR and generate a promotion commit list.

Comments suppressed due to low confidence (1)

.github/workflows/create-lts-pr.yml:81

• gh pr list --head main can match PRs from forks whose branch name is also main (since --head can be ambiguous when not owner-qualified). To avoid accidentally editing the wrong PR, consider using an owner-qualified head ref (e.g., ${{ github.repository_owner }}:main) and passing -R ${{ github.repository }} consistently for the gh calls.

          EXISTING=$(gh pr list \
            --base lts \
            --head main \
            --state open \
            --json number \
            --jq '.[0].number' \
            2>/dev/null || echo "")

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