Add WARP_SESSION_ID env var and warp://session/<id> deep link #2368

	# Fails a required status check if a pull request from one `repo-sync/*`
	# branch targets another `repo-sync/*` branch. Combined with branch
	# protection on `repo-sync/**` requiring this check, this prevents one sync
	# PR from being merged into another sync PR's branch (which would bypass the
	# restacking flow and corrupt the sync stack).
	#
	# PRs from non-`repo-sync/` branches into `repo-sync/` branches (e.g. for
	# conflict resolution) are intentionally allowed. Direct pushes to
	# `repo-sync/*` branches are also unaffected, since only the `pull_request`
	# trigger is used here.

	name: Sync PR Checks
	on:
	pull_request:
	types: [opened, reopened, edited, synchronize, ready_for_review]

	jobs:
	check:
	name: Verify PR base is the default branch
	runs-on: ubuntu-slim
	steps:
	- name: Fail if merging a repo-sync branch into another repo-sync branch
	env:
	BASE_REF: ${{ github.base_ref }}
	HEAD_REF: ${{ github.head_ref }}
	run: \|
	if [[ "$BASE_REF" == repo-sync/* && "$HEAD_REF" == repo-sync/* ]]; then
	echo "::error::repo-sync/* PRs cannot be merged into other repo-sync/* branches."
	echo "Wait for repo-sync to retarget this PR to the default branch before merging."
	exit 1
	fi
	echo "Base branch '$BASE_REF' and head branch '$HEAD_REF' are OK."

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