chore: import upstream snapshot with attribution

.github/scripts/ci/integration-matrix.sh

@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+# Emits the integration-test harness matrix as `matrix=<json>` on $GITHUB_OUTPUT.
+#
+# Returns an EMPTY matrix ({"include":[]}) to skip: zero jobs, NO check-runs.
+# This is the whole reason for the indirection (mirrors e2e-shard-matrix.sh): a
+# job-level `if:` skip would instead leave one check-run with an unexpanded
+# `Integration (${{ matrix.name }})` name.
+#
+# Skips only draft PRs. Integration is mock-LLM (no secrets), so fork PRs run
+# directly, like CI -- no fork-e2e/** mirror needed.
+#
+# Single openai-agents leg: all tests now run against the mock LLM server.
+# claude-sdk and codex reject "mock-model" as an unknown model (they validate
+# against the Databricks model catalog even when mock_llm_base_url is set), so
+# only openai-agents works without real credentials. The model name is unused
+# in mock mode (model_name fixture returns "mock-model" regardless).
+#
+# Env in:  EVENT_NAME (github.event_name), IS_DRAFT.
+# Out:     matrix={"include":[{"name":..,"harness":..,"model":..,"workers":..}, ...]}
+#          (or {"include":[]} when skipped).
+
+set -euo pipefail
+
+skip=false
+if [[ "${IS_DRAFT:-false}" == "true" ]]; then
+  skip=true
+fi
+
+if [[ "$skip" == "true" ]]; then
+  echo 'matrix={"include":[]}' >> "$GITHUB_OUTPUT"
+  echo "skip: empty matrix (event=$EVENT_NAME draft=${IS_DRAFT:-})"
+  exit 0
+fi
+
+read -r -d '' matrix <<'JSON' || true
+{"include":[
+{"name":"openai-agents","harness":"openai-agents","model":"databricks-gpt-5-4-mini","workers":4}
+]}
+JSON
+# Collapse to one line so the GITHUB_OUTPUT key=value contract holds.
+echo "matrix=$(echo "$matrix" | tr -d '\n ')" >> "$GITHUB_OUTPUT"
+echo "run: integration harness matrix (event=$EVENT_NAME)"