name: Backwards-Compat

# Cross-version backwards-compatibility sweep against main's e2e + integration
# suites, over the FULL pairwise (server, runner) version matrix.
#
# The version universe is `main` (the checked-out code = client + tests, always)
# plus every non-rc release tag; we cross every server version with every runner
# version. Each cell pins the server and/or runner subprocess to that build
# (a "main" axis value leaves that component on the checked-out code) while the
# client and tests stay on main. The (main, main) cell is omitted — it pins
# nothing and is exactly the normal e2e gate. So the matrix subsumes the old
# single-pin jobs: (old, main) = Config 1; (main, old) = Config 2; (old, old) =
# both old; etc. Runner and host are colocated, so the runner axis pins both.
#
# The test runs are the SAME composite actions the normal gates use
# (.github/actions/e2e-run, integration-run); a cell differs only in which
# subprocess(es) are the old build.
#
# Triggers:
#   workflow_dispatch   manual; optional `versions` CSV overrides the set.
#   schedule            every 12h; full pairwise over main + all non-rc tags.

on:
  workflow_dispatch:
    inputs:
      versions:
        description: "Comma-separated version set for BOTH axes (e.g. 'main,v0.2.0'). Empty = main + all non-rc tags."
        required: false
        default: ""
  schedule:
    # Every 12 hours (00:00 and 12:00 UTC).
    - cron: "0 */12 * * *"

concurrency:
  group: backcompat-${{ github.workflow }}-${{ github.sha }}
  cancel-in-progress: true

permissions:
  contents: read

jobs:
  # Compute the full pairwise (server, runner) matrices. Integration is the
  # single openai-agents leg (claude-sdk/codex reject the mock LLM's
  # "mock-model"); e2e is sharded per cell. See backcompat-pairwise-matrix.sh.
  setup:
    name: setup
    runs-on: ubuntu-latest
    timeout-minutes: 5
    outputs:
      e2e_matrix: ${{ steps.matrix.outputs.e2e_matrix }}
      integration_matrix: ${{ steps.matrix.outputs.integration_matrix }}
    steps:
      - name: Check out CI scripts + tags
        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0  # v7.0.0
        with:
          sparse-checkout: .github/scripts/ci
          # Full history so `git tag` sees every release tag for the matrix.
          fetch-depth: 0
          persist-credentials: false
      - name: Compute pairwise matrices
        id: matrix
        env:
          VERSIONS: ${{ github.event.inputs.versions }}
          NUM_SHARDS: "4"
        run: bash .github/scripts/ci/backcompat-pairwise-matrix.sh

  # tests/e2e for every (server, runner) cell × shard.
  backcompat-e2e:
    name: Backcompat e2e (server ${{ matrix.server }} / runner ${{ matrix.runner }}, shard ${{ matrix.shard_id }}/${{ matrix.num_shards }})
    needs: setup
    runs-on: ubuntu-latest
    # Job-level cap (composite run steps can't set timeout-minutes); mirrors
    # e2e.yml's ~30-min test budget + setup + up to two old-build installs.
    timeout-minutes: 45
    strategy:
      fail-fast: false
      # Bound concurrency: the full matrix is large (versions² × shards). Tune
      # here if the org's runner pool is over/under-subscribed.
      max-parallel: 10
      matrix: ${{ fromJSON(needs.setup.outputs.e2e_matrix) }}
    steps:
      - name: Checkout
        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0  # v7.0.0
        with:
          # fetch-depth 0 so the action can `git worktree add` the old tags.
          ref: ${{ github.ref }}
          fetch-depth: 0

      - name: Run e2e suite for this cell
        uses: ./.github/actions/e2e-run
        with:
          # "main" axis -> empty input (use checked-out code); else the tag.
          # GHA ternary: `!= 'main' && x || ''` (the naive `== 'main' && '' || x`
          # breaks because '' is falsy and falls through to x).
          server_version: ${{ matrix.server != 'main' && matrix.server || '' }}
          runner_version: ${{ matrix.runner != 'main' && matrix.runner || '' }}
          # Unique per cell so upload-artifact@v4 doesn't collide across the
          # matrix (every integration cell shares the harness; e2e cells share
          # a shard_id).
          artifact_suffix: "-s${{ matrix.server }}-r${{ matrix.runner }}"
          shard_id: ${{ matrix.shard_id }}
          num_shards: ${{ matrix.num_shards }}
          parallelism: "2"
          nightly_full: ${{ github.event_name == 'schedule' || github.event_name == 'workflow_dispatch' }}

  # tests/integration for every (server, runner) cell (openai-agents leg).
  backcompat-integration:
    name: Backcompat integration (server ${{ matrix.server }} / runner ${{ matrix.runner }}, ${{ matrix.harness }})
    needs: setup
    runs-on: ubuntu-latest
    timeout-minutes: 40
    strategy:
      fail-fast: false
      max-parallel: 5
      matrix: ${{ fromJSON(needs.setup.outputs.integration_matrix) }}
    steps:
      - name: Checkout
        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0  # v7.0.0
        with:
          ref: ${{ github.ref }}
          fetch-depth: 0

      - name: Run integration suite for this cell
        uses: ./.github/actions/integration-run
        with:
          server_version: ${{ matrix.server != 'main' && matrix.server || '' }}
          runner_version: ${{ matrix.runner != 'main' && matrix.runner || '' }}
          # Unique per cell so upload-artifact@v4 doesn't collide across the
          # matrix (every integration cell shares the harness; e2e cells share
          # a shard_id).
          artifact_suffix: "-s${{ matrix.server }}-r${{ matrix.runner }}"
          harness: ${{ matrix.harness }}
          model: ${{ matrix.model }}
          workers: ${{ matrix.workers }}