Add upstream sync automation

Author: pRizz

.github/workflows/sync-upstream.yml

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+name: sync-upstream
+
+on:
+  schedule:
+    - cron: "0 */3 * * *"
+  workflow_dispatch:
+
+concurrency:
+  group: sync-upstream
+  cancel-in-progress: true
+
+jobs:
+  sync:
+    runs-on: ubuntu-24.04
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          token: ${{ secrets.UPSTREAM_SYNC_TOKEN }}
+
+      - name: Setup Bun
+        uses: ./.github/actions/setup-bun
+
+      - name: Sync upstream
+        run: ./script/sync-upstream.ts
+        env:
+          GH_TOKEN: ${{ secrets.UPSTREAM_SYNC_TOKEN }}
+          UPSTREAM_SYNC_TOKEN: ${{ secrets.UPSTREAM_SYNC_TOKEN }}

docs/upstream-sync.md

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+# Upstream Sync Playbook
+
+## Baseline Snapshot (2026-02-05)
+- Upstream repo/branch: `anomalyco/opencode` `dev`
+- Fork repo/branch: `pRizz/opencode` `dev`
+- Merge base: `dac099a4892689d11abedb0fcc1098b50e0958c8` (source: `docs/upstream-sync/merge-base.txt`)
+- Fork commits ahead: 410 (source: `docs/upstream-sync/fork-commits.log`)
+- Upstream first-parent commits behind: 1307 (source: `docs/upstream-sync/upstream-first-parent.txt`)
+- Batch boundaries (every 200 commits): 6 (source: `docs/upstream-sync/boundary-commits.txt`)
+
+## Patchset Report
+- Fork commits: `docs/upstream-sync/fork-commits.log`
+- Range-diff: `docs/upstream-sync/range-diff.txt`
+- Upstream first-parent list: `docs/upstream-sync/upstream-first-parent.txt`
+- Boundary commits: `docs/upstream-sync/boundary-commits.txt`
+
+To regenerate:
+```bash
+git fetch upstream --tags
+git branch -f parent-dev upstream/dev
+git log --oneline parent-dev..dev > docs/upstream-sync/fork-commits.log
+git range-diff parent-dev...dev > docs/upstream-sync/range-diff.txt
+MERGE_BASE=$(git merge-base parent-dev dev)
+echo "$MERGE_BASE" > docs/upstream-sync/merge-base.txt
+git rev-list --first-parent ${MERGE_BASE}..parent-dev > docs/upstream-sync/upstream-first-parent.txt
+awk 'NR % 200 == 0 {print NR ":" $0}' docs/upstream-sync/upstream-first-parent.txt > docs/upstream-sync/boundary-commits.txt
+wc -l docs/upstream-sync/upstream-first-parent.txt > docs/upstream-sync/upstream-first-parent.count
+```
+
+## Must-Keep Fork Areas (Verify and Extend)
+- `docs/docker-install-fork.md` (fork installation guidance)
+- `docs/README.md` references fork-specific usage
+- Any fork-only auth features or configuration paths (audit during conflict resolution)
+
+## Known Conflict Notes
+- None recorded yet. Add entries here as they appear during the merge train.
+
+## Merge Train Procedure (One-Time Catch-Up)
+1. Pause new work on `dev` until catch-up completes.
+2. Use `docs/upstream-sync/boundary-commits.txt` to select boundary commits.
+3. For each boundary commit:
+   - Create a branch `sync/catchup-<n>` from `dev`.
+   - Merge the boundary commit, resolve conflicts, and update this doc with resolutions.
+   - Regenerate SDK artifacts if the SDK changes: `./packages/sdk/js/script/build.ts`.
+   - Open a PR to `dev` labeled `sync` and merge after CI passes.
+
+## Ongoing Sync Automation
+- Script: `script/sync-upstream.ts`
+- Workflow: `.github/workflows/sync-upstream.yml` (runs every 3 hours)
+- Secrets required: `UPSTREAM_SYNC_TOKEN` (fine-grained PAT or GitHub App token)
+- Workflow behavior:
+  - Updates `parent-dev` to match `upstream/dev` (force push).
+  - Opens a sync PR when upstream is ahead.
+  - Enables auto-merge once checks pass.
+  - On conflict, opens an issue labeled `sync-conflict` with merge details.
+
+## Repo Settings Checklist
+- Enable auto-merge on the repository.
+- Require `test` and `typecheck` checks on `dev`.
+- Allow merge commits.
+- Ensure the PAT/App used by `UPSTREAM_SYNC_TOKEN` can create PRs, labels, and enable auto-merge.

docs/upstream-sync/boundary-commits.txt

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+200:3577d829c2b0002e3697932b71a22dd9fbabc28a
+400:7ad165fbdce352786c52b99503cc6f34422e3084
+600:32a0dcedcbc01243ecc81d4d0144fb22138c3088
+800:75cccc305aea05bc605da93ba441e0891461e8df
+1000:b746c006cfacb1729e40829fa598fb77f94e1e9a
+1200:4ddfa86e7fe8d6eb23ab973fdf65175cd8a750a7

docs/upstream-sync/fork-commits.log

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+dac099a4892689d11abedb0fcc1098b50e0958c8

docs/upstream-sync/merge-base.txt

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+    1307 docs/upstream-sync/upstream-first-parent.txt