LOCAL: gate only the fork's own lines on an upstream sync PR

.github/workflows/pr.yml

@@ -218,12 +218,36 @@ jobs:
       - uses: ./.github/actions/install-mobile-dependencies
         if: needs.code_paths.outputs.mobile_dependencies == 'true'
 
+      # LOCAL: a sync PR merges all of upstream into swaplabs/main, and every upstream line
+      # would otherwise count as changed here. Gate only the fork's own lines: those added
+      # since the upstream commit the PR merges, where it meets this repository's mirror `main`.
+      # Only the two changed-line gates read it; trigger checks below keep diffing against HEAD^1.
+      - name: Scope changed-line gates to the fork's own lines on a sync PR
+        id: sync-pr-diff-base
+        if: >-
+          github.event.pull_request.head.repo.full_name == github.repository &&
+          github.base_ref == 'swaplabs/main' &&
+          (github.head_ref == 'main' || startsWith(github.head_ref, 'sync/upstream-'))
+        run: |
+          set -uo pipefail
+          if git fetch --no-tags --depth=50 origin main &&
+            upstream="$(git merge-base HEAD FETCH_HEAD)"; then
+            echo "base=$upstream" >> "$GITHUB_OUTPUT"
+            echo "Gating the fork's lines since upstream $upstream"
+          else
+            echo "::warning::Could not find where this sync PR meets upstream main; gating every changed line."
+          fi
+
       - name: Enforce changed-code quality
         id: changed-code-quality
         background: true
+        env:
+          ORCA_SYNC_PR_DIFF_BASE: ${{ steps.sync-pr-diff-base.outputs.base }}
         run: pnpm run check:code-quality:changed -- "${{ github.event.pull_request.base.sha }}"
 
       - name: Enforce React Doctor on changed lines
+        env:
+          ORCA_SYNC_PR_DIFF_BASE: ${{ steps.sync-pr-diff-base.outputs.base }}
         run: pnpm run check:react-doctor:changed -- "${{ github.event.pull_request.base.sha }}"
 
       - wait: changed-code-quality

config/scripts/git-pull-request-diff-base.mjs

@@ -2,7 +2,12 @@ import { execFileSync } from 'node:child_process'
 import process from 'node:process'
 import { pathToFileURL } from 'node:url'
 
-export function selectPullRequestDiffBase(requestedBase, headParents, eventName) {
+export function selectPullRequestDiffBase(requestedBase, headParents, eventName, syncBase) {
+  // LOCAL: a SwapLabs sync PR brings in all of upstream, which upstream's own CI already gated.
+  // The workflow sets the upstream commit it merges so changed-line gates see only the fork's lines.
+  if (syncBase) {
+    return syncBase
+  }
   if (eventName === 'pull_request' && headParents.length >= 2) {
     return headParents[0]
   }
@@ -20,7 +25,12 @@ export function resolvePullRequestDiffBase(
   })
     .trim()
     .split(/\s+/)
-  return selectPullRequestDiffBase(requestedBase, headParents, eventName)
+  return selectPullRequestDiffBase(
+    requestedBase,
+    headParents,
+    eventName,
+    process.env.ORCA_SYNC_PR_DIFF_BASE
+  )
 }
 
 // Why a CLI: the workflow's inline gates used `git diff --merge-base "$BASE_SHA" "$HEAD_SHA"`,

config/scripts/git-pull-request-diff-base.test.mjs

@@ -16,4 +16,19 @@ describe('pull request diff base selection', () => {
       'requested-base'
     )
   })
+
+  // LOCAL: set only for the fork's own upstream sync PRs.
+  it('prefers the sync base over the merge commit first parent', () => {
+    expect(
+      selectPullRequestDiffBase(
+        'event-base',
+        ['current-base', 'sync-head'],
+        'pull_request',
+        'upstream-tip'
+      )
+    ).toBe('upstream-tip')
+    expect(
+      selectPullRequestDiffBase('event-base', ['current-base', 'sync-head'], 'pull_request', '')
+    ).toBe('current-base')
+  })
 })