## Thinking Path
> - Paperclip’s PR workflow is part of the control-plane safety surface
because it decides whether a branch is allowed to merge.
> - This issue started in that workflow: the lockfile and manifest
policy checks were diffing `base.sha..head.sha`, which incorrectly
treated unrelated `master` commits as if they belonged to the PR branch.
> - The right fix there is to diff from the PR merge base
(`base...head`) so policy checks only evaluate files introduced by the
branch itself.
> - Once that workflow fix was in place, `/checkpr` exposed a second
blocker on the PR merge ref: `verify` was failing in newer `master`-side
tests that were not part of the original branch diff.
> - The actionable repeated failure came from the ACPX local adapter
test suite, where a test hard-coded the managed Codex home under
`instances/default` even though the stable Vitest runner sets a
non-default `PAPERCLIP_INSTANCE_ID`.
> - This pull request now includes both the original CI diff-scope fix
and the targeted ACPX test fix so the PR’s actual checks align with
current base-branch execution.
> - The benefit is that the original false-positive lockfile failure is
removed, and the merge-ref verify path is hardened against the
instance-id isolation used in CI.
## What Changed
- Updated `.github/workflows/pr.yml` so the lockfile policy and manifest
policy steps diff `pull_request.base.sha...pull_request.head.sha` from
the merge base instead of using a two-dot base/head diff.
- Added an inline workflow comment explaining why the three-dot diff is
required for PR-scoped file detection.
- Updated `packages/adapters/acpx-local/src/server/execute.test.ts` so
the managed Codex home assertion uses a test-specific
`PAPERCLIP_INSTANCE_ID` instead of hard-coding `default`.
- Restored `PAPERCLIP_INSTANCE_ID` after that ACPX test finishes so the
test remains isolated and does not leak process env changes.
## Verification
- Reproduced the original false positive locally by comparing PR heads
`#4901` and `#4902` with the old `base..head` logic; both incorrectly
included `pnpm-lock.yaml` from unrelated `master` commits.
- Verified the new `base...head` logic reduces those PRs to only their
actual changed files and excludes `pnpm-lock.yaml`.
- Verified a real manifest-changing PR (`#4893`) still reports
`package.json` changes under the new logic.
- Ran `pnpm -r typecheck` successfully.
- Ran `pnpm vitest run
packages/adapters/acpx-local/src/server/execute.test.ts` successfully
after the ACPX test fix.
- Ran `pnpm vitest run packages/db/src/backup-lib.test.ts` successfully
against the merge-ref-related DB failure path observed during
`/checkpr`.
- Pushed commit `9520a976` and allowed PR `#4903` checks to rerun on the
updated branch.
## Risks
- Low risk: the workflow change only affects how PR policy checks
determine the changed file set.
- Low risk: the ACPX change is test-only and aligns the test with the
instance-isolation behavior already used by
`scripts/run-vitest-stable.mjs` in CI.
- The remaining operational risk is limited to other unrelated
merge-ref-only failures that were not reproduced in the targeted local
verification above.
> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.
## Model Used
- OpenAI Codex, `gpt-5-codex`, via the Codex local adapter in Paperclip.
- Tool-using coding model with shell execution, git, GitHub CLI, and
repository inspection in a local worktree.
- Context included the current repo, the Paperclip task thread, PR check
output, and the isolated execution workspace.
## Checklist
- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [ ] If this change affects the UI, I have included before/after
screenshots
- [ ] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge
Devin Foley
b02e67cea5