## Thinking Path
> - Paperclip Runner already has a hardened ACPX path for Codex.
> - Claude can reuse that protocol only with an exact package/model
profile and provider-lifetime fencing.
> - Pi needs a separately spawned runtime whose executable does not yet
have the descriptor-confined verified launch used by the ACP server.
> - This pull request therefore activates Claude only and keeps Pi
unavailable before installation or process launch.
## Linked Issues or Issue Description
**Subsystem affected**
Paperclip Runner ACPX driver, runtime host, sidecar, backend factory,
package dependency, and provider conformance tests.
**Problem or motivation**
The production ACPX backend was Codex-only. Claude needs the same
fail-closed model, authorization, cancellation, cleanup, and recovery
boundaries without exposing an unsafe secondary runtime path.
**Proposed solution**
Generalize the hardened ACPX runtime for the exact qualified `claude`
profile, add the pinned Claude ACP package and reviewed isolation patch,
and reject Pi before installation, backend construction, sidecar
initialization, Rust session admission, or process creation.
**Alternatives considered**
Activating Pi in this PR was rejected after security review because its
secondary runtime executable was pathname-based and lacked the verified
descriptor/snapshot boundary. Pi is deferred to a dedicated follow-up.
Replaying the older generic ACPX implementation was rejected because it
predates current hardening.
**Roadmap alignment**
ROADMAP.md does not list a conflicting ACPX-provider project. This
extends the existing Runner provider architecture.
## What Changed
- Generalized the ACPX backend, driver, runtime adapter, host, and
sidecar for the qualified Claude profile.
- Added Claude ACPX activation through its exact pinned package/model
pair and isolated-settings patch.
- Added provider-lifetime fencing for non-Codex qualified ACPX sessions.
- Kept Pi dependencies and its patch out of the package and build
configuration.
- Added fail-closed Pi rejection at driver validation, backend
construction, runtime-host admission, sidecar initialization, and Rust
session validation.
- Added focused tests for Claude selection, model enforcement, lifecycle
fencing, cancellation, recovery, and Pi rejection.
- Did not change or commit `pnpm-lock.yaml`; CI regenerates the PR
lockfile under the existing repository policy.
## Verification
- GitHub Actions is the authoritative verification environment for this
PR.
- CI runs dependency policy, runner package checks, protocol parity,
typecheck, build, security, and stack policy.
- Local tests were not run because this checkout is resource
constrained, per the requested workflow.
## Risks
- Claude package behavior can drift from the qualified protocol; the
package and patch are pinned and admission verifies the exact profile.
- Unsupported providers and models fail closed.
- Pi remains unavailable until descriptor-confined verified launch
exists for its separate runtime.
- Existing Codex ACPX behavior remains covered by shared conformance
tests.
> 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.
## Model Used
OpenAI Codex, GPT-5.6, with repository tools, code execution, and
parallel agent review.
## Checklist
- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs
- [x] I have described the issue in the PR
- [x] I have not referenced internal or instance-local Paperclip issues
or links
- [x] My branch name contains no internal task identifier
- [ ] I have run tests locally and they pass — GitHub Actions is
authoritative for this resource-constrained checkout
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation
- [x] I have considered and documented risks
- [ ] All applicable Paperclip CI gates are green
- [ ] Greptile is 5/5 with no actionable findings
## Stack
- Position: lowest unmerged PR
- Base: `master`
- Previous:
[#12588](https://github.com/paperclipai/paperclip/pull/12588), merged
qualified OpenCode runtime
- Next: [#12591](https://github.com/paperclipai/paperclip/pull/12591),
native application integration
Dotta