## Thinking Path
> - Paperclip runs AI agents inside Daytona sandbox environments
> - The Daytona plugin wraps agent commands in bwrap to prevent
accidental writes outside the workspace
> - bwrap previously used `--unshare-user --uid <uid> --gid <gid>` to
run commands as the sandbox user inside the container
> - This creates a uid_map of `<uid> 0 1` — inside-uid maps to
outside-uid 0 (root)
> - Files owned by the sandbox user (outside-uid 1001) appear as
overflow uid 65534 (nobody) from inside the namespace
> - So all writes to the workspace fail with Permission denied, and the
agent cannot run
> - This PR replaces the user-namespace approach with `su -s /bin/sh
<user>`, which gives the correct uid mapping
> - The benefit is that bwrap works correctly on Daytona: writes succeed
and the advisory isolation is preserved
## Linked Issues or Issue Description
No existing issue. Describing the bug inline per the bug report
template.
**What happened?**
Running a Codex agent in a Daytona sandbox failed immediately. The agent
could not create directories inside the workspace:
```
mkdir /home/daytona/paperclip-workspace/.paperclip-runtime/codex/paperclip-bridge/queue ... failed with exit code 1:
bwrap: Can't find source path /home/daytona/paperclip-workspace: Permission denied
```
Root cause: bwrap used `--unshare-user --uid 1001 --gid 1001` (via
sudo/root). This writes uid_map `1001 0 1` — inside-uid 1001 maps to
outside-uid 0. Files owned by outside-uid 1001 (the workspace) appear as
overflow uid 65534 (nobody) from inside the namespace. `--bind-try`
suppresses ENOENT but not EACCES, so the bind exits 0 and the wrapper
proceeds — but every write inside then fails with Permission denied.
The bwrap capability probe (`sudo -n bwrap --unshare-user --uid 0 --gid
0 --ro-bind / / -- true`) did not test the workspace bind or the su
invocation, so it incorrectly reported bwrap as available.
**Expected behavior**
The agent should start and run normally inside the Daytona sandbox.
Directory creation and file writes in the workspace should succeed.
**Steps to reproduce**
1. Configure Paperclip with a Daytona sandbox provider
2. Start a Codex agent task targeting a Daytona sandbox
3. Observe the `adapter_failed` error: `mkdir ... failed with exit code
1: bwrap: Can't find source path /home/daytona/paperclip-workspace:
Permission denied`
**Paperclip version or commit**
master (reproducible on current HEAD before this fix)
**Deployment mode**
Self-hosted server
**Agent adapter(s) involved**
- [x] Codex
**Relevant logs or output**
```
mkdir /home/daytona/paperclip-workspace/.paperclip-runtime/codex/paperclip-bridge/queue \
/home/daytona/paperclip-workspace/.paperclip-runtime/codex/paperclip-bridge/queue/requests \
/home/daytona/paperclip-workspace/.paperclip-runtime/codex/paperclip-bridge/queue/responses \
/home/daytona/paperclip-workspace/.paperclip-runtime/codex/paperclip-bridge/queue/logs \
failed with exit code 1: bwrap: Can't find source path /home/daytona/paperclip-workspace: Permission denied
(adapter_failed)
```
## What Changed
- Replaced `--unshare-user --uid <uid> --gid <gid>` with `su -s /bin/sh
<username>` in `buildBwrapCommand`. bwrap runs as real root (for
bind-mount capability), then `su` drops into the sandbox user. Inside
uid=1001 maps to outside uid=1001, so workspace files are writable.
- Removed `detectSandboxUidGid` (ran `id -u` + `id -g`). Added
`detectSandboxUsername` (runs `id -un`) — the username is what `su`
needs.
- Updated `detectBwrapAvailable` probe to test the actual invocation:
`sudo -n bwrap --ro-bind / / [--bind-try <workspace> <workspace>] -- su
-s /bin/sh '<user>' -c true`. This catches both the su failure mode and
the EACCES-on-workspace-bind case.
- Updated `detectBwrapCapability` to run sequentially (username first,
then probe with that username and remoteCwd).
- Replaced `sandboxUid`/`sandboxGid` in lease metadata with
`sandboxUsername`.
- All three `detectBwrapCapability` call sites now pass `remoteCwd`.
- Updated `BwrapExecPlan` type and `resolveBwrapExecPlan` to use
`username: string` instead of `identity: { uid, gid }`.
- Updated tests TDD-style: rewrote tests to describe the new behavior
first, then implemented to pass them.
## Verification
**SSH verification** (run against a live Daytona sandbox before writing
the fix):
```bash
# Old approach — fails
sudo -n bwrap --unshare-user --uid 1001 --gid 1001 \
--ro-bind / / --bind-try /home/daytona/paperclip-workspace /home/daytona/paperclip-workspace \
-- sh -c "mkdir -p /home/daytona/paperclip-workspace/test"
# → mkdir: cannot create directory: Permission denied
# New approach — works
sudo -n bwrap --ro-bind / / \
--bind-try /home/daytona/paperclip-workspace /home/daytona/paperclip-workspace \
-- su -s /bin/sh daytona -c "mkdir -p /home/daytona/paperclip-workspace/test && echo ok"
# → ok (files owned by uid 1001)
```
**Unit tests:**
```
cd packages/plugins/sandbox-providers/daytona && npx vitest run
# 114 passed, 2 pre-existing failures (macOS tar compatibility in file-sync.ts, unrelated)
```
## Risks
- `su` must be available in the Daytona sandbox image. It is a standard
POSIX tool present in every image tested. If absent,
`detectBwrapAvailable` returns false and execution falls back to the
unwrapped path (same behavior as before).
- The advisory bwrap wrapper was never a security boundary — it is
best-effort. The behavioral change (root → sandbox user inside the
container) is strictly better: files created by the agent now have the
correct ownership.
- `sandboxUid` and `sandboxGid` are removed from lease metadata. Any
external code reading those fields will get `undefined`. They were only
used internally by `resolveBwrapExecPlan`, which now reads
`sandboxUsername`.
## Model Used
Claude Sonnet 4.6 (`claude-sonnet-4-6`) via Claude Code CLI — tool use
enabled, extended context. The model diagnosed the bug via SSH
inspection, designed the fix, and implemented it TDD-style (tests first,
then implementation).
## 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 searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge
---------
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
bd7a13eb9c