paperclip/packages/paperclip-runner/docs/codex-driver.md

# Codex Skillless Codex Driver

## Scope

Codex implements a direct Codex app-server v2 driver behind the package's
existing `HarnessDriver` contract. The driver, mock core, example CLI, tests,
and evidence stay inside `packages/paperclip-runner/`. They do not import or
change Paperclip server, UI, database, or production control-plane behavior.

The app-server process is local to the execution environment and uses newline
delimited JSON-RPC over stdio. It is not exposed as a network service.

## Identity mapping

| Runner identity | Codex source | Persistence rule |
| --- | --- | --- |
| run ID | mock-core input | Never replaced during recovery. |
| normalized session ID | controller-owned mock-core input | A distinct identity, independent of the run and provider IDs, that stays stable across transport/process recovery. |
| driver session ID | `thread.id` | Resumed by exact ID. A different returned ID fails recovery. |
| provider session ID | `thread.sessionId` | Kept separately from the driver thread ID. |
| turn ID | `turn.id` | Required by steer and interrupt preconditions. |
| item ID | `item.id`, request ID, or deterministic turn/kind key | Preserved on lifecycle and delta events. |
| source event ID | runner instance + run + source sequence | Source sequence continues from the persisted snapshot. |

The persisted session snapshot records run, normalized session, driver
session, provider session, the exact active turn, committed semantic-result
content/call binding, observed terminal-turn fingerprints, and the last source
sequence. Recovery starts a new local app-server transport, reads the exact
persisted thread to validate identity and working directory, resumes that
thread, and then reads it again for reconciliation. Reconciliation considers
only the persisted active turn: it retains that turn when active, terminalizes
that turn when terminal, and fails recoverably when it is missing or a
different active turn appears. Historical terminal turns never substitute for
the persisted active turn, and a terminal already in the durable snapshot is
not emitted again.

## App-server operations

| Driver operation | App-server method | Degradation |
| --- | --- | --- |
| initialize | `initialize`, then `initialized` | Startup fails visibly. |
| create | `thread/start` | Required. |
| resume | `thread/resume` | `recovered: false` with a redacted reason. |
| read | `thread/read` | Explicit `HarnessCapabilityUnavailableError`. |
| start turn | `turn/start` | Required. |
| steer | `turn/steer` with `expectedTurnId` | Explicit unsupported diagnostic; no stdin fallback. |
| interrupt | `turn/interrupt` | Explicit unsupported diagnostic; session is not killed. |
| usage | `thread/tokenUsage/updated` | Returns the last snapshot or explicit unsupported error. |
| reconcile | `thread/read` plus `session.reconciled` | Disabled when read is unavailable. |

Capability flags are descriptive and executable. Unsupported operations emit
canonical `harness.diagnostic` events with secret-redacted detail. No
harness-specific branch is required in the mock core.

## Skillless context boundary

The model receives one text input containing `paperclip.skillless_task.v1`:

- objective;
- completion-contract revision and criteria;
- task constraints; and
- the expected canonical result schema name.

The thread config explicitly disables automatic skill and app instruction
blocks. Codex's built-in collaboration instructions are enabled by default so
interactive runs receive native commentary and tool preambles; a driver caller
may explicitly disable them for a specialized deterministic fixture. This
does not enable skills, apps, plugins, memories, or extra model-input kinds.
The model input accepts only text, never a Codex `skill` input. The driver
captures the returned instruction-source list and requires it to be empty for
the skillless assertion.

The trusted app-server process has an allowlisted environment. It retains host
`HOME` and `CODEX_HOME` only so the provider can authenticate. Model-issued
commands have a separate boundary: an empty-by-default environment with no
`HOME` or `CODEX_HOME`, no network, and a named Codex
permission profile requesting read-only minimal runtime files, no host-home or
Codex-home access, and write access to the assigned workspace. The driver
refuses filesystem-root workspaces, workspaces containing host `HOME`, and any
workspace overlapping host `CODEX_HOME`. A workspace below host `HOME` is
valid, but when `PAPERCLIP_WORKSPACE_CWD` is present its canonical path must be
equal to or below that assigned workspace so sibling and symlink escapes fail
before provider startup.

The returned sandbox facts remain authoritative. Codex 0.132.0 may inject a
provider-managed writable root such as `~/.codex/memories` after a first run,
even with `features.memories=false` and an explicit Codex-home deny. That makes
the Codex-home directory discoverable in a warmed environment, so Codex does
not claim whole-directory unreadability. Its authenticated proof instead
requires each readable `auth.json`/`config.toml` file and an unrelated host
secret to remain unreadable and unwritable, while recording any injected root
in `context.sandbox.legacyPolicy`.

Paperclip bearer values, `OPENAI_API_KEY`, arbitrary skill paths, and other
inherited variables are not passed. Diagnostics redact bearer/basic
credentials, credentialed proxy URLs, secret query parameters, sensitive JSON
keys, and common key assignments.

The context snapshot records configuration and environment **key names**, not
secret values.

## Semantic completion

The provider-facing structured-output schema covers `done` and `needs_review`.
It uses the strict OpenAI shape: every object rejects additional properties and
the constant schema field includes both `type: "string"` and `const`.

Two dynamic semantic tools are registered when supported:

- `paperclip_finish` accepts `done` or `needs_review`;
- `paperclip_block` accepts `blocked` and requires a blocker owner, action,
  reason, and scope.

Both normalize through the canonical `paperclip.run_result.v1` validator. The
first valid result is proposed. Any canonically identical result retry is
idempotent even when the provider assigned a new call ID; the original call
binding remains persisted for audit, while changed content is rejected. Tool
calls and provider notifications must name the exact opened thread and active turn. Missing,
pre-turn, cross-thread, cross-turn, and post-terminal bindings fail the provider
session closed. Canonically identical terminal replays are no-ops; conflicting
terminal facts are rejected. Process exit or prose alone never implies
completion.

The provider cannot commit controller state. It emits `run.result.proposed` and
a provider turn terminal; the mock core validates the proposal against its
task envelope, emits `run.result.accepted` or `run.result.rejected`, and alone
emits `run.terminal`.

## Canonical event mapping

- thread lifecycle -> `session.started`, `session.resumed`,
  `session.reconciled`;
- turn lifecycle -> `turn.submitted`, `turn.accepted`, `turn.started`, and one
  terminal turn event;
- messages, reasoning, plans, commands, file changes, dynamic tools, and diffs
  -> `item.started`, `item.delta`, `item.completed`;
- model selection -> a completed `model` item;
- app-server decisions -> `runtime_request.created` and
  `runtime_request.resolved` with redacted detail;
- token snapshots -> completed `usage` items;
- semantic verification rows -> completed `verification` items;
- provider completion -> at most one `run.result.proposed` and one turn
  terminal;
- controller decision -> one `run.result.accepted` or `run.result.rejected`,
  followed by one `run.terminal`.

The JSON-RPC transport limits each input line, pending client requests,
in-flight server requests, queued notification count and bytes, diagnostic
lines, and retained provider payloads. Malformed or oversized messages close
the transport and reject pending work.

The existing Replay reducer consumes the live stream. Replay crosses a
serialized JSONL boundary that validates byte and event counts, line size,
schema, run/session binding, unique source event IDs, continuous per-source
sequence, and exactly one final run terminal before reducing. The Codex
tracer requires byte-equivalent live and replay snapshots.

## Runnable example

`trace:codex` starts a real local `codex app-server` session through the mock
core. Its safe task creates `hello.txt` with network disabled. The evidence
recorder additionally probes all readable host Codex credential/config files
and an unrelated host secret, requiring reads and writes to be denied while
workspace output and app-server authentication still succeed. It gates output
reads on an accepted `done` result and reports missing files by name rather
than surfacing a raw filesystem `ENOENT`. See the
[Codex tutorial](tutorials/codex.md).

This phase changes no browser surface, so no new browser screenshot applies.
The canonical events are proved through the existing reducer/replay path and
JSON trace evidence.