paperclip/packages/paperclip-runner/docs/durable-recovery.md

Durable recovery Durable Transport and Recovery

Durable recovery adds a real outbound WebSocket path to the standalone package. The Rust paperclip-runnerd process is the client. The TypeScript mock core is the remote peer. Neither side imports Paperclip server, UI, database, or shared control-plane code.

This is a local reliability and authenticated-transport proof. The mock keeps the RFC 6455 carrier on ws://127.0.0.1, but PRP application frames use a mutually authenticated, encrypted session. Loopback position and the WebSocket acceptance header are not authentication. A production bridge should still use wss:// for defense in depth and remains a separately reviewed deployment phase.

Connection and authentication

The connection starts in this order:

1. The mock core creates a random bootstrap ticket with a five-second lifetime.
2. The ticket is passed to the runner through PAPERCLIP_RUNNER_BOOTSTRAP_TICKET. It is not a command-line argument.
3. The runner opens an unauthenticated WebSocket upgrade with no bearer header, then sends only a public credential locator, a fresh client nonce, complete runner/run/session identity, approved runner version and digest, negotiated protocol range, and durable resume cursors.
4. The core returns a fresh server nonce plus an HMAC-SHA-256 proof over the complete transcript. The proof binds runner, environment lease, run, normalized session, turn, item, runner artifact, selected protocol, credential/connection lease identity, expiry, and revocation epoch.
5. The runner validates that proof before returning its own transcript-bound proof. The bootstrap ticket or connection lease token itself never crosses the socket. A failed proof does not consume a one-use bootstrap ticket.
6. Both sides derive directional AES-256-GCM keys from the capability and both nonces. Strict per-direction counters reject replays and out-of-order frames.
7. Only after mutual authentication does the core send an encrypted welcome. The welcome selects a supported PRP version, returns a short-lived connection lease, reports the cumulative committed event cursor, and carries at most one pending command. Every later ACK, command, revoke, event, and command result remains inside the encrypted session.
8. Later connections authenticate with the connection lease. A real runner process restart receives a new one-time bootstrap ticket and loads the same durable state before it connects.

The runner keeps the live connection lease token in memory only. Its state file does not contain the bootstrap ticket or connection lease token. The mock core persists domain-separated SHA-256 authentication keys instead of raw capabilities. Used, expired, revoked, or identity-mismatched credentials fail closed during the challenge. The runner validates the complete encrypted welcome and every control envelope against the authenticated connection, runner, environment lease, run, normalized session, turn, item, protocol, lease ID, expiry, and revocation metadata before applying an ACK or command.

The daemon captures and removes the bootstrap environment variable before it parses arguments or starts child work. Secret buffers are overwritten when they are dropped. It resolves the destination once before sending a bearer value and accepts only concrete loopback addresses. Userinfo, query strings, fragments, wildcards, private-network addresses, public addresses, and mixed DNS answers fail closed.

WebSocket limits

The package client implements the RFC 6455 upgrade and masked client text frames with Node-free Rust standard-library code. The mock core validates the upgrade and parses bounded masked frames.

• Maximum HTTP upgrade headers: 16 KiB.
• Maximum PRP frame: 1 MiB.
• Unknown frame opcodes and unmasked client frames close the connection.
• Malformed JSON is recorded as a bounded diagnostic. Durable state remains available for reconnect.
• WebSocket ping/pong and PRP diagnostic pong state are supported.

Durable runner state

The runner writes runner-state.json below its private state directory. The directory uses mode 0700 and the file uses mode 0600 on Unix. Every update is written to an exclusive unpredictable sibling file, synchronized, atomically renamed, and followed by a parent-directory sync. Symlinked directories or state files, wrong ownership, and wrong modes fail closed.

The state contains:

• stable runner, environment lease, run, session, turn, and item IDs;
• next source event sequence and cumulative acknowledged source sequence;
• unacknowledged event envelopes and their byte counts;
• a bounded recent processed-command cache with a SHA-256 command digest and prior result, plus a fixed-size fail-closed replay filter for compacted IDs;
• lifecycle, reconnect, backpressure, harness generation, and recovery facts;
• bounded, redacted diagnostics.

Raw runner stdout and stderr are never redirected to durable files. The runner itself redacts and bounds a terminal diagnostic before publishing it through an atomic private-file replacement, so neither an output burst nor controller restart can create a transient unbounded or unredacted diagnostic file.

Authentication capabilities and arbitrary command bodies are not stored. A recent command is represented by a SHA-256 comparison digest from the vetted RustCrypto implementation, its stable ID and controller sequence, the redacted result, and the logical-effect count. The exact cache keeps at most 128 entries. Older IDs are added to a fixed 4 KiB Bloom filter before their exact records are removed. A possible filter match is rejected with zero effects, so Bloom false positives can reject new work but can never make an old command effective again. The durable controller sequence remains monotonic across compaction and restart.

Event delivery and ACKs

The runner writes an event to the outbox before it sends the event. Event IDs and source sequence numbers do not change after reconnect or restart.

The mock core commits or deduplicates an event before it sends this cumulative ACK:

{
  "kind": "ack",
  "payload": { "ackedSourceSeq": 9 }
}

The ACK means that every source event through sequence 9 is committed or deduplicated. The runner rejects an ACK that moves backward or beyond its produced source cursor. It removes only events at or below a valid ACK.

For the lost-ACK fault, the mock commits an event, drops the ACK and socket, and reports the prior cursor once after reconnect. The runner sends the same bytes again. The mock increments delivery count, keeps one logical event, and sends the committed cumulative ACK.

Command delivery and effects

Mock-core commands are durable before delivery. Only the lowest pending controller sequence is sent. A command result advances the queue.

The runner stores a command result before it sends the result. When a result or socket is lost, the same command is delivered again. An equal command ID and digest returns the stored result. It does not add events or repeat a process effect. Reusing the ID with different bytes is rejected.

The trace records logicalEffectCount. Every completed command has exactly one logical effect. A policy rejection, such as a new turn during drain or storage pressure, has zero effects.

Residual local trust and revocation window

The authenticated session removes trust in whichever process wins the configured loopback port: a relay can forward opaque bytes, but it cannot learn a bootstrap or lease capability, decrypt control data, or forge a welcome, ACK, command, or revoke frame. The remaining local-host assumption is that the OS protects the runner process memory, inherited bootstrap environment at launch, private 0700/0600 state paths, and the mock core's derived authentication keys from other same-user processes with debugging, memory-reading, or filesystem access. An attacker with those privileges is outside this transport boundary.

Lease expiry is checked locally before control data is applied. Explicit revocation reaches an already-connected runner through an authenticated revoke frame; if that frame cannot be delivered, the session remains usable until the connection closes or the runner reaches the signed lease expiry. The mock uses a 30-second lease, so that is the maximum demonstrated revocation window. A production core should close active sessions when it revokes a lease and choose the lease TTL to match its required revocation bound.

Restart and reconciliation

A socket drop keeps the same Rust process and in-memory lease. The process reconnects and reloads the mock-core command and event cursor.

A runner restart kills the real Rust process with unacknowledged work. A new Rust process receives a fresh ticket, reads the same state file, emits a P0 runner.reconciled event, and continues the same runner, session, turn, item, command, and source-event identities.

The harness-restart fault starts the real Local runner fake-harness child, waits for its ready message, terminates its process group, and starts a second child. The runner then emits harness.exited, harness.ready, and session.reconciled events with the same normalized session, turn, and item IDs.

If a lease expires, reconnect fails closed. The runner records lease_expired_requires_bootstrap and exits with its state intact. The mock then gives the replacement runner a fresh ticket. Recovery continues from the same cursor.

If recovery cannot be truthful, state names the outcome. For example, failure to reserve storage for a P0 event records p0_storage_exhausted and the unrecoverable lifecycle. It never reports a fresh session as resumed.

Protocol versions and warm handoff

Ordinary PRP v1 connections remain supported. A warm run.attach that changes run authority requires negotiated PRP v2, as well as the warm-transition capability. The runner refuses a v1 warm attachment before provider work. A v1 peer acknowledges placeholders for native session-goal and capability events; those acknowledgements do not prove that the peer observed the native state. Rotation must not discard that retained evidence or relabel it as a new run.

A connection lease fixes its protocol version. Advertising v2 on reconnect does not upgrade an existing v1 lease. For a v2-capable runner holding a v1 lease, the owned transport's process-recovery path can replace the process with fresh authorization when configured with a reconnect grace. It preserves validated state and original authority and issues a new one-use bootstrap. The old process must exit first; any old provider owner must also be retired. The connection lease exists only in process memory; no credential or journal file needs to be edited. The replacement negotiates v2 and replays retained native session state on the original authority. Its native event acknowledgements must settle before warm handoff. The controller must still authorize replacement and verify current process, artifact, and run ownership. This is not an automatic in-place lease upgrade or a general operator UI migration flow. An old binary stays old when its immutable launcher restarts it. Replacing a legacy binary or an adopted owner requires separate artifact and ownership admission; this path does not qualify that migration. Pending warm-transition receipts require their separate exact recovery admission, not an ordinary bootstrap.

Backpressure and bounded storage

The runner has a byte limit and a reserved P0 region.

• P2 item deltas coalesce before delivery.
• P1 events cannot consume the P0 reserve.
• New turns are rejected while backpressure is active.
• A P0 runner.backpressure event explains the state.
• P0 events are never dropped to make room.
• The state records peak outbox bytes so the final empty outbox does not hide a limit violation.

The storage-pressure trace emits 250 P2 updates. They become one coalesced event, all P0 facts reach the mock core, peak bytes remain below the configured limit, and the next turn is rejected without an effect.

Drain and revoke

runner.drain persists the draining lifecycle and a P0 runner.draining event. It rejects later turn.start commands but continues to deliver the existing outbox. runner.shutdown stops only after the outbox is acknowledged.

A revoke envelope persists the revoked lifecycle. The runner flushes any existing durable events and exits. It does not accept new work or delete unacknowledged facts.

Verification

The production durable control plane and live-session suites cover reconnect, ACK replay, restart recovery, backpressure, lease expiry, drain, and revoke.

Use --json for the complete trace or --output <path> to write it. The CLI and browser show connection counts, safe lease ID and expiry, stable identities, source and ACK cursors, outbox current/peak bytes, command delivery/effect counts, replay counts, restart counts, outcomes, and redaction assertions.

They never show bootstrap tickets or connection lease tokens.

Regenerate the checked fault matrix and every exact per-fault trace with:

# Recorded evidence generation is deferred from this release.