PaperClipAI/packages/paperclip-runner/docs/protocol-compatibility.md

PRP Compatibility and Versioning Policy

Authority

The JSON Schema files in protocol/schemas/ are the language-neutral source of truth for the Phase 1 and Phase 2 executable contract. The generated TypeScript schema module is checked against those files before every TypeScript typecheck. Rust consumes the same fixtures and must produce the same golden parity summaries.

The broader normative protocol remains the native-runner spike specification. Phase 2 reuses this contract for local live events. It adds package-local stdio and stream envelopes, but it does not add durable transport, persistence, or production control-plane behavior.

Version fields

Field	Phase 1 support	Compatibility rule
protocolVersion	1	Required. Negotiate the highest overlapping version; no overlap fails closed.
fixtureVersion	1	Required by the conformance corpus. Unknown values fail closed.
event.schemaVersion	1	Required on every event. Unknown values fail closed before reduction.
Typed schema discriminators	*.v1	Required. Unknown required schema identities fail JSON Schema validation.

Wire protocol versions and fixture-corpus versions are independent. A fixture format can evolve without changing PRP, and a future PRP version can be represented only after the consumer advertises support for it.

Forward compatibility

• Unknown object properties are accepted and preserved by validation. Reducers ignore fields they do not understand until a later schema version gives those fields defined behavior.
• Unknown required versions, schema discriminators, enum values, and required fields fail closed. A consumer must never guess at their semantics.
• Scripted fixtures bind every event to the fixture run/session, require contiguous controller command order, exactly one unique proposed result, and exactly one unique terminal event.
• The top-level fixture result must equal the run.result.proposed payload after canonical key ordering. Repeated sourceEventId deliveries must be byte-equivalent after the same normalization.

The forward-compatibility fixture proves that optional fields survive validation without changing the v1 snapshot. The unsupported-version fixture proves that a required v2 protocol cannot be replayed by this consumer.

Replay semantics

• Events are applied in fixture order and ordered independently by (sourceKind, sourceInstanceId, sourceSeq).
• A repeated source event ID has no second projection effect.
• A forward source-sequence gap is recorded explicitly; the reducer never invents a missing event.
• An event at or behind the committed source cursor is ignored and recorded as out of order.
• Replaying an already-applied batch leaves the snapshot unchanged.

The CLI and browser import the same replayPhase1FixtureText function, so validation, compatibility errors, and final snapshots cannot drift between the two surfaces.

Phase 2 local envelope rules

• Mock-core commands use paperclip.prp.command.v1 over stdin JSONL.
• Runner output uses paperclip.runner.stream.v1 over stdout JSONL.
• Fake-harness commands use paperclip.fake_harness.command.v1.
• Fake-harness output uses paperclip.fake_harness.message.v1.
• An equivalent repeated commandId returns a duplicate receipt and has no second driver effect. Reuse with different data is rejected.
• A new command must use the next contiguous controllerSeq.
• Harness logs are bounded diagnostic data. They are not canonical PRP events.
• run.result.proposed, harness.exited, and run.terminal are separate facts and appear in that order when a semantic result exists.
• The live browser rejects an event with an invalid schema, run ID, or session ID before it reaches the reducer.

These envelopes are local Phase 2 implementation contracts.

Phase 3 durable wire rules

• The runner opens an outbound WebSocket and sends PRP v1 hello before any command result or event.
• A one-use bootstrap bearer capability returns a short-lived connection lease in welcome. Later connections use that lease. Neither raw capability is durable state.
• hello.resume reports the last processed controller sequence, next source sequence, cumulative ACK cursor, and current unacknowledged range.
• welcome selects the one overlapping protocol version, returns the core's cumulative ACK cursor, and carries at most one durable pending command.
• An event is durable before send. Event IDs and source sequences stay stable across replay and process restart.
• An ACK is cumulative. The runner rejects a cursor behind its durable ACK or beyond its produced source cursor.
• An equal repeated command ID and canonical digest returns its stored result. Reuse with different bytes fails closed and cannot repeat an effect.
• Frames are bounded at 1 MiB and upgrade headers at 16 KiB. Unknown or invalid required protocol data fails closed; malformed JSON is a bounded diagnostic.

These are package-local Phase 3 rules. Production TLS, control-plane admission, and deployment policy remain separately reviewed work.

Change policy

1. Change JSON Schema first.
2. Regenerate the TypeScript schema module.
3. Add or revise a shared fixture and its golden snapshot/summary.
4. Prove TypeScript and Rust parity.
5. Update this policy and the normative spike specification when behavior changes.

Breaking changes require a new required version. Additive optional fields may remain in v1 only when old consumers can safely ignore them.