[Graph MVP] Append-only coordination journal and scoped mailbox #110

Parent: #108
Blocked by: #124

Goal

Provide the live, replayable coordination channel used by the manager and isolated workers without assuming that every agent host supports direct peer chat.

Event contract

Every event records:

• monotonic sequence;
• run ID, task ID, producer/actor ID;
• event type and concise summary;
• declared scopes;
• evidence or artifact references;
• optional recipient/task audience;
• timestamp and schema version.

Initial event types:

• finding
• question
• blocked
• failed_approach
• test_result
• artifact_available
• scope_expansion_requested
• scope_expansion_decided
• handoff_offered
• handoff_decided
• verification_result

Visibility

• The manager can read the complete run journal.
• A worker receives events addressed to it or relevant to its granted scope/dependencies.
• Peer findings remain unverified claims until checked.
• Revisions append new events; they do not erase history.
• Persist decision summaries and evidence, never hidden chain-of-thought.

Persistence and replay

• Append atomically.
• Resume from the last durable sequence after restart.
• Detect malformed, duplicated, or out-of-order events.
• Preserve failed/null/abandoned paths.
• Allow deterministic reconstruction of task state without scraping prose comments.

Explicit non-goals

• Unstructured hidden group chat.
• A second findings/report format.
• Git mutation through the mailbox.
• Automatic trust in peer claims.
• Provider-specific message APIs as the source of truth.

Acceptance criteria

• Versioned event schema with fixture coverage.
• Atomic append and monotonic ordering.
• Manager and scoped worker views.
• Restart/replay reconstructs the same observable state.
• Producer, consumer, scope, and evidence provenance are retained.
• Corrupt or incompatible events fail visibly.
• Adapter hooks allow provider-native messaging without making it authoritative.

Related transport contract: #21
Unblocks: #113 and #111

Planning synthesis: OpenAI Codex, 2026-08-31.