Reconcile conversation history into a compact MEMORY.md

[owainlewis]

Status

Prerequisites #56 and #62 have shipped. The feature remains intentionally deferred until real usage shows that canonical SQLite history plus fresh-session rehydration are insufficient.

Goal

Optionally distil Push's canonical conversation history into a small, inspectable MEMORY.md that Claude Code, Codex, and Pi can read when relevant.

Prerequisites

• Canonical SQLite history shipped in Persist canonical conversation history in SQLite #56.
• Fresh-session rehydration shipped in Rehydrate fresh backend sessions from canonical history #62.
• Proceed only with evidence from real usage that the current model is insufficient.

Scope

• Run reconciliation outside the message response path.
• Read completed exchanges after a durable message watermark.
• Produce a bounded MEMORY.md containing durable preferences, active projects, and confirmed decisions.
• Update the file atomically and make reconciliation safe to retry.
• Treat explicit user statements and confirmed decisions as stronger evidence than agent-generated or externally retrieved content.
• Keep SQLite history as the source of truth and MEMORY.md as replaceable derived context.
• Add the gateway-owned SOUL footer only when MEMORY.md exists.
• A reconciliation failure must never block replies.
• Do not add embeddings, semantic retrieval, autonomous identity changes, or agent-owned writes.

Acceptance criteria

• Document the real usage failure that justifies adding reconciliation.
• MEMORY.md stays within a documented size bound.
• Re-running from the same watermark is idempotent.
• Source messages remain traceable when inspecting or regenerating memory.
• Untrusted retrieved content cannot silently become a durable instruction.
• Backends can read the file but Push remains the intended writer.
• The feature can be disabled and removed without losing canonical history.
• Tests cover watermark restart, atomic replacement, retry, size bounds, and conflicting updates.

Design

Follow the deferred memory section of docs/core-system/design.md.