[FEATURE]: Native auto-memory for cross-session learning #20322

Verification

• I searched existing issues and found related proposals: [FEATURE] Persistent Session Memory #16077, Feature Request: Model-Agnostic Memory Layer (Global & Per-Project) #8043, [FEATURE]: Advanced Dual-Scope Memory System for OpenCode #9211
• This issue adds a specific, focused implementation approach not covered in those

Problem

OpenCode has no native mechanism to persist learnings across sessions. Users have to manually add everything to AGENTS.md. Related issues (#16077, #8043, #9211) discuss this conceptually but none have an implementation PR.

Proposed Solution

A lightweight memory module that:

1. Extracts patterns from session events (repeated build commands, error+fix sequences, user corrections)
2. Stores in SQLite + auto-generates .opencode/MEMORY.md
3. Injects MEMORY.md into system prompt at session start

Configurable:

{ "memory": { "enabled": true, "auto_extract": true, "max_memory_lines": 200 } }

Why now

I'm working on a PR for this and want to link it properly per the issue-first policy.