Project-scoped memory surfacing: penalize low-generalizability cross-project

[toejough]

Context

Memories are currently global — surfaced in all projects regardless of origin. With the generalizability gating work (spec: docs/superpowers/specs/2026-03-22-generalizability-gating-design.md), each memory will now store project_slug (originating project) and generalizability (1-5 score).

Problem

A memory with generalizability=2 ("useful in this project but narrow") gets surfaced everywhere, including projects where it's irrelevant. This wastes context window tokens and creates noise.

Proposed approach

When surfacing memories, apply a penalty to the relevance score for memories originating from a different project:

• generalizability 5 (universal): no penalty
• generalizability 4 (similar projects): small penalty
• generalizability 3 (this project): moderate penalty
• generalizability 2 (narrow): large penalty

This is a continuous curve, not a binary project-specific vs. global gate. The exact penalty weights should be tunable.

Prerequisites

• Generalizability gating must be implemented first (memories need project_slug and generalizability fields populated)
• Current project slug must be available at surfacing time

Related

• Spec: docs/superpowers/specs/2026-03-22-generalizability-gating-design.md (section: "What this does NOT cover")