test(memory): assert owner gating blocks relay through foreign memories

[Yeriahz]

What does this PR do?

Adds a regression test for a property that the code delivers but nothing asserts. Test-only; no production code touched.

Background

_spread() in packages/nooa-memory/src/nooa_memory/retrieval.py gates spreading activation by owner. Its docstring claims an edge "must not leak — or amplify through — another agent's memory in an owner-scoped recall."

Both halves hold, because the continue on the visibility check fires before nxt[e.target_id] is written and not only before the spread write. An invisible memory therefore never enters the next hop's frontier and cannot relay activation between two visible ones.

Existing coverage is test_spread_does_not_leak_foreign_memories here and test_spread_confined_to_role in test_memory_owner_roles.py. Both build a single edge across an owner boundary, so they pin the leak half. Neither builds the three-node own -> foreign -> own case, which means the position of the continue is load-bearing but asserted nowhere. Moving the visibility check to just before the spread write looks harmless and quietly reopens the path.

This gap was identified by @neoneye while reviewing NOOA's memory system for the Agent Memory Atlas: https://neoneye.github.io/agent-memory-atlas/systems/nooa-memory/

Why it asserts on _spread rather than recall

The property is not observable at the public API. A relay target owned by a third party is gated on its own merits; one owned by the reader is retrieved directly regardless of the graph. What a relay changes is activation, and therefore ranking, which only exists inside _spread.

The test includes an unscoped positive control asserting the two-hop path is live, so the scoped assertion cannot pass merely because nothing was reachable.

Related issues

None.

Validation

uv run pytest packages/nooa-memory/ -q          # 265 passed, 13 skipped
uv run ruff format --check / ruff check         # clean

Run against main at e505bb9.

Checklist

• Code follows the project style (uv run ruff check . and uv run ruff format --check . pass)
• Tests added/updated and passing (uv run pytest)
• Docs updated if behavior or public APIs changed — no behavior change
• New source files carry an SPDX license header — no new files