Memory context injection — feed MemoryBank + SpatialMemory into every Gemma 4 call

[chatde]

Parent PRD

#1

What to build

Upgrade process_frame() to prepend Vector's full observation history and known-objects inventory to every Gemma 4 prompt. This is the key feature that makes Gemma 4 context-aware — it knows what Vector has seen before, so it can notice changes and reason about its environment over time.

Acceptance criteria

• _build_memory_context(memory_bank, spatial_memory) returns a formatted string with recent observations + known objects
• Context string is prepended to the prompt in process_frame(), describe_view(), and answer_question()
• With 5+ observations in MemoryBank, Gemma 4 references prior observations in its response
• memory_note field in response is saved to MemoryBank when non-null
• Context is capped (max 5 recent observations, top 8 objects) — no prompt overflow
• SpatialMemory summary included when available

Blocked by

• Blocked by Gemma4Brain: core process_frame() — unified vision + nav JSON #2 (core process_frame must work first)

User stories addressed

• Vector remembers what it has seen before and notices changes
• Vector reasons about its environment history, not just the current frame