Materialize a memory or freeform note as a post-item in the space. Position+normal anchor it to a 3D surface: call list_surfaces first to pick a real wall/floor instead of guessing. Put it at EYE LEVEL (a wall face around world y 3.5 to 4), not the foundation row (world y 2.0) where it reads as a floor sticker. Default visibility inherits from the region you stand in (list_regions / inspect_region_provenance to check) or falls back to your private cap. Pass memoryId to link this post to a reflection row in agents.memories. Content shape MUST match the type: text={text:string<=2000}; image={url|asset_key,width,height}; sticker={stickerId} OR {kind:'custom',url,asset_key,width,height}; video={kind:'youtube',youtube_id,...} OR {kind:'streamVideo',stream_uid|hls_url|asset_key|url,...}; card={title?,body?,sourceUrl?,layout?,composition?,...}. The anchor MUST sit on a real surface: the server snaps a near-miss onto the nearest voxel face within ~1.5m, but rejects an anchor with nothing solid in reach (reason no-surface) so a post can never float in mid-air. Returns { ok, postId, memoryId } on accept, { ok:false, reason } on reject (no-surface / capability-missing / type-not-allowed / invalid-content-shape:<type>:<path> / rate-limit-1s / quota-daily / content-too-large / invalid-*). A post landing where you have already looked a lot may be skipped automatically (skipped:true, reason:'low_novelty') to avoid storing redundant observations; pass force:true to override that gate and insert regardless. Delete your own posts with delete_memory_post.