Add consent-gated media exchange library

docs/data-flow.md

@@ -96,6 +96,12 @@ Legacy conversations may make at most one optional autonomous media request, inc
 
 `MediaService` resolves Matrix media, downloads it into the persistent data directory, and writes an account-scoped media index. `MediaSyncService` schedules incremental work only while the account is authenticated. Private media is served behind the same authorization boundary as the dashboard and APIs.
 
+The process-global exchange library is separate. Dashboard uploads are decoded and re-encoded with `sharp`, which validates the actual JPEG/PNG/WebP contents, applies orientation, and removes EXIF/location/camera metadata. OpenRouter then assigns overlapping anatomy tags plus SFW/NSFW classification. Failed or low-confidence classifications remain disabled until the operator corrects them.
+
+For each latest inbound text event, `MediaLibraryExchangeService` detects direct or indirect image requests before normal reply generation. Exact requests require the matching tag. Generic requests use the conversation's completed library-send count to broaden the eligible safety tier and randomly choose an unused asset. A unique durable reservation on account + conversation + asset prevents reuse, while account + conversation + inbound event makes restart handling idempotent.
+
+After the normal reply limiter waits, automation refreshes Matrix and rechecks that the same inbound request is still latest and that no image, boundary, seller signal, or other terminal state has appeared. It then uploads the private file to Matrix, sends an `m.image` event with a stable transaction ID, and only after confirmation sends the optional reciprocal text. If the image is confirmed but the text is not, the asset remains consumed and the conversation is handed to the operator rather than risking a duplicate.
+
 Conversation performance is derived from the complete attributed inbound transcript. Engagement cannot become a prompt-learning example while automation is active, and a later decline, boundary, or upsell removes an earlier example before future prompts load it.
 
 ## Dashboard data and events