Cleaned dead code and updated documents

docs/PRODUCT_ARCHITECTURE.md

@@ -22,17 +22,16 @@ multi-state privacy. ~$5–8K legal costs.
 TS "Deploy" exists via Workers for Platforms at no additional
 compliance cost.
 
-## Free framework: mizan-cache (origin-side cache)
+## Free framework: origin-side cache (`mizan.cache`)
 
-Python package implementing the **full cache protocol locally** —
-same HMAC key derivation, metadata schema, and purge semantics as
-Edge.
+Shipped in `mizan_core.cache` (re-exported as `mizan.cache` from the
+Django adapter) implementing the **full cache protocol locally** —
+same HMAC key derivation and purge semantics as Edge.
 
-Three backends:
+Two backends behind a `CacheBackend` protocol:
 
-- In-memory dict (default)
-- Redis
-- SQLite
+- `MemoryCache` — in-memory dict (testing)
+- `RedisCache` — production
 
 ### Dual purpose
 
@@ -44,8 +43,8 @@ Three backends:
 ## Spec additions
 
 - `@client(cache=False)` — uncacheable; emits `Cache-Control: no-store`.
-- Cache ABI: `get(key)`, `put(key, response, metadata)`,
-  `purge(context, params)`.
+- Cache ABI (`mizan.cache`): `cache_get(secret, backend, context, params)`,
+  `cache_put(...)`, `cache_purge(backend, context, params=…, secret=…)`.
 
 ## Launch compliance (Render only)