p2: digest with in-sift FIFO, SQLite caches, Honcho context, recover

Dixie is capped (max_inflight 2, queue_depth 8, queue_wait 20s) and
never queued on llama-server. Streaming chat, thinking off, 45s
fallback to clean. Digest and chunk-embedding caches are
content-addressed SQLite (Honcho context is not cached). Recover
uses the guarded Fetcher. guardian-star is refused in code.

vendor/modernc.org/memory/README.md

@@ -0,0 +1,13 @@
+![logo-png](logo.png)
+
+Package memory implements a memory allocator.
+
+## Build status
+
+available at https://modern-c.appspot.com/-/builder/?importpath=modernc.org%2fmemory
+
+Installation
+
+    $ go get modernc.org/memory
+
+[![Go Reference](https://pkg.go.dev/badge/modernc.org/memory.0.svg)](https://pkg.go.dev/modernc.org/memory)