persist: stream catalog — enumerate streams + 10 tests

New backend op :streams (from seq high-water marks, so compacted streams still
list), threaded through mem-backend + durable serve/io-backend. catalog.sx:
persist/streams, stream-count, stream-exists?, total-events. 143/143.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

plans/persist-on-sx.md

@@ -42,7 +42,7 @@ read models (feeds, indices, audit logs) update incrementally.
 
 ## Status (rolling)
 
-`bash lib/persist/conformance.sh` → **133/133** (Phases 1–4 complete + extensions)
+`bash lib/persist/conformance.sh` → **143/143** (Phases 1–4 complete + extensions)
 
 ## Ground rules
 
@@ -154,11 +154,20 @@ over an in-process disk (the mock-IO harness).
   (create-only): atomic current-state updates, conflict as a real value (kv
   analogue of log `append-expect`). For sessions, acl grants, stock counts.
 
+- [x] `catalog.sx` — stream catalog: `persist/streams`/`stream-count`/
+  `stream-exists?`/`total-events`. Backend `:streams` op (from seq high-water
+  marks, so compacted streams still list), threaded through mem + durable.
+
 ## Consumers (post-foundation, not in scope here)
 feed/-log, flow store, mod/audit, search index, acl grants, identity sessions all
 become `persist` log or kv. Track each migration in that subsystem's plan.
 
 ## Progress log
+- **Ext: stream catalog (143/143).** New backend op `:streams` (keys of the seq
+  high-water-mark dict, threaded through mem-backend + durable serve/io-backend)
+  so fully-compacted streams still enumerate. `catalog.sx`:
+  `persist/streams`/`stream-count`/`stream-exists?`/`total-events`. 10 tests
+  incl. durable + restart.
 - **Ext: kv compare-and-swap (133/133).** `persist/kv-cas` sets a key only if
   its current value equals expected, else returns `{:conflict :expected
   :actual}`; `persist/kv-put-new` is create-only. The kv analogue of log