docs: update CHANGELOG + STATE for proof_attempts loop + Zig client

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.machine_readable/6a2/STATE.a2ml

@@ -7,7 +7,7 @@
     (version "1.1.0")
     (schema-version "1.0")
     (created "2026-01-03")
-    (updated "2026-04-04")
+    (updated "2026-04-05")
     (project "verisimdb")
     (repo "github.com/hyperpolymath/verisimdb")
     (crg-grade "C"))
@@ -40,7 +40,9 @@
       ("Full-text search" "working")
       ("Graph relationships" "working")
       ("Temporal versioning" "working")
-      ("Atomic transactions" "working")))
+      ("Atomic transactions" "working")
+      ("proof_attempts learning loop" "working")
+      ("Zig client SDK with C ABI" "working")))
 
   (route-to-mvp
     (milestones
@@ -80,4 +82,5 @@
       ("Plan grade B work (mutation testing)" "TODO")))
 
   (session-history
-    ("2026-04-04: CRG C blitz - added 55 tests across E2E, contract, aspect, reflexive, property categories"))))
+    ("2026-04-04: CRG C blitz - added 55 tests across E2E, contract, aspect, reflexive, property categories")
+    ("2026-04-05: added proof_attempts learning loop (table + MV + /strategy endpoint) and Zig client SDK; closes loop with echidna/hypatia"))))

CHANGELOG.adoc

@@ -11,6 +11,18 @@ All notable changes to VeriSimDB are documented here. This project uses https://
 
 === Added
 
+==== Proof-Attempts Learning Loop (2026-04-05)
+- **proof_attempts ClickHouse table**: Records every prover invocation across the estate (attempt_id, obligation_id, repo, file, claim, obligation_class, prover_used, outcome, duration_ms, confidence, strategy_tag, timestamps). 20-prover enum covering the echidna portfolio.
+- **mv_prover_success_by_class materialized view**: SummingMergeTree aggregation of success_count / total_attempts / total_duration_ms per (obligation_class, prover_used) — the source of truth for strategy recommendations.
+- **POST /api/v1/proof_attempts**: echidna's `verisimdb_bridge` posts here on every attempt.
+- **GET /api/v1/proof_attempts/strategy?class=<class>&limit=<n>**: Returns provers ranked by success_rate DESC, avg_duration_ms ASC. Consumed by hypatia's `ProofStrategySelection` rule.
+- Closes the learning loop: echidna runs prover → this table → hypatia reads MV → strategy recommendation fed back to echidnabot as prover hint in the GraphQL mutation.
+
+==== Zig Client SDK
+- **connectors/clients/zig/**: Native Zig client with thin C ABI wrapper. Produces `libverisimdb_zig.{a,so}`. Aligns with hyperpolymath ABI/FFI standard (Idris2 ABI + Zig FFI).
+- Exposes: `verisimdb_health`, `verisimdb_create_octad`, `verisimdb_get_octad`, `verisimdb_update_octad`, `verisimdb_delete_octad`, `verisimdb_vql_execute`, `verisimdb_free`.
+- 9 integration tests against live verisim-api.
+
 ==== Security Hardening (Phase 1)
 - **RwLock poisoning protection**: 35+ locations across 7 Rust files converted from `.expect("poisoned")` panics to graceful `map_err` error propagation. Server no longer crashes on lock contention.
 - **API error sanitization**: Internal Rust error strings no longer leak to clients. All `ApiError::Internal` responses now log the real error via tracing and return a generic "Internal server error" to the client.