feat(verisimdb): add V-lang API for entity consistency client

Octad store, drift detection, drift score clamping.

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

Author: hyperpolymath

verisimdb/api/v/verisimdb.v

@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: PMPL-1.0-or-later
+// Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+//
+// VeriSimDB V-lang API — Cross-modal entity consistency engine client.
+module verisimdb
+
+pub enum OctadField {
+	name
+	description
+	provenance
+	temporal
+	spatial
+	relational
+	categorical
+	metric
+}
+
+pub struct Octad {
+pub:
+	id          string
+	fields      map[string]string
+	version     int
+	created_at  i64
+	modified_at i64
+}
+
+pub struct DriftReport {
+pub:
+	entity_id   string
+	field       OctadField
+	old_value   string
+	new_value   string
+	drift_score f64 // 0.0 = identical, 1.0 = completely changed
+}
+
+fn C.verisimdb_store_octad(id_ptr &u8, data_ptr &u8, data_len int) int
+fn C.verisimdb_get_octad(id_ptr &u8, out_ptr &&u8, out_len &int) int
+fn C.verisimdb_detect_drift(id_ptr &u8) int
+fn C.verisimdb_clamp_drift_score(score f64) f64
+
+// store saves an octad to VeriSimDB.
+pub fn store(id string, data []u8) !int {
+	result := C.verisimdb_store_octad(id.str, data.data, data.len)
+	if result != 0 {
+		return error('store failed: ${result}')
+	}
+	return result
+}
+
+// detect_drift checks for entity drift on a given ID.
+pub fn detect_drift(id string) bool {
+	return C.verisimdb_detect_drift(id.str) == 1
+}
+
+// clamp_drift_score ensures drift is within [0.0, 1.0].
+pub fn clamp_drift_score(score f64) f64 {
+	return C.verisimdb_clamp_drift_score(score)
+}