v7-7: Implement Learner for dynamic C5 route switching

- Add SmallLearnerStatsV7 type + API to policy box
- Hook ColdIface refill/retire to collect stats (capacity-based)
- Implement C5 route switching: if C5 ratio < 30%, switch to MID_V3
- Version-based TLS cache invalidation for policy updates
- Evaluation interval: every 100 refills

Tested with c6heavy scenario: C5 ratio=12% triggers V7 → MID_V3 switch

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

core/box/smallobject_policy_v7_box.h

@@ -1,9 +1,10 @@
-// smallobject_policy_v7_box.h - SmallObject Policy v7 (Phase v7-4)
+// smallobject_policy_v7_box.h - SmallObject Policy v7 (Phase v7-7: Learner integration)
 //
 // Purpose:
 //   - Centralized routing policy for ULTRA / v7 / MID_v3 / LEGACY
 //   - Single source of truth for class → route_kind mapping
 //   - ENV configuration managed in one place (L3 Policy layer)
+//   - Learner: dynamic route switching based on workload stats (v7-7)
 
 #ifndef HAKMEM_SMALLOBJECT_POLICY_V7_BOX_H
 #define HAKMEM_SMALLOBJECT_POLICY_V7_BOX_H
@@ -46,4 +47,58 @@ void small_policy_v7_init_from_env(SmallPolicyV7* policy);
 /// Get route kind name for debugging
 const char* small_route_kind_name(SmallRouteKind kind);
 
+// ============================================================================
+// Learner Stats (Phase v7-7)
+// ============================================================================
+
+/// Per-class stats for Learner
+typedef struct SmallLearnerClassStatsV7 {
+    uint64_t total_allocs;      // Total allocs for this class (all routes)
+    uint64_t v7_allocs;         // Allocs via v7 route
+    uint64_t v7_retires;        // Page retires from v7
+    uint32_t sample_count;      // Number of samples
+} SmallLearnerClassStatsV7;
+
+/// Aggregate Learner stats
+typedef struct SmallLearnerStatsV7 {
+    SmallLearnerClassStatsV7 per_class[8];  // C0-C7
+    uint64_t total_retires;                  // Total page retires
+    uint64_t eval_count;                     // Number of evaluations
+} SmallLearnerStatsV7;
+
+// ============================================================================
+// Learner API (Phase v7-7)
+// ============================================================================
+
+/// Record a page retire for Learner stats (called from ColdIface)
+/// @param class_idx: Size class of the retired page
+/// @param capacity: Capacity of the page (used as traffic proxy)
+void small_learner_v7_record_retire(uint32_t class_idx, uint64_t capacity);
+
+/// Record a page refill for Learner stats (called from ColdIface)
+/// @param class_idx: Size class of the refilled page
+/// @param capacity: Capacity of the page (used as traffic proxy)
+void small_learner_v7_record_refill(uint32_t class_idx, uint64_t capacity);
+
+/// Update policy from Learner stats (called periodically)
+/// Decision rule: if C5 alloc ratio > 30%, route C5 to v7, else MID_v3
+/// @param stats: Learner stats to evaluate
+/// @param policy_out: Policy to update
+void small_policy_v7_update_from_learner(
+    const SmallLearnerStatsV7* stats,
+    SmallPolicyV7* policy_out
+);
+
+/// Get current Learner stats snapshot (for debugging/OBSERVE)
+const SmallLearnerStatsV7* small_learner_v7_stats_snapshot(void);
+
+/// Force re-evaluation of policy from current stats
+void small_learner_v7_evaluate(void);
+
+/// Learner threshold for C5 route decision (default: 30%)
+#define SMALL_LEARNER_C5_THRESHOLD_PCT  30
+
+/// Evaluation interval (every N refills)
+#define SMALL_LEARNER_EVAL_INTERVAL     100
+
 #endif // HAKMEM_SMALLOBJECT_POLICY_V7_BOX_H