Tiny: fix header/stride mismatch and harden refill paths

- Root cause: header-based class indexing (HEADER_CLASSIDX=1) wrote a 1-byte
  header during allocation, but linear carve/refill and initial slab capacity
  still used bare class block sizes. This mismatch could overrun slab usable
  space and corrupt freelists, causing reproducible SEGV at ~100k iters.

Changes
- Superslab: compute capacity with effective stride (block_size + header for
  classes 0..6; class7 remains headerless) in superslab_init_slab(). Add a
  debug-only bound check in superslab_alloc_from_slab() to fail fast if carve
  would exceed usable bytes.
- Refill (non-P0 and P0): use header-aware stride for all linear carving and
  TLS window bump operations. Ensure alignment/validation in tiny_refill_opt.h
  also uses stride, not raw class size.
- Drain: keep existing defense-in-depth for remote sentinel and sanitize nodes
  before splicing into freelist (already present).

Notes
- This unifies the memory layout across alloc/linear-carve/refill with a single
  stride definition and keeps class7 (1024B) headerless as designed.
- Debug builds add fail-fast checks; release builds remain lean.

Next
- Re-run Tiny benches (256/1024B) in debug to confirm stability, then in
  release. If any remaining crash persists, bisect with HAKMEM_TINY_P0_BATCH_REFILL=0
  to isolate P0 batch carve, and continue reducing branch-miss as planned.

core/box/ace_pool_connector.h

@@ -0,0 +1,70 @@
+// ace_pool_connector.h - ACE-Pool Connection Box
+// Box Theory: Single Responsibility - Validate and route ACE ↔ Pool connections
+//
+// Purpose:
+//   - Make ACE-Pool connection VISIBLE and VALIDATED
+//   - Centralize error handling and logging
+//   - Health check API for diagnostics
+//
+// Responsibilities:
+//   ✅ Validate Pool is initialized before ACE uses it
+//   ✅ Log connection status (success/failure/reason)
+//   ✅ Provide health check API
+//   ❌ NOT responsible for: allocation logic, size rounding, or memory management
+//
+// Box Boundaries:
+//   INPUT:  ACE requests allocation from Pool (size, site_id)
+//   OUTPUT: Pool allocation result (ptr or NULL) + reason code
+//   ERROR:  Clear error messages (not silent failures!)
+
+#ifndef ACE_POOL_CONNECTOR_H
+#define ACE_POOL_CONNECTOR_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+// ============================================================================
+// Box API: ACE-Pool Connection
+// ============================================================================
+
+// Connection status codes
+typedef enum {
+    ACE_POOL_OK = 0,           // Connection healthy
+    ACE_POOL_NOT_INIT,         // Pool not initialized
+    ACE_POOL_NO_PAGES,         // Pool has no pre-allocated pages
+    ACE_POOL_WRAPPER_BLOCKED,  // Wrapper protection blocking
+    ACE_POOL_SIZE_MISMATCH,    // Size not in Pool range
+    ACE_POOL_ALLOC_FAILED,     // Pool allocation returned NULL
+} AcePoolStatus;
+
+// Health check result
+typedef struct {
+    int pool_initialized;      // 1 if Pool is initialized
+    int ace_enabled;           // 1 if ACE is enabled
+    int wrap_l2_enabled;       // 1 if WRAP_L2 is enabled
+    int bridge_class_5_size;   // Size of Bridge class 5 (40KB expected)
+    int bridge_class_6_size;   // Size of Bridge class 6 (52KB expected)
+    int preallocated_pages;    // Number of pre-allocated pages (should be > 0)
+    AcePoolStatus status;      // Overall status
+    const char* message;       // Human-readable status message
+} AcePoolHealth;
+
+// ============================================================================
+// Box Functions
+// ============================================================================
+
+// Get health status (for debugging and monitoring)
+AcePoolHealth ace_pool_get_health(void);
+
+// Validate connection is ready (called by ACE before using Pool)
+// Returns: 1 if ready, 0 if not (sets reason code)
+int ace_pool_validate_connection(AcePoolStatus* out_status);
+
+// Connect ACE to Pool (wrapper around hak_pool_try_alloc with validation)
+// Returns: Allocated pointer or NULL (logs reason if NULL)
+void* ace_pool_try_alloc(size_t size, uintptr_t site_id, AcePoolStatus* out_status);
+
+// Print health status (for debugging)
+void ace_pool_print_health(void);
+
+#endif // ACE_POOL_CONNECTOR_H