Fix Conv LHS packing padding/uninitialized ptrs V2 (#27215)

### Description

Refer to V1 of the fix here:
#27214

This PR includes all fixes from the V1 PR + logic to invalidate the lhs
cache pointers in case the pad buffer's underlying buffer has changed
due to a resize. The ARM team will look at potentially enhancing this
logic after the 1.24.0 release.

### Motivation and Context
Fix #26669

Author: hariharans29

onnxruntime/core/mlas/lib/kleidiai/convolve_kleidiai.cpp

@@ -395,6 +395,12 @@ static std::shared_ptr<const void*[]> LhsPtrFill(const size_t ci, const size_t i
     auto lhs_ptrs = std::shared_ptr<const void*[]>(new const void*[lhs_ptrs_k * lhs_ptrs_m],
                                                 std::default_delete<const void*[]>());
 
+    // Initialize all padding entries. For partial tiles (m < m_step),
+    // the kai LHS packing kernel may still read pointer entries beyond the logically
+    // filled 'm' positions. Leaving these uninitialized can cause non-deterministic
+    // reads and corrupt packed LHS data.
+    auto lhs_ptrs_ = lhs_ptrs.get();
+    std::fill(lhs_ptrs_, lhs_ptrs_ + (lhs_ptrs_k * lhs_ptrs_m), reinterpret_cast<const void*>(&pad_ptr[0]));
 
     auto ih_out_size = ComputeConvOutSize(ih, kh, padding, 1);
     auto iw_out_size = ComputeConvOutSize(iw, kw, padding, 1);
@@ -430,7 +436,6 @@ static std::shared_ptr<const void*[]> LhsPtrFill(const size_t ci, const size_t i
     };
 
     size_t m_{0};
-    auto lhs_ptrs_ = lhs_ptrs.get();
     for (size_t ih_ = 0; ih_ < ih_out_size; ih_ += sh) {
         for (size_t iw_ = 0; iw_ < iw_out_size; iw_ += sw, ++m_) {
             size_t k_{0};
@@ -460,7 +465,23 @@ static std::unique_ptr<std::byte[]> LhsPackImageDataSme(const size_t ci, const s
         // figure out how many blocks needed to correctly fill padding
         padsize = ((ci + padsize - 1) / padsize) * padsize;
     }
-    static std::vector<float>pad_ptr(padsize, 0.f);
+
+    // pad_ptr must be at least 'ci' floats for padding pixels.
+    // Using a thread_local grow-only buffer to avoid cross-thread interference and ensure sizing is correct.
+    thread_local std::vector<float> pad_ptr;
+    const float* old_pad_ptr = pad_ptr.data();
+    bool has_pad_ptr_changed = false;
+
+    if (pad_ptr.size() < padsize) {
+        pad_ptr.resize(padsize, 0.f);
+        if (pad_ptr.data() != old_pad_ptr) {
+            has_pad_ptr_changed = true;
+        }
+    } else {
+        // Ensure any previously-used region remains zeroed (grow-only means it should already be zeros,
+        // but keep this explicit for safety).
+        std::fill(pad_ptr.begin(), pad_ptr.end(), 0.f);
+    }
 
     LhsCacheKey key = {
         ci, ih, iw,
@@ -481,6 +502,16 @@ static std::unique_ptr<std::byte[]> LhsPackImageDataSme(const size_t ci, const s
     // Cache of computed lhs ptr offsets.  thread_local to prevent interference from parallel sessions.
     thread_local std::unordered_map<LhsCacheKey, std::shared_ptr<const void*[]>> lhs_ptrs_cache;
 
+    if (has_pad_ptr_changed)
+    {
+        // If the pad buffer was resized and a re-allocation has occurred, the cached lhs ptrs are invalid as they
+        // would be referencing the old pad buffer.
+        // See discussion in https://github.com/microsoft/onnxruntime/pull/27214.
+        // TODO(hasesh / JonathanC-ARM): A better approach would be to include the pad buffer address in the cache key
+        // or any other approach that would reduce unnecessary cache invalidations.
+        lhs_ptrs_cache.clear();
+    }
+
     std::shared_ptr<const void*[]> lhs_ptrs;
     if (auto found = lhs_ptrs_cache.find(key); found != lhs_ptrs_cache.end()) {
         lhs_ptrs = found->second;