gh-151424: Fix impossible stack traces in RemoteUnwinder(..., cache_frames=True) by copying chunks on cache miss (GH-151426)

(cherry picked from commit 6ce088e)

Co-authored-by: Maurycy Pawłowski-Wieroński <maurycy@maurycy.com>

Author: maurycy

Misc/NEWS.d/next/Library/2026-06-13-04-11-00.gh-issue-151426.f2V67e.rst

@@ -0,0 +1,4 @@
+Fix impossible stack traces (callers and callees cross called, orphans and
+incorrect lines) in the Tachyon profiler when caching frames, by snapshotting
+the stack chunks before walking the frame chain on a cache miss. Patch by
+Maurycy Pawłowski-Wieroński.

Modules/_remote_debugging/frames.c

@@ -580,6 +580,14 @@ collect_frames_with_cache(
         return full_hit < 0 ? -1 : 0;
     }
 
+    assert(ctx->chunks != NULL);
+
+    if (ctx->chunks->count == 0) {
+        if (copy_stack_chunks(unwinder, ctx->thread_state_addr, ctx->chunks) < 0) {
+            PyErr_Clear();
+        }
+    }
+
     Py_ssize_t frames_before = PyList_GET_SIZE(ctx->frame_info);
 
     if (process_frame_chain(unwinder, ctx) < 0) {