fix(debug): make ptrace sessions reliable on Go tracees

CHANGELOG.md

@@ -28,6 +28,14 @@ Unreleased changes on the `development` branch.
   the hits per instruction and reports the executed instructions with
   their hit counts, with the label coverage derived from the same run.
   Expect the run to slow to ptrace speed.
+- **Debugger reliability fixes.**  The ptrace session now drains runtime
+  signal-delivery-stops (a Go tracee reports SIGURG preemption to the
+  tracer) instead of mistaking them for the launch barrier, pins the
+  tracer thread the fork ran on (ptrace requests from another thread fail
+  with ESRCH), prefers the debuggee's reported code base over an RWX scan,
+  and single-steps over a hit breakpoint so resuming cannot re-trap on the
+  same instruction.  A ptrace integration test
+  (`debug/ptrace_integration_test.go`) drives a real session end to end.
 - **FP register display on riscv64 and loong64.**  The debugger `regs`
   command shows the 32 FP registers plus fcsr (and fcc on loong64) via
   `PTRACE_GETREGSET`, where it previously printed nothing.