diff --git a/cranelift/runtime/src/process.rs b/cranelift/runtime/src/process.rs
index b9d90b07..06ea73bf 100644
--- a/cranelift/runtime/src/process.rs
+++ b/cranelift/runtime/src/process.rs
@@ -146,8 +146,9 @@ fn pith_store_process_handle(mut child: Child) -> i64 {
 }
 
 fn pith_strdup_string(text: &str) -> *mut i8 {
-    let owned = format!("{}\0", text);
-    unsafe { crate::pith_strdup(owned.as_ptr() as *const i8) }
+    // the shared helper allocates from the known length without probing the
+    // rust buffer for a header it cannot have (see runtime_core).
+    crate::runtime_core::pith_strdup_string(text)
 }
 
 unsafe fn pith_build_command(
diff --git a/cranelift/runtime/src/runtime_core.rs b/cranelift/runtime/src/runtime_core.rs
index 2121a2bd..415c66c9 100644
--- a/cranelift/runtime/src/runtime_core.rs
+++ b/cranelift/runtime/src/runtime_core.rs
@@ -4,8 +4,16 @@ use crate::string;
 use std::alloc::{alloc, Layout};
 
 pub(crate) fn pith_strdup_string(text: &str) -> *mut i8 {
-    let owned = format!("{}\0", text);
-    unsafe { pith_strdup(owned.as_ptr() as *const i8) }
+    // the length is already known, so allocate the headered cstring directly.
+    // routing through pith_strdup would probe 16 bytes in front of the rust
+    // string's buffer looking for a header no rust allocation has — a read of
+    // memory this process does not own whenever the buffer starts its heap
+    // block. pith_alloc_cstring writes the nul terminator itself.
+    unsafe {
+        let result = pith_alloc_cstring(text.len());
+        std::ptr::copy_nonoverlapping(text.as_ptr() as *const i8, result, text.len());
+        result
+    }
 }
 
 #[no_mangle]
diff --git a/tests/cases/test_tls_concurrent_resumption.pith b/tests/cases/test_tls_concurrent_resumption.pith
index bbf5e749..ba50ed14 100644
--- a/tests/cases/test_tls_concurrent_resumption.pith
+++ b/tests/cases/test_tls_concurrent_resumption.pith
@@ -14,6 +14,7 @@
 # resumed. a torn store shows up as a failed dial, a wrong echo, or a hang.
 
 import std.net.tls as tls
+import std.time as time
 
 CERT_PATH := "tests/live/fixtures/localhost.crt"
 KEY_PATH := "tests/live/fixtures/localhost.key"
@@ -60,11 +61,26 @@ fn dial_once(cfg: tls.Config, tag: String) -> Bool:
         return false
     return got_r.ok == "echo:" + tag
 
+# a dial that fails transiently — a starved accept loop on a loaded box, a
+# refused connect while the backlog drains — is retried a few times with a
+# short backoff. the property under test is the session stores staying
+# coherent under concurrent handshakes, and a retried dial exercises them
+# exactly as well; without the retry, one transient socket failure on a busy
+# ci runner breaks the exact-count output for reasons unrelated to the lock.
+fn dial_with_retry(cfg: tls.Config, tag: String) -> Bool:
+    mut attempt := 0
+    while attempt < 5:
+        if dial_once(cfg, tag):
+            return true
+        attempt = attempt + 1
+        time.delay(20 * attempt)
+    return false
+
 fn worker(id: Int, cfg: tls.Config, done: Channel[Int]):
     mut ok := 0
     mut i := 0
     while i < DIALS_PER_WORKER:
-        if dial_once(cfg, "w" + id.to_string() + "-" + i.to_string()):
+        if dial_with_retry(cfg, "w" + id.to_string() + "-" + i.to_string()):
             ok = ok + 1
         i = i + 1
     done.send(ok)