Set vk_sub_in_frame under the submission lock from the place the submitting thread noted, so a thread about to submit no longer changes it under another thread's replay.

vk_sub_in_frame says which of its frame's submissions the one being recorded is; vk_memory.c sub_place files the mirror
pre-snapshot's statistics by it during the replay, on the replaying thread and its workers. vk_be_submit wrote it on
every submitting thread before submit_sync, outside sub_lock, so with the replay on the submitting threads another
thread entering a submit changed it under a replay in progress, and the replay filed its work at the other
submission's place. Each thread now notes the place in a thread-local (vk_be_submit, and replay_main for the
asynchronous replay), and vk_sync.c submit publishes it right after taking the lock for a submission with commands
(vk_sub_in_frame_publish, a weak no-op without the back end). Submissions without commands of their own (held work, the
present thread's blit) leave it as it was, as before. Performance heuristics only; no timing change.

Not reproduced before the change. Checks that passed: pass_cc_check on every runtime file (a header changed), no new
-Wall -Wextra warnings in vk_backend.c and vk_sync.c.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

runtime/vk.h

@@ -963,6 +963,9 @@ void vk_gpu_parts_log(uint64_t frame, uint64_t t0, uint64_t t1, double fence_ms)
 void vk_gtl_note(int kind, uint64_t sub_ns, uint64_t start_tick, uint64_t end_tick);
 void vk_gtl_log(uint64_t frame, int frames);
 extern int vk_sub_in_frame;   // replay: the submission being recorded is the frame's n-th (0 the first; vk_backend.c)
+// vk_sync.c submit, sub_lock held, for a submission with commands: vk_sub_in_frame takes the place in its frame the
+// submitting thread noted for it (vk_backend.c vk_be_submit, replay_main).
+void vk_sub_in_frame_publish(void);
 // Runs fn(arg) on the completion thread once fence is done on the GPU (event writes, counter reports, sync state).
 // Callbacks run in the order they were added, after those of earlier values; a value already done runs at once there.
 void vk_completion_add(uint64_t fence, void (*fn)(void *), void *arg);

runtime/vk_backend.c

@@ -634,7 +634,14 @@ static uint64_t submit_sync(const uint64_t *handles, int n) {
     return f;
 }
 
+// vk_sub_in_frame is the replay's: vk_sync.c submit sets it under the submission lock from the place the submitting
+// thread noted for its submission (vk_sub_in_frame_publish), so another thread about to submit cannot change it under
+// a replay in progress (vk_memory.c sub_place reads it there and on the replay workers). Submissions without commands
+// of their own (held work, the present thread's blit) leave it as it was.
 int vk_sub_in_frame;
+static _Thread_local int sub_place_next;   // this thread's next submission's place in its frame
+
+void vk_sub_in_frame_publish(void) { vk_sub_in_frame = sub_place_next; }
 
 static void replay_main(void *arg) {
     (void)arg;
@@ -650,7 +657,7 @@ static void replay_main(void *arg) {
         plat_cond_broadcast(&rcv);
         plat_mutex_unlock(&rl);
         if (it.kind == RI_SUBMIT) {
-            vk_sub_in_frame = sub_idx++;
+            sub_place_next = sub_idx++;
             uint64_t f = submit_sync(it.h, it.n);
             if (f != it.value)
                 rt_fatal("vk: replayed submission signalled %llu, queued as %llu", (unsigned long long)f,
@@ -933,7 +940,7 @@ static void vk_be_program_release(const prog_t *p) { replay_drain(DR_PROG_RELEAS
 static uint64_t vk_be_submit(const uint64_t *handles, int n) {
     vk_lowlat_submit_start();   // a frame's first submission: its simulation is over (nothing while low latency is off)
     if (!gfx_replay_async()) {
-        vk_sub_in_frame = __atomic_load_n(&nvn_submits_in_frame, __ATOMIC_RELAXED);   // the front end counts it up after the submit returns
+        sub_place_next = __atomic_load_n(&nvn_submits_in_frame, __ATOMIC_RELAXED);   // counted up after the submit returns
         return submit_sync(handles, n);
     }
     vk_sync_start();

runtime/vk_sync.c

@@ -1483,6 +1483,7 @@ static uint64_t submit(const uint64_t *handles, int n, const OwnCommands *own) {
     VkCtx *c = vk_ctx();
     plat_mutex_lock(&sub_lock);
     vk_present_frames_owed();   // frames presented while another thread replayed close before this replay begins
+    if (n > 0 && !own) vk_sub_in_frame_publish();   // this submission's place in its frame, for the replay
     vk_mem_dirty_submit();   // NX2NAVI_TRACE=perf: what a mirror would upload before this submit
     uint64_t fence = __atomic_load_n(&issued, __ATOMIC_ACQUIRE) + 1;
     cur_fence = fence;
@@ -1581,8 +1582,10 @@ int vk_sync_try_locked(void (*fn)(void)) {
     return 1;
 }
 
-// vk_backend.c's, which runs the frames' bookkeeping (vk_frame_owed.h); builds without the back end have none.
+// vk_backend.c's, which run the frames' bookkeeping (vk_frame_owed.h) and set the place in the frame of the submission
+// being recorded; builds without the back end have neither.
 WEAK void vk_present_frames_owed(void) {}
+WEAK void vk_sub_in_frame_publish(void) {}
 
 // st_lock held: p at the end of the queue *q.
 static void pending_push(Pending **q, int *head, int *n, int *cap, Pending p) {