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server: auto-discard reload-loop checkpoints (frontier-contradicted) #1021

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server: auto-discard reload-loop checkpoints (frontier-contradicted) #1021

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46 changes: 43 additions & 3 deletions ds4_server.c
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Original file line number Diff line number Diff line change
Expand Up @@ -9188,6 +9188,8 @@ struct server_slot {
live_tool_state anthropic_live;
visible_live_state thinking_live;
int continued_last_store_tokens;
char disk_reload_path[128]; /* last disk-restored file (repeat-loop guard) */
int disk_reload_frontier; /* its frontier; same file+depth twice = dead tail */

job *assigned;
job *running;
Expand Down Expand Up @@ -10511,6 +10513,27 @@ static void kv_cache_slot_restore_suppressed(server_slot *slot,
}
}

/* Reload-loop guard: a disk checkpoint restored twice by the same slot at
* the same frontier proves its tail can never match future prompts'
* re-tokenizations (text-keyed tiers validate text, not tokens). Discard it
* exactly like the prefill-failed path does and let the retry land on the
* next candidate or a cold rebuild, which rewrites fresh under the key. */
static bool kv_cache_reload_repeat(server *s, server_slot *slot,
const char *path, int frontier) {
if (!slot || !path || !slot->disk_reload_path[0]) return false;
if (slot->disk_reload_frontier != frontier ||
strcmp(slot->disk_reload_path, path) != 0) return false;
server_log(DS4_LOG_KVCACHE,
"ds4-server: kv cache discarded reason=frontier-contradicted file=%s",
path);
pthread_mutex_lock(&s->kv_mu);
unlink(path);
pthread_mutex_unlock(&s->kv_mu);
slot->disk_reload_path[0] = '\0';
slot->disk_reload_frontier = 0;
return true;
}

static void kv_cache_discard_failed_disk_entry(server *s, server_slot *slot,
const char *path) {
if (!s || !slot || !path) return;
Expand Down Expand Up @@ -12435,6 +12458,10 @@ static void generate_job_inner(server *s, server_slot *slot, job *j) {
j->req.image_count, cached, prompt_for_sync->len);
}
if (cached == 0) slot->continued_last_store_tokens = 0;
if (cached > 0 && cache_source && cache_source[0] != 'd') {
slot->disk_reload_path[0] = '\0';
slot->disk_reload_frontier = 0;
}
if (!multimodal && s->kv.enabled && cached == 0 &&
old_pos >= s->kv.opt.min_tokens) {
/* Loading a disk snapshot replaces the live Metal session. Persist the
Expand All @@ -12443,10 +12470,23 @@ static void generate_job_inner(server *s, server_slot *slot, job *j) {
kv_cache_store_current(s, slot, "evict");
}
if (!multimodal && cached == 0) {
disk_cached = kv_cache_try_load(s, slot, &j->req, &effective_prompt,
&disk_cache_path,
&disk_cache_ext_flags);
for (int kv_reload_try = 0; kv_reload_try < 2; kv_reload_try++) {
disk_cached = kv_cache_try_load(s, slot, &j->req, &effective_prompt,
&disk_cache_path,
&disk_cache_ext_flags);
if (disk_cached > 0 && kv_reload_try == 0 &&
kv_cache_reload_repeat(s, slot, disk_cache_path, disk_cached)) {
free(disk_cache_path);
disk_cache_path = NULL;
disk_cached = 0;
continue;
}
break;
}
if (disk_cached > 0) {
snprintf(slot->disk_reload_path, sizeof(slot->disk_reload_path),
"%s", disk_cache_path ? disk_cache_path : "");
slot->disk_reload_frontier = disk_cached;
cached = disk_cached;
cache_source = "disk-text";
prompt_for_sync = &effective_prompt;
Expand Down