The listing showed end_coroutine as the left-hand side of 34 comparisons disc-wide.
That is impossible -- it returns no value a script can test -- so it was the bug
reporting itself.
The recorded fix ("set special[0] only for built-ins that write [phase+164]") is
REFUTED. end_coroutine's handler 0x82272624 is `addi r11,r0,1 ; addi r3,r0,3 ;
stw r11,164(r31)` -- it DOES write [phase+164], so that filter would have kept it.
Reading the handler before writing the filter is what caught this.
The real cause: end_coroutine returns 3, which DESTROYS the thread. Execution does
not continue past it, so the instructions following it in the flat stream belong to
a different routine and every tracked value is stale. The linear walk that makes
the decode possible is exactly what walks across that boundary.
A/B over all 28 stages, 7563 sites, resetting the tracker at end_coroutine:
sites whose operands change 34 (0.45%)
LHS = end_coroutine, before -> after 34 -> 0
left as an explicit unknown 34 (0.45%)
The two counts being equal is the result: the leak was confined to exactly the sites
that displayed the impossible value, so the other 7529 conditions were never
affected. Those 34 now print "<unknown: reached after a coroutine boundary>".
Not done, and said so: their RHS is still exact and the LHS is recoverable by seeding
the tracker at coroutine entries, whose targets are staged slot 0 of start_coroutine.
data/isl-stage02-conditions.txt regenerated; calls and phase-ends both byte-identical.
1ac9aa1d7d