The .bif format was bumped 1->2->3 internally across this development cycle, but
the last PUBLIC commit (d56bdbf, release v0.11.x) shipped IFACE_VERSION = 1 with
COMPILER_ID +bif1. None of the intermediate v2/v3 layouts ever reached a public
reader, so the cumulative format change since v1 is a SINGLE public step: collapse
it to v2.
- IFACE_VERSION 3 -> 2; comment now lists all the META/record additions made this
cycle under v2 (ImplUsedUnits + HasInitialization, block local var decls,
Exit value, parameter defaults, free-routine ResolvedQbeName, generic-class
template properties, TRoutineSig vtable facts).
- COMPILER_ID stays blaise-0.12.0-SNAPSHOT+bif2 (now matches IFACE_VERSION).
- Magic-string test updated to expect 'BLAISE-IFACE 2'.
v1 .bif written by v0.11.x are rejected and recompiled from source, as intended.
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