Hojun-Cho
b630a7cf20
Re-key the append() lowering from BP-displacement assumptions onto a resolver-provided header PLACE (task #15, the add_thread hard-blocker; cgplaceaddr's third consumer after C1/C1.25). One mirrored choke-point, two failure modes: cstage 0-defaulted sn_off for any non-ident target, so 0(BP)/8(BP) became the "slice header" and rt_ensure corrupted the CALLER frame (SIGSEGV); wwstage cgappend silently emitted nothing (gate-blind cs!=ww). cg_append_grow/cg_append_slot (mirror cgappendgrow/cgappendslot) factor the 5 grow + 5 slot header-access sites. Ident-local targets keep the legacy BP-disp emission byte-identical (probed across all 9 existing source shapes, before/after .s). Non-ident targets resolve once through cgplaceaddr and spill the header address to an @apphdrscr slot: rt_ensure may realloc .ptr but never moves the header, so the slot stays valid; every access reloads from it. The slot is allocated fresh per append SITE, not cached per fn: a nested append-through-pointer inside a value expression (match-yield arm) spills its own resolve, and a shared slot would hand the outer grow/slot reloads the inner target's header — silent cross-slice corruption (pinned by the reentrant_value row). Indirect mode keys esz/element-kind/load-op off the checker-stamped target tinfo (no declared tnode behind `*p`; the #209/#211 discipline). Unwired target places die LOUD "#15: append() target place unsupported (rule-7)" on BOTH stages — the silent-corruption class is closed by construction. The FA4/#35 boundary is unchanged: non-ident spread SOURCES stay loud (pinned by a reject row). Surfaced pre-existing checker divergence filed as task #34 (wwstage rejects global slice-lit let). test/wcc/806: 14 runtime rows (element kinds x target shapes, spread, narrow-signed spread load, cap-crossing realloc loop with branched callee + caller-frame sentinels, deref-spine target, nested-append reentrancy, direct-arm neutrality pin) + 2 exact-text reject rows, both drivers + per-row cs==ww asm byte-id.