swung0x48 767e6c8084 [MG_Pipe, MG_Test, docs] (P7): the reverse channel is nine callbacks, and the prose says what the tree does ...

P3b/P4b espryt D1 slice 3, landing under the P7 program (notes/p7/PLAN-PH-P34B-P7.md
§1.2 row "XFB scatter" item 3; CONTRACT-P7.md §139 already records the deletion).

Plan B section 7.1 named ten reverse-channel callbacks. The tenth, OnXfbScatterReady,
belonged to a design the tree does not have: plan B put the XFB scatter on the CLIENT - the
server would hand back the packed scratch and the client would run the patch loop over its
own shadow - so something had to tell the client the layout. P5c/P5f went the other way,
and the declaration was left behind with zero producers, zero consumers and no EventKind of
its own, while the static_assert beside kMGPipeCallbackCount made it look load-bearing.
Deleted; kMGPipeCallbackCount 10 -> 9.

Three pieces of prose that still described the old design go with it. MGPipeCallbacks.h's
own header said "ten callbacks", and now says nine and why the tenth went.
MGPipeTypes.h's MGPXfbAccounting comment said the scatter "is a read-modify-write of the
client's shadow and lives there"; it lives on the server's staged shadow, and nothing about
the scatter crosses in that record. ARCHITECTURE.md §8.5, titled "XFB scatter 搬到 client",
is rewritten to what the tree does: the pre-capture bytes are the server's own staged
shadow (rule C, since MappedData() on the apply thread is Fatal{RoleViolation,
"buffer-legacy-arm"}), the reconciled whole range comes back as one OnBufferWriteback
sliced against SEG_EVENT's capacity (slice 2), and an orphaned target is a legal one (slice
1). Its row in §8.1's callback table goes too - leaving it would be a new staleness rather
than an inherited one.

PipeCatalogue.ReverseChannelHasTenCallbacks now asserts 9. The CASE NAME IS DELIBERATELY
NOT RENAMED: G2/G14 say the ctest name set only ever grows, so renaming would delete a name
the gate watches. The count it asserts is what has to be right and the comment carries the
number.

Red-once (R-16): with the member and the count restored the case fails with
"kMGPipeCallbackCount Which is: 10 / 9u Which is: 9", which is what makes the struct's
shrink a measured fact - the static_assert beside the constant only proves the two agree
with each other.

G1 matters for this slice in particular, because MGPipeCallbacks.h is included from
MG_Backend and the struct is NOT behind MOBILEGL_BUILD_DISAGGREGATED, so
sizeof(gMGPipeCallbacks) really does shrink by 8 bytes in the pull build. The shrink is in
.bss and nothing indexes the table by count: .text is still 0xa52203 and both nm lists are
byte-identical to ~/w7/p7-before.

Gates: integration-split 202/202, integration-spawn 118/118, integration-tcp 121/121,
ctest -L unit 2408/2408, spawn_lane_parity / fatal_census / link_ratchet (186, unchanged)
green.

2026-09-22 16:41:54 -04:00

..

Disaggregated

[MG_Pipe, MG_Test, docs] (P7): the reverse channel is nine callbacks, and the prose says what the tree does

2026-09-22 16:41:54 -04:00