docs(technical-debt): name the SPIR-V rule behind keeping the loop back edge

Co-Authored-By: Claude <noreply@anthropic.com>

docs/dev/TechnicalDebt.md

@@ -105,7 +105,7 @@ Throughout the project, every function at every stage either **does exactly what
 - [sceAudiodecDecode](../../core/libs/prx/libSceAudiodec/src/Codecs.cpp) (libSceAudiodec) - a raw M4AAC stream carries no channel configuration, so the decoder tries the mono/stereo configuration and then configurations 3 to 7 within `ui_max_channels` until one decodes the first access unit, and keeps that one. No reference documents how the library picks the layout (shadPS4 maps the channel count straight to the configuration; SharpProspero only describes the maximum). With the stereo configuration a mono raw stream decodes as 2 channels, so 2 is reported, not 1
 - [sceAudio3dObjectReserve](../../core/libs/prx/libSceAudio3d/Export.cpp) (libSceAudio3d) - object ids, the `max_objects` limit and the checks of `sceAudio3dObjectReserve` and `sceAudio3dObjectUnreserve` follow [shadPS4](https://github.com/shadps4-emu/shadPS4) (PS4), the only reference with a body: ids count up from 1 per port, skipping 0, 0xFFFFFFFF and ids in use, and a failed reserve writes 0xFFFFFFFF
 - [s_sethalt](../../core/shader/recompiler/Translation/src/ScalarInstructions.cpp) (core/shader/recompiler) - with SIMM16[0] clear it is a no-op: the RDNA 2 ISA guide describes that value as resuming a halted wave, and a wave that executes it is not halted; measured on a gfx1035 (RDNA 2) wave: `s_sethalt 0` followed by a VALU op completes and gives the normal result. Only SIMM16[0] is read; with it set the instruction throws
-- [s_subvector_loop_begin and s_subvector_loop_end](../../core/shader/recompiler/Translation/src/ControlFlowInstructions.cpp) (core/shader/recompiler) - follow AMD's RDNA 2 instruction set reference and a gfx1036 (wave64) measurement, pinned in [SubvectorLoop.cpp](../../core/libs/prx/libSceAgcDriver/tests/execution/SubvectorLoop.cpp); `S0` in the end instruction's `elif(S0 == 0)` is read as its SGPR operand. A wave32 shader and a destination other than an SGPR throw because neither is measured. Measured on PC RDNA2 (Radeon 610M), not on a PS5. The [specialization pass](../../core/shader/recompiler/SpirvBackend/src/SpirvSpecialization.cpp) keeps a constant-condition branch whose untaken target is a loop header, since folding it removes the loop's back edge and the NVIDIA driver 615.78.08 crashes compiling such a loop; a loop whose back-edge block becomes unreachable in another way is not handled
+- [s_subvector_loop_begin and s_subvector_loop_end](../../core/shader/recompiler/Translation/src/ControlFlowInstructions.cpp) (core/shader/recompiler) - follow AMD's RDNA 2 instruction set reference and a gfx1036 (wave64) measurement, pinned in [SubvectorLoop.cpp](../../core/libs/prx/libSceAgcDriver/tests/execution/SubvectorLoop.cpp); `S0` in the end instruction's `elif(S0 == 0)` is read as its SGPR operand. A wave32 shader and a destination other than an SGPR throw because neither is measured. Measured on PC RDNA2 (Radeon 610M), not on a PS5. The [specialization pass](../../core/shader/recompiler/SpirvBackend/src/SpirvSpecialization.cpp) keeps a constant-condition branch whose untaken target is a loop header, since folding it removes the loop's back edge, which SPIR-V requires exactly once per loop header (SPIRV-Tools rejects the module and the NVIDIA driver 615.78.08 crashes compiling it); a loop whose back-edge block becomes unreachable in another way is not handled
 - [AMPR WriteAddressFromCounterPairOnCompletion](../../core/libs/prx/libSceAmpr/Export.cpp) (libSceAmpr) - the pair of an even counter n is assumed to give counter n in the low 32 bits and n + 1 in the high 32 bits. Wait compare values, wait flush and counter index ranges follow the [ampr_emu](https://github.com/drakmor/ampr_emu) reimplementation; the flush is accepted and has no effect, as commands run in order
 - [AMPR command sizes](../../core/libs/prx/libSceAmpr/Export.cpp) (libSceAmpr) - commands use the emulator's own encoding with an 8-byte header, so `Nop(n)` takes 8 + 4n bytes where the console record is n dwords including its header (`NopWithData(n)`: (n + 1) dwords). The measure functions agree with the appended sizes, but a title that pads to an exact offset or the end of the buffer with `Nop(remaining / 4)` gets `SCE_AMPR_ERROR_BUFFER_FULL` or a shifted offset. The at-start flag of the `_04_00` writes is ignored; commands run in order, each after the previous one completes
 - [AMPR object layout and compact gathers](../../core/libs/prx/libkernel/Apr/include/AprCommandBuffer.hpp) - the 24-byte object and offsets (type 0, cursor 4, count 8, capacity 12, pointer 16) follow [ampr_emu assertions](https://github.com/drakmor/ampr_emu/blob/cfa85df379f6eeeb165d7badf9b648e266fe77b7/include/ampr_emu_command_buffer_types.h#L138-L143) and its [C declaration](https://github.com/drakmor/ampr_emu/blob/cfa85df379f6eeeb165d7badf9b648e266fe77b7/include/ampr.h#L41-L47). AnyPS5 represents the 32-bit type word as low 16-bit type and high 16-bit recording flags. Command encoding is AnyPS5 internal: opcode 29 and three 32-bit words encode the high offset byte, length minus one and low offset word. The 12-byte size reduces HFW's 1 MiB buffer pressure; it is not a claim about console opcode encoding. Existing 40-bit offsets and lengths 1 through 2^32 are retained; console behavior outside those limits is unverified.