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docs/pre13-low-e.md

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+# Pre13 L-E
+
+The BSD-only miscellaneous `erofs_defs.h` has been removed. Its three owners
+now keep their constants in the files responsible for those values:
+
+- `super.c` owns the named private CRC32C seed.
+- `dir.c` uses `sizeof(struct erofs_dirent)` directly.
+- `decompressor_lz4.c` owns its private LZ4 format constants.
+
+The former header had exactly these three production source consumers. All
+constant values and use-site expressions remain equivalent. Two already
+retired userspace decompression test files still referenced the removed header;
+they were deleted because they also depended on obsolete userspace ABIs and did
+not compile independently. No current source or test entry retains the old
+include. The LZ4 macro names remain private to `decompressor_lz4.c`; the former
+shared CRC and dirent macro names have no current consumers. The current
+architecture file was updated; historical reports were not changed.
+
+No KLD build, QEMU, smoke, or feature test was run for this batch.