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tests/TC087-lz4-random-read.md

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+# Test Case: LZ4 Deterministic Random-Offset Reads
+
+**Test ID**: TC087-lz4-random-read
+
+**G5 fixture contract**: Use [G5-MANUAL-SETUP.md](G5-MANUAL-SETUP.md).
+Its generated paths, source comparisons, structured corruption offsets, and
+cleanup rules supersede placeholder examples in this file.
+**Category**: Compression
+**Priority**: High
+
+## Objective
+
+Verify non-sequential reads from deterministic offsets in an LZ4-compressed
+file and compare every returned byte with the source. `$RANDOM` and timing-only
+checks are not evidence of data correctness.
+
+## Fixture and Helper
+
+```sh
+work=$(mktemp -d /tmp/repo22-tc087.XXXXXX)
+tests/prepare_error_fixtures.sh "$work/fixtures"
+cc -O2 -Wall -Wextra -std=c17 tests/read_probe.c -o "$work/read_probe"
+dump.erofs --path=/compressed.bin -e "$work/fixtures/valid-lz4.erofs"
+```
+
+## FreeBSD Procedure
+
+```sh
+mkdir "$work/mnt"
+unit=$(mdconfig -a -t vnode -f "$work/fixtures/valid-lz4.erofs")
+mount -t erofs -o ro "/dev/$unit" "$work/mnt"
+size=$(stat -f %z "$work/fixtures/source/compressed.bin")
+test "$size" -gt 1052672
+
+index=0
+for offset in 0 4096 65536 1048576 $((size - 4096)); do
+  "$work/read_probe" pread "$work/mnt/compressed.bin" \
+    "$offset" 4096 "$work/guest-$index.bin"
+  "$work/read_probe" pread "$work/fixtures/source/compressed.bin" \
+    "$offset" 4096 "$work/source-$index.bin"
+  cmp "$work/source-$index.bin" "$work/guest-$index.bin"
+  index=$((index + 1))
+done
+
+umount "$work/mnt"
+mdconfig -d -u "${unit#md}"
+```
+
+## Expected Results
+
+All five fixed reads, including the final 4 KiB of the file, return exactly
+4096 bytes and compare equal to their corresponding source ranges. No
+performance ordering is asserted.