docs: the SchFS suite is red, and Gate 0 says why

Two failures found by running `make schfs-check` rather than by reading it, both
predating the current work -- confirmed by stashing the session's changes and
re-running to byte-identical output.

  * AddressSanitizer: 2121728 bytes leaked in 518 allocations, every one from
    md_palloc in tools/schfs_objtest.c, the test's own page allocator. The
    target exits non-zero, so the whole suite fails whatever the assertions say.
    The cost is not the memory -- it is that a real leak in the filesystem would
    now arrive as noise inside 2 MB of expected noise.

  * UndefinedBehaviorSanitizer: 31 misaligned accesses across obj.c, objw.c,
    attr.c and space.c, one root cause. Records are read by casting a pointer
    into a tree leaf, and a record's offset within a leaf is not a multiple of
    8. This works on x86, which is why it has never shown as a bug, and it is
    undefined in C: a compiler entitled to assume 8-byte alignment may emit an
    instruction that requires it, and the failure would then look like
    filesystem corruption rather than codegen.

Recorded as Gate 0 items rather than as nice-to-haves for one reason: a suite
that is red for known reasons stops being read, and then it is red for unknown
reasons too. guides/testing.md now says so up front, so nobody reads the [ok]
lines and ignores the exit code.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2

docs/plan/1.0.md

@@ -139,6 +139,46 @@ These are the galling ones — the replacement exists, is tested, and is unused.
       suite runs before DHCP binds and the `ENFILE` above made the refusal look
       real. A test asserting a failure has to say *which* failure.
 
+**The suite itself:**
+
+Both of these were found by running `make schfs-check` rather than by reading
+it, and both predate the current work — confirmed by stashing and re-running.
+They are here rather than filed as nice-to-haves because a suite that is red for
+known reasons stops being read, and then it is red for unknown reasons too.
+
+- [ ] **`make schfs-check` fails at baseline.** AddressSanitizer reports
+      **2121728 bytes leaked in 518 allocations**, every one of them from
+      `md_palloc` (`tools/schfs_objtest.c:84`) — the test's own page allocator,
+      which hands out pages for the allocation map and never frees them. The
+      target exits non-zero, so the *whole* SchFS suite is failing whatever the
+      assertions say.
+
+      The cost is not the leaked memory, it is that **the leak check is now
+      useless**: a real leak in the filesystem would arrive as noise inside
+      2 MB of expected noise. Fixing it means the test freeing what it
+      allocated, not suppressing the report — a suppression keeps the number
+      quiet and keeps the detector off.
+
+- [ ] **31 UndefinedBehaviorSanitizer errors**, all one root cause: records are
+      read straight out of a tree leaf by casting a pointer into the block, and
+      a record's offset within a leaf is not a multiple of 8. Sites:
+      `obj.c` (9), `objw.c` (11), `attr.c` (7), `space.c` (5), across
+      `schfs_dirent_rec`, `schfs_extent`, `schfs_extref`, `schfs_index_rec` and
+      `schfs_snap`.
+
+      **This is a real hazard, not sanitizer pedantry.** Unaligned access
+      happens to work on x86, which is why it has never shown as a bug — but it
+      is undefined in C, and a compiler that knows a pointer is 8-aligned is
+      entitled to emit an instruction that requires it. The failure would appear
+      under a different optimisation level or on a different architecture, and
+      would look like filesystem corruption rather than a codegen problem.
+
+      The fix that keeps the format unchanged is to stop casting: copy the bytes
+      into an aligned local with `memmove`, or declare the records packed so the
+      compiler stops assuming. Padding the records to 8 bytes would also work
+      and costs on-disk space — and is now a **format change**, which is what
+      the version policy above is for.
+
 **The identity item:**
 
 - [ ] **Boot from a USB disk.** The xHCI stack, bulk-only transport, SCSI and