Record the fuzzdata seeds in the README, and the sqllogictest decision

The one remaining item of milestone 7 is not being built, so PLAN.md should
say why rather than leave it looking pending: everything the tests download
is pinned by SHA-256, and sqllogictest has no stable release artifact to
pin.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JzBeCg7rjweVW3uGPg5G7T

Author: claude

.github/workflows/difftest.yml

@@ -3,8 +3,9 @@
 # This is separate from CI because it downloads the pinned SQLite release
 # and compiles it, which the ordinary test run must not depend on. It is the
 # only thing that exercises error fidelity at scale: the vendored corpus is
-# almost all valid SQL, so mutating it is how divergent messages and offsets
-# get found.
+# almost all valid SQL, so mutating it -- and mutating the ~36k inputs of
+# SQLite's own fuzzdata databases, which are the opposite -- is how
+# divergent messages and offsets get found.
 name: difftest
 
 on:

PLAN.md

@@ -180,7 +180,11 @@ domain):
   merely "terminate without panic".)*
 - **sqllogictest** (~millions of statements, license: "no attribution
   required") — bulk smoke corpus; low grammar diversity. Optional, behind an
-  env-var-gated test, not vendored.
+  env-var-gated test, not vendored. *(Not built. Everything else the tests
+  download is pinned by SHA-256; sqllogictest is distributed as a Fossil
+  checkout with no stable release artifact to pin, and what it would add is
+  volume of ordinary SELECTs — the axis `cmd/difftest` is already furthest
+  along. Worth revisiting only if a pinnable mirror appears.)*
 
 Tooling (`cmd/regenerate`):
 

README.md

@@ -63,8 +63,10 @@ so conformance is defined three ways, in decreasing order of authority:
 Plus two searches for cases the corpus does not contain: a fuzz target
 asserting that arbitrary bytes terminate without panicking, that a rejection
 is always a `*parser.Error`, and that anything accepted survives the round
-trip; and `cmd/difftest`, which mutates corpus SQL one token at a time and
-checks meyer against a live SQLite build, message and byte offset included.
+trip; and `cmd/difftest`, which checks meyer against a live SQLite build,
+message and byte offset included, over corpus SQL and the ~36k inputs of
+SQLite's own `fuzzdata` databases — each one directly and then mutated a
+token at a time.
 
 ## Acknowledgments