feat(kb): add a maintained consistency check, and fix what it found

kb_report/0 and kb_consistent/0 enumerate kb_error/1 solutions across four
classes: domain integrity (layers, concerns and dependency edges name real
crates), layering (no inverted crate dependency), rule soundness (rules must
REJECT a sentinel drawn from no declared domain), and functional keys (a
predicate declared functional/1 must not carry conflicting values for one
key), plus cross-references between recorded work.

Wired into CI as a third job, since kb.pl is executable knowledge and
deserves checking like code.

Proving the checker fires found two bugs in it. depends_transitively/2 was a
naive transitive closure, so illegal_dependency/2 — whose entire purpose is
detecting an inverted edge — looped forever on exactly that input; it now
carries a visited set. And the :- discontiguous declarations added in the
previous commit are a syntax error in trealla, which wants the parenthesized
form; the MCP server had silently tolerated them, so validating kb.pl through
the session alone had hidden it.

Every check class is now verified by injecting the fault it targets and
confirming it is reported, then reverting. A consistency check that has only
ever said "consistent" has demonstrated nothing.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V69PGQfMJuGRmtSWpfVAqn

.github/workflows/ci.yml

@@ -41,3 +41,17 @@ jobs:
         run: cargo check -p improvise-io --target wasm32-unknown-unknown
       - name: improvise-command
         run: cargo check -p improvise-command --target wasm32-unknown-unknown
+
+  kb:
+    name: Knowledge base consistency
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v27
+      # kb.pl is executable knowledge, so it gets checked like code: rules
+      # must reject what they should, domains must close, and functional keys
+      # must not carry conflicting values. See kb_report/0 in the file.
+      - name: kb_consistent
+        run: |
+          nix shell nixpkgs#trealla --command tpl prolog-sessions/kb.pl \
+            -g "(kb_consistent -> halt(0) ; (kb_report, halt(1)))"