mod: Phase 3 — lifecycle state machine + escalation + appeal, 106/106

Pure SX state machine (lib/mod/lifecycle.sx) over the engine:
open→triaged→decided→appealed→final, transition table guards illegal moves.
Auto-tier resolves terminal actions; escalate parks at human-tier (resolve
blocked until review supplies evidence). Appeal re-runs the engine — new
exonerated-keep rule at top precedence lets exoneration override a prior hide.
Api façade (mod/triage/resolve/review/appeal/finalize) over a case registry,
logging committed decisions to the audit trail. +46 escalation tests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/mod/policy.sx

@@ -9,6 +9,10 @@
 ;; cond->goal takes an id-term so the same condition can be compiled with the
 ;; head variable "Id" (for clause bodies) or a concrete report id (for proof-tree
 ;; goal-by-goal re-querying in the engine).
+;;
+;; Precedence (top wins): exoneration evidence (appeal override) > confirmed-abuse
+;; evidence (human review) > spam/abuse classification > repeated-report count >
+;; default keep.
 
 (define mod/mk-rule (fn (name action conds) {:when conds :name name :action action}))
 
@@ -19,6 +23,9 @@
 (define
   mod/default-rules
   (list
+    (mod/mk-rule
+      "exonerated-keep"
+      :keep (list (list :evidence "exonerated")))
     (mod/mk-rule
       "reviewer-remove"
       :remove (list (list :evidence "confirmed-abuse")))