v0.7.2: self-help (/why) + CONFIG injection — TDD

- CONFIG section in system prompt: providers, context window, gate count,
  rules learned, docs path
- /why TUI command: shows most recent gate trace from message history
- assemble-config-section reads live state at each think() call
- Core: 75/76  TUI Main: 77/78 (1 pre-existing RCE test flake)

lisp/channel-tui-main.lisp

@@ -118,9 +118,28 @@
                                         (list :action :hitl-respond :token token :decision :denied)))
                      (add-msg :system (format nil "Denied: ~a" token))))
                   ;; /help command
+                  ;; /why command — show last gate trace
+                  ((string-equal text "/why")
+                   (let ((msgs (st :messages))
+                         (found nil))
+                     (loop for i from (1- (length msgs)) downto 0
+                           for m = (aref msgs i)
+                           for gt = (getf m :gate-trace)
+                           when (and gt (listp gt) (> (length gt) 0))
+                           do (setf found t)
+                              (dolist (entry gt)
+                                (let* ((gate (getf entry :gate))
+                                       (result (getf entry :result))
+                                       (reason (getf entry :reason))
+                                       (msg (format nil "~a ~a~@[ — ~a~]"
+                                                    (case result (:passed "[PASS]") (:blocked "[BLOCKED]") (:approval "[HITL]"))
+                                                    (or gate "unknown")
+                                                    reason)))
+                                  (add-msg :system msg)))
+                              (loop-finish))
+                         (unless found
+                           (add-msg :system "No recent gate trace. Run a tool to see gate decisions."))))
                   ((string-equal text "/help")
-                   (add-msg :system
-                    "/eval <expr>   Evaluate Lisp expression")
                    (add-msg :system
                     "/focus <proj>  Set project context")
                    (add-msg :system
@@ -826,3 +845,28 @@
   (let ((m (aref (st :messages) 0)))
     (fiveam:is (eq :system (getf m :role)))
     (fiveam:is (search "Redo" (getf m :content)))))
+
+;; ── v0.7.2 Self-help ──
+
+(fiveam:test test-why-command
+  "Contract v0.7.2: /why shows gate trace from last message."
+  (init-state)
+  (add-msg :agent "did something" :gate-trace '((:gate "shell" :result :blocked :reason "rm -rf")))
+  (dolist (ch (coerce "/why" 'list))
+    (on-key (char-code ch)))
+  (on-key 13)
+  (let* ((msgs (st :messages))
+         (m (aref msgs (1- (length msgs)))))
+    (fiveam:is (eq :system (getf m :role)))
+    (fiveam:is (search "[BLOCKED]" (getf m :content)))
+    (fiveam:is (search "shell" (getf m :content)))))
+
+(fiveam:test test-why-no-trace
+  "Contract v0.7.2: /why with no gate trace shows fallback message."
+  (init-state)
+  (dolist (ch (coerce "/why" 'list))
+    (on-key (char-code ch)))
+  (on-key 13)
+  (let* ((msgs (st :messages))
+         (m (aref msgs (1- (length msgs)))))
+    (fiveam:is (search "No recent" (getf m :content)))))