cl: Phase 3 complete — *debugger-hook*, *break-on-signals*, invoke-restart-interactively (147 tests)

cl-debugger-hook: mutable global (fn (c hook) result); cl-invoke-debugger
calls it with infinite-recursion guard (sets hook nil during call).
cl-error now routes unhandled errors through cl-invoke-debugger instead of
bare host error — allows the hook to invoke a restart and resume.
cl-break-on-signals: when set to a type name, cl-signal fires the debugger
hook before walking handlers if the condition matches.
cl-invoke-restart-interactively: calls the restart fn with no args (no
terminal protocol — equivalent to (invoke-restart name)).
4 new tests in conditions.sx covering all three; Phase 3 fully complete.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/common-lisp/runtime.sx

@@ -495,6 +495,47 @@
     (n)
     (set! cl-restart-stack (slice cl-restart-stack n (len cl-restart-stack)))))
 
+;; ── *debugger-hook* + invoke-debugger ────────────────────────────────────
+;;
+;; cl-debugger-hook: called when an error propagates with no handler.
+;; Signature: (fn (condition hook) result). The hook arg is itself
+;; (so the hook can rebind it to nil to prevent recursion).
+;; nil = use default (re-raise as host error).
+
+(define cl-debugger-hook nil)
+
+(define cl-invoke-debugger
+  (fn (c)
+    (if (nil? cl-debugger-hook)
+      (error (str "Debugger: " (cl-condition-message c)))
+      (let ((hook cl-debugger-hook))
+        (set! cl-debugger-hook nil)
+        (let ((result (hook c hook)))
+          (set! cl-debugger-hook hook)
+          result)))))
+
+;; ── *break-on-signals* ────────────────────────────────────────────────────
+;;
+;; When set to a type name string, cl-signal invokes the debugger hook
+;; before walking handlers if the condition is of that type.
+;; nil = disabled (ANSI default).
+
+(define cl-break-on-signals nil)
+
+;; ── invoke-restart-interactively ──────────────────────────────────────────
+;;
+;; Like invoke-restart but calls the restart's fn with no arguments
+;; (real CL would prompt the user for each arg via :interactive).
+
+(define cl-invoke-restart-interactively
+  (fn (name)
+    (let ((entry (cl-find-restart-entry name cl-restart-stack)))
+      (if (nil? entry)
+        (error (str "No active restart: " name))
+        (let ((restart-fn (get entry "fn"))
+              (escape     (get entry "escape")))
+          (escape (restart-fn)))))))
+
 ;; ── cl-signal (non-unwinding) ─────────────────────────────────────────────
 ;;
 ;; Walks cl-handler-stack; for each matching entry, calls the handler fn.
@@ -514,12 +555,16 @@
           (begin ((get entry "fn") obj) (cl-signal-obj obj (rest stack)))
           (cl-signal-obj obj (rest stack)))))))
 
-(define
-  cl-signal
-  (fn
-    (c)
-    (let
-      ((obj (if (cl-condition? c) c (cl-make-condition "simple-condition" "format-control" (str c)))))
+(define cl-signal
+  (fn (c)
+    (let ((obj (if (cl-condition? c)
+                 c
+                 (cl-make-condition "simple-condition"
+                   "format-control" (str c)))))
+      ;; *break-on-signals*: invoke debugger hook when type matches
+      (when (and (not (nil? cl-break-on-signals))
+                 (cl-condition-of-type? obj cl-break-on-signals))
+        (cl-invoke-debugger obj))
       (cl-signal-obj obj cl-handler-stack))))
 
 ;; ── cl-error ───────────────────────────────────────────────────────────────
@@ -533,7 +578,7 @@
     (let
       ((obj (cond ((cl-condition? c) c) ((string? c) (cl-make-condition "simple-error" "format-control" c "format-arguments" args)) (:else (cl-make-condition "simple-error" "format-control" (str c))))))
       (cl-signal-obj obj cl-handler-stack)
-      (error (str "Unhandled CL error: " (cl-condition-message obj))))))
+      (cl-invoke-debugger obj))))
 
 ;; ── cl-warn ────────────────────────────────────────────────────────────────
 
@@ -660,12 +705,20 @@
 ;; Signals a continuable error. The "continue" restart is established;
 ;; invoke-restart "continue" to proceed past the error.
 
-(define
-  cl-cerror
-  (fn
-    (continue-string c &rest args)
-    (let
-      ((obj (if (cl-condition? c) c (cl-make-condition "simple-error" "format-control" (str c) "format-arguments" args))))
+
+
+;; ── cl-cerror ──────────────────────────────────────────────────────────────
+;;
+;; Signals a continuable error. The "continue" restart is established;
+;; invoke-restart "continue" to proceed past the error.
+
+(define cl-cerror
+  (fn (continue-string c &rest args)
+    (let ((obj (if (cl-condition? c)
+                 c
+                 (cl-make-condition "simple-error"
+                   "format-control" (str c)
+                   "format-arguments" args))))
       (cl-restart-case
         (fn () (cl-signal-obj obj cl-handler-stack))
         (list "continue" (list) (fn () nil))))))