diff --git a/lisp/core-defpackage.lisp b/lisp/core-defpackage.lisp
index adc5a23..e7aba4b 100644
--- a/lisp/core-defpackage.lisp
+++ b/lisp/core-defpackage.lisp
@@ -15,12 +15,13 @@
    #:stop-daemon
    #:log-message
    #:main
-   #:doctor-run-all
-   #:doctor-main
-   #:doctor-check-dependencies
-   #:doctor-check-env
-   #:register-provider
-   #:system-ready-p
+    #:diagnostics-run-all
+    #:diagnostics-main
+    #:diagnostics-dependencies-check
+    #:diagnostics-env-check
+    #:register-provider
+    #:provider-openai-request
+    #:system-ready-p
    #:run-setup-wizard
    #:skill-gateway-register
    #:skill-gateway-link
@@ -242,7 +243,7 @@
   (format t "┌─────────────────────────────────────────────┐~%")
   (format t "│  ERROR: ~A~%" (type-of condition))
   (format t "│~%")
-  (format t "│  Run: passepartout doctor~%")
+   (format t "│  Run: passepartout diagnostics~%")
   (format t "│  For system diagnostics~%")
   (format t "└─────────────────────────────────────────────┘~%")
   (format t "~%")
diff --git a/lisp/core-loop.lisp b/lisp/core-loop.lisp
index d8c04b8..6e280a5 100644
--- a/lisp/core-loop.lisp
+++ b/lisp/core-loop.lisp
@@ -88,8 +88,8 @@
   (format t "==================================================~%")
   (handler-case
       (progn
-        (when (fboundp 'doctor-run-all)
-          (let ((result (doctor-run-all :auto-install nil)))
+         (when (fboundp 'diagnostics-run-all)
+           (let ((result (diagnostics-run-all :auto-install nil)))
             (setf *health-check-ran* t)
             (if result
                 (progn
@@ -98,10 +98,10 @@
                 (progn
                   (setf *system-health* :degraded)
                   (format t "DAEMON: Health check found issues.~%")
-                  (format t "         Run 'passepartout doctor --fix' to repair.~%")))))
+                   (format t "         Run 'passepartout diagnostics' to repair.~%")))))
         (setf *health-check-ran* t))
     (error (c)
-      (format t "DOCTOR ERROR: ~a~%" c)
+       (format t "DIAGNOSTICS ERROR: ~a~%" c)
       (setf *system-health* :unhealthy)
       (setf *health-check-ran* t)))
   (format t "==================================================~%~%"))
@@ -117,7 +117,7 @@
   (actuator-initialize)
   (skill-initialize-all)
   
-  ;; Run proactive doctor before starting services
+  ;; Run proactive diagnostics before starting services
   (diagnostics-startup-run)
   
   (heartbeat-start)
diff --git a/lisp/gateway-tui-main.lisp b/lisp/gateway-tui-main.lisp
index 28fb8a3..9b1d5b8 100644
--- a/lisp/gateway-tui-main.lisp
+++ b/lisp/gateway-tui-main.lisp
@@ -162,4 +162,4 @@
         (redraw sw cw ch iw)
         (refresh scr)
         (sleep 0.03))
-      (disconnect-daemon))))
+       (disconnect-daemon))))
diff --git a/lisp/system-diagnostics.lisp b/lisp/system-diagnostics.lisp
index 8f02f6c..adfdf69 100644
--- a/lisp/system-diagnostics.lisp
+++ b/lisp/system-diagnostics.lisp
@@ -1,3 +1,5 @@
+(in-package :passepartout)
+
 (defvar *diagnostics-binaries* '("sbcl" "emacs" "git" "socat" "nc")
   "List of external binaries required for full system operation.")
 
diff --git a/org/core-defpackage.org b/org/core-defpackage.org
index 1f016e7..ea95848 100644
--- a/org/core-defpackage.org
+++ b/org/core-defpackage.org
@@ -40,12 +40,13 @@ The package definition. All public symbols are exported here.
    #:stop-daemon
    #:log-message
    #:main
-   #:doctor-run-all
-   #:doctor-main
-   #:doctor-check-dependencies
-   #:doctor-check-env
-   #:register-provider
-   #:system-ready-p
+    #:diagnostics-run-all
+    #:diagnostics-main
+    #:diagnostics-dependencies-check
+    #:diagnostics-env-check
+    #:register-provider
+    #:provider-openai-request
+    #:system-ready-p
    #:run-setup-wizard
    #:skill-gateway-register
    #:skill-gateway-link
@@ -304,7 +305,7 @@ Friendly error handler that replaces the raw SBCL debugger with a diagnostic mes
   (format t "┌─────────────────────────────────────────────┐~%")
   (format t "│  ERROR: ~A~%" (type-of condition))
   (format t "│~%")
-  (format t "│  Run: passepartout doctor~%")
+   (format t "│  Run: passepartout diagnostics~%")
   (format t "│  For system diagnostics~%")
   (format t "└─────────────────────────────────────────────┘~%")
   (format t "~%")
diff --git a/org/core-loop.org b/org/core-loop.org
index 236caed..1cbbf54 100644
--- a/org/core-loop.org
+++ b/org/core-loop.org
@@ -225,8 +225,8 @@ This is the "fail open" principle applied to boot: the system should start even
   (format t "==================================================~%")
   (handler-case
       (progn
-        (when (fboundp 'doctor-run-all)
-          (let ((result (doctor-run-all :auto-install nil)))
+         (when (fboundp 'diagnostics-run-all)
+           (let ((result (diagnostics-run-all :auto-install nil)))
             (setf *health-check-ran* t)
             (if result
                 (progn
@@ -235,10 +235,10 @@ This is the "fail open" principle applied to boot: the system should start even
                 (progn
                   (setf *system-health* :degraded)
                   (format t "DAEMON: Health check found issues.~%")
-                  (format t "         Run 'passepartout doctor --fix' to repair.~%")))))
+                   (format t "         Run 'passepartout diagnostics' to repair.~%")))))
         (setf *health-check-ran* t))
     (error (c)
-      (format t "DOCTOR ERROR: ~a~%" c)
+       (format t "DIAGNOSTICS ERROR: ~a~%" c)
       (setf *system-health* :unhealthy)
       (setf *health-check-ran* t)))
   (format t "==================================================~%~%"))
@@ -272,7 +272,7 @@ Boot sequence:
   (actuator-initialize)
   (skill-initialize-all)
   
-  ;; Run proactive doctor before starting services
+  ;; Run proactive diagnostics before starting services
   (diagnostics-startup-run)
   
   (heartbeat-start)
diff --git a/org/core-manifest.org b/org/core-manifest.org
index 49e6ec8..497f1b0 100644
--- a/org/core-manifest.org
+++ b/org/core-manifest.org
@@ -51,9 +51,9 @@ Note: not every harness or skill file has a corresponding test file. Tests exist
                (:file "tests/programming-lisp-tests")
                (:file "tests/boot-sequence-tests")
                (:file "tests/model-explorer-tests")
+               (:file "tests/diagnostics-tests")
                (:file "tests/tui-tests")
-               (:file "tests/llm-gateway-tests")
-               (:file "tests/doctor-tests")))
+               (:file "tests/llm-gateway-tests")))
 #+end_src
 
 ** TUI System
diff --git a/org/gateway-tui-main.org b/org/gateway-tui-main.org
index 052b220..ef59b1c 100644
--- a/org/gateway-tui-main.org
+++ b/org/gateway-tui-main.org
@@ -180,5 +180,30 @@ Event handlers + daemon I/O + main loop.
         (redraw sw cw ch iw)
         (refresh scr)
         (sleep 0.03))
-      (disconnect-daemon))))
+       (disconnect-daemon))))
+
+#+end_src
+
+* Test Suite
+#+begin_src lisp :tangle ../tests/tui-tests.lisp
+(eval-when (:compile-toplevel :load-toplevel :execute)
+  (ql:quickload :fiveam :silent t))
+
+(defpackage :passepartout-tui-tests
+  (:use :cl :passepartout)
+  (:export #:tui-suite))
+
+(in-package :passepartout-tui-tests)
+
+(fiveam:def-suite tui-suite :description "Verification of the TUI parsing and styling logic")
+(fiveam:in-suite tui-suite)
+
+(fiveam:test test-tui-connection-drop
+  "Tier 2 Chaos: Verify that handle-return degrades gracefully when the daemon connection is lost."
+  (let ((passepartout.gateway-tui::*incoming-msgs* nil)
+        (passepartout.gateway-tui::*input-buffer* (make-array 5 :element-type 'character :initial-contents "hello" :fill-pointer 5 :adjustable t))
+        (mock-stream (make-string-output-stream)))
+    (close mock-stream)
+    (passepartout.gateway-tui::handle-return mock-stream)
+    (fiveam:is (member "ERROR: Connection to daemon lost." passepartout.gateway-tui::*incoming-msgs* :test #'string=))))
 #+end_src
diff --git a/org/system-diagnostics.org b/org/system-diagnostics.org
index 2ba5fd8..d2ccf03 100644
--- a/org/system-diagnostics.org
+++ b/org/system-diagnostics.org
@@ -21,6 +21,11 @@ Binary detection must use shell probing (`which`) to account for varying `$PATH`
 
 * Phase C: Implementation (Build)
 
+** Package Context
+#+begin_src lisp
+(in-package :passepartout)
+#+end_src
+
 ** Global Configuration
 ;; REPL-VERIFIED: 2026-05-03T13:00:00
 #+begin_src lisp
@@ -238,24 +243,34 @@ The doctor checks all supported LLM providers and detects local Ollama instances
 
 * Phase D: Verification (Testing)
 
-** Dependency Test
-#+begin_src lisp :tangle no
-(test test-doctor-dependency-check
+#+begin_src lisp :tangle ../tests/diagnostics-tests.lisp
+(eval-when (:compile-toplevel :load-toplevel :execute)
+  (ql:quickload :fiveam :silent t))
+
+(defpackage :passepartout-diagnostics-tests
+  (:use :cl :fiveam :passepartout)
+  (:export #:diagnostics-suite))
+
+(in-package :passepartout-diagnostics-tests)
+
+(def-suite diagnostics-suite :description "Verification of the System Diagnostics logic")
+(in-suite diagnostics-suite)
+
+(test test-diagnostics-dependency-fail
   "Verify that missing binaries are correctly identified as failures."
   (let ((passepartout::*diagnostics-binaries* '("non-existent-binary-123")))
-    (is (null (passepartout:diagnostics-dependencies-check)))))
-#+end_src
+    (is (null (diagnostics-dependencies-check)))))
 
-** Environment Test
-#+begin_src lisp :tangle no
-(test test-doctor-env-check
+(test test-diagnostics-env-fail
   "Verify that an invalid MEMEX_DIR triggers a critical failure."
-  (let ((old-m (uiop:getenv "MEMEX_DIR")))
+  (let ((old-m (uiop:getenv "MEMEX_DIR"))
+        (old-d (uiop:getenv "PASSEPARTOUT_DATA_DIR")))
     (unwind-protect
          (progn
            (setf (uiop:getenv "MEMEX_DIR") "/non/existent/path/999")
-           (is (null (passepartout:diagnostics-env-check))))
-      (setf (uiop:getenv "MEMEX_DIR") (or old-m "")))))
+           (is (null (diagnostics-env-check))))
+      (setf (uiop:getenv "MEMEX_DIR") (or old-m ""))
+      (setf (uiop:getenv "PASSEPARTOUT_DATA_DIR") (or old-d "")))))
 #+end_src
 
 * Phase E: Lifecycle
diff --git a/org/system-model-provider.org b/org/system-model-provider.org
index 937dd0b..57212fa 100644
--- a/org/system-model-provider.org
+++ b/org/system-model-provider.org
@@ -161,3 +161,23 @@ If API-KEY is nil, reads from environment."
   :priority 50
   :trigger (lambda (ctx) (declare (ignore ctx)) nil))
 #+end_src
+
+* Test Suite
+#+begin_src lisp :tangle ../tests/llm-gateway-tests.lisp
+(eval-when (:compile-toplevel :load-toplevel :execute)
+  (ql:quickload :fiveam :silent t))
+
+(defpackage :passepartout-llm-gateway-tests
+  (:use :cl :passepartout)
+  (:export #:llm-gateway-suite))
+
+(in-package :passepartout-llm-gateway-tests)
+
+(fiveam:def-suite llm-gateway-suite :description "Tests for the LLM provider backend")
+(fiveam:in-suite llm-gateway-suite)
+
+(fiveam:test test-provider-rejects-bad-keyword
+  "Verify that provider-openai-request returns :error for an unregistered provider."
+  (let ((result (provider-openai-request "hello" "test" :provider :not-a-real-provider)))
+    (fiveam:is (eq (getf result :status) :error))))
+#+end_src
diff --git a/passepartout.asd b/passepartout.asd
index 6ac172a..6638e5c 100644
--- a/passepartout.asd
+++ b/passepartout.asd
@@ -22,9 +22,9 @@
                (:file "tests/programming-lisp-tests")
                (:file "tests/boot-sequence-tests")
                (:file "tests/model-explorer-tests")
+               (:file "tests/diagnostics-tests")
                (:file "tests/tui-tests")
-               (:file "tests/llm-gateway-tests")
-               (:file "tests/doctor-tests")))
+               (:file "tests/llm-gateway-tests")))
 
 (defsystem :passepartout/tui
   :depends-on (:passepartout :croatoan :usocket :bordeaux-threads)