diff --git a/Makefile b/Makefile
index 7dd0000..fae5990 100644
--- a/Makefile
+++ b/Makefile
@@ -1,8 +1,8 @@
 EMACS ?= emacs
 LOAD_PATH = -L . -L examples -L ../ebox -L ../tp -L ../ecss
-SOURCES = etaf-view.el etaf-compiler.el etaf-component.el etaf-reactive.el etaf-context.el etaf-theme-tp.el etaf-resource.el etaf-data.el etaf-renderer.el etaf-runtime.el etaf-behavior.el etaf-actions.el etaf-events.el etaf-performance.el etaf.el
+SOURCES = etaf-view.el etaf-compiler.el etaf-component.el etaf-reactive.el etaf-observer.el etaf-context.el etaf-theme-tp.el etaf-resource.el etaf-data.el etaf-renderer.el etaf-runtime.el etaf-behavior.el etaf-actions.el etaf-events.el etaf-performance.el etaf.el
 EXAMPLES = examples/etaf-counter-example.el examples/etaf-data-example.el examples/etaf-resource-example.el
-TESTS = tests/etaf-tests.el tests/etaf-compiler-tests.el tests/etaf-resource-tests.el tests/etaf-data-tests.el tests/etaf-theme-tp-tests.el tests/etaf-examples-tests.el tests/etaf-performance-tests.el
+TESTS = tests/etaf-tests.el tests/etaf-compiler-tests.el tests/etaf-resource-tests.el tests/etaf-data-tests.el tests/etaf-theme-tp-tests.el tests/etaf-examples-tests.el tests/etaf-observer-tests.el tests/etaf-performance-tests.el
 
 .PHONY: test compile load checkdoc docs-check check clean
 
diff --git a/etaf-actions.el b/etaf-actions.el
index f75d94b..6e6eb6d 100644
--- a/etaf-actions.el
+++ b/etaf-actions.el
@@ -14,6 +14,11 @@
 (require 'etaf-runtime)
 
 (defvar etaf--current-runtime)
+(defvar etaf--observer-context)
+
+(declare-function etaf-runtime-observer "etaf-runtime" (runtime))
+(declare-function etaf-runtime-call-operation
+                  "etaf-runtime" (runtime kind label function))
 
 (define-error 'etaf-action-error "Invalid ETAF Action")
 
@@ -77,8 +82,14 @@ RUNTIME ACTION ...)'.  Action functions receive Runtime first."
     (unless spec
       (signal 'etaf-action-error
               (list (format "Unknown ETAF Action: %S" action))))
-    (let ((etaf--current-runtime runtime))
-      (apply (etaf-action-spec-function spec) runtime arguments))))
+    (if (or etaf--observer-context (etaf-runtime-observer runtime))
+        (etaf-runtime-call-operation
+         runtime 'action (format "%S" action)
+         (lambda ()
+           (let ((etaf--current-runtime runtime))
+             (apply (etaf-action-spec-function spec) runtime arguments))))
+      (let ((etaf--current-runtime runtime))
+        (apply (etaf-action-spec-function spec) runtime arguments)))))
 
 ;;;###autoload
 (defun etaf-action-undefine (name)
diff --git a/etaf-data.el b/etaf-data.el
index 8938025..498796f 100644
--- a/etaf-data.el
+++ b/etaf-data.el
@@ -12,6 +12,7 @@
 ;;; Code:
 
 (require 'cl-lib)
+(require 'etaf-observer)
 (require 'etaf-reactive)
 
 (define-error 'etaf-data-error "Invalid ETAF data operation")
@@ -48,16 +49,22 @@ CAPABILITIES is a plist.  `:load' is required and receives QUERY, PAGE, and
 PAGE-SIZE.  It must return a plist containing at least `:items', and may return
 `:total', `:page', and `:page-size'.  `:mutate' is optional and receives
 OPERATION and PAYLOAD.  `:dispose' is optional and runs when the owning
-controller stops."
+controller stops.  `:provider' may name the source in observation reports and
+defaults to `data'."
   (let ((load (plist-get capabilities :load))
         (mutate (plist-get capabilities :mutate))
-        (dispose (plist-get capabilities :dispose)))
+        (dispose (plist-get capabilities :dispose))
+        (provider (plist-get capabilities :provider)))
     (unless (functionp load)
       (signal 'wrong-type-argument (list 'functionp load)))
     (dolist (entry `((:mutate . ,mutate)
                     (:dispose . ,dispose)))
       (when (and (cdr entry) (not (functionp (cdr entry))))
         (signal 'wrong-type-argument (list 'functionp (cdr entry)))))
+    (when (and (plist-member capabilities :provider)
+               (not (and provider (symbolp provider)
+                         (not (keywordp provider)))))
+      (signal 'wrong-type-argument (list 'symbolp provider)))
     (append (list :etaf-data-source t) capabilities)))
 
 (defun etaf-data-source-p (value)
@@ -75,6 +82,25 @@ controller stops."
       (error "ETAF Data source lacks %S capability" key))
     function))
 
+(defun etaf-data--source-provider (source)
+  "Return SOURCE's observation provider, defaulting to `data'."
+  (or (plist-get source :provider) 'data))
+
+(defun etaf-data--source-load (source query page page-size)
+  "Invoke SOURCE load capability for QUERY, PAGE, and PAGE-SIZE."
+  (etaf-observer-with-stage
+      ((etaf-data--source-provider source) 'load
+       :page page :page-size page-size)
+    (funcall (etaf-data--source-function source :load t)
+             query page page-size)))
+
+(defun etaf-data--source-mutate (source operation payload)
+  "Invoke SOURCE mutation OPERATION with PAYLOAD."
+  (etaf-observer-with-stage
+      ((etaf-data--source-provider source) 'mutate :operation operation)
+    (funcall (etaf-data--source-function source :mutate t)
+             operation payload)))
+
 (defun etaf-data--record-value (record key)
   "Return RECORD value at KEY for plist, alist, or hash table records."
   (cond
@@ -155,6 +181,7 @@ and `reset'."
              current))))
     (etaf-data-source
      :name name
+     :provider 'memory
      :load (lambda (query page page-size)
              (let* ((all (etaf-value records))
                     (filtered (funcall query-function query all)))
@@ -213,9 +240,10 @@ and `reset'."
 QUERY is passed through unchanged.  PAGE and PAGE-SIZE default to 1 and 20.
 This public preparation boundary performs no reactive publication; callers may
 use its result as `:initial-result' for `etaf-data-controller'."
-  (etaf-data--normalize-result
-   (funcall (etaf-data--source-function source :load t)
-            query (max 1 (or page 1)) (max 1 (or page-size 20)))))
+  (let ((page (max 1 (or page 1)))
+        (page-size (max 1 (or page-size 20))))
+    (etaf-data--normalize-result
+     (etaf-data--source-load source query page page-size))))
 
 (defun etaf-data--apply-load-success (controller request-id result)
   "Publish successful RESULT for CONTROLLER when REQUEST-ID is current."
@@ -381,11 +409,11 @@ load.  INITIAL-RESULT and AUTO-LOAD are mutually exclusive."
         (etaf-data--apply-load-success
          controller
          request-id
-         (funcall (etaf-data--source-function
-                   (etaf-data--controller-source controller) :load t)
-                  (etaf-value (etaf-data--controller-query controller))
-                  (etaf-value (etaf-data--controller-page controller))
-                  (etaf-value (etaf-data--controller-page-size controller))))
+         (etaf-data--source-load
+          (etaf-data--controller-source controller)
+          (etaf-value (etaf-data--controller-query controller))
+          (etaf-value (etaf-data--controller-page controller))
+          (etaf-value (etaf-data--controller-page-size controller))))
       (error
        (etaf-data--apply-error controller request-id err)
        (signal (car err) (cdr err))))))
@@ -408,9 +436,9 @@ source mutation result after the reload succeeds."
     (setf (etaf-value (etaf-data--controller-error controller)) nil)
     (condition-case err
         (let ((result
-               (funcall (etaf-data--source-function
-                         (etaf-data--controller-source controller) :mutate t)
-                        operation payload)))
+               (etaf-data--source-mutate
+                (etaf-data--controller-source controller)
+                operation payload)))
           (etaf-data-load controller)
           result)
       (error
diff --git a/etaf-events.el b/etaf-events.el
index 3607594..db7c970 100644
--- a/etaf-events.el
+++ b/etaf-events.el
@@ -15,6 +15,7 @@
 (require 'etaf-runtime)
 
 (defvar etaf--current-runtime)
+(defvar etaf--observer-context)
 
 (declare-function etaf-runtime-require-mounted "etaf-runtime" (&optional runtime))
 (declare-function etaf-runtime-p "etaf-runtime" (value))
@@ -28,6 +29,9 @@
 (declare-function etaf-runtime-set-focus-ref "etaf-runtime" (runtime host-ref))
 (declare-function etaf-runtime-event-begin "etaf-runtime" (runtime))
 (declare-function etaf-runtime-event-end "etaf-runtime" (runtime))
+(declare-function etaf-runtime-observer "etaf-runtime" (runtime))
+(declare-function etaf-runtime-call-operation
+                  "etaf-runtime" (runtime kind label function))
 (declare-function ebox-call-with-render-burst
                   "ebox-buffer-backend" (function &rest arguments))
 
@@ -61,9 +65,9 @@
 
   When PAYLOAD-P is non-nil, pass PAYLOAD as the callback's only argument;
 otherwise call the local callback with no arguments."
+  (setq runtime (etaf-runtime-require-mounted runtime))
   (let ((dispatch
          (lambda ()
-           (setq runtime (etaf-runtime-require-mounted runtime))
            (let ((callback (etaf--event-handler runtime host-ref kind)))
              (unless callback
                (signal 'etaf-event-error
@@ -79,7 +83,12 @@ otherwise call the local callback with no arguments."
                        (funcall callback payload)
                      (funcall callback))
                  (etaf-runtime-event-end runtime)))))))
-    (ebox-call-with-render-burst dispatch)))
+    (if (or etaf--observer-context (etaf-runtime-observer runtime))
+        (etaf-runtime-call-operation
+         runtime 'event
+         (format "%s %S" (etaf-event-kind kind) host-ref)
+         (lambda () (ebox-call-with-render-burst dispatch)))
+      (ebox-call-with-render-burst dispatch))))
 
 ;;;###autoload
 (defun etaf-host-ref-bounds (runtime host-ref)
diff --git a/etaf-observer.el b/etaf-observer.el
new file mode 100644
index 0000000..fb3057d
--- /dev/null
+++ b/etaf-observer.el
@@ -0,0 +1,202 @@
+;;; etaf-observer.el --- Scoped ETAF Runtime observation -*- lexical-binding: t; -*-
+
+;; SPDX-License-Identifier: GPL-3.0-or-later
+
+;;; Commentary:
+
+;; This file defines the deliberately small observation port used by the ETAF
+;; Runtime.  Observation is scoped to one dynamic operation; it is neither a
+;; global subscription service nor publication authority.  When no context is
+;; active, instrumented stages execute their original body directly.
+
+;;; Code:
+
+(require 'cl-lib)
+
+(define-error 'etaf-observer-error "Invalid ETAF observer operation")
+
+(defconst etaf-observer-report-format-version 1
+  "Format version of flat ETAF observation reports.")
+
+(defconst etaf--observer-context-keys
+  '(:format-version :operation-id :sequence :runtime-id :buffer-name)
+  "Report fields owned exclusively by the active operation context.")
+
+(cl-defstruct (etaf--observer-context
+               (:constructor etaf--observer-context--make))
+  "Dynamic observation state for one ETAF Runtime operation."
+  sink
+  operation-id
+  runtime-id
+  buffer-name
+  (sequence 0)
+  diagnostic)
+
+(defvar etaf--observer-context nil
+  "Dynamically active ETAF observation context, or nil.")
+
+(defun etaf--observer-provider-report-valid-p (report)
+  "Return non-nil when REPORT is a valid provider report."
+  (and (proper-list-p report)
+       (zerop (% (length report) 2))
+       (let ((tail report)
+             keys
+             valid)
+         (setq valid t)
+         (while (and tail valid)
+           (let ((key (pop tail)))
+             (pop tail)
+             (setq valid
+                   (and (keywordp key)
+                        (not (memq key keys))
+                        (not (memq key etaf--observer-context-keys))))
+             (push key keys)))
+         (and valid
+              (plist-member report :provider)
+              (let ((provider (plist-get report :provider)))
+                (and provider (symbolp provider) (not (keywordp provider))))
+              (plist-member report :stage)
+              (let ((stage (plist-get report :stage)))
+                (and stage (symbolp stage) (not (keywordp stage))))
+              (or (not (plist-member report :status))
+                  (memq (plist-get report :status) '(success error quit)))
+              (plist-member report :duration-ms)
+              (numberp (plist-get report :duration-ms))
+              (>= (plist-get report :duration-ms) 0)))))
+
+(defun etaf--observer-copy-value (value)
+  "Return a defensive observation copy of VALUE."
+  (cond
+   ((stringp value) (copy-sequence value))
+   ((consp value)
+    (cons (etaf--observer-copy-value (car value))
+          (etaf--observer-copy-value (cdr value))))
+   ((vectorp value)
+    (apply #'vector
+           (mapcar #'etaf--observer-copy-value (append value nil))))
+   (t value)))
+
+(defun etaf--observer-report-copy (report)
+  "Return an isolated snapshot of validated provider REPORT."
+  (etaf--observer-copy-value report))
+
+(defun etaf--observer-diagnose (kind condition)
+  "Contain KIND and CONDITION with the active context diagnostic sink."
+  (when-let* ((context etaf--observer-context)
+              (diagnostic (etaf--observer-context-diagnostic context)))
+    (let ((inhibit-quit t)
+          (quit-flag nil))
+      (condition-case nil
+          (funcall diagnostic
+                   (list :kind kind :condition (copy-tree condition)))
+        ((error quit) nil))))
+  nil)
+
+(cl-defun etaf--observer-context-create
+    (&key sink operation-id runtime-id buffer-name diagnostic)
+  "Create scoped observer state for one Runtime operation.
+
+SINK receives one defensive report snapshot.  OPERATION-ID and RUNTIME-ID are
+stable scalar identities, BUFFER-NAME is a string or nil, and DIAGNOSTIC
+receives contained observer-port failures.  This internal constructor is the
+only Runtime entry point that allocates observation state."
+  (unless (functionp sink)
+    (signal 'etaf-observer-error '(Observer sink must be a function)))
+  (unless (integerp operation-id)
+    (signal 'etaf-observer-error '(Operation identity must be an integer)))
+  (unless (integerp runtime-id)
+    (signal 'etaf-observer-error '(Runtime identity must be an integer)))
+  (unless (or (null buffer-name) (stringp buffer-name))
+    (signal 'etaf-observer-error '(Buffer name must be a string or nil)))
+  (unless (functionp diagnostic)
+    (signal 'etaf-observer-error '(Diagnostic sink must be a function)))
+  (etaf--observer-context--make
+   :sink sink
+   :operation-id operation-id
+   :runtime-id runtime-id
+   :buffer-name (and buffer-name (copy-sequence buffer-name))
+   :diagnostic diagnostic))
+
+(defun etaf--observer-call-with-context (context function)
+  "Call FUNCTION with internal observer CONTEXT dynamically active."
+  (unless (etaf--observer-context-p context)
+    (signal 'etaf-observer-error '(Invalid observer context)))
+  (unless (functionp function)
+    (signal 'etaf-observer-error '(Observed operation must be a function)))
+  (let ((etaf--observer-context context))
+    (funcall function)))
+
+(defun etaf-observer-emit (report)
+  "Decorate and deliver immutable provider REPORT in the active context.
+
+The observer receives a defensive copy.  Observer errors, quits, and invalid
+reports are contained by the context diagnostic sink and never affect product
+execution.  The dynamic context is cleared during delivery so an observer can
+reenter ETAF without recursively observing itself."
+  (when etaf--observer-context
+    (if (not (etaf--observer-provider-report-valid-p report))
+        (etaf--observer-diagnose 'invalid-report report)
+      (let* ((context etaf--observer-context)
+             (sequence (1+ (etaf--observer-context-sequence context)))
+             (sink (etaf--observer-context-sink context))
+             (provider-report (etaf--observer-report-copy report))
+             (snapshot
+              (append
+               (list :format-version etaf-observer-report-format-version
+                     :operation-id
+                     (etaf--observer-context-operation-id context)
+                     :sequence sequence
+                     :runtime-id (etaf--observer-context-runtime-id context)
+                     :buffer-name
+                     (etaf--observer-copy-value
+                      (etaf--observer-context-buffer-name context)))
+               provider-report
+               (unless (plist-member provider-report :status)
+                 (list :status 'success))))
+            (inhibit-quit t)
+            (quit-flag nil))
+        (setf (etaf--observer-context-sequence context) sequence)
+        (condition-case condition
+            (let ((etaf--observer-context nil))
+              (funcall sink snapshot))
+          ((error quit)
+           (etaf--observer-diagnose 'observer-failure condition))))))
+  nil)
+
+(defun etaf--observer-finish-stage (provider stage metadata status started)
+  "Emit PROVIDER STAGE with METADATA, STATUS, and STARTED timestamp."
+  (let ((duration-ms (max 0.0 (* 1000.0 (- (float-time) started)))))
+    (etaf-observer-emit
+     (append (list :provider provider :stage stage :status status
+                   :duration-ms duration-ms)
+             metadata))))
+
+(defun etaf--observer-call-stage (provider stage metadata function)
+  "Call observed PROVIDER STAGE FUNCTION with METADATA."
+  (let ((started (float-time)))
+    (condition-case condition
+        (prog1 (funcall function)
+          (etaf--observer-finish-stage
+           provider stage metadata 'success started))
+      (quit
+       (etaf--observer-finish-stage provider stage metadata 'quit started)
+       (signal (car condition) (cdr condition)))
+      (error
+       (etaf--observer-finish-stage provider stage metadata 'error started)
+       (signal (car condition) (cdr condition))))))
+
+(cl-defmacro etaf-observer-with-stage
+    ((provider stage &rest metadata) &rest body)
+  "Execute BODY as PROVIDER STAGE with optional METADATA.
+
+The nil path is a single branch directly to BODY: it takes no timestamp,
+allocates no closure or report, and reads no garbage-collection state."
+  (declare (indent 1) (debug ((form form &rest form) body)))
+  `(if (null etaf--observer-context)
+       (progn ,@body)
+     (etaf--observer-call-stage
+      ,provider ,stage (list ,@metadata) (lambda () ,@body))))
+
+(provide 'etaf-observer)
+
+;;; etaf-observer.el ends here
diff --git a/etaf-resource.el b/etaf-resource.el
index cf88f6e..a6cc21c 100644
--- a/etaf-resource.el
+++ b/etaf-resource.el
@@ -12,6 +12,7 @@
 ;;; Code:
 
 (require 'cl-lib)
+(require 'etaf-observer)
 (require 'etaf-reactive)
 
 (define-error 'etaf-resource-error "Invalid ETAF Resource operation"
@@ -142,9 +143,10 @@ wrong Resource usage continue to signal normally."
   (let (result error-data)
     (condition-case err
         (setq result
-              (etaf-scope-run
-               (etaf-resource-scope resource)
-               (etaf-resource-loader resource)))
+              (etaf-observer-with-stage ('resource 'load)
+                (etaf-scope-run
+                 (etaf-resource-scope resource)
+                 (etaf-resource-loader resource))))
       (error (setq error-data err)))
     (if error-data
         (etaf--resource-set-state resource 'error nil error-data)
diff --git a/etaf-runtime.el b/etaf-runtime.el
index 85f225f..3843396 100644
--- a/etaf-runtime.el
+++ b/etaf-runtime.el
@@ -18,6 +18,7 @@
 (require 'etaf-renderer)
 (require 'etaf-context)
 (require 'etaf-behavior)
+(require 'etaf-observer)
 
 (declare-function etaf--render-value-list "etaf-renderer" (value path))
 (declare-function etaf--apply-inline-style-rules "etaf-renderer" (node styles &optional root-p))
@@ -47,6 +48,8 @@
 (defvar etaf--render-style-stack)
 (defvar etaf--render-parent-style-stack)
 (defvar etaf--current-context)
+(defvar gcs-done)
+(defvar gc-elapsed)
 
 (define-error 'etaf-runtime-error "ETAF runtime error")
 
@@ -326,6 +329,8 @@ the sequential `etaf--pvec-put' contract."
   flushing-p
   pending-p
   diagnostics
+  observer
+  (next-operation-id 0)
   (event-depth 0)
   dirty-effect-queue-tail)
 
@@ -1086,6 +1091,104 @@ effect-to-source edges.  It is intentionally immutable and suitable as an
   "Return the dynamically active Runtime, or nil outside a Runtime."
   etaf--current-runtime)
 
+(defun etaf--runtime-forward-ebox-report (_buffer report)
+  "Forward accepted Ebox or TP REPORT into the active Runtime operation."
+  (etaf-observer-emit report))
+
+(defun etaf--runtime-record-observer-diagnostic (runtime diagnostic)
+  "Record contained observer DIAGNOSTIC on RUNTIME."
+  (push (append (list :phase 'observer) (copy-tree diagnostic))
+        (etaf-runtime-diagnostics runtime))
+  nil)
+
+(defun etaf-runtime-call-operation (runtime kind label function)
+  "Call FUNCTION as one observed RUNTIME operation.
+KIND is a stable symbol and LABEL is a user-facing string.  Nested calls for
+the same Runtime reuse the active operation.  Calls for another Runtime own a
+separate operation.  Return FUNCTION's exact result and re-signal its exact
+error or quit."
+  (unless (and (etaf-runtime-p runtime)
+               (etaf-runtime-mounted-p runtime))
+    (signal 'etaf-runtime-error (list "ETAF runtime is not mounted")))
+  (unless (and (symbolp kind) kind)
+    (signal 'wrong-type-argument (list 'symbolp kind)))
+  (unless (stringp label)
+    (signal 'wrong-type-argument (list 'stringp label)))
+  (unless (functionp function)
+    (signal 'wrong-type-argument (list 'functionp function)))
+  (let* ((runtime-id (etaf-runtime-mount-epoch runtime))
+         (current etaf--observer-context)
+         (same-runtime
+          (and current
+               (= runtime-id
+                  (etaf--observer-context-runtime-id current))))
+         (observer (etaf-runtime-observer runtime)))
+    (cond
+     (same-runtime
+      (funcall function))
+     ((null observer)
+      ;; A different Runtime must not leak provider reports into the outer
+      ;; operation merely because its own observer is disabled.
+      (let ((etaf--observer-context nil))
+        (funcall function)))
+     (t
+      (let* ((operation-id
+              (1+ (or (etaf-runtime-next-operation-id runtime) 0)))
+             (generation-before (etaf-runtime-generation runtime))
+             (started (float-time))
+             (gc-count-before gcs-done)
+             (gc-elapsed-before gc-elapsed)
+             (status 'error)
+             (context
+              (etaf--observer-context-create
+               :sink observer
+               :operation-id operation-id
+               :runtime-id runtime-id
+               :buffer-name (buffer-name (etaf-runtime-buffer runtime))
+               :diagnostic
+               (lambda (diagnostic)
+                 (etaf--runtime-record-observer-diagnostic
+                  runtime diagnostic))))
+             result)
+        (setf (etaf-runtime-next-operation-id runtime) operation-id)
+        (etaf--observer-call-with-context
+         context
+         (lambda ()
+           (unwind-protect
+               (condition-case condition
+                   (prog1 (setq result (funcall function))
+                     (setq status 'success))
+                 (quit
+                  (setq status 'quit)
+                  (signal (car condition) (cdr condition))))
+             (etaf-observer-emit
+              (list
+               :provider 'etaf
+               :stage 'runtime-operation
+               :kind kind
+               :label (copy-sequence label)
+               :generation-before generation-before
+               :generation-after (etaf-runtime-generation runtime)
+               :status status
+               :duration-ms
+               (max 0.0 (* 1000.0 (- (float-time) started)))
+               :gc-count (- gcs-done gc-count-before)
+               :gc-duration-ms
+               (max 0.0
+                    (* 1000.0 (- gc-elapsed gc-elapsed-before))))))))
+        result)))))
+
+(cl-defmacro etaf--runtime-with-operation ((runtime kind label) &rest body)
+  "Evaluate BODY in RUNTIME operation KIND and LABEL when observed."
+  (declare (indent 1) (debug ((form form form) body)))
+  (let ((runtime-value (make-symbol "runtime")))
+    `(let ((,runtime-value ,runtime))
+       (if (and (null etaf--observer-context)
+                (null (etaf-runtime-observer ,runtime-value)))
+           (progn ,@body)
+         (etaf-runtime-call-operation
+          ,runtime-value ,kind ,label (lambda () ,@body))))))
+
 (defun etaf-runtime-set-focus-ref (runtime host-ref)
   "Set RUNTIME's focused Host reference to HOST-REF and return it."
   (setf (etaf-runtime-focus-ref runtime) host-ref)
@@ -1128,6 +1231,44 @@ when the requested boundary is no longer mounted."
               (list "ETAF runtime is not mounted")))
     runtime))
 
+;;;###autoload
+(defun etaf-runtime-set-observer (runtime observer-or-nil)
+  "Set mounted RUNTIME's observer to OBSERVER-OR-NIL and return it.
+The observer receives one immutable flat report argument.  Nil detaches the
+Runtime from its Ebox surface.  Replacing observation during an active
+operation is rejected so the operation keeps one stable sink."
+  (setq runtime (etaf-runtime-require-mounted runtime))
+  (unless (or (null observer-or-nil) (functionp observer-or-nil))
+    (signal 'wrong-type-argument (list 'functionp observer-or-nil)))
+  (unless (eq observer-or-nil (etaf-runtime-observer runtime))
+    (when (and etaf--observer-context
+               (= (etaf-runtime-mount-epoch runtime)
+                  (etaf--observer-context-runtime-id
+                   etaf--observer-context)))
+      (error "ETAF observer cannot change during an active operation"))
+    (ebox-buffer-set-observer
+     (etaf-runtime-buffer runtime)
+     (and observer-or-nil #'etaf--runtime-forward-ebox-report))
+    (setf (etaf-runtime-observer runtime) observer-or-nil))
+  observer-or-nil)
+
+;;;###autoload
+(defun etaf-runtime-compare-and-set-observer (runtime expected replacement)
+  "Replace RUNTIME observer EXPECTED with REPLACEMENT atomically.
+
+EXPECTED and REPLACEMENT are functions or nil.  Return non-nil only when the
+current observer is `eq' to EXPECTED; in that case REPLACEMENT is installed
+through the ordinary observer boundary.  A mismatch leaves the Runtime
+untouched.  This lets optional consumers detach only the sink they own without
+reading Runtime storage fields."
+  (setq runtime (etaf-runtime-require-mounted runtime))
+  (dolist (observer (list expected replacement))
+    (unless (or (null observer) (functionp observer))
+      (signal 'wrong-type-argument (list 'functionp observer))))
+  (when (eq expected (etaf-runtime-observer runtime))
+    (etaf-runtime-set-observer runtime replacement)
+    t))
+
 (defun etaf--runtime-watch-scheduler (runtime job _flush)
   "Run watcher JOB while RUNTIME remains mounted."
   (when (etaf-runtime-mounted-p runtime)
@@ -4975,7 +5116,10 @@ RENDERED-IDENTITIES names the Component render participants."
                    (etaf--runtime-participant-publish participant))
                  (lambda (_report)
                    (etaf--runtime-participant-rollback participant))))
-            (ebox-render-to-buffer (etaf-runtime-buffer runtime) next-root)
+            (ebox-render-to-buffer
+             (etaf-runtime-buffer runtime) next-root
+             (when (etaf-runtime-observer runtime)
+               (list :observer #'etaf--runtime-forward-ebox-report)))
             (etaf--runtime-participant-publish participant))
           (etaf--runtime-complete-generation
            runtime old-generation candidate-generation)
@@ -5018,8 +5162,8 @@ backend anchor proof failed; ordinary root turns keep their artifact reuse."
           (etaf--runtime-evaluate-root-candidate runtime))
     (etaf--runtime-render-effect runtime)))
 
-(defun etaf--runtime-request-flush (runtime)
-  "Synchronously flush RUNTIME, or mark one follow-up flush while busy."
+(defun etaf--runtime-request-flush-now (runtime)
+  "Flush RUNTIME now, or mark one follow-up flush while busy."
   (when (etaf-runtime-mounted-p runtime)
     (if (or (> (etaf-runtime-event-depth runtime) 0)
             (etaf-runtime-flushing-p runtime))
@@ -5050,6 +5194,11 @@ backend anchor proof failed; ordinary root turns keep their artifact reuse."
                     (etaf--runtime-render-root-turn runtime t)))))
           (setf (etaf-runtime-flushing-p runtime) nil))))))
 
+(defun etaf--runtime-request-flush (runtime)
+  "Flush RUNTIME within one optional Runtime operation boundary."
+  (etaf--runtime-with-operation (runtime 'flush "reactive flush")
+    (etaf--runtime-request-flush-now runtime)))
+
 ;;;###autoload
 (defun etaf-runtime-flush (&optional runtime)
   "Flush mounted RUNTIME immediately and return its root Ebox node."
@@ -5057,8 +5206,8 @@ backend anchor proof failed; ordinary root turns keep their artifact reuse."
     (etaf--runtime-request-flush runtime)
     (etaf-runtime-root-node runtime)))
 
-(defun etaf--runtime-mount-now (buffer-or-name view)
-  "Mount VIEW into BUFFER-OR-NAME and return the live buffer."
+(defun etaf--runtime-mount-now (buffer-or-name view observer)
+  "Mount VIEW with optional OBSERVER into BUFFER-OR-NAME."
   (let* ((buffer (get-buffer-create buffer-or-name))
          (old (gethash buffer etaf--runtime-table)))
     (when old
@@ -5087,6 +5236,7 @@ backend anchor proof failed; ordinary root turns keep their artifact reuse."
                      :theme-paint-slots (make-hash-table :test #'eq)
                      :behaviors (make-hash-table :test #'equal)
                      :behavior-resource-keys (make-hash-table :test #'equal)
+                     :observer observer
                      :root-dirty-p t)))
       (puthash buffer runtime etaf--runtime-table)
       (let ((route (etaf-runtime-route-create
@@ -5097,25 +5247,28 @@ backend anchor proof failed; ordinary root turns keep their artifact reuse."
         (puthash (etaf-runtime-mount-epoch runtime) runtime
                  etaf--runtime-route-registry))
       (condition-case err
-          (progn
+          (etaf--runtime-with-operation
+              (runtime 'mount
+                       (format "mount %s" (buffer-name buffer)))
             (etaf--runtime-begin-candidate runtime)
             (setf (etaf-runtime-flushing-p runtime) t
                   (etaf-runtime-root-view-cache runtime)
                   (etaf--runtime-evaluate-root-candidate runtime))
             (unwind-protect
                 (etaf--runtime-render-effect runtime)
-              (setf (etaf-runtime-flushing-p runtime) nil)))
+              (setf (etaf-runtime-flushing-p runtime) nil))
+            (when (etaf-runtime-pending-p runtime)
+              (setf (etaf-runtime-pending-p runtime) nil)
+              (etaf--runtime-request-flush runtime))
+            (when (fboundp 'etaf-events-enable-input)
+              (etaf-events-enable-input buffer))
+            buffer)
         ((error quit)
          (remhash buffer etaf--runtime-table)
          (remhash (etaf-runtime-mount-epoch runtime)
                   etaf--runtime-route-registry)
          (etaf-scope-stop scope)
          (signal (car err) (cdr err))))
-      (when (etaf-runtime-pending-p runtime)
-        (setf (etaf-runtime-pending-p runtime) nil)
-        (etaf--runtime-request-flush runtime))
-      (when (fboundp 'etaf-events-enable-input)
-        (etaf-events-enable-input buffer))
       buffer)))
 
 (defun etaf--runtime-validate-mount-options (options)
@@ -5126,7 +5279,7 @@ backend anchor proof failed; ordinary root turns keep their artifact reuse."
         (unless tail
           (error "ETAF mount option %S has no value" key))
         (pop tail)
-        (unless (memq key '(:viewport-width :viewport-height))
+        (unless (memq key '(:viewport-width :viewport-height :observer))
           (error "Unknown ETAF mount option: %S" key)))))
   (when-let* ((width (plist-get options :viewport-width)))
     (unless (and (numberp width) (> width 0))
@@ -5134,6 +5287,11 @@ backend anchor proof failed; ordinary root turns keep their artifact reuse."
   (when-let* ((height (plist-get options :viewport-height)))
     (unless (and (numberp height) (> height 0))
       (error "ETAF mount :viewport-height must be positive: %S" height)))
+  (when (and (plist-member options :observer)
+             (not (or (null (plist-get options :observer))
+                      (functionp (plist-get options :observer)))))
+    (signal 'wrong-type-argument
+            (list 'functionp (plist-get options :observer))))
   options)
 
 ;;;###autoload
@@ -5141,18 +5299,18 @@ backend anchor proof failed; ordinary root turns keep their artifact reuse."
   "Mount VIEW into BUFFER-OR-NAME and return the live buffer.
 Setup, reactive publication, Ebox rendering, and lifecycle work share one
 framework render-burst allocation budget when the installed Ebox supports it.
-OPTIONS may provide `:viewport-width' in pixels and `:viewport-height' in
-lines, allowing the first publication to use its final layout context instead
-of requiring an immediate viewport rerender."
+OPTIONS may provide `:viewport-width' in pixels, `:viewport-height' in lines,
+and `:observer' as a one-argument flat-report sink.  The observer is installed
+before the first Ebox publication."
   (setq options (etaf--runtime-validate-mount-options options))
   (let ((ebox-viewport-width (plist-get options :viewport-width))
         (ebox-viewport-height (plist-get options :viewport-height)))
     (ebox-call-with-render-burst
-     #'etaf--runtime-mount-now buffer-or-name view)))
+     #'etaf--runtime-mount-now buffer-or-name view
+     (plist-get options :observer))))
 
-;;;###autoload
-(defun etaf-runtime-unmount (&optional runtime)
-  "Unmount RUNTIME and dispose its Component scopes."
+(defun etaf--runtime-unmount-now (runtime)
+  "Unmount RUNTIME and dispose its Component scopes now."
   (let ((runtime (etaf-runtime-require-mounted runtime)))
     (setf (etaf-runtime-mounted-p runtime) nil)
     (when (fboundp 'etaf-events-disable-input)
@@ -5184,6 +5342,24 @@ of requiring an immediate viewport rerender."
     (clrhash (etaf-runtime-resource-registry runtime))
     runtime))
 
+;;;###autoload
+(defun etaf-runtime-unmount (&optional runtime)
+  "Unmount RUNTIME, report the operation, and detach its observer."
+  (let* ((runtime (etaf-runtime-require-mounted runtime))
+         (observer (etaf-runtime-observer runtime))
+         (buffer (etaf-runtime-buffer runtime)))
+    (unwind-protect
+        (etaf--runtime-with-operation (runtime 'unmount "unmount")
+          (etaf--runtime-unmount-now runtime))
+      (when observer
+        (condition-case condition
+            (when (buffer-live-p buffer)
+              (ebox-buffer-set-observer buffer nil))
+          ((error quit)
+           (etaf--runtime-record-observer-diagnostic
+            runtime (list :kind 'detach-failure :condition condition))))
+        (setf (etaf-runtime-observer runtime) nil)))))
+
 ;;;###autoload
 (defun etaf-unmount (&optional runtime)
   "Unmount RUNTIME, defaulting to the active or `current-buffer' Runtime."
diff --git a/etaf.el b/etaf.el
index 9965cfc..fe55b23 100644
--- a/etaf.el
+++ b/etaf.el
@@ -31,6 +31,7 @@
 (require 'etaf-compiler)
 (require 'etaf-component)
 (require 'etaf-reactive)
+(require 'etaf-observer)
 (require 'etaf-context)
 (require 'etaf-resource)
 (require 'etaf-data)
@@ -40,7 +41,6 @@
 (require 'etaf-behavior)
 (require 'etaf-actions)
 (require 'etaf-events)
-(require 'etaf-performance)
 
 (unless (fboundp 'ebox-call-with-render-burst)
   (error "ETAF requires an Ebox build with framework render-burst support"))
diff --git a/tests/etaf-data-tests.el b/tests/etaf-data-tests.el
index 4bc45c5..4a52cc6 100644
--- a/tests/etaf-data-tests.el
+++ b/tests/etaf-data-tests.el
@@ -6,6 +6,7 @@
 
 (require 'ert)
 (require 'etaf-data)
+(require 'etaf-observer)
 
 (defconst etaf-data-test-records
   '((:id 1 :name "Ada" :group "compiler")
@@ -325,4 +326,94 @@
     (should-error (etaf-data-set-page controller 2)
                   :type 'etaf-data-stopped-error)))
 
+(ert-deftest etaf-data-observes-source-capabilities-once-in-call-order ()
+  "Report source load and mutation without timing controller publication."
+  (let* ((source (etaf-data-memory-source '((:id 1)) :id-key :id))
+         (controller (etaf-data-controller source))
+         reports
+         diagnostics
+         (context
+          (etaf--observer-context-create
+           :sink (lambda (report) (push report reports))
+           :operation-id 41
+           :runtime-id 7
+           :buffer-name nil
+           :diagnostic (lambda (diagnostic) (push diagnostic diagnostics)))))
+    (unwind-protect
+        (progn
+          (etaf--observer-call-with-context
+           context
+           (lambda ()
+             (etaf-data-load controller)
+             (etaf-data-mutate controller 'insert '(:id 2))))
+          (setq reports (nreverse reports))
+          (should-not diagnostics)
+          (should (equal '(load mutate load)
+                         (mapcar (lambda (report)
+                                   (plist-get report :stage))
+                                 reports)))
+          (should (equal '(memory memory memory)
+                         (mapcar (lambda (report)
+                                   (plist-get report :provider))
+                                 reports)))
+          (should (equal '(1 nil 1)
+                         (mapcar (lambda (report)
+                                   (plist-get report :page))
+                                 reports)))
+          (should (eq 'insert (plist-get (cadr reports) :operation)))
+          (should (equal '((:id 1) (:id 2))
+                         (etaf-value (etaf-data-items controller))))
+          (should (eq 'success (etaf-value
+                                (etaf-data-status controller)))))
+      (etaf-data-stop controller))))
+
+(ert-deftest etaf-data-observed-source-error-preserves-controller-state ()
+  "Report a source error and preserve the ordinary Data error contract."
+  (let* ((source (etaf-data-source
+                  :load (lambda (&rest _args) (error "unavailable"))))
+         (controller (etaf-data-controller source))
+         reports
+         (context
+          (etaf--observer-context-create
+           :sink (lambda (report) (push report reports))
+           :operation-id 42
+           :runtime-id 7
+           :buffer-name nil
+           :diagnostic #'ignore)))
+    (unwind-protect
+        (progn
+          (should-error
+           (etaf--observer-call-with-context
+            context (lambda () (etaf-data-load controller)))
+           :type 'error)
+          (should (= 1 (length reports)))
+          (should (eq 'data (plist-get (car reports) :provider)))
+          (should (eq 'load (plist-get (car reports) :stage)))
+          (should (eq 'error (plist-get (car reports) :status)))
+          (should (eq 'error (etaf-value (etaf-data-status controller))))
+          (should (string-match-p
+                   "unavailable"
+                   (cadr (etaf-value (etaf-data-error controller))))))
+      (etaf-data-stop controller))))
+
+(ert-deftest etaf-data-source-rejects-invalid-observation-provider ()
+  "Require an explicit source provider to be a non-nil symbol."
+  (should-error
+   (etaf-data-source :provider nil
+                     :load (lambda (&rest _args) (list :items nil)))
+   :type 'wrong-type-argument)
+  (should-error
+   (etaf-data-source :provider 7
+                     :load (lambda (&rest _args) (list :items nil)))
+   :type 'wrong-type-argument))
+
+(ert-deftest etaf-data-unobserved-source-call-bypasses-stage-runtime ()
+  "Keep the standalone source path free of observation work."
+  (let ((source (etaf-data-memory-source '((:id 1)) :id-key :id)))
+    (cl-letf (((symbol-function 'etaf--observer-call-stage)
+               (lambda (&rest _args)
+                 (ert-fail "unobserved Data call entered stage runtime"))))
+      (should (equal '((:id 1))
+                     (plist-get (etaf-data-source-load-page source) :items))))))
+
 ;;; etaf-data-tests.el ends here
diff --git a/tests/etaf-observer-tests.el b/tests/etaf-observer-tests.el
new file mode 100644
index 0000000..4ee1728
--- /dev/null
+++ b/tests/etaf-observer-tests.el
@@ -0,0 +1,168 @@
+;;; etaf-observer-tests.el --- Scoped observer port tests -*- lexical-binding: t; -*-
+
+;; SPDX-License-Identifier: GPL-3.0-or-later
+
+;;; Commentary:
+
+;; Tests for the dynamically scoped ETAF observer port.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(require 'etaf-observer)
+
+(defun etaf-test-observer-context (sink &optional diagnostic)
+  "Return a test observer context using SINK and DIAGNOSTIC."
+  (etaf--observer-context-create
+   :sink sink
+   :operation-id 41
+   :runtime-id 9
+   :buffer-name "*etaf-test*"
+   :diagnostic (or diagnostic #'ignore)))
+
+(ert-deftest etaf-observer-stage-preserves-success-and-metadata ()
+  "Observed stages preserve results and emit required flat metadata."
+  (let (reports)
+    (should
+     (eq 'result
+         (etaf--observer-call-with-context
+          (etaf-test-observer-context
+           (lambda (report) (push report reports)))
+          (lambda ()
+            (etaf-observer-with-stage ('etaf 'render :detail "root")
+              'result)))))
+    (let ((report (car reports)))
+      (should (= 1 (length reports)))
+      (should (= etaf-observer-report-format-version
+                 (plist-get report :format-version)))
+      (should (eq 'etaf (plist-get report :provider)))
+      (should (eq 'render (plist-get report :stage)))
+      (should (= 41 (plist-get report :operation-id)))
+      (should (= 1 (plist-get report :sequence)))
+      (should (= 9 (plist-get report :runtime-id)))
+      (should (equal "*etaf-test*" (plist-get report :buffer-name)))
+      (should (eq 'success (plist-get report :status)))
+      (should (equal "root" (plist-get report :detail)))
+      (should (>= (plist-get report :duration-ms) 0.0)))))
+
+(ert-deftest etaf-observer-stage-preserves-error-and-quit ()
+  "Observed failures are reported and re-signaled without translation."
+  (let (reports error-condition quit-condition)
+    (let ((context
+           (etaf-test-observer-context
+            (lambda (report) (push report reports)))))
+      (setq error-condition
+            (condition-case condition
+                (etaf--observer-call-with-context
+                 context
+                 (lambda ()
+                   (etaf-observer-with-stage ('etaf 'render)
+                     (signal 'wrong-type-argument '(integerp bad)))))
+              (error condition)))
+      (setq quit-condition
+            (condition-case condition
+                (etaf--observer-call-with-context
+                 context
+                 (lambda ()
+                   (etaf-observer-with-stage ('ebox 'commit)
+                     (signal 'quit '(requested)))))
+              (quit condition))))
+    (should (equal '(wrong-type-argument integerp bad) error-condition))
+    (should (equal '(quit requested) quit-condition))
+    (setq reports (nreverse reports))
+    (should (equal '(error quit)
+                   (mapcar (lambda (report) (plist-get report :status))
+                           reports)))
+    (should (equal '(1 2)
+                   (mapcar (lambda (report) (plist-get report :sequence))
+                           reports)))))
+
+(ert-deftest etaf-observer-emits-defensive-flat-copy ()
+  "Observer mutation cannot alter the producer's report snapshot."
+  (let* ((detail (copy-sequence "producer"))
+         (report (list :provider 'ebox :stage 'commit
+                       :status 'success :duration-ms 1.0
+                       :detail (list detail)))
+         (original (copy-tree report)))
+    (etaf--observer-call-with-context
+     (etaf-test-observer-context
+      (lambda (delivered)
+        (setcar delivered :mutated)
+        (setcar (cdr delivered) 99)
+        (aset (car (plist-get delivered :detail)) 0 ?!)))
+     (lambda () (etaf-observer-emit report)))
+    (should (equal original report))
+    (should (equal "producer" detail))))
+
+(ert-deftest etaf-observer-contains-observer-failures-and-invalid-reports ()
+  "Observer and validation failures are diagnostics, not product failures."
+  (let (diagnostics failure)
+    (let ((context
+           (etaf-test-observer-context
+            (lambda (_report)
+              (if (eq failure 'error)
+                  (error "Observer error")
+                (signal 'quit '(observer-quit))))
+            (lambda (diagnostic) (push diagnostic diagnostics)))))
+      (setq failure 'error)
+      (should
+       (eq 'product-result
+           (etaf--observer-call-with-context
+            context
+            (lambda ()
+              (prog1 'product-result
+                (etaf-observer-emit
+                 '(:provider etaf :stage render
+                   :status success :duration-ms 0.0)))))))
+      (setq failure 'quit)
+      (etaf--observer-call-with-context
+       context
+       (lambda ()
+         (etaf-observer-emit
+          '(:provider etaf :stage commit
+            :status success :duration-ms 0.0))))
+      (etaf--observer-call-with-context
+       context
+       (lambda ()
+         (etaf-observer-emit '(:provider etaf :nested (not flat))))))
+    (should (equal '(observer-failure observer-failure invalid-report)
+                   (mapcar (lambda (diagnostic)
+                             (plist-get diagnostic :kind))
+                           (nreverse diagnostics))))))
+
+(ert-deftest etaf-observer-clears-context-during-reentrant-delivery ()
+  "Observer reentry sees no active observation context."
+  (let (context-seen reports)
+    (etaf--observer-call-with-context
+     (etaf-test-observer-context
+      (lambda (report)
+        (push report reports)
+        (setq context-seen etaf--observer-context)
+        (etaf-observer-with-stage ('etaf 'reentrant) 'ignored)))
+     (lambda ()
+       (etaf-observer-with-stage ('etaf 'outer) 'done)))
+    (should-not context-seen)
+    (should (= 1 (length reports)))
+    (should (eq 'outer (plist-get (car reports) :stage)))))
+
+(ert-deftest etaf-observer-nil-path-does-zero-instrumentation ()
+  "The unobserved path does not time, allocate delivery, or inspect GC state."
+  (let ((body-count 0)
+        (etaf--observer-context nil))
+    (cl-letf (((symbol-function 'float-time)
+               (lambda (&optional _time) (error "Unexpected clock read")))
+              ((symbol-function 'etaf--observer-call-stage)
+               (lambda (&rest _arguments) (error "Unexpected stage wrapper")))
+              ((symbol-function 'etaf-observer-emit)
+               (lambda (&rest _arguments) (error "Unexpected report"))))
+      (should
+       (eq 'plain-result
+           (etaf-observer-with-stage ('etaf 'render)
+             (setq body-count (1+ body-count))
+             'plain-result))))
+    (should (= 1 body-count))))
+
+(provide 'etaf-observer-tests)
+
+;;; etaf-observer-tests.el ends here
diff --git a/tests/etaf-resource-tests.el b/tests/etaf-resource-tests.el
index 977e1af..a4523f7 100644
--- a/tests/etaf-resource-tests.el
+++ b/tests/etaf-resource-tests.el
@@ -5,6 +5,7 @@
 ;;; Code:
 
 (require 'ert)
+(require 'etaf-observer)
 (require 'etaf-resource)
 
 (ert-deftest etaf-resource-loads-synchronous-value ()
@@ -108,4 +109,84 @@
     (lambda (_condition) (error "handler")))
    :type 'error))
 
+(ert-deftest etaf-resource-observes-only-loader-execution ()
+  "Report Resource loads while preserving replacement cleanup semantics."
+  (let* ((loads 0)
+         (cleanups 0)
+         reports
+         resource
+         (context
+         (etaf--observer-context-create
+          :sink (lambda (report) (push report reports))
+          :operation-id 51
+          :runtime-id 8
+          :buffer-name nil
+          :diagnostic #'ignore)))
+    (unwind-protect
+        (progn
+          (etaf--observer-call-with-context
+           context
+           (lambda ()
+             (setq resource
+                   (etaf-resource
+                    (lambda ()
+                      (etaf-resource-result
+                       (cl-incf loads)
+                       :cleanup (lambda () (cl-incf cleanups))))))
+             (etaf-resource-load resource)))
+          (setq reports (nreverse reports))
+          (should (equal '(resource resource)
+                         (mapcar (lambda (report)
+                                   (plist-get report :provider))
+                                 reports)))
+          (should (equal '(load load)
+                         (mapcar (lambda (report)
+                                   (plist-get report :stage))
+                                 reports)))
+          (should (equal '(success success)
+                         (mapcar (lambda (report)
+                                   (plist-get report :status))
+                                 reports)))
+          (should (= 2 (etaf-resource-value resource)))
+          (should (= 1 cleanups))
+          (etaf-resource-dispose resource)
+          (should (= 2 cleanups)))
+      (when resource
+        (etaf-resource-dispose resource)))))
+
+(ert-deftest etaf-resource-observed-error-keeps-captured-error-contract ()
+  "Report loader failure without changing Resource error containment."
+  (let* (reports resource
+         (context
+         (etaf--observer-context-create
+          :sink (lambda (report) (push report reports))
+          :operation-id 52
+          :runtime-id 8
+          :buffer-name nil
+          :diagnostic #'ignore)))
+    (unwind-protect
+        (progn
+          (etaf--observer-call-with-context
+           context
+           (lambda ()
+             (setq resource (etaf-resource (lambda () (error "boom"))))))
+          (should (= 1 (length reports)))
+          (should (eq 'error (plist-get (car reports) :status)))
+          (should (eq 'error (etaf-resource-status resource)))
+          (should (string-match-p "boom" (cadr (etaf-resource-error resource)))))
+      (when resource
+        (etaf-resource-dispose resource)))))
+
+(ert-deftest etaf-resource-unobserved-load-bypasses-stage-runtime ()
+  "Keep standalone Resource loading free of observation work."
+  (let (resource)
+    (unwind-protect
+        (cl-letf (((symbol-function 'etaf--observer-call-stage)
+                   (lambda (&rest _args)
+                     (ert-fail "unobserved Resource entered stage runtime"))))
+          (setq resource (etaf-resource (lambda () "ready")))
+          (should (equal "ready" (etaf-resource-value resource))))
+      (when resource
+        (etaf-resource-dispose resource)))))
+
 ;;; etaf-resource-tests.el ends here
diff --git a/tests/etaf-tests.el b/tests/etaf-tests.el
index ce9d2ef..5d85f53 100644
--- a/tests/etaf-tests.el
+++ b/tests/etaf-tests.el
@@ -2410,6 +2410,130 @@ Event composition is a Runtime contract, not a UI-library helper contract."
       (when-let* ((buffer (get-buffer buffer-name)))
         (kill-buffer buffer)))))
 
+(ert-deftest etaf-runtime-observer-covers-initial-publication ()
+  "Observed mount emits TP, Ebox, then one final ETAF operation report."
+  (let ((buffer-name " *etaf-observed-mount-test*") reports)
+    (unwind-protect
+        (progn
+          (etaf-mount
+           buffer-name (etaf-view (box "Observed"))
+           (list :observer
+                 (lambda (report) (push report reports))))
+          (setq reports (nreverse reports))
+          (should (equal (mapcar (lambda (report)
+                                   (plist-get report :provider))
+                                 reports)
+                         '(tp ebox etaf)))
+          (should (equal (mapcar (lambda (report)
+                                   (plist-get report :sequence))
+                                 reports)
+                         '(1 2 3)))
+          (should (equal (delete-dups
+                          (mapcar (lambda (report)
+                                    (plist-get report :operation-id))
+                                  reports))
+                         '(1)))
+          (let ((final (car (last reports))))
+            (should (eq (plist-get final :stage) 'runtime-operation))
+            (should (eq (plist-get final :kind) 'mount))
+            (should (eq (plist-get final :status) 'success))
+            (should (= (plist-get final :generation-before) 0))
+            (should (= (plist-get final :generation-after) 1))))
+      (when-let* ((runtime (etaf-runtime-for-buffer buffer-name)))
+        (etaf-runtime-set-observer runtime nil)
+        (etaf-unmount runtime))
+      (when-let* ((buffer (get-buffer buffer-name)))
+        (kill-buffer buffer)))))
+
+(ert-deftest etaf-runtime-observer-flattens-nested-event-and-detaches ()
+  "Nested event/flush work shares one operation and detach stops reports."
+  (let ((buffer-name " *etaf-observed-event-test*") reports)
+    (unwind-protect
+        (progn
+          (etaf-mount buffer-name
+                      (etaf-view (etaf-test-event-batch-nested)))
+          (let ((runtime (etaf-runtime-for-buffer buffer-name)))
+            (etaf-runtime-set-observer
+             runtime (lambda (report) (push report reports)))
+            (etaf-dispatch-event
+             runtime 'event-batch-nested-outer 'press)
+            (setq reports (nreverse reports))
+            (should (equal (mapcar (lambda (report)
+                                     (plist-get report :provider))
+                                   reports)
+                           '(tp ebox etaf)))
+            (should (= 1 (cl-count 'etaf reports
+                                   :key (lambda (report)
+                                          (plist-get report :provider)))))
+            (should (= 1 (length
+                          (delete-dups
+                           (mapcar (lambda (report)
+                                     (plist-get report :operation-id))
+                                   reports)))))
+            (should (equal "Outer Inner nested"
+                           (etaf-test--buffer-text buffer-name)))
+            (should-not (etaf-runtime-set-observer runtime nil))
+            (setq reports nil)
+            (etaf-dispatch-event
+             runtime 'event-batch-nested-outer 'press)
+            (should-not reports)))
+      (when-let* ((runtime (etaf-runtime-for-buffer buffer-name)))
+        (etaf-unmount runtime))
+      (when-let* ((buffer (get-buffer buffer-name)))
+        (kill-buffer buffer)))))
+
+(ert-deftest etaf-runtime-observer-noop-and-failure-cannot-change-state ()
+  "No-op observation and observer errors preserve exact committed state."
+  (let ((buffer-name " *etaf-observed-noop-test*") reports)
+    (unwind-protect
+        (progn
+          (etaf-mount buffer-name (etaf-view (etaf-test-event-batch-noop)))
+          (let* ((runtime (etaf-runtime-for-buffer buffer-name))
+                 (generation (etaf-runtime-generation runtime))
+                 (before (with-current-buffer buffer-name (buffer-string))))
+            (etaf-runtime-set-observer
+             runtime
+             (lambda (report)
+               (push report reports)
+               (error "observer failure")))
+            (etaf-dispatch-event runtime 'event-batch-noop 'press)
+            (should (= generation (etaf-runtime-generation runtime)))
+            (should (equal-including-properties
+                     before (with-current-buffer buffer-name (buffer-string))))
+            (should (= 1 (length reports)))
+            (should (eq (plist-get (car reports) :provider) 'etaf))
+            (should (cl-find 'observer
+                             (etaf-runtime-diagnostics runtime)
+                             :key (lambda (entry)
+                                    (plist-get entry :phase))))))
+      (when-let* ((runtime (etaf-runtime-for-buffer buffer-name)))
+        (etaf-runtime-set-observer runtime nil)
+        (etaf-unmount runtime))
+      (when-let* ((buffer (get-buffer buffer-name)))
+        (kill-buffer buffer)))))
+
+(ert-deftest etaf-runtime-observer-compare-and-set-preserves-foreign-owner ()
+  "Observer consumers replace only the exact sink they own."
+  (let ((buffer-name " *etaf-observer-owner-test*")
+        (first #'ignore)
+        (second (lambda (_report) nil)))
+    (unwind-protect
+        (progn
+          (etaf-mount buffer-name (etaf-view (box "Observer owner")))
+          (let ((runtime (etaf-runtime-for-buffer buffer-name)))
+            (should (etaf-runtime-compare-and-set-observer runtime nil first))
+            (should-not
+             (etaf-runtime-compare-and-set-observer runtime nil second))
+            (should (etaf-runtime-compare-and-set-observer runtime first second))
+            (should-not
+             (etaf-runtime-compare-and-set-observer runtime first nil))
+            (should (etaf-runtime-compare-and-set-observer runtime second nil))))
+      (when-let* ((runtime (etaf-runtime-for-buffer buffer-name)))
+        (etaf-runtime-set-observer runtime nil)
+        (etaf-unmount runtime))
+      (when-let* ((buffer (get-buffer buffer-name)))
+        (kill-buffer buffer)))))
+
 (ert-deftest etaf-pvec-put-many-preserves-values-and-shares-untouched-branches ()
   "Batch persistent-vector updates match sequential puts and share untouched paths."
   (let* ((untouched-id (* 31 (expt 2 30)))