diff --git a/pi-coding-agent-menu.el b/pi-coding-agent-menu.el
index c705b08..aab40e7 100644
--- a/pi-coding-agent-menu.el
+++ b/pi-coding-agent-menu.el
@@ -189,14 +189,36 @@ from either chat or input buffer."
                              (message "Pi: New session started"))
                          (message "Pi: New session cancelled")))))))
 
-(defun pi-coding-agent--session-dir-name (dir)
-  "Convert DIR to session directory name.
-Matches pi's encoding: --path-with-dashes--.
-Note: Handles both Unix and Windows path separators."
-  (let* ((clean-dir (directory-file-name dir))  ; Remove trailing slash
-         (safe-path (replace-regexp-in-string "[/\\\\:]" "-"
-                                              (replace-regexp-in-string "^[/\\\\]" "" clean-dir))))
-    (concat "--" safe-path "--")))
+(defun pi-coding-agent--session-list-directory (&optional chat-buf)
+  "Return the directory containing CHAT-BUF's current JSONL session file.
+Return nil when the current state has no usable session file.  Relative
+session file names are resolved from the chat buffer's stable session
+directory."
+  (let ((chat-buf (or chat-buf (pi-coding-agent--get-chat-buffer))))
+    (when (and chat-buf (buffer-live-p chat-buf))
+      (with-current-buffer chat-buf
+        (when-let* ((session-file (plist-get pi-coding-agent--state
+                                             :session-file))
+                    ((stringp session-file))
+                    ((not (string-empty-p session-file))))
+          (file-name-directory
+           (expand-file-name session-file
+                             (pi-coding-agent--chat-session-directory
+                              chat-buf))))))))
+
+(defun pi-coding-agent--with-session-list-directory (proc chat-buf callback)
+  "Call CALLBACK with the session list directory for CHAT-BUF.
+When cached state has no session file, fetch fresh state from PROC first."
+  (if-let* ((session-dir (pi-coding-agent--session-list-directory chat-buf)))
+      (funcall callback session-dir)
+    (pi-coding-agent--rpc-async proc '(:type "get_state")
+      (lambda (response)
+        (when (and (plist-get response :success)
+                   (buffer-live-p chat-buf))
+          (pi-coding-agent--apply-state-response chat-buf response))
+        (when (buffer-live-p chat-buf)
+          (funcall callback
+                   (pi-coding-agent--session-list-directory chat-buf)))))))
 
 (defun pi-coding-agent--session-metadata (path)
   "Extract metadata from session file PATH.
@@ -251,43 +273,43 @@ Call this from the chat buffer after switching or loading a session."
     (let ((metadata (pi-coding-agent--session-metadata session-file)))
       (setq pi-coding-agent--session-name (plist-get metadata :session-name)))))
 
-(defun pi-coding-agent--list-sessions (dir)
-  "List available session files for project DIR.
-Returns list of absolute paths to .jsonl files, sorted by modification
-time with most recently used first."
-  (let* ((sessions-base (expand-file-name "~/.pi/agent/sessions/"))
-         (session-dir (expand-file-name (pi-coding-agent--session-dir-name dir) sessions-base)))
-    (when (file-directory-p session-dir)
-      ;; Sort by modification time descending (most recently used first)
-      (sort (directory-files session-dir t "\\.jsonl$")
+(defun pi-coding-agent--list-sessions (session-dir)
+  "List valid session files in SESSION-DIR.
+Returns absolute paths to JSONL pi sessions, sorted by modification time with
+most recently used first."
+  (when (and session-dir (file-directory-p session-dir))
+    (let ((sessions (delq nil
+                          (mapcar (lambda (path)
+                                    (and (pi-coding-agent--session-metadata path)
+                                         path))
+                                  (directory-files session-dir t
+                                                   "\\.jsonl\\'")))))
+      (sort sessions
             (lambda (a b)
-              (time-less-p (file-attribute-modification-time (file-attributes b))
-                           (file-attribute-modification-time (file-attributes a))))))))
+              (time-less-p (file-attribute-modification-time
+                            (file-attributes b))
+                           (file-attribute-modification-time
+                            (file-attributes a))))))))
 
 (defun pi-coding-agent--format-session-choice (path)
   "Format session PATH for display in selector.
-Returns (display-string . path) for `completing-read'.
-Prefers session name over first message when available."
-  (let ((metadata (pi-coding-agent--session-metadata path)))
-    (if metadata
-        (let* ((modified-time (plist-get metadata :modified-time))
-               (session-name (plist-get metadata :session-name))
-               (first-msg (plist-get metadata :first-message))
-               (msg-count (plist-get metadata :message-count))
-               (relative-time (pi-coding-agent--format-relative-time modified-time))
-               ;; Prefer session name, fall back to first message preview
-               (label (cond
-                       (session-name (pi-coding-agent--truncate-string session-name 50))
-                       (first-msg (pi-coding-agent--truncate-string first-msg 50))
-                       (t nil)))
-               (display (if label
-                            (format "%s · %s (%d msgs)"
-                                    label relative-time msg-count)
-                          (format "[empty session] · %s" relative-time))))
-          (cons display path))
-      ;; Fallback to filename if metadata extraction fails
-      (let ((filename (file-name-nondirectory path)))
-        (cons filename path)))))
+Returns (display-string . path) for `completing-read', or nil when PATH is not
+a valid pi session.  Prefers session name over first message when available."
+  (when-let* ((metadata (pi-coding-agent--session-metadata path)))
+    (let* ((modified-time (plist-get metadata :modified-time))
+           (session-name (plist-get metadata :session-name))
+           (first-msg (plist-get metadata :first-message))
+           (msg-count (plist-get metadata :message-count))
+           (relative-time (pi-coding-agent--format-relative-time modified-time))
+           (label (cond
+                   (session-name (pi-coding-agent--truncate-string session-name 50))
+                   (first-msg (pi-coding-agent--truncate-string first-msg 50))
+                   (t nil)))
+           (display (if label
+                        (format "%s · %s (%d msgs)"
+                                label relative-time msg-count)
+                      (format "[empty session] · %s" relative-time))))
+      (cons display path))))
 
 (defun pi-coding-agent--reset-session-state ()
   "Reset all session-specific state for a new session.
@@ -465,43 +487,65 @@ chat buffer from session history."
                  (message "Pi: Failed to reload - %s"
                           (or (plist-get response :error) "unknown error"))))))))))))
 
+(defun pi-coding-agent--resume-selected-session (proc chat-buf selected-path)
+  "Resume SELECTED-PATH using PROC and rebuild CHAT-BUF from its history."
+  (pi-coding-agent--rpc-async
+   proc
+   (list :type "switch_session" :sessionPath selected-path)
+   (lambda (response)
+     (let* ((data (plist-get response :data))
+            (cancelled (plist-get data :cancelled)))
+       (if (and (plist-get response :success)
+                (pi-coding-agent--json-false-p cancelled))
+           (progn
+             (pi-coding-agent--refresh-session-state proc chat-buf selected-path)
+             (pi-coding-agent--load-session-history
+              proc
+              (lambda (count)
+                (message "Pi: Resumed session (%d messages)" count))
+              chat-buf))
+         (message "Pi: Failed to resume session"))))))
+
+(defun pi-coding-agent--resume-session-from-directory (proc chat-buf session-dir)
+  "Prompt for a session from SESSION-DIR, then resume it using PROC.
+CHAT-BUF is rebuilt from the selected session history."
+  (let ((sessions (pi-coding-agent--list-sessions session-dir)))
+    (if (null sessions)
+        (message "Pi: No previous sessions found")
+      (let* ((choices (delq nil
+                            (mapcar #'pi-coding-agent--format-session-choice
+                                    sessions)))
+             (choice-strings (mapcar #'car choices)))
+        (if (null choices)
+            (message "Pi: No previous sessions found")
+          (let* ((choice (completing-read
+                          "Resume session: "
+                          (lambda (string pred action)
+                            (if (eq action 'metadata)
+                                '(metadata (display-sort-function . identity))
+                              (complete-with-action action choice-strings
+                                                    string pred)))
+                          nil t))
+                 (selected-path (cdr (assoc choice choices))))
+            (when selected-path
+              (pi-coding-agent--resume-selected-session
+               proc chat-buf selected-path))))))))
+
 (defun pi-coding-agent-resume-session ()
-  "Resume a previous pi session from the current project."
+  "Resume a previous pi session stored beside the current session file."
   (interactive)
   (when-let* ((proc (pi-coding-agent--get-process))
-              (dir (pi-coding-agent--session-directory))
               (chat-buf (pi-coding-agent--get-chat-buffer)))
     (when (pi-coding-agent--session-transition-ready-p chat-buf "resume")
-      (let ((sessions (pi-coding-agent--list-sessions dir)))
-        (if (null sessions)
-            (message "Pi: No previous sessions found")
-          (let* ((choices (mapcar #'pi-coding-agent--format-session-choice sessions))
-                 (choice-strings (mapcar #'car choices))
-                 (choice (completing-read "Resume session: "
-                                          (lambda (string pred action)
-                                            (if (eq action 'metadata)
-                                                '(metadata (display-sort-function . identity))
-                                              (complete-with-action action choice-strings string pred)))
-                                          nil t))
-                 (selected-path (cdr (assoc choice choices))))
-            (when selected-path
-              (pi-coding-agent--rpc-async
-               proc
-               (list :type "switch_session" :sessionPath selected-path)
-               (lambda (response)
-                 (let* ((data (plist-get response :data))
-                        (cancelled (plist-get data :cancelled)))
-                   (if (and (plist-get response :success)
-                            (pi-coding-agent--json-false-p cancelled))
-                       (progn
-                         (pi-coding-agent--refresh-session-state
-                          proc chat-buf selected-path)
-                         (pi-coding-agent--load-session-history
-                          proc
-                          (lambda (count)
-                            (message "Pi: Resumed session (%d messages)" count))
-                          chat-buf))
-                     (message "Pi: Failed to resume session"))))))))))))
+      (pi-coding-agent--with-session-list-directory
+       proc chat-buf
+       (lambda (session-dir)
+         (cond
+          ((not session-dir)
+           (message "Pi: Session file not available"))
+          ((pi-coding-agent--session-transition-ready-p chat-buf "resume")
+           (pi-coding-agent--resume-session-from-directory
+            proc chat-buf session-dir))))))))
 
 ;;;; Model and Thinking
 
diff --git a/test/pi-coding-agent-input-test.el b/test/pi-coding-agent-input-test.el
index 74ca247..1a1da64 100644
--- a/test/pi-coding-agent-input-test.el
+++ b/test/pi-coding-agent-input-test.el
@@ -1367,48 +1367,6 @@ This ensures history loads correctly when callback runs in arbitrary context."
       (when (buffer-live-p chat-buf)
         (kill-buffer chat-buf)))))
 
-(ert-deftest pi-coding-agent-test-session-dir-name ()
-  "Session directory name derived from project path."
-  (should (equal (pi-coding-agent--session-dir-name "/home/daniel/co/pi-coding-agent")
-                 "--home-daniel-co-pi-coding-agent--"))
-  (should (equal (pi-coding-agent--session-dir-name "/tmp/test")
-                 "--tmp-test--")))
-
-(ert-deftest pi-coding-agent-test-list-sessions-sorted-by-mtime ()
-  "Sessions are sorted by modification time, most recent first.
-Regression test for #25: sessions were sorted by filename (creation time)
-and then re-sorted alphabetically by completing-read."
-  (let* ((temp-base (make-temp-file "pi-coding-agent-sessions-" t))
-         (session-dir (expand-file-name "--test-project--" temp-base))
-         ;; Create files with names that would sort differently alphabetically
-         (old-file (expand-file-name "2024-01-01_10-00-00.jsonl" session-dir))
-         (new-file (expand-file-name "2024-01-01_09-00-00.jsonl" session-dir)))
-    (unwind-protect
-        (progn
-          (make-directory session-dir t)
-          (let* ((now (current-time))
-                 (old-time (time-subtract now (seconds-to-time 10)))
-                 (new-time (time-subtract now (seconds-to-time 5))))
-            ;; Create "old" file first
-            (with-temp-file old-file (insert "{}"))
-            (set-file-times old-file old-time)
-            ;; Create "new" file second (more recent mtime despite earlier filename)
-            (with-temp-file new-file (insert "{}"))
-            (set-file-times new-file new-time))
-          ;; Directly call directory-files and sort logic to test sorting
-          (let* ((files (directory-files session-dir t "\\.jsonl$"))
-                 (sorted (sort files
-                               (lambda (a b)
-                                 (time-less-p
-                                  (file-attribute-modification-time (file-attributes b))
-                                  (file-attribute-modification-time (file-attributes a)))))))
-            ;; new-file should be first (most recent mtime)
-            ;; even though "09-00-00" < "10-00-00" alphabetically
-            (should (equal (length sorted) 2))
-            (should (string-suffix-p "09-00-00.jsonl" (car sorted)))))
-      ;; Cleanup
-      (delete-directory temp-base t))))
-
 (ert-deftest pi-coding-agent-test-session-metadata-extracts-first-message ()
   "pi-coding-agent--session-metadata extracts first user message text."
   (let ((temp-file (make-temp-file "pi-coding-agent-test-session" nil ".jsonl")))
diff --git a/test/pi-coding-agent-menu-test.el b/test/pi-coding-agent-menu-test.el
index d14cbf0..ace3938 100644
--- a/test/pi-coding-agent-menu-test.el
+++ b/test/pi-coding-agent-menu-test.el
@@ -1049,71 +1049,151 @@ replaced by the resumed or forked history."
                            (overlay-get ov 'pi-coding-agent-tool-block))
                          (overlays-in (point-min) (point-max))))))
 
+(defun pi-coding-agent-test--write-session-file (path &optional text)
+  "Write a minimal pi session file to PATH with optional first message TEXT."
+  (with-temp-file path
+    (insert (json-encode '(:type "session" :id "test")) "\n")
+    (when text
+      (insert (json-encode `(:type "message"
+                             :message (:role "user"
+                                       :content [(:type "text" :text ,text)])))
+              "\n"))))
+
+(ert-deftest pi-coding-agent-test-session-list-directory-uses-session-file-parent ()
+  "Session listing uses the current JSONL session file parent directory."
+  (let* ((project-dir (pi-coding-agent-test--make-temp-directory
+                       "pi-coding-agent-project-"))
+         (expected-dir (file-name-as-directory
+                        (expand-file-name "sessions" project-dir))))
+    (unwind-protect
+        (with-temp-buffer
+          (pi-coding-agent-chat-mode)
+          (pi-coding-agent--set-chat-session-identity project-dir)
+          (setq pi-coding-agent--state '(:session-file "sessions/current.jsonl"))
+          (should (equal (pi-coding-agent--session-list-directory (current-buffer))
+                         expected-dir))
+          (setq pi-coding-agent--state '(:session-file ""))
+          (should-not (pi-coding-agent--session-list-directory (current-buffer)))
+          (setq pi-coding-agent--state '(:session-file :json-false))
+          (should-not (pi-coding-agent--session-list-directory (current-buffer))))
+      (delete-directory project-dir t))))
+
+(ert-deftest pi-coding-agent-test-list-sessions-sorted-by-mtime ()
+  "Session files are sorted by modification time, most recent first."
+  (let* ((session-dir (pi-coding-agent-test--make-temp-directory
+                       "pi-coding-agent-sessions-"))
+         (old-file (expand-file-name "2024-01-01_10-00-00.jsonl" session-dir))
+         (new-file (expand-file-name "2024-01-01_09-00-00.jsonl" session-dir)))
+    (unwind-protect
+        (progn
+          (let* ((now (current-time))
+                 (old-time (time-subtract now (seconds-to-time 10)))
+                 (new-time (time-subtract now (seconds-to-time 5))))
+            (pi-coding-agent-test--write-session-file old-file "old")
+            (set-file-times old-file old-time)
+            (pi-coding-agent-test--write-session-file new-file "new")
+            (set-file-times new-file new-time))
+          (let ((sessions (pi-coding-agent--list-sessions session-dir)))
+            (should (equal (length sessions) 2))
+            (should (string-suffix-p "09-00-00.jsonl" (car sessions)))))
+      (delete-directory session-dir t))))
+
+(ert-deftest pi-coding-agent-test-list-sessions-filters-invalid-jsonl-files ()
+  "Session listing ignores JSONL files that are not pi sessions."
+  (let* ((session-dir (pi-coding-agent-test--make-temp-directory
+                       "pi-coding-agent-sessions-"))
+         (session-file (expand-file-name "session.jsonl" session-dir))
+         (other-file (expand-file-name "other.jsonl" session-dir)))
+    (unwind-protect
+        (progn
+          (pi-coding-agent-test--write-session-file session-file "hello")
+          (with-temp-file other-file (insert "{}\n"))
+          (should (equal (pi-coding-agent--list-sessions session-dir)
+                         (list session-file))))
+      (delete-directory session-dir t))))
+
 (ert-deftest pi-coding-agent-test-resume-session-from-input-switches-session-and-rebuilds-history ()
   "Resuming from the input buffer refreshes the linked chat and session state."
-  (let ((dir "/tmp/pi-coding-agent-test-resume-happy/")
-        (shown-message nil)
-        (rpc-calls nil))
-    (pi-coding-agent-test-with-mock-session dir
-      (let* ((chat-buf (get-buffer (pi-coding-agent-test--chat-buffer-name dir)))
-             (input-buf (get-buffer (pi-coding-agent-test--input-buffer-name dir)))
-             (target-session "/tmp/resume-target.jsonl")
-             (messages [(:role "assistant"
-                         :content [(:type "text" :text "Resumed history")]
-                         :timestamp 1704067200000)]))
-        (pi-coding-agent-test--seed-stale-session-rebuild-state
-         chat-buf "STALE RESUME CONTENT")
-        (cl-letf (((symbol-function 'pi-coding-agent--session-directory)
-                   (lambda () dir))
-                  ((symbol-function 'pi-coding-agent--list-sessions)
-                   (lambda (_dir) (list target-session)))
-                  ((symbol-function 'pi-coding-agent--format-session-choice)
-                   (lambda (_path)
-                     (cons "Resume target" target-session)))
-                  ((symbol-function 'completing-read)
-                   (lambda (&rest _) "Resume target"))
-                  ((symbol-function 'pi-coding-agent--rpc-async)
-                   (lambda (_proc cmd cb)
-                     (push (plist-get cmd :type) rpc-calls)
-                     (pcase (plist-get cmd :type)
-                       ("switch_session"
-                        (should (equal (plist-get cmd :sessionPath)
-                                       target-session))
-                        (funcall cb '(:success t :data (:cancelled :false))))
-                       ("get_state"
-                        (funcall cb '(:success t
-                                      :data (:model (:name "resumed-model")
-                                             :thinkingLevel "medium"
-                                             :isStreaming :json-false
-                                             :isCompacting :json-false
-                                             :sessionId "resumed-session-id"
-                                             :sessionFile "/tmp/resumed.jsonl"
-                                             :messageCount 1
-                                             :pendingMessageCount 0))))
-                       ("get_messages"
-                        (funcall cb (list :success t :data (list :messages messages))))
-                       (_
-                        (ert-fail (format "Unexpected RPC during resume test: %S"
-                                          cmd))))))
-                  ((symbol-function 'pi-coding-agent--update-session-name-from-file)
-                   #'ignore)
-                  ((symbol-function 'pi-coding-agent--refresh-header) #'ignore)
-                  ((symbol-function 'message)
-                   (lambda (fmt &rest args)
-                     (setq shown-message (apply #'format fmt args)))))
-          (with-current-buffer input-buf
-            (pi-coding-agent-resume-session)))
-        (with-current-buffer chat-buf
-          (should (equal (plist-get pi-coding-agent--state :session-id)
-                         "resumed-session-id"))
-          (should (equal (plist-get pi-coding-agent--state :session-file)
-                         "/tmp/resumed.jsonl"))
-          (should (string-match-p "Resumed history" (buffer-string))))
-        (pi-coding-agent-test--assert-clean-session-rebuild
-         chat-buf messages "STALE RESUME CONTENT")
-        (should (equal (nreverse rpc-calls)
-                       '("switch_session" "get_state" "get_messages")))
-        (should (equal shown-message "Pi: Resumed session (1 messages)"))))))
+  (let* ((dir (pi-coding-agent-test--make-temp-directory
+               "pi-coding-agent-test-resume-happy-"))
+         (session-dir (pi-coding-agent-test--make-temp-directory
+                       "pi-coding-agent-test-current-sessions-"))
+         (current-session (expand-file-name "current.jsonl" session-dir))
+         (target-session (expand-file-name "target.jsonl" session-dir))
+         (resumed-session (expand-file-name "resumed.jsonl" session-dir))
+         (shown-message nil)
+         (listed-dir nil)
+         (rpc-calls nil))
+    (unwind-protect
+        (pi-coding-agent-test-with-mock-session dir
+          (let* ((chat-buf (get-buffer (pi-coding-agent-test--chat-buffer-name dir)))
+                 (input-buf (get-buffer
+                             (pi-coding-agent-test--input-buffer-name dir)))
+                 (messages [(:role "assistant"
+                             :content [(:type "text" :text "Resumed history")]
+                             :timestamp 1704067200000)]))
+            (pi-coding-agent-test--seed-stale-session-rebuild-state
+             chat-buf "STALE RESUME CONTENT")
+            (with-current-buffer chat-buf
+              (setq pi-coding-agent--state
+                    (plist-put pi-coding-agent--state :session-file
+                               current-session)))
+            (cl-letf (((symbol-function 'pi-coding-agent--list-sessions)
+                       (lambda (session-dir)
+                         (setq listed-dir session-dir)
+                         (list target-session)))
+                      ((symbol-function 'pi-coding-agent--format-session-choice)
+                       (lambda (_path)
+                         (cons "Resume target" target-session)))
+                      ((symbol-function 'completing-read)
+                       (lambda (&rest _) "Resume target"))
+                      ((symbol-function 'pi-coding-agent--rpc-async)
+                       (lambda (_proc cmd cb)
+                         (push (plist-get cmd :type) rpc-calls)
+                         (pcase (plist-get cmd :type)
+                           ("switch_session"
+                            (should (equal (plist-get cmd :sessionPath)
+                                           target-session))
+                            (funcall cb '(:success t :data (:cancelled :false))))
+                           ("get_state"
+                            (funcall cb `(:success t
+                                          :data (:model (:name "resumed-model")
+                                                 :thinkingLevel "medium"
+                                                 :isStreaming :json-false
+                                                 :isCompacting :json-false
+                                                 :sessionId "resumed-session-id"
+                                                 :sessionFile ,resumed-session
+                                                 :messageCount 1
+                                                 :pendingMessageCount 0))))
+                           ("get_messages"
+                            (funcall cb (list :success t
+                                              :data (list :messages messages))))
+                           (_
+                            (ert-fail
+                             (format "Unexpected RPC during resume test: %S"
+                                     cmd))))))
+                      ((symbol-function 'pi-coding-agent--update-session-name-from-file)
+                       #'ignore)
+                      ((symbol-function 'pi-coding-agent--refresh-header) #'ignore)
+                      ((symbol-function 'message)
+                       (lambda (fmt &rest args)
+                         (setq shown-message (apply #'format fmt args)))))
+              (with-current-buffer input-buf
+                (pi-coding-agent-resume-session)))
+            (with-current-buffer chat-buf
+              (should (equal (plist-get pi-coding-agent--state :session-id)
+                             "resumed-session-id"))
+              (should (equal (plist-get pi-coding-agent--state :session-file)
+                             resumed-session))
+              (should (string-match-p "Resumed history" (buffer-string))))
+            (pi-coding-agent-test--assert-clean-session-rebuild
+             chat-buf messages "STALE RESUME CONTENT")
+            (should (equal listed-dir session-dir))
+            (should (equal (nreverse rpc-calls)
+                           '("switch_session" "get_state" "get_messages")))
+            (should (equal shown-message "Pi: Resumed session (1 messages)"))))
+      (delete-directory dir t)
+      (delete-directory session-dir t))))
 
 (ert-deftest pi-coding-agent-test-fork-from-input-switches-session-rebuilds-history-and-prefills-input ()
   "Forking from the input buffer rebuilds chat history and prefills input."
@@ -1191,29 +1271,117 @@ replaced by the resumed or forked history."
 
 (ert-deftest pi-coding-agent-test-resume-session-skips-while-streaming ()
   "Resume refuses to switch sessions while the current chat is busy."
-  (let ((shown-message nil)
-        (listed-sessions nil))
-    (pi-coding-agent-test-with-mock-session "/tmp/pi-coding-agent-test-resume-streaming/"
-      (let ((chat-buf (get-buffer (pi-coding-agent-test--chat-buffer-name
-                                   "/tmp/pi-coding-agent-test-resume-streaming/"))))
-        (with-current-buffer chat-buf
-          (setq pi-coding-agent--status 'streaming))
-        (cl-letf (((symbol-function 'pi-coding-agent--get-process) (lambda () 'mock-proc))
-                  ((symbol-function 'pi-coding-agent--session-directory)
-                   (lambda () "/tmp/pi-coding-agent-test-resume-streaming/"))
-                  ((symbol-function 'pi-coding-agent--list-sessions)
-                   (lambda (_dir)
-                     (setq listed-sessions t)
-                     '("/tmp/pi-coding-agent-test-resume-streaming/session.jsonl")))
-                  ((symbol-function 'message)
-                   (lambda (fmt &rest args)
-                     (setq shown-message (apply #'format fmt args)))))
-          (with-current-buffer chat-buf
-            (pi-coding-agent-resume-session)))))
+  (let* ((dir (pi-coding-agent-test--make-temp-directory
+               "pi-coding-agent-test-resume-streaming-"))
+         (shown-message nil)
+         (listed-sessions nil))
+    (unwind-protect
+        (pi-coding-agent-test-with-mock-session dir
+          (let ((chat-buf (get-buffer
+                           (pi-coding-agent-test--chat-buffer-name dir))))
+            (with-current-buffer chat-buf
+              (setq pi-coding-agent--status 'streaming))
+            (cl-letf (((symbol-function 'pi-coding-agent--get-process)
+                       (lambda () 'mock-proc))
+                      ((symbol-function 'pi-coding-agent--list-sessions)
+                       (lambda (_dir)
+                         (setq listed-sessions t)
+                         (list "session.jsonl")))
+                      ((symbol-function 'message)
+                       (lambda (fmt &rest args)
+                         (setq shown-message (apply #'format fmt args)))))
+              (with-current-buffer chat-buf
+                (pi-coding-agent-resume-session)))))
+      (delete-directory dir t))
     (should-not listed-sessions)
     (should (equal shown-message
                    "Pi: Cannot resume while streaming"))))
 
+(ert-deftest pi-coding-agent-test-resume-session-fetches-missing-session-file ()
+  "Resume asks pi for state before listing sessions when the cache is empty."
+  (let* ((dir (pi-coding-agent-test--make-temp-directory
+               "pi-coding-agent-test-resume-no-state-"))
+         (session-dir (pi-coding-agent-test--make-temp-directory
+                       "pi-coding-agent-test-session-files-"))
+         (session-file (expand-file-name "current.jsonl" session-dir))
+         (shown-message nil)
+         (listed-dir nil)
+         (rpc-calls nil))
+    (unwind-protect
+        (pi-coding-agent-test-with-mock-session dir
+          (let ((chat-buf (get-buffer
+                           (pi-coding-agent-test--chat-buffer-name dir))))
+            (with-current-buffer chat-buf
+              (setq pi-coding-agent--status 'idle
+                    pi-coding-agent--state nil))
+            (cl-letf (((symbol-function 'pi-coding-agent--get-process)
+                       (lambda () 'mock-proc))
+                      ((symbol-function 'pi-coding-agent--rpc-async)
+                       (lambda (_proc cmd cb)
+                         (push (plist-get cmd :type) rpc-calls)
+                         (should (equal (plist-get cmd :type) "get_state"))
+                         (funcall cb `(:success t
+                                       :data (:model (:name "model")
+                                              :thinkingLevel "medium"
+                                              :isStreaming :json-false
+                                              :isCompacting :json-false
+                                              :sessionId "session-id"
+                                              :sessionFile ,session-file
+                                              :messageCount 0
+                                              :pendingMessageCount 0)))))
+                      ((symbol-function 'pi-coding-agent--list-sessions)
+                       (lambda (session-dir)
+                         (setq listed-dir session-dir)
+                         nil))
+                      ((symbol-function 'message)
+                       (lambda (fmt &rest args)
+                         (setq shown-message (apply #'format fmt args)))))
+              (with-current-buffer chat-buf
+                (pi-coding-agent-resume-session)))))
+      (delete-directory dir t)
+      (delete-directory session-dir t))
+    (should (equal listed-dir session-dir))
+    (should (equal (nreverse rpc-calls) '("get_state")))
+    (should (equal shown-message "Pi: No previous sessions found"))))
+
+(ert-deftest pi-coding-agent-test-resume-session-reports-missing-session-file ()
+  "Resume stops clearly when pi state has no session file."
+  (let* ((dir (pi-coding-agent-test--make-temp-directory
+               "pi-coding-agent-test-resume-no-file-"))
+         (shown-message nil)
+         (listed-sessions nil))
+    (unwind-protect
+        (pi-coding-agent-test-with-mock-session dir
+          (let ((chat-buf (get-buffer
+                           (pi-coding-agent-test--chat-buffer-name dir))))
+            (with-current-buffer chat-buf
+              (setq pi-coding-agent--status 'idle
+                    pi-coding-agent--state nil))
+            (cl-letf (((symbol-function 'pi-coding-agent--get-process)
+                       (lambda () 'mock-proc))
+                      ((symbol-function 'pi-coding-agent--rpc-async)
+                       (lambda (_proc _cmd cb)
+                         (funcall cb '(:success t
+                                       :data (:model (:name "model")
+                                              :thinkingLevel "medium"
+                                              :isStreaming :json-false
+                                              :isCompacting :json-false
+                                              :sessionId "session-id"
+                                              :messageCount 0
+                                              :pendingMessageCount 0)))))
+                      ((symbol-function 'pi-coding-agent--list-sessions)
+                       (lambda (_session-dir)
+                         (setq listed-sessions t)
+                         nil))
+                      ((symbol-function 'message)
+                       (lambda (fmt &rest args)
+                         (setq shown-message (apply #'format fmt args)))))
+              (with-current-buffer chat-buf
+                (pi-coding-agent-resume-session)))))
+      (delete-directory dir t))
+    (should-not listed-sessions)
+    (should (equal shown-message "Pi: Session file not available"))))
+
 (ert-deftest pi-coding-agent-test-fork-waits-for-local-user-echo ()
   "Fork refuses to switch sessions while a local prompt is awaiting echo."
   (let ((shown-message nil)