feat: display inline images from tool results in chat buffer

When a tool (e.g. read) returns image content blocks alongside text,
the images are now rendered inline inside the tool block overlay.

In GUI Emacs: decoded and displayed via create-image/insert-image with
max-width/max-height scaling to fit the window.

In terminal Emacs: a text placeholder showing MIME type and size.

Implementation:
- New struct slot: tool-block.image-blocks stores content for toggle
- pi-coding-agent--mime-to-image-type: MIME string to Emacs type symbol
- pi-coding-agent--insert-inline-image: decode + insert or placeholder
- pi-coding-agent--insert-tool-images: iterate content, insert images
- display-tool-end: calls insert-tool-images after text rendering
- toggle-tool-output: re-inserts images from stored blocks after toggle

Handles: corrupt base64, unknown MIME types, empty data, vectors and
lists, multiple image blocks, image-only results (no text).

12 new tests covering all paths. 942/942 full suite passes.

Author: Conor Nash

pi-coding-agent-render.el

@@ -1383,7 +1383,8 @@ are left alone."
   path
   offset
   line-map
-  last-tail)
+  last-tail
+  image-blocks)
 
 (defun pi-coding-agent--ensure-live-tool-blocks ()
   "Return the live tool block registry for the current buffer."
@@ -1524,6 +1525,67 @@ needed for compatibility, the current non-keyed pending block."
     (pi-coding-agent--tool-block-refresh-overlay block))
   block)
 
+(defun pi-coding-agent--tool-block-set-image-blocks (block image-blocks)
+  "Store IMAGE-BLOCKS on BLOCK for re-insertion after toggle."
+  (when block
+    (setf (pi-coding-agent--tool-block-image-blocks block) image-blocks))
+  block)
+
+(defun pi-coding-agent--mime-to-image-type (mime-type)
+  "Convert MIME-TYPE string to Emacs image type symbol.
+Returns nil for unsupported types."
+  (pcase mime-type
+    ((or "image/jpeg" "image/jpg") 'jpeg)
+    ("image/png" 'png)
+    ("image/gif" 'gif)
+    ("image/webp" 'webp)
+    (_ nil)))
+
+(defun pi-coding-agent--insert-inline-image (data mime-type)
+  "Insert inline image decoded from base64 DATA with MIME-TYPE.
+In GUI Emacs with the required image type support, decodes DATA and
+inserts a scaled image via `insert-image'.  Otherwise inserts a text
+placeholder.  Returns non-nil if a graphical image was inserted."
+  (condition-case nil
+      (let* ((type (pi-coding-agent--mime-to-image-type mime-type))
+             (gui-p (and type
+                        (display-images-p)
+                        (image-type-available-p type)))
+             (raw (base64-decode-string data)))
+        (if (and gui-p (> (length raw) 0))
+            (let ((img (create-image raw type t
+                         :max-width (truncate
+                                     (* 0.9 (max 400 (window-pixel-width))))
+                         :max-height (truncate
+                                      (* 0.5 (max 300 (window-pixel-height)))))))
+              (insert-image img "[image]")
+              t)
+          (insert (propertize
+                   (format "[Image: %s, %s]"
+                           (or mime-type "unknown")
+                           (file-size-human-readable (length raw)))
+                   'face 'pi-coding-agent-tool-header
+                   'pi-coding-agent-no-fontify t))
+          nil))
+    (error
+     (insert (propertize
+              (format "[Image: %s, decode error]" (or mime-type "unknown"))
+              'face 'pi-coding-agent-tool-header
+              'pi-coding-agent-no-fontify t))
+     nil)))
+
+(defun pi-coding-agent--insert-tool-images (content)
+  "Insert inline images from CONTENT blocks at point.
+CONTENT is a sequence of content block plists.  Only blocks with
+:type \"image\" are processed.  A newline is inserted before each image."
+  (seq-doseq (block content)
+    (when (equal (plist-get block :type) "image")
+      (let ((data (plist-get block :data))
+            (mime (plist-get block :mimeType)))
+        (when (and data (> (length data) 0))
+          (insert "\n")
+          (pi-coding-agent--insert-inline-image data mime))))))
+
 (defun pi-coding-agent--tool-block-create
     (tool-name args &optional tool-call-id order preview-state)
   "Insert a live tool block for TOOL-NAME with ARGS and return it.
@@ -2018,6 +2080,9 @@ if none exists, render the result at point without a live overlay."
                  (string-trim-right display-content "\n+")
                  lang
                  is-edit-diff))
+              ;; Insert any image content blocks after text
+              (pi-coding-agent--insert-tool-images content)
+              (pi-coding-agent--tool-block-set-image-blocks block content)
               (set-marker end-marker (point))
               (pi-coding-agent--tool-block-refresh-overlay block)
               ;; Note: no [error] badge — error content in the block is sufficient,
@@ -2044,6 +2109,8 @@ if none exists, render the result at point without a live overlay."
                (string-trim-right display-content "\n+")
                lang
                is-edit-diff))
+            ;; Insert any image content blocks after text
+            (pi-coding-agent--insert-tool-images content)
             (insert "\n")))))))
 
 (defun pi-coding-agent--ranges-excluding-property (start end prop)
@@ -2108,6 +2175,10 @@ Preserves window scroll position during the toggle."
           ;; Toggle: if currently expanded, show collapsed (and vice versa)
           (pi-coding-agent--insert-tool-content-with-toggle
            preview-content full-content lang is-edit-diff hidden-count (not expanded))
+          ;; Re-insert any image blocks stored on the tool block struct
+          (when-let* ((block (pi-coding-agent--tool-block-from-overlay ov))
+                      (img-content (pi-coding-agent--tool-block-image-blocks block)))
+            (pi-coding-agent--insert-tool-images img-content))
           ;; Ensure fontification of inserted content (JIT font-lock is lazy)
           ;; while excluding metadata-like details payload.
           (pi-coding-agent--font-lock-ensure-excluding-property

test/pi-coding-agent-render-test.el

@@ -6231,5 +6231,171 @@ events where the header text hasn't changed."
       (goto-char (marker-position pi-coding-agent--hot-tail-start))
       (should (looking-at "Assistant")))))
 
+;;; Inline Image Display
+
+(ert-deftest pi-coding-agent-test-mime-to-image-type ()
+  "MIME type conversion covers backend types and rejects unknowns."
+  (should (eq (pi-coding-agent--mime-to-image-type "image/png") 'png))
+  (should (eq (pi-coding-agent--mime-to-image-type "image/jpeg") 'jpeg))
+  (should (eq (pi-coding-agent--mime-to-image-type "image/jpg") 'jpeg))
+  (should (eq (pi-coding-agent--mime-to-image-type "image/gif") 'gif))
+  (should (eq (pi-coding-agent--mime-to-image-type "image/webp") 'webp))
+  (should-not (pi-coding-agent--mime-to-image-type "image/tga"))
+  (should-not (pi-coding-agent--mime-to-image-type "text/plain")))
+
+(ert-deftest pi-coding-agent-test-insert-inline-image-placeholder ()
+  "insert-inline-image produces a placeholder in batch mode."
+  ;; In batch mode display-images-p is nil, so we always get the placeholder.
+  (with-temp-buffer
+    (pi-coding-agent--insert-inline-image "iVBORw0KGgo=" "image/png")
+    (let ((content (buffer-substring-no-properties (point-min) (point-max))))
+      ;; Should contain MIME type and a size indicator
+      (should (string-match-p "Image:" content))
+      (should (string-match-p "image/png" content)))))
+
+(ert-deftest pi-coding-agent-test-insert-inline-image-error-path ()
+  "insert-inline-image handles corrupt base64 gracefully."
+  (with-temp-buffer
+    (pi-coding-agent--insert-inline-image "!!!invalid!!!" "image/png")
+    (should (string-match-p "decode error"
+                            (buffer-substring-no-properties
+                             (point-min) (point-max))))))
+
+(ert-deftest pi-coding-agent-test-tool-end-image-block-renders ()
+  "Image content block in tool result is displayed."
+  (with-temp-buffer
+    (pi-coding-agent-chat-mode)
+    (pi-coding-agent--display-tool-end
+     "read" '(:path "photo.png")
+     '((:type "text" :text "Read image file [image/png]")
+       (:type "image" :data "iVBORw0KGgo=" :mimeType "image/png"))
+     nil nil)
+    (let ((content (buffer-substring-no-properties (point-min) (point-max))))
+      (should (string-match-p "Read image file" content))
+      ;; In batch: placeholder text; in GUI: [image] fallback from insert-image
+      (should (or (string-match-p "\\[Image:" content)
+                  (string-match-p "\\[image\\]" content))))))
+
+(ert-deftest pi-coding-agent-test-tool-end-text-only-no-image ()
+  "Tool result with only text blocks has no image placeholder."
+  (with-temp-buffer
+    (pi-coding-agent-chat-mode)
+    (pi-coding-agent--display-tool-end
+     "bash" '(:command "ls")
+     '((:type "text" :text "file1\nfile2"))
+     nil nil)
+    (let ((content (buffer-substring-no-properties (point-min) (point-max))))
+      (should (string-match-p "file1" content))
+      (should-not (string-match-p "\\[Image:" content))
+      (should-not (string-match-p "\\[image\\]" content)))))
+
+(ert-deftest pi-coding-agent-test-tool-end-image-inside-overlay ()
+  "Image content is contained within the tool block overlay."
+  (with-temp-buffer
+    (pi-coding-agent-chat-mode)
+    (let ((block (pi-coding-agent--display-tool-start
+                  "read" '(:path "photo.png"))))
+      (pi-coding-agent--display-tool-end
+       "read" '(:path "photo.png")
+       '((:type "text" :text "Read image file [image/png]")
+         (:type "image" :data "iVBORw0KGgo=" :mimeType "image/png"))
+       nil nil block)
+      (let ((ov (seq-find (lambda (o) (overlay-get o 'pi-coding-agent-tool-block))
+                          (overlays-in (point-min) (point-max)))))
+        (should ov)
+        (let ((ov-content (buffer-substring-no-properties
+                           (overlay-start ov) (overlay-end ov))))
+          (should (or (string-match-p "\\[Image:" ov-content)
+                      (string-match-p "\\[image\\]" ov-content))))))))
+
+(ert-deftest pi-coding-agent-test-tool-end-image-blocks-stored ()
+  "Image content blocks are stored on the tool block struct."
+  (with-temp-buffer
+    (pi-coding-agent-chat-mode)
+    (let ((block (pi-coding-agent--display-tool-start
+                  "read" '(:path "photo.png"))))
+      (pi-coding-agent--display-tool-end
+       "read" '(:path "photo.png")
+       '((:type "text" :text "Read image")
+         (:type "image" :data "iVBORw0KGgo=" :mimeType "image/png"))
+       nil nil block)
+      (should (pi-coding-agent--tool-block-image-blocks block))
+      ;; Content should include image block
+      (should (seq-some (lambda (b) (equal (plist-get b :type) "image"))
+                        (pi-coding-agent--tool-block-image-blocks block))))))
+
+(ert-deftest pi-coding-agent-test-tool-end-multiple-images ()
+  "Multiple image blocks each produce output."
+  (with-temp-buffer
+    (pi-coding-agent-chat-mode)
+    (pi-coding-agent--display-tool-end
+     "read" '(:path "photo.png")
+     '((:type "text" :text "Two images")
+       (:type "image" :data "iVBORw0KGgo=" :mimeType "image/png")
+       (:type "image" :data "/9j/4AAQ" :mimeType "image/jpeg"))
+     nil nil)
+    (let ((content (buffer-substring-no-properties (point-min) (point-max))))
+      ;; Both image indicators should be present
+      (should (or (>= (length (split-string content "\\[Image:\\|\\[image\\]" t)) 2)
+                  ;; GUI mode: two [image] from insert-image
+                  (string-match-p "\\[image\\].*\\[image\\]" content))))))
+
+(ert-deftest pi-coding-agent-test-tool-end-image-only ()
+  "Tool result with only image blocks, no text, still renders."
+  (with-temp-buffer
+    (pi-coding-agent-chat-mode)
+    (pi-coding-agent--display-tool-end
+     "read" '(:path "photo.png")
+     '((:type "image" :data "iVBORw0KGgo=" :mimeType "image/png"))
+     nil nil)
+    (let ((content (buffer-substring-no-properties (point-min) (point-max))))
+      (should (or (string-match-p "\\[Image:" content)
+                  (string-match-p "\\[image\\]" content))))))
+
+(ert-deftest pi-coding-agent-test-tool-end-unknown-mime-type ()
+  "Unknown MIME type produces a placeholder, not an error."
+  (with-temp-buffer
+    (pi-coding-agent-chat-mode)
+    (pi-coding-agent--display-tool-end
+     "read" '(:path "file.tga")
+     '((:type "text" :text "Read image")
+       (:type "image" :data "AAAA" :mimeType "image/tga"))
+     nil nil)
+    (let ((content (buffer-substring-no-properties (point-min) (point-max))))
+      (should (string-match-p "image/tga" content)))))
+
+(ert-deftest pi-coding-agent-test-history-tool-with-image ()
+  "History replay renders image from tool result."
+  (with-temp-buffer
+    (pi-coding-agent-chat-mode)
+    (let ((messages [(:role "assistant"
+                      :content [(:type "toolCall" :id "tc1"
+                                 :name "read"
+                                 :arguments (:path "photo.png"))]
+                      :timestamp 1704067200000)
+                     (:role "toolResult" :toolCallId "tc1"
+                      :toolName "read"
+                      :content [(:type "text" :text "Read image file [image/png]")
+                                (:type "image" :data "iVBORw0KGgo=" :mimeType "image/png")]
+                      :isError :json-false
+                      :timestamp 1704067201000)]))
+      (pi-coding-agent--display-history-messages messages))
+    (let ((content (buffer-substring-no-properties (point-min) (point-max))))
+      (should (or (string-match-p "\\[Image:.*image/png" content)
+                  (string-match-p "\\[image\\]" content))))))
+
+(ert-deftest pi-coding-agent-test-tool-end-image-with-vector-content ()
+  "Image blocks work when content is a vector (JSON parse format)."
+  (with-temp-buffer
+    (pi-coding-agent-chat-mode)
+    (pi-coding-agent--display-tool-end
+     "read" '(:path "photo.png")
+     [(:type "text" :text "Read image")
+      (:type "image" :data "iVBORw0KGgo=" :mimeType "image/png")]
+     nil nil)
+    (let ((content (buffer-substring-no-properties (point-min) (point-max))))
+      (should (or (string-match-p "\\[Image:" content)
+                  (string-match-p "\\[image\\]" content))))))
+
 (provide 'pi-coding-agent-render-test)
 ;;; pi-coding-agent-render-test.el ends here