fix(chat): skip empty assistant tool-call placeholder rows in REST transcript (#953)

* fix(chat): skip empty assistant tool-call placeholder rows in REST transcript

Non-reasoning models (e.g. gemini-3.5-flash) store a tool-call turn as an
empty assistant row (content = "", no reasoning) with a tool_calls list.
The REST transcript returns these verbatim, and mapServerMessages was only
filtering empty assistant rows that carried reasoning text (the issue #771
thinking-model case). With no reasoning, the filter check failed and the
placeholder rows fell through — rendering as empty bubbles with Copy buttons
in the chat list.

Fix: skip ANY empty assistant row regardless of whether reasoning is present.
If it carries reasoning, stash it for folding (issue #771 path unchanged).
If it doesn't, it's a pure tool-call placeholder — silently drop it.
No user-visible content is lost: these rows never held displayable text.

Verified on device (hermes37 emulator): session 'Friendly greeting #9' had
10 ghost empty bubbles; after fix the transcript shows only real messages.

Issue: #956

* fix(chat): blank-content guard in FullBleedAgentMessage prose renderer

Defense-in-depth for the ghost-bubble fix (#953): never render an empty
prose block (blank text + lone Copy button) if a placeholder row ever
slips past upstream mapping. Streaming messages keep rendering so the
live cursor survives until the first delta lands.

Verified on device: cold start of 'Friendly greeting #9' renders only
real content — no empty bubbles.

---------

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/java/com/m57/hermescontrol/ui/chat/ChatViewModel.kt

@@ -2929,11 +2929,18 @@ class ChatViewModel(
                     existingReasoningMap[rawContent]?.reasoningText.orEmpty()
                 }
 
-            // Reasoning-only assistant row (the gateway's split storage of a
-            // reasoning turn): stash the trace, skip the empty bubble, and
-            // attach it to the next assistant message that has content.
-            if (role == MessageRole.ASSISTANT && rawContent.isBlank() && rowReasoning.isNotBlank()) {
-                pendingReasoning = rowReasoning
+            // Empty assistant row — two cases stored by the gateway:
+            //  1. Reasoning-only: thinking-model split storage (content = "",
+            //     reasoning = trace). Stash the trace and fold it into the
+            //     next assistant message that has content (issue #771).
+            //  2. Tool-call placeholder: non-reasoning models emit content = ""
+            //     with tool_calls metadata and no reasoning. These carry no
+            //     user-visible text and must not render as empty bubbles
+            //     (issue #956).
+            if (role == MessageRole.ASSISTANT && rawContent.isBlank()) {
+                if (rowReasoning.isNotBlank()) {
+                    pendingReasoning = rowReasoning
+                }
                 return@forEachIndexed
             }
 

app/src/main/java/com/m57/hermescontrol/ui/chat/fullbleed/FullBleedAgentMessage.kt

@@ -103,15 +103,21 @@ internal fun FullBleedAgentMessage(
             Spacer(modifier = Modifier.height(6.dp))
         }
 
-        SelectionContainer {
-            MarkdownText(
-                text = message.content,
-                textColor = textColor,
-                isStreaming = message.isStreaming,
-                searchQuery = searchQuery,
-                isCurrentMatch = isCurrentMatch,
-                onImageClick = onImageClick,
-            )
+        // Defense-in-depth: never render an empty prose block (blank bubble +
+        // lone Copy button). Blank settled rows are tool-call placeholders that
+        // slipped through upstream mapping; streaming keeps rendering so the
+        // live cursor survives until the first delta lands.
+        if (message.content.isNotBlank() || message.isStreaming) {
+            SelectionContainer {
+                MarkdownText(
+                    text = message.content,
+                    textColor = textColor,
+                    isStreaming = message.isStreaming,
+                    searchQuery = searchQuery,
+                    isCurrentMatch = isCurrentMatch,
+                    onImageClick = onImageClick,
+                )
+            }
         }
 
         // Render inline attachments (mirrors ChatBubble so agent-delivered