refactor(desktop): one live-tail vocabulary for transcript reconciliation

Two fixes landed overlapping helpers on the same statement: the mid-turn
reply guard grew `isLiveProjectionRow` / `hasStreamedContent`, while the
inflight-dump guard grew `isLiveTailRow` / `hasStructuralParts`. Two
definitions of "is this row live" and "does it carry content" in one
function is how the next change silently reshapes one of them.

Collapse to a single module-level pair. `isLiveTailRow` now covers pending,
stream ids, inflight projections and sealed interim rows, so the reply guard
also stops treating an interim row as committed history; `hasStreamedContent`
is defined in terms of `hasStructuralParts`. Both text-extension checks route
through `isStrictAnswerTextExtension` rather than a bare `startsWith`.

Also hoists the live-tail lookup out of an inline IIFE and fixes the lint
warnings it carried.

Co-authored-by: 686f6c61 <github@00b.tech>

apps/desktop/src/app/session/hooks/use-session-actions/utils.ts

@@ -52,6 +52,20 @@ function hasStructuralParts(message: ChatMessage): boolean {
   return message.parts.some(part => part.type === 'reasoning' || part.type === 'tool-call')
 }
 
+/**
+ * A live-turn row — the gateway's text-only `inflight` projection, a
+ * still-streaming local bubble, or an interim row sealed inside the running
+ * turn — as opposed to a committed transcript row.
+ */
+function isLiveTailRow(message: ChatMessage): boolean {
+  return (
+    message.pending === true ||
+    message.id.startsWith('assistant-stream-') ||
+    message.id.startsWith('inflight-assistant-') ||
+    message.interim === true
+  )
+}
+
 /**
  * True when `next` is a pure forward extension of the previous *answer* text.
  * Empty previous answer never accepts a dump as an extension — that is how the
@@ -301,11 +315,6 @@ export function reconcileResumeMessages(nextMessages: ChatMessage[], previousMes
     // live is not enough — after compression a new live assistant can share a
     // role ordinal with an unrelated historical structured row and must not
     // inherit its reasoning/tool parts (#76444 review / salvage).
-    const isLiveTailRow = (row: ChatMessage): boolean =>
-      Boolean(row.pending) ||
-      row.id.startsWith('assistant-stream-') ||
-      Boolean(row.interim)
-
     const sameTurn =
       sameText ||
       (nextText.length > 0 && previousTrimmed.length > 0 && isStrictAnswerTextExtension(nextText, previousTrimmed)) ||
@@ -394,19 +403,12 @@ const isGatewaySystemMarker = (message: ChatMessage): boolean =>
   message.role === 'user' && chatMessageText(message).trimStart().startsWith('[System:')
 
 /**
- * Does the local pending row carry anything a viewer would miss — streamed
- * text, reasoning, or tool calls? An empty inflight shell carries none of it.
+ * Does the row carry anything a viewer would miss — streamed answer text, or
+ * the reasoning / tool-call structure the gateway's flat dump cannot express?
+ * An empty inflight shell carries none of it.
  */
 const hasStreamedContent = (message: ChatMessage): boolean =>
-  chatMessageText(message).trim().length > 0 ||
-  message.parts.some(part => part.type === 'tool-call' || part.type === 'reasoning')
-
-/**
- * A live-turn projection row — the gateway's text-only `inflight` snapshot or a
- * still-streaming local bubble — as opposed to a committed transcript row.
- */
-const isLiveProjectionRow = (message: ChatMessage): boolean =>
-  message.pending === true || message.id.startsWith('assistant-stream-') || message.id.startsWith('inflight-assistant-')
+  chatMessageText(message).trim().length > 0 || hasStructuralParts(message)
 
 /**
  * May the cached local row stand in for this authoritative assistant?
@@ -419,11 +421,11 @@ const isLiveProjectionRow = (message: ChatMessage): boolean =>
  * from the local partial would hide the error and mark the turn healthy again.
  */
 const localPendingSupersedes = (local: ChatMessage, authoritative: ChatMessage): boolean => {
-  if (local.role !== 'assistant' || !isLiveProjectionRow(local)) {
+  if (local.role !== 'assistant' || !isLiveTailRow(local)) {
     return false
   }
 
-  if (!isLiveProjectionRow(authoritative) || authoritative.error) {
+  if (!isLiveTailRow(authoritative) || authoritative.error) {
     return false
   }
 
@@ -435,7 +437,7 @@ const localPendingSupersedes = (local: ChatMessage, authoritative: ChatMessage):
 
   const localText = chatMessageText(local).trim()
 
-  return localText.length > authoritativeText.length && localText.startsWith(authoritativeText)
+  return localText.length > authoritativeText.length && isStrictAnswerTextExtension(localText, authoritativeText)
 }
 
 /**
@@ -705,28 +707,32 @@ export function appendLiveSessionProjection(
   // Only inspect the live tail after the latest user run — never a completed
   // historical tool-bearing reply earlier in the transcript (review feedback).
   const liveStreamId = `assistant-stream-${sessionId}`
-  const liveAssistantOfCurrentTurn = (() => {
+
+  const liveAssistantOfCurrentTurn = ((): ChatMessage | null => {
     const byStreamId = messages.find(message => message.id === liveStreamId)
+
     if (byStreamId) {
       return byStreamId
     }
+
     // Assistants after the latest user row belong to this turn's tail.
     if (latestUserIndex < 0) {
       return null
     }
+
     for (let index = messages.length - 1; index > latestUserIndex; index -= 1) {
       if (messages[index].role === 'assistant') {
         return messages[index]
       }
     }
+
     return null
   })()
+
   const turnAlreadyStructured = Boolean(
     liveAssistantOfCurrentTurn &&
-      hasStructuralParts(liveAssistantOfCurrentTurn) &&
-      (liveAssistantOfCurrentTurn.pending ||
-        liveAssistantOfCurrentTurn.id === liveStreamId ||
-        liveAssistantOfCurrentTurn.interim)
+    hasStructuralParts(liveAssistantOfCurrentTurn) &&
+    isLiveTailRow(liveAssistantOfCurrentTurn)
   )
 
   if (inflightAssistant || inflightStreaming || inflightError || (inflightUser && queuedUser)) {