fix: orchestrator race conditions, diff preview, session snapshot tools, and test fixes

- Fix duplicate inference requests after approval resume by registering orchestrator
  jobs in activeSessionJobs (ServerModule.launchSessionRun), so the guard in the
  OrchestrationResumedEvent subscription prevents spurious duplicate resume.
- Replace blocking Files.readString in computeToolPreview with withContext(Dispatchers.IO)
  by making the function suspend — no blocking I/O on the coroutine dispatcher.
- Guard orderedIds.add() in rebuildTools against duplicate invocation IDs on replayed
  ToolInvocationRequestedEvent to prevent duplicate tool records in snapshots.
- Add unified-diff preview for file_write tools: computeToolPreview reads existing
  file and generates ---/+++ diff before emitting ApprovalRequestedEvent.
- Render diff preview with color coding in ApprovalSurface (@@ yellow, +/- green/red).
- Include current-stage tool records in SessionSnapshot via rebuildTools event replay.
- Fix RouterContextBuilderTest: recursive buildPack helper and 2 tests using class-level
  builder instead of their local builder instances (conversationKeepLast mismatch).
- Add suspend keyword to RouterFacadeTest mock, fix buildPack recursion.

apps/tui/src/main/kotlin/com/correx/apps/tui/components/ApprovalSurface.kt

@@ -15,9 +15,14 @@ import dev.tamboui.widgets.block.Title
 import dev.tamboui.widgets.paragraph.Paragraph
 
 private const val PREVIEW_MAX_LINES = 20
+private const val DIFF_LINE_MAX_LENGTH = 100
+
+private val dimStyle = Style.create().dim().gray()
+private val greenStyle = Style.create().green()
+private val redStyle = Style.create().red()
+private val yellowStyle = Style.create().yellow()
 
 fun approvalSurfaceWidget(state: TuiState): Paragraph {
-    val dimStyle = Style.create().dim().gray()
     val approval = state.selectedPendingApproval()
     val pendingDecision = state.pendingDecision
 
@@ -32,13 +37,31 @@ fun approvalSurfaceWidget(state: TuiState): Paragraph {
             val riskSpan = Span.styled(approval.riskSummary, dimStyle)
             add(Line.from(toolSpan, Span.raw("  "), tierBadge, Span.raw("  "), riskSpan))
 
-            // Command preview (monospace, max 20 lines, truncation notice)
-            if (approval.preview != null) {
-                val previewLines = approval.preview.lines()
+            // Preview: unified diff for file_write/file_edit, raw text otherwise
+            val preview = approval.preview
+            val isDiff = preview?.startsWith("--- a/") == true
+            if (preview != null) {
+                val previewLines = preview.lines()
                 if (previewLines.isNotEmpty()) {
                     val visibleLines = previewLines.take(PREVIEW_MAX_LINES)
                     for (line in visibleLines) {
-                        add(Line.from(Span.raw("  $line")))
+                        if (isDiff) {
+                            val truncated = if (line.length > DIFF_LINE_MAX_LENGTH) {
+                                line.take(DIFF_LINE_MAX_LENGTH - 3) + "..."
+                            } else {
+                                line
+                            }
+                            val span = when {
+                                truncated.startsWith("@@") -> Span.styled("  $truncated", yellowStyle)
+                                truncated.startsWith("+++") || truncated.startsWith("---") -> Span.styled("  $truncated", dimStyle)
+                                truncated.startsWith("+") -> Span.styled("  $truncated", greenStyle)
+                                truncated.startsWith("-") -> Span.styled("  $truncated", redStyle)
+                                else -> Span.raw("  $truncated")
+                            }
+                            add(Line.from(span))
+                        } else {
+                            add(Line.from(Span.raw("  $line")))
+                        }
                     }
                     if (previewLines.size > PREVIEW_MAX_LINES) {
                         val remaining = previewLines.size - PREVIEW_MAX_LINES

apps/tui/src/main/kotlin/com/correx/apps/tui/reducer/SessionsReducer.kt

@@ -274,6 +274,21 @@ object SessionsReducer {
                 detail = entry.detail,
             )
         }
+        val tools = msg.tools.map { tool ->
+            val displayStatus = when (tool.status) {
+                "COMPLETED" -> ToolDisplayStatus.COMPLETED
+                "FAILED" -> ToolDisplayStatus.FAILED
+                "REJECTED" -> ToolDisplayStatus.REJECTED
+                else -> ToolDisplayStatus.STARTED
+            }
+            TuiToolRecord(
+                name = tool.name,
+                tier = tool.tier,
+                status = displayStatus,
+                argsPreview = null,
+                diff = tool.diff,
+            )
+        }
         val summary = SessionSummary(
             id = msg.sessionId.value,
             status = status,
@@ -284,6 +299,7 @@ object SessionsReducer {
             currentStageId = msg.state.currentStageId,
             pendingApproval = approvalInfo,
             recentEvents = eventEntries,
+            tools = tools,
         )
         val selected = sessionState.selectedId ?: msg.sessionId.value
         return sessionState.copy(