fix(approval): resolve preview paths against workspace root, not server CWD (#57)

computeToolPreview/readFileIfExists resolved relative file_write/file_edit
paths against the daemon CWD, so the diff shown to the operator for approval
read the wrong file (or nothing) when server CWD != workspace_root. Thread the
bound workspaceRoot (effectives.policy.workspaceRoot) through and resolve
relative paths against it, same as the tools do.

core/kernel/src/main/kotlin/com/correx/core/kernel/orchestration/SessionOrchestrator.kt

@@ -1275,7 +1275,9 @@ abstract class SessionOrchestrator(
                     mode = approvalMode,
                 )
                 val requestId = ApprovalRequestId(UUID.randomUUID().toString())
-                val toolPreview = computeToolPreview(toolCall.function.name, parameters)
+                val toolPreview = computeToolPreview(
+                    toolCall.function.name, parameters, effectives.policy?.workspaceRoot,
+                )
                 val domainRequest = DomainApprovalRequest(
                     id = requestId,
                     tier = tier,
@@ -3382,10 +3384,14 @@ abstract class SessionOrchestrator(
  * This function performs blocking I/O (file reads) and must be called from a suspend context
  * that will dispatch it on [Dispatchers.IO].
  */
-private suspend fun computeToolPreview(toolName: String, parameters: Map<String, Any>): String? {
+private suspend fun computeToolPreview(
+    toolName: String,
+    parameters: Map<String, Any>,
+    workspaceRoot: java.nio.file.Path?,
+): String? {
     if (toolName == "shell") return shellCommandPreview(parameters)
     if (toolName == "task_decompose") return renderDecomposePreview(parameters)
-    if (toolName == "file_edit") return computeFileEditPreview(parameters)
+    if (toolName == "file_edit") return computeFileEditPreview(parameters, workspaceRoot)
     if (toolName != "file_write") return null
     val path = parameters["path"] as? String ?: return null
     // file_write no longer carries an `operation` param (delete was split into file_delete), so the
@@ -3393,13 +3399,18 @@ private suspend fun computeToolPreview(toolName: String, parameters: Map<String,
     // silently bailed to the raw-JSON args fallback for every file_write.
     val proposedContent = parameters["content"] as? String ?: return null
 
-    val existingContent = readFileIfExists(path)
+    val existingContent = readFileIfExists(path, workspaceRoot)
     return buildDiffString(path, existingContent, proposedContent)
 }
 
-private suspend fun readFileIfExists(path: String): String? = withContext(Dispatchers.IO) {
+private suspend fun readFileIfExists(path: String, workspaceRoot: java.nio.file.Path?): String? =
+    withContext(Dispatchers.IO) {
         runCatching {
-        val filePath = java.nio.file.Paths.get(path)
+            // Resolve relative paths against the session's workspace root, same as the tools do —
+            // resolving against the daemon CWD showed the operator the wrong file (or nothing) when
+            // server CWD ≠ workspace_root.
+            val raw = java.nio.file.Paths.get(path)
+            val filePath = if (raw.isAbsolute || workspaceRoot == null) raw else workspaceRoot.resolve(raw)
             if (java.nio.file.Files.exists(filePath)) {
                 java.nio.file.Files.readString(filePath)
             } else null
@@ -3412,10 +3423,13 @@ private suspend fun readFileIfExists(path: String): String? = withContext(Dispat
  * to the raw-JSON-args fallback — simulating `patch -p1` application here isn't worth the risk of
  * the preview silently disagreeing with what the tool actually does.
  */
-private suspend fun computeFileEditPreview(parameters: Map<String, Any>): String? {
+private suspend fun computeFileEditPreview(
+    parameters: Map<String, Any>,
+    workspaceRoot: java.nio.file.Path?,
+): String? {
     val path = parameters["path"] as? String ?: return null
     val operation = parameters["operation"] as? String ?: return null
-    val existingContent = readFileIfExists(path) ?: return null
+    val existingContent = readFileIfExists(path, workspaceRoot) ?: return null
 
     val proposedContent = when (operation) {
         "append" -> existingContent + (parameters["content"] as? String ?: return null)