diff --git a/agent/sandbox/v2/claude/oscompat.go b/agent/sandbox/v2/claude/oscompat.go
index ba0f24d7..1d492225 100644
--- a/agent/sandbox/v2/claude/oscompat.go
+++ b/agent/sandbox/v2/claude/oscompat.go
@@ -146,6 +146,23 @@ func (e *osEnv) buildPowerShellScript(args []string, systemPrompt, inputJSONL, w
 	var b strings.Builder
 	noBOM := "(New-Object System.Text.UTF8Encoding $false)"
 
+	// Force UTF-8 for both input and output streams.
+	// On CJK Windows the default codepage is often GBK/GB2312 (936)
+	// which corrupts Claude CLI's UTF-8 JSON output.
+	b.WriteString("[Console]::InputEncoding = [System.Text.Encoding]::UTF8\n")
+	b.WriteString("[Console]::OutputEncoding = [System.Text.Encoding]::UTF8\n")
+	b.WriteString("$OutputEncoding = [System.Text.Encoding]::UTF8\n")
+
+	// Ensure claude.exe can be found even when Tai runs as a different user.
+	// Claude CLI is typically installed per-user (e.g. C:\Users\X\.local\bin)
+	// which isn't in the PATH when Tai runs as a service or another account.
+	// Scan all user profiles for common install locations.
+	b.WriteString("foreach ($d in (Get-ChildItem 'C:\\Users' -Directory -ErrorAction SilentlyContinue)) {\n")
+	b.WriteString("  $p = Join-Path $d.FullName '.local\\bin'\n")
+	b.WriteString("  if (Test-Path (Join-Path $p 'claude.exe')) { $env:PATH = \"$p;$env:PATH\"; break }\n")
+	b.WriteString("}\n")
+	b.WriteString("if ($env:APPDATA) { $env:PATH = \"$env:APPDATA\\npm;$env:PATH\" }\n")
+
 	yaoDir := e.pathJoin(workDir, ".yao")
 	b.WriteString(fmt.Sprintf("if (!(Test-Path '%s')) { New-Item -ItemType Directory -Path '%s' -Force | Out-Null }\n", yaoDir, yaoDir))
 
diff --git a/agent/sandbox/v2/claude/runner.go b/agent/sandbox/v2/claude/runner.go
index 51a38c24..80bf34af 100644
--- a/agent/sandbox/v2/claude/runner.go
+++ b/agent/sandbox/v2/claude/runner.go
@@ -104,7 +104,7 @@ func (r *ClaudeRunner) Stream(ctx context.Context, req *types.StreamRequest, han
 		streamOpts = append(streamOpts, infra.WithStdin(stdin))
 	}
 
-	fmt.Fprintf(os.Stderr, "[claude] Stream cmd=%v hasMCP=%v isContinuation=%v stdinLen=%d\n", cmd, r.hasMCP, isContinuation, len(stdin))
+	fmt.Fprintf(os.Stderr, "[claude] Stream cmd=%v hasMCP=%v isContinuation=%v stdinLen=%d workDir=%q\n", cmd, r.hasMCP, isContinuation, len(stdin), oe.WorkDir)
 
 	execStream, err := computer.Stream(ctx, cmd, streamOpts...)
 	if err != nil {