diff --git a/internal/adapter/openai/tool_history_sanitize.go b/internal/adapter/openai/tool_history_sanitize.go
index 18b05e9..b2c740d 100644
--- a/internal/adapter/openai/tool_history_sanitize.go
+++ b/internal/adapter/openai/tool_history_sanitize.go
@@ -8,7 +8,15 @@ var leakedToolHistoryPattern = regexp.MustCompile(`(?is)\[TOOL_CALL_HISTORY\][\s
 var emptyJSONFencePattern = regexp.MustCompile("(?is)```json\\s*```")
 var leakedToolCallArrayPattern = regexp.MustCompile(`(?is)\[\{\s*"function"\s*:\s*\{[\s\S]*?\}\s*,\s*"id"\s*:\s*"call[^"]*"\s*,\s*"type"\s*:\s*"function"\s*}\]`)
 var leakedToolResultBlobPattern = regexp.MustCompile(`(?is)<\s*\|\s*tool\s*\|\s*>\s*\{[\s\S]*?"tool_call_id"\s*:\s*"call[^"]*"\s*}`)
-var leakedMetaMarkerPattern = regexp.MustCompile(`(?is)<\s*\|\s*(?:assistant|tool|end_of_sentence|end_of_thinking)\s*\|\s*>`)
+
+// leakedMetaMarkerPattern matches DeepSeek special tokens in BOTH forms:
+//   - ASCII underscore: <｜end_of_sentence｜>
+//   - U+2581 variant:   <｜end▁of▁sentence｜>  (used in some DeepSeek outputs)
+var leakedMetaMarkerPattern = regexp.MustCompile(`(?i)<[｜\|]\s*(?:assistant|tool|end[_▁]of[_▁]sentence|end[_▁]of[_▁]thinking)\s*[｜\|]>`)
+
+// leakedAgentXMLPattern catches agent-style XML tags that leak through when
+// the sieve fails to capture them (e.g. incomplete blocks at stream end).
+var leakedAgentXMLPattern = regexp.MustCompile(`(?is)</?(?:attempt_completion|ask_followup_question|new_task|result)>`)
 
 func sanitizeLeakedToolHistory(text string) string {
 	if text == "" {
@@ -19,5 +27,6 @@ func sanitizeLeakedToolHistory(text string) string {
 	out = leakedToolCallArrayPattern.ReplaceAllString(out, "")
 	out = leakedToolResultBlobPattern.ReplaceAllString(out, "")
 	out = leakedMetaMarkerPattern.ReplaceAllString(out, "")
+	out = leakedAgentXMLPattern.ReplaceAllString(out, "")
 	return out
 }
diff --git a/internal/adapter/openai/tool_history_sanitize_test.go b/internal/adapter/openai/tool_history_sanitize_test.go
index 3eb434a..5c12fb0 100644
--- a/internal/adapter/openai/tool_history_sanitize_test.go
+++ b/internal/adapter/openai/tool_history_sanitize_test.go
@@ -86,13 +86,21 @@ func TestSanitizeLeakedToolHistoryRemovesLeakedWireToolCallAndResult(t *testing.
 }
 
 func TestSanitizeLeakedToolHistoryRemovesStandaloneMetaMarkers(t *testing.T) {
-	raw := "A<| end_of_sentence |><| Assistant |>B<| end_of_thinking |>C"
+	raw := "A<| end_of_sentence |><| Assistant |>B<| end_of_thinking |>C<｜end▁of▁thinking｜>D<｜end▁of▁sentence｜>E"
 	got := sanitizeLeakedToolHistory(raw)
-	if got != "ABC" {
+	if got != "ABCDE" {
 		t.Fatalf("unexpected sanitize result for meta markers: %q", got)
 	}
 }
 
+func TestSanitizeLeakedToolHistoryRemovesAgentXMLLeaks(t *testing.T) {
+	raw := "Done.<attempt_completion><result>Some final answer</result></attempt_completion>"
+	got := sanitizeLeakedToolHistory(raw)
+	if got != "Done.Some final answer" {
+		t.Fatalf("unexpected sanitize result for agent XML leak: %q", got)
+	}
+}
+
 func TestProcessToolSieveChunkSplitsResultHistoryBoundary(t *testing.T) {
 	var state toolStreamSieveState
 	parts := []string{
diff --git a/internal/adapter/openai/tool_sieve_xml.go b/internal/adapter/openai/tool_sieve_xml.go
index aa97b5e..37cb8b3 100644
--- a/internal/adapter/openai/tool_sieve_xml.go
+++ b/internal/adapter/openai/tool_sieve_xml.go
@@ -9,8 +9,12 @@ import (
 
 // --- XML tool call support for the streaming sieve ---
 
-var xmlToolCallClosingTags = []string{"</tool_calls>", "</tool_call>", "</invoke>", "</function_call>", "</function_calls>", "</tool_use>"}
-var xmlToolCallOpeningTags = []string{"<tool_calls", "<tool_call", "<invoke", "<function_call", "<function_calls", "<tool_use"}
+var xmlToolCallClosingTags = []string{"</tool_calls>", "</tool_call>", "</invoke>", "</function_call>", "</function_calls>", "</tool_use>",
+	// Agent-style XML tags (Roo Code, Cline, etc.)
+	"</attempt_completion>", "</ask_followup_question>", "</new_task>", "</result>"}
+var xmlToolCallOpeningTags = []string{"<tool_calls", "<tool_call", "<invoke", "<function_call", "<function_calls", "<tool_use",
+	// Agent-style XML tags
+	"<attempt_completion", "<ask_followup_question", "<new_task", "<result"}
 
 // xmlToolCallTagPairs maps each opening tag to its expected closing tag.
 // Order matters: longer/wrapper tags must be checked first.
@@ -21,14 +25,22 @@ var xmlToolCallTagPairs = []struct{ open, close string }{
 	{"<function_call", "</function_call>"},
 	{"<invoke", "</invoke>"},
 	{"<tool_use", "</tool_use>"},
+	// Agent-style: these are XML "tool call" patterns from coding agents.
+	// They get captured → parsed. If parsing fails, the block is consumed
+	// (swallowed) to prevent raw XML from leaking to the client.
+	{"<attempt_completion", "</attempt_completion>"},
+	{"<ask_followup_question", "</ask_followup_question>"},
+	{"<new_task", "</new_task>"},
 }
 
 // xmlToolCallBlockPattern matches a complete XML tool call block (wrapper or standalone).
-var xmlToolCallBlockPattern = regexp.MustCompile(`(?is)(<tool_calls>\s*(?:.*?)\s*</tool_calls>|<tool_call>\s*(?:.*?)\s*</tool_call>|<invoke\b[^>]*>(?:.*?)</invoke>|<function_calls?\b[^>]*>(?:.*?)</function_calls?>|<tool_use>(?:.*?)</tool_use>)`)
+var xmlToolCallBlockPattern = regexp.MustCompile(`(?is)(<tool_calls>\s*(?:.*?)\s*</tool_calls>|<tool_call>\s*(?:.*?)\s*</tool_call>|<invoke\b[^>]*>(?:.*?)</invoke>|<function_calls?\b[^>]*>(?:.*?)</function_calls?>|<tool_use>(?:.*?)</tool_use>|<attempt_completion>(?:.*?)</attempt_completion>|<ask_followup_question>(?:.*?)</ask_followup_question>|<new_task>(?:.*?)</new_task>)`)
 
 // xmlToolTagsToDetect is the set of XML tag prefixes used by findToolSegmentStart.
 var xmlToolTagsToDetect = []string{"<tool_calls>", "<tool_calls\n", "<tool_call>", "<tool_call\n",
-	"<invoke ", "<invoke>", "<function_call", "<function_calls", "<tool_use>"}
+	"<invoke ", "<invoke>", "<function_call", "<function_calls", "<tool_use>",
+	// Agent-style tags
+	"<attempt_completion>", "<ask_followup_question>", "<new_task>"}
 
 // consumeXMLToolCapture tries to extract complete XML tool call blocks from captured text.
 func consumeXMLToolCapture(captured string, toolNames []string) (prefix string, calls []util.ParsedToolCall, suffix string, ready bool) {
@@ -120,6 +132,11 @@ func looksLikeXMLToolTagFragment(s string) bool {
 		"function_calls>", "function_call>", "/function_calls>", "/function_call>",
 		"invoke>", "/invoke>", "tool_use>", "/tool_use>",
 		"tool_name>", "/tool_name>", "parameters>", "/parameters>",
+		// Agent-style tag fragments
+		"attempt_completion>", "/attempt_completion>",
+		"ask_followup_question>", "/ask_followup_question>",
+		"new_task>", "/new_task>",
+		"result>", "/result>",
 	}
 	for _, f := range fragments {
 		if strings.Contains(lower, f) {
diff --git a/internal/adapter/openai/tool_sieve_xml_test.go b/internal/adapter/openai/tool_sieve_xml_test.go
index b678345..9201189 100644
--- a/internal/adapter/openai/tool_sieve_xml_test.go
+++ b/internal/adapter/openai/tool_sieve_xml_test.go
@@ -285,3 +285,35 @@ func TestOpeningXMLTagNotLeakedAsContent(t *testing.T) {
 		t.Fatal("expected tool calls to be extracted")
 	}
 }
+
+func TestProcessToolSieveInterceptsAttemptCompletionLeak(t *testing.T) {
+	var state toolStreamSieveState
+	// Simulate an agent outputting attempt_completion XML tag 
+	// which shouldn't leak to text output, even if it fails to parse as a valid tool.
+	chunks := []string{
+		"Done with task.\n",
+		"<attempt_completion>\n",
+		"  <result>Here is the answer</result>\n",
+		"</attempt_completion>",
+	}
+	var events []toolStreamEvent
+	for _, c := range chunks {
+		events = append(events, processToolSieveChunk(&state, c, []string{"attempt_completion"})...)
+	}
+	events = append(events, flushToolSieve(&state, []string{"attempt_completion"})...)
+
+	var textContent string
+	for _, evt := range events {
+		if evt.Content != "" {
+			textContent += evt.Content
+		}
+	}
+
+	if !strings.Contains(textContent, "Done with task.\n") {
+		t.Fatalf("expected leading text to be emitted, got %q", textContent)
+	}
+
+	if strings.Contains(textContent, "<attempt_completion>") || strings.Contains(textContent, "result>") {
+		t.Fatalf("agent XML tag content leaked to text: %q", textContent)
+	}
+}