diff --git a/runtime/argschema/argschema.go b/runtime/argschema/argschema.go
new file mode 100644
index 0000000..f9c9892
--- /dev/null
+++ b/runtime/argschema/argschema.go
@@ -0,0 +1,85 @@
+// Package argschema checks tool-call arguments against the small JSON-schema
+// subset that tool declarations use. It has no dependencies beyond the
+// standard library so both the tool registry and the LLM client can share it.
+package argschema
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+)
+
+// Validate reports whether args satisfy schema: the top-level type is object,
+// required keys are present and not blank strings, declared properties have
+// their primitive type, and unknown keys are rejected when properties are
+// declared.
+func Validate(schema, args json.RawMessage) error {
+	var spec struct {
+		Type       string                     `json:"type"`
+		Required   []string                   `json:"required"`
+		Properties map[string]json.RawMessage `json:"properties"`
+	}
+	if len(schema) > 0 {
+		if err := json.Unmarshal(schema, &spec); err != nil {
+			return fmt.Errorf("invalid tool schema")
+		}
+	}
+	var obj map[string]any
+	if err := json.Unmarshal(args, &obj); err != nil {
+		return fmt.Errorf("arguments must be a JSON object")
+	}
+	if spec.Type != "" && spec.Type != "object" {
+		return fmt.Errorf("unsupported schema type %s", spec.Type)
+	}
+	for _, req := range spec.Required {
+		v, ok := obj[req]
+		if !ok || v == nil {
+			return fmt.Errorf("missing required argument %s", req)
+		}
+		if s, ok := v.(string); ok && strings.TrimSpace(s) == "" {
+			return fmt.Errorf("missing required argument %s", req)
+		}
+	}
+	for key, raw := range spec.Properties {
+		v, ok := obj[key]
+		if !ok {
+			continue
+		}
+		var prop struct {
+			Type string `json:"type"`
+		}
+		if err := json.Unmarshal(raw, &prop); err != nil || prop.Type == "" {
+			continue
+		}
+		if !matchesType(prop.Type, v) {
+			return fmt.Errorf("argument %s must be %s", key, prop.Type)
+		}
+	}
+	if len(spec.Properties) > 0 {
+		for key := range obj {
+			if _, ok := spec.Properties[key]; !ok {
+				return fmt.Errorf("unknown argument %s", key)
+			}
+		}
+	}
+	return nil
+}
+
+func matchesType(kind string, v any) bool {
+	switch kind {
+	case "string":
+		_, ok := v.(string)
+		return ok
+	case "number":
+		_, ok := v.(float64)
+		return ok
+	case "integer":
+		f, ok := v.(float64)
+		return ok && f == float64(int64(f))
+	case "boolean":
+		_, ok := v.(bool)
+		return ok
+	default:
+		return true
+	}
+}
diff --git a/runtime/argschema/argschema_test.go b/runtime/argschema/argschema_test.go
new file mode 100644
index 0000000..12614fc
--- /dev/null
+++ b/runtime/argschema/argschema_test.go
@@ -0,0 +1,44 @@
+package argschema
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestValidate(t *testing.T) {
+	schema := json.RawMessage(`{"type":"object","required":["path"],"properties":{"path":{"type":"string"},"limit":{"type":"integer"},"ratio":{"type":"number"},"all":{"type":"boolean"},"any":{}}}`)
+	tests := []struct {
+		name   string
+		schema json.RawMessage
+		args   string
+		want   string
+	}{
+		{"valid", schema, `{"path":"a.txt","limit":3,"ratio":0.5,"all":true,"any":[1]}`, ""},
+		{"no-schema-accepts-object", nil, `{"x":1}`, ""},
+		{"no-properties-accepts-unknown", json.RawMessage(`{"type":"object"}`), `{"x":1}`, ""},
+		{"invalid-schema", json.RawMessage(`[`), `{}`, "invalid tool schema"},
+		{"array-arguments", schema, `[1]`, "arguments must be a JSON object"},
+		{"broken-arguments", schema, `{"path":`, "arguments must be a JSON object"},
+		{"non-object-schema", json.RawMessage(`{"type":"array"}`), `{}`, "unsupported schema type array"},
+		{"missing-required", schema, `{}`, "missing required argument path"},
+		{"null-required", schema, `{"path":null}`, "missing required argument path"},
+		{"blank-required", schema, `{"path":"  "}`, "missing required argument path"},
+		{"wrong-string", schema, `{"path":7}`, "argument path must be string"},
+		{"fractional-integer", schema, `{"path":"a","limit":1.5}`, "argument limit must be integer"},
+		{"wrong-number", schema, `{"path":"a","ratio":"x"}`, "argument ratio must be number"},
+		{"wrong-boolean", schema, `{"path":"a","all":1}`, "argument all must be boolean"},
+		{"unknown-key", schema, `{"path":"a","extra":1}`, "unknown argument extra"},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			err := Validate(tc.schema, json.RawMessage(tc.args))
+			got := ""
+			if err != nil {
+				got = err.Error()
+			}
+			if got != tc.want {
+				t.Fatalf("Validate(%s, %s) = %q, want %q", tc.schema, tc.args, got, tc.want)
+			}
+		})
+	}
+}
diff --git a/runtime/llm/client.go b/runtime/llm/client.go
index 766208b..295a5a0 100644
--- a/runtime/llm/client.go
+++ b/runtime/llm/client.go
@@ -26,6 +26,9 @@ type Client struct {
 	// SSE 的 reasoning_content 捕获照常生效）。对不认识该字段的服务器
 	// 属未知字段，多数按忽略处理；宿主按模型名自行决定是否置位。
 	ReasoningSplit bool
+	// RouteContract optionally releases tool calls from an openai-chat stream
+	// that ended without [DONE]; nil or the zero value is off.
+	RouteContract *RouteContractEOF
 }
 
 // Stream implements StreamFunc. Transport and provider failures are encoded as
@@ -127,12 +130,36 @@ func (c *Client) run(ctx context.Context, model string, messages []Message, tool
 		return
 	}
 	observed := newBodyObserver(resp)
-	for ev := range ParseSSE(ctx, observed) {
+	contract := c.newRouteContract(model, base, req, resp, tools)
+	var facts sseFacts
+	var hooks sseHooks
+	if contract != nil {
+		hooks.facts = &facts
+		hooks.decideEOF = func(success, failure Event) Event {
+			check := contract.check(observed.snapshot(), failure.TerminalObservation, facts, success.Message.ToolCalls)
+			if check != "" {
+				failure.TerminalObservation.ContractCheck = check
+				return failure
+			}
+			success.CompletionBasis = CompletionRouteContractEOF
+			success.TerminalObservation.CompletionBasis = CompletionRouteContractEOF
+			return success
+		}
+	}
+	for ev := range parseSSE(ctx, observed, hooks) {
 		if ev.Kind == KindMessageEnd || ev.Kind == KindError {
 			ev.HTTPStatus = resp.StatusCode
 			// ParseSSE sends its terminal event only after its last body read.
-			if ev.TerminalObservation != nil {
-				ev.TerminalObservation.BodyBoundary = observed.snapshot()
+			if obs := ev.TerminalObservation; obs != nil {
+				obs.BodyBoundary = observed.snapshot()
+				if ev.Kind == KindMessageEnd && ev.Err == nil && ev.StreamComplete {
+					ev.CompletionBasis = CompletionDoneMarker
+					obs.CompletionBasis = CompletionDoneMarker
+				}
+				if contract != nil && ev.Err != nil && !ev.StreamComplete &&
+					ev.Message.StopReason != StopAborted && obs.ContractCheck == "" {
+					obs.ContractCheck = contract.check(obs.BodyBoundary, obs, facts, ev.Message.ToolCalls)
+				}
 			}
 		}
 		out <- ev
diff --git a/runtime/llm/route_contract.go b/runtime/llm/route_contract.go
new file mode 100644
index 0000000..db6f2c0
--- /dev/null
+++ b/runtime/llm/route_contract.go
@@ -0,0 +1,164 @@
+package llm
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"net/http"
+	"net/url"
+	"strings"
+
+	"agent-native/runtime/argschema"
+)
+
+// Completion bases recorded on a successful OpenAI-chat message_end.
+const (
+	CompletionDoneMarker       = "done_marker"
+	CompletionRouteContractEOF = "route_contract_eof"
+)
+
+// RouteContractEOF lets one exact OpenAI-chat route release tool calls from a
+// stream that ended without [DONE], when the HTTP body boundary and every
+// frame prove the calls complete. The zero value is off. IdentitySHA256 must
+// equal RouteContractIdentity(Model, BaseURL), and BaseURL must already be in
+// NormalizeRouteBaseURL form.
+type RouteContractEOF struct {
+	Model          string
+	BaseURL        string
+	IdentitySHA256 string
+}
+
+// RouteContractIdentity is the lowercase hex sha256 of
+// "openai-chat\n" + model + "\n" + baseURL.
+func RouteContractIdentity(model, baseURL string) string {
+	sum := sha256.Sum256([]byte("openai-chat\n" + model + "\n" + baseURL))
+	return hex.EncodeToString(sum[:])
+}
+
+// NormalizeRouteBaseURL returns the https base URL with lowercase scheme and
+// host and no trailing '/'. Any other scheme, userinfo, query or fragment is
+// not a match.
+func NormalizeRouteBaseURL(raw string) (string, bool) {
+	if strings.ContainsAny(raw, "?#") {
+		return "", false
+	}
+	u, err := url.Parse(raw)
+	if err != nil || !strings.EqualFold(u.Scheme, "https") || u.Opaque != "" ||
+		u.User != nil || u.Host == "" || u.RawQuery != "" || u.ForceQuery || u.Fragment != "" {
+		return "", false
+	}
+	return "https://" + strings.ToLower(u.Host) + strings.TrimRight(u.EscapedPath(), "/"), true
+}
+
+func (rc *RouteContractEOF) off() bool {
+	return rc == nil || *rc == RouteContractEOF{}
+}
+
+// admits is condition C1 apart from the redirect check.
+func (rc *RouteContractEOF) admits(protocol Protocol, model, base string) bool {
+	if protocol != "" && protocol != ProtocolOpenAIChat {
+		return false
+	}
+	if model != rc.Model {
+		return false
+	}
+	normalized, ok := NormalizeRouteBaseURL(base)
+	if !ok || normalized != rc.BaseURL {
+		return false
+	}
+	return RouteContractIdentity(rc.Model, rc.BaseURL) == rc.IdentitySHA256
+}
+
+// routeContract evaluates a configured RouteContractEOF for one response.
+type routeContract struct {
+	active bool
+	tools  []ToolDecl
+}
+
+// newRouteContract returns nil when the client has no contract configured.
+func (c *Client) newRouteContract(model, base string, req *http.Request, resp *http.Response, tools []ToolDecl) *routeContract {
+	if c.RouteContract.off() {
+		return nil
+	}
+	return &routeContract{
+		active: c.RouteContract.admits(c.Protocol, model, base) && sameTarget(req, resp),
+		tools:  tools,
+	}
+}
+
+// sameTarget rejects any redirect that changed scheme, host, port or path.
+func sameTarget(req *http.Request, resp *http.Response) bool {
+	if req == nil || req.URL == nil || resp == nil || resp.Request == nil || resp.Request.URL == nil {
+		return false
+	}
+	sent, final := req.URL, resp.Request.URL
+	return strings.EqualFold(sent.Scheme, final.Scheme) &&
+		strings.EqualFold(sent.Hostname(), final.Hostname()) &&
+		sent.Port() == final.Port() &&
+		sent.EscapedPath() == final.EscapedPath()
+}
+
+// check returns the first failing condition id, or "" when all hold.
+func (rc *routeContract) check(boundary *BodyBoundaryObservation, obs *TerminalObservation, facts sseFacts, calls []ToolCall) string {
+	switch {
+	case !rc.active:
+		return "C1"
+	case !boundaryProven(boundary):
+		return "C2"
+	case obs == nil || obs.ReadOutcome != "clean_eof":
+		return "C3"
+	case facts.finishChunks != 1 || facts.finishReason != "tool_calls" || facts.multiChoice:
+		return "C4"
+	case !obs.UsagePresent:
+		return "C5"
+	case facts.fragmentAfterFinish:
+		return "C6"
+	case !callsComplete(calls):
+		return "C7"
+	case !callsDeclared(calls, rc.tools):
+		return "C8"
+	case obs.TailEventKind != "json_frame" || !obs.LastFrameJSONComplete:
+		return "C9"
+	}
+	return ""
+}
+
+func boundaryProven(b *BodyBoundaryObservation) bool {
+	if b == nil {
+		return false
+	}
+	return (b.FramingClass == "http2_stream" && b.EOFSeen) ||
+		(b.FramingClass == "known_length" && b.LengthRelation == "match")
+}
+
+func callsComplete(calls []ToolCall) bool {
+	if len(calls) == 0 {
+		return false
+	}
+	for _, call := range calls {
+		var args map[string]json.RawMessage
+		if call.ID == "" || call.Name == "" {
+			return false
+		}
+		if err := json.Unmarshal([]byte(call.Arguments), &args); err != nil || args == nil {
+			return false
+		}
+	}
+	return true
+}
+
+func callsDeclared(calls []ToolCall, tools []ToolDecl) bool {
+	for _, call := range calls {
+		idx := -1
+		for i, decl := range tools {
+			if decl.Name == call.Name {
+				idx = i
+				break
+			}
+		}
+		if idx < 0 || argschema.Validate(tools[idx].Parameters, json.RawMessage(call.Arguments)) != nil {
+			return false
+		}
+	}
+	return true
+}
diff --git a/runtime/llm/route_contract_test.go b/runtime/llm/route_contract_test.go
new file mode 100644
index 0000000..87af915
--- /dev/null
+++ b/runtime/llm/route_contract_test.go
@@ -0,0 +1,630 @@
+package llm
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"reflect"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+const (
+	rcModel     = "fixture-model"
+	rcEOFReason = "tool call stream ended before [DONE]"
+)
+
+var rcTools = []ToolDecl{
+	{Name: "read_PRIVATE_I1", Parameters: json.RawMessage(`{"type":"object","required":["path"],"properties":{"path":{"type":"string"}}}`)},
+	{Name: "list_PRIVATE_I1", Parameters: json.RawMessage(`{"type":"object","properties":{"dir":{"type":"string"}}}`)},
+}
+
+func rcFrame(v any) string {
+	raw, err := json.Marshal(v)
+	if err != nil {
+		panic(err)
+	}
+	return "data: " + string(raw) + "\n\n"
+}
+
+func rcChunk(choices ...map[string]any) string {
+	return rcFrame(map[string]any{"choices": choices})
+}
+
+func rcFrag(index int, id, name, args string) map[string]any {
+	fn := map[string]any{}
+	if name != "" {
+		fn["name"] = name
+	}
+	if args != "" {
+		fn["arguments"] = args
+	}
+	frag := map[string]any{"index": index, "function": fn}
+	if id != "" {
+		frag["id"] = id
+	}
+	return frag
+}
+
+func rcToolChoice(finish string, frags ...map[string]any) map[string]any {
+	choice := map[string]any{"delta": map[string]any{"tool_calls": frags}}
+	if finish != "" {
+		choice["finish_reason"] = finish
+	}
+	return choice
+}
+
+func rcFinishChunk(reason string) string {
+	return rcChunk(map[string]any{"delta": map[string]any{}, "finish_reason": reason})
+}
+
+var (
+	rcText   = rcChunk(map[string]any{"delta": map[string]any{"content": "PRIVATE_TEXT_I1", "reasoning_content": "PRIVATE_THINK_I1"}})
+	rcCall1  = rcChunk(rcToolChoice("", rcFrag(0, "call_PRIVATE_I1", "read_PRIVATE_I1", `{"path":`)))
+	rcCall2  = rcChunk(rcToolChoice("", rcFrag(0, "", "", `"PRIVATE_I1.txt"}`)))
+	rcFinish = rcFinishChunk("tool_calls")
+	rcUsage  = rcFrame(map[string]any{"choices": []any{}, "usage": map[string]any{"prompt_tokens": 5, "completion_tokens": 2, "total_tokens": 7}})
+	rcDone   = "data: [DONE]\n\n"
+	rcStream = rcText + rcCall1 + rcCall2 + rcFinish + rcUsage
+	rcCall   = ToolCall{ID: "call_PRIVATE_I1", Name: "read_PRIVATE_I1", Arguments: `{"path":"PRIVATE_I1.txt"}`}
+
+	rcErrorFrame = rcFrame(map[string]any{"error": map[string]any{"message": "PRIVATE_PROVIDER_I1"}})
+)
+
+// rcSingleCall streams one complete call in one fragment with the given parts.
+func rcSingleCall(id, name, args string) string {
+	return rcText + rcChunk(rcToolChoice("", rcFrag(0, id, name, args))) + rcFinish + rcUsage
+}
+
+func rcWrite(stream string) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = io.WriteString(w, stream)
+		w.(http.Flusher).Flush()
+	}
+}
+
+func rcHTTP2(t *testing.T, h http.Handler) *httptest.Server {
+	t.Helper()
+	server := httptest.NewUnstartedServer(h)
+	server.EnableHTTP2 = true
+	server.StartTLS()
+	t.Cleanup(server.Close)
+	return server
+}
+
+func rcTLS1(t *testing.T, h http.Handler) *httptest.Server {
+	t.Helper()
+	server := httptest.NewTLSServer(h)
+	t.Cleanup(server.Close)
+	return server
+}
+
+func rcPlain(t *testing.T, h http.Handler) *httptest.Server {
+	t.Helper()
+	server := httptest.NewServer(h)
+	t.Cleanup(server.Close)
+	return server
+}
+
+// rcHTTPClient trusts server like server.Client() but owns its connection
+// pool, so each run starts on a fresh connection and HTTP/2 stream ids match.
+func rcHTTPClient(t *testing.T, server *httptest.Server) *http.Client {
+	t.Helper()
+	base := server.Client().Transport.(*http.Transport)
+	transport := &http.Transport{TLSClientConfig: base.TLSClientConfig.Clone(), ForceAttemptHTTP2: true}
+	t.Cleanup(transport.CloseIdleConnections)
+	return &http.Client{Transport: transport}
+}
+
+func rcClientFor(t *testing.T, server *httptest.Server) *Client {
+	return &Client{BaseURL: server.URL, APIKey: "fixture", HTTPClient: rcHTTPClient(t, server)}
+}
+
+func rcContract(model, base string) *RouteContractEOF {
+	return &RouteContractEOF{Model: model, BaseURL: base, IdentitySHA256: RouteContractIdentity(model, base)}
+}
+
+func rcFixtureClient(resp func() *http.Response) *Client {
+	return &Client{BaseURL: "https://fixture.invalid", APIKey: "fixture", HTTPClient: &http.Client{
+		Transport: terminalRoundTripFunc(func(r *http.Request) (*http.Response, error) {
+			res := resp()
+			res.Request = r
+			return res, nil
+		}),
+	}}
+}
+
+type rcSetup struct {
+	client   *Client
+	contract *RouteContractEOF
+	opts     StreamOptions
+	tools    []ToolDecl
+}
+
+type rcResult struct {
+	end              Event
+	releasedMessages int
+	releasedCalls    int
+}
+
+func rcRun(t *testing.T, ctx context.Context, base *Client, contract *RouteContractEOF, tools []ToolDecl, opts StreamOptions, onEvent func(Event)) rcResult {
+	t.Helper()
+	client := *base
+	client.RouteContract = contract
+	var res rcResult
+	terminals := 0
+	for ev := range client.Stream(ctx, rcModel, []Message{{Role: RoleUser, Content: "hello"}}, tools, opts) {
+		if onEvent != nil {
+			onEvent(ev)
+		}
+		if ev.Kind != KindMessageEnd && ev.Kind != KindError {
+			continue
+		}
+		terminals++
+		res.end = ev
+		if ev.Kind == KindMessageEnd && ev.Err == nil && len(ev.Message.ToolCalls) > 0 {
+			res.releasedMessages++
+			res.releasedCalls += len(ev.Message.ToolCalls)
+		}
+	}
+	if terminals != 1 {
+		t.Fatalf("terminal events = %d, want 1", terminals)
+	}
+	rcRequireSafeLabels(t, res.end)
+	return res
+}
+
+// rcRequireSafeLabels is the sentinel scan: the new labels hold only their
+// fixed enums and the observation never carries content, tool identity,
+// arguments or error text.
+func rcRequireSafeLabels(t *testing.T, end Event) {
+	t.Helper()
+	obs := end.TerminalObservation
+	if obs == nil {
+		t.Fatalf("terminal without observation: %#v", end)
+	}
+	switch end.CompletionBasis {
+	case "", CompletionDoneMarker, CompletionRouteContractEOF:
+	default:
+		t.Fatalf("completion basis outside enum: %q", end.CompletionBasis)
+	}
+	if obs.CompletionBasis != end.CompletionBasis {
+		t.Fatalf("observation basis %q != event basis %q", obs.CompletionBasis, end.CompletionBasis)
+	}
+	if c := obs.ContractCheck; c != "" && (len(c) != 2 || c[0] != 'C' || c[1] < '1' || c[1] > '9') {
+		t.Fatalf("contract check outside enum: %q", c)
+	}
+	raw, err := json.Marshal(obs)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, secret := range []string{"PRIVATE", "[DONE]", "tool call", "fixture-model"} {
+		if strings.Contains(string(raw), secret) {
+			t.Fatalf("observation leaked %q: %s", secret, raw)
+		}
+	}
+	for _, label := range []string{end.CompletionBasis, obs.CompletionBasis, obs.ContractCheck} {
+		if strings.Contains(label, "PRIVATE") || strings.Contains(label, " ") {
+			t.Fatalf("label carries content: %q", label)
+		}
+	}
+}
+
+func rcStreamCase(server func(*testing.T, http.Handler) *httptest.Server, stream string) func(*testing.T) rcSetup {
+	return func(t *testing.T) rcSetup {
+		s := server(t, rcWrite(stream))
+		return rcSetup{client: rcClientFor(t, s), contract: rcContract(rcModel, s.URL)}
+	}
+}
+
+func rcH2(stream string) func(*testing.T) rcSetup { return rcStreamCase(rcHTTP2, stream) }
+
+func rcRedirectCase(target func(t *testing.T) string) func(*testing.T) rcSetup {
+	return func(t *testing.T) rcSetup {
+		location := target(t)
+		mux := http.NewServeMux()
+		mux.HandleFunc("/chat/completions", func(w http.ResponseWriter, r *http.Request) {
+			http.Redirect(w, r, location, http.StatusTemporaryRedirect)
+		})
+		mux.HandleFunc("/final/chat/completions", rcWrite(rcStream))
+		s := rcHTTP2(t, mux)
+		return rcSetup{client: rcClientFor(t, s), contract: rcContract(rcModel, s.URL)}
+	}
+}
+
+type rcCase struct {
+	name  string
+	setup func(*testing.T) rcSetup
+	// want is done_marker, route_contract_eof, off, or a check id C1..C9.
+	want string
+	// reason is the contract-off failure text; empty skips the check.
+	reason  string
+	calls   []ToolCall
+	noUsage bool
+}
+
+func rcCases() []rcCase {
+	twoCalls := rcText + rcCall1 + rcCall2 +
+		rcChunk(rcToolChoice("", rcFrag(1, "call_PRIVATE_I1_b", "list_PRIVATE_I1", `{}`))) + rcFinish + rcUsage
+	return []rcCase{
+		// [DONE] keeps today's path whether or not the contract is configured.
+		{name: "done/contract-on", setup: rcH2(rcStream + rcDone), want: CompletionDoneMarker},
+		{name: "done/contract-c1-failing", setup: func(t *testing.T) rcSetup {
+			s := rcH2(rcStream + rcDone)(t)
+			s.contract = rcContract("other-model", s.client.BaseURL)
+			return s
+		}, want: CompletionDoneMarker},
+		{name: "done/known-length", setup: rcKnownLength(rcStream + rcDone), want: CompletionDoneMarker},
+
+		// Released only when every condition holds.
+		{name: "release/http2", setup: rcH2(rcStream), want: CompletionRouteContractEOF},
+		{name: "release/known-length-match", setup: rcKnownLength(rcStream), want: CompletionRouteContractEOF},
+		{name: "release/usage-before-finish", setup: rcH2(rcText + rcUsage + rcCall1 + rcCall2 + rcFinish), want: CompletionRouteContractEOF},
+		{name: "release/usage-after-finish", setup: rcH2(rcText + rcCall1 + rcCall2 + rcFinish + rcUsage), want: CompletionRouteContractEOF},
+		{name: "release/fragment-in-finish-chunk", setup: rcH2(rcText + rcCall1 +
+			rcChunk(rcToolChoice("tool_calls", rcFrag(0, "", "", `"PRIVATE_I1.txt"}`))) + rcUsage), want: CompletionRouteContractEOF},
+		{name: "release/two-calls", setup: rcH2(twoCalls), want: CompletionRouteContractEOF,
+			calls: []ToolCall{rcCall, {ID: "call_PRIVATE_I1_b", Name: "list_PRIVATE_I1", Arguments: `{}`}}},
+		{name: "release/api-base-override-to-contract", setup: func(t *testing.T) rcSetup {
+			s := rcH2(rcStream)(t)
+			s.opts.APIBase = s.client.BaseURL + "/"
+			s.client.BaseURL = "https://unused.invalid"
+			return s
+		}, want: CompletionRouteContractEOF},
+
+		// The zero value is off.
+		{name: "off/zero-contract", setup: func(t *testing.T) rcSetup {
+			s := rcH2(rcStream)(t)
+			s.contract = &RouteContractEOF{}
+			return s
+		}, want: "off", reason: rcEOFReason},
+
+		// C1 route identity.
+		{name: "c1/model-mismatch", setup: func(t *testing.T) rcSetup {
+			s := rcH2(rcStream)(t)
+			s.contract = rcContract("other-model", s.client.BaseURL)
+			return s
+		}, want: "C1", reason: rcEOFReason},
+		{name: "c1/base-http", setup: rcStreamCase(rcPlain, rcStream), want: "C1", reason: rcEOFReason},
+		{name: "c1/base-userinfo", setup: func(t *testing.T) rcSetup {
+			s := rcH2(rcStream)(t)
+			s.client.BaseURL = strings.Replace(s.client.BaseURL, "https://", "https://user@", 1)
+			return s
+		}, want: "C1", reason: rcEOFReason},
+		{name: "c1/base-query", setup: func(t *testing.T) rcSetup {
+			s := rcH2(rcStream)(t)
+			s.client.BaseURL += "?x=1"
+			return s
+		}, want: "C1", reason: rcEOFReason},
+		{name: "c1/digest-mismatch", setup: func(t *testing.T) rcSetup {
+			s := rcH2(rcStream)(t)
+			s.contract.IdentitySHA256 = strings.Repeat("0", 64)
+			return s
+		}, want: "C1", reason: rcEOFReason},
+		{name: "c1/digest-uppercase", setup: func(t *testing.T) rcSetup {
+			s := rcH2(rcStream)(t)
+			s.contract.IdentitySHA256 = strings.ToUpper(s.contract.IdentitySHA256)
+			return s
+		}, want: "C1", reason: rcEOFReason},
+		{name: "c1/protocol-not-openai-chat", setup: func(t *testing.T) rcSetup {
+			s := rcH2(rcStream)(t)
+			s.client.Protocol = ProtocolGoogle
+			return s
+		}, want: "C1", reason: rcEOFReason},
+		{name: "c1/api-base-override-elsewhere", setup: func(t *testing.T) rcSetup {
+			other := rcHTTP2(t, rcWrite(rcStream))
+			s := rcH2(rcStream)(t)
+			s.opts.APIBase = other.URL
+			s.client.HTTPClient = rcHTTPClient(t, other)
+			return s
+		}, want: "C1", reason: rcEOFReason},
+		{name: "c1/redirect-other-host", setup: rcRedirectCase(func(t *testing.T) string {
+			return rcHTTP2(t, rcWrite(rcStream)).URL + "/chat/completions"
+		}), want: "C1", reason: rcEOFReason},
+		{name: "c1/redirect-same-host-other-path", setup: rcRedirectCase(func(t *testing.T) string {
+			return "/final/chat/completions"
+		}), want: "C1", reason: rcEOFReason},
+		{name: "c1/redirect-https-downgrade", setup: rcRedirectCase(func(t *testing.T) string {
+			return rcPlain(t, rcWrite(rcStream)).URL + "/chat/completions"
+		}), want: "C1", reason: rcEOFReason},
+
+		// C2 body boundary.
+		{name: "c2/known-length-mismatch", setup: func(t *testing.T) rcSetup {
+			client := rcFixtureClient(func() *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, ProtoMajor: 1, ProtoMinor: 1,
+					ContentLength: int64(len(rcStream) + 64), Header: http.Header{},
+					Body: io.NopCloser(strings.NewReader(rcStream))}
+			})
+			return rcSetup{client: client, contract: rcContract(rcModel, client.BaseURL)}
+		}, want: "C2", reason: rcEOFReason},
+		{name: "c2/unknown-framing", setup: func(t *testing.T) rcSetup {
+			client := rcFixtureClient(func() *http.Response {
+				return &http.Response{StatusCode: http.StatusOK, ContentLength: -1, Header: http.Header{},
+					Body: io.NopCloser(strings.NewReader(rcStream))}
+			})
+			return rcSetup{client: client, contract: rcContract(rcModel, client.BaseURL)}
+		}, want: "C2", reason: rcEOFReason},
+		{name: "c2/chunked", setup: rcStreamCase(rcTLS1, rcStream), want: "C2", reason: rcEOFReason},
+		{name: "c2/close-delimited", setup: func(t *testing.T) rcSetup {
+			s := rcTLS1(t, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.Header().Set("Content-Type", "text/event-stream")
+				w.Header().Set("Transfer-Encoding", "identity")
+				w.WriteHeader(http.StatusOK)
+				_, _ = io.WriteString(w, rcStream)
+				w.(http.Flusher).Flush()
+			}))
+			return rcSetup{client: rcClientFor(t, s), contract: rcContract(rcModel, s.URL)}
+		}, want: "C2", reason: rcEOFReason},
+		// A reset or dropped stream never reaches body EOF, so the boundary
+		// condition fails before the read-outcome condition is evaluated.
+		{name: "c2/http2-rst-stream", setup: func(t *testing.T) rcSetup {
+			s := rcHTTP2(t, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				rcWrite(rcStream)(w, r)
+				panic(http.ErrAbortHandler)
+			}))
+			return rcSetup{client: rcClientFor(t, s), contract: rcContract(rcModel, s.URL)}
+		}, want: "C2", reason: "stream read failed after reported usage"},
+		{name: "c2/mid-stream-disconnect", setup: func(t *testing.T) rcSetup {
+			s := rcTLS1(t, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				rcWrite(rcStream)(w, r)
+				conn, _, err := w.(http.Hijacker).Hijack()
+				if err == nil {
+					_ = conn.Close()
+				}
+			}))
+			return rcSetup{client: rcClientFor(t, s), contract: rcContract(rcModel, s.URL)}
+		}, want: "C2", reason: "stream read failed after reported usage"},
+
+		// The parser stops at a bad frame; with a trailing delimiter it never
+		// reads to body EOF, so the boundary condition fails first.
+		{name: "c2/invalid-frame-before-eof", setup: rcH2(rcStream + "data: PRIVATE_not_json\n\n"), want: "C2",
+			reason: "malformed stream chunk after reported usage"},
+		{name: "c2/provider-error-before-eof", setup: rcH2(rcStream + rcErrorFrame), want: "C2",
+			reason: "provider error after reported usage: PRIVATE_PROVIDER_I1"},
+
+		// C3 read outcome: the bad frame is the last bytes, so body EOF is seen.
+		{name: "c3/half-frame", setup: rcH2(rcStream + `data: {"choices":[{"delta":{"content":"PRIVATE_HALF`), want: "C3",
+			reason: "malformed stream chunk after reported usage"},
+		{name: "c3/invalid-frame", setup: rcH2(rcStream + "data: PRIVATE_not_json"), want: "C3",
+			reason: "malformed stream chunk after reported usage"},
+		{name: "c3/provider-error-after-usage", setup: rcH2(rcStream + strings.TrimRight(rcErrorFrame, "\n")),
+			want: "C3", reason: "provider error after reported usage: PRIVATE_PROVIDER_I1"},
+		{name: "c3/provider-error-before-usage", setup: rcH2(rcText + rcCall1 + rcCall2 + rcFinish + strings.TrimRight(rcErrorFrame, "\n")),
+			want: "C3", reason: "PRIVATE_PROVIDER_I1", noUsage: true},
+
+		// C4 finish reason and choices.
+		{name: "c4/two-finish-chunks", setup: rcH2(rcText + rcCall1 + rcCall2 + rcFinish + rcFinish + rcUsage), want: "C4", reason: rcEOFReason},
+		{name: "c4/finish-stop-with-tools", setup: rcH2(rcText + rcCall1 + rcCall2 + rcFinishChunk("stop") + rcUsage), want: "C4", reason: rcEOFReason},
+		{name: "c4/finish-length-with-tools", setup: rcH2(rcText + rcCall1 + rcCall2 + rcFinishChunk("length") + rcUsage), want: "C4", reason: rcEOFReason},
+		{name: "c4/multi-choice-chunk", setup: rcH2(rcText +
+			rcChunk(map[string]any{"delta": map[string]any{"content": "a"}}, map[string]any{"delta": map[string]any{"content": "b"}}) +
+			rcCall1 + rcCall2 + rcFinish + rcUsage), want: "C4", reason: rcEOFReason},
+		{name: "c4/truncated-at-frame-boundary-without-finish", setup: rcH2(rcText + rcCall1 + rcCall2 + rcUsage), want: "C4", reason: rcEOFReason},
+
+		// C5 usage.
+		{name: "c5/missing-usage", setup: rcH2(rcText + rcCall1 + rcCall2 + rcFinish), want: "C5", reason: rcEOFReason, noUsage: true},
+
+		// C6 fragments after finish.
+		{name: "c6/fragment-after-finish-chunk", setup: rcH2(rcText + rcCall1 + rcFinish + rcCall2 + rcUsage), want: "C6", reason: rcEOFReason},
+
+		// C7 call identity and argument shape.
+		{name: "c7/missing-id", setup: rcH2(rcSingleCall("", "read_PRIVATE_I1", `{"path":"PRIVATE_I1.txt"}`)), want: "C7", reason: rcEOFReason},
+		{name: "c7/missing-name", setup: rcH2(rcSingleCall("call_PRIVATE_I1", "", `{"path":"PRIVATE_I1.txt"}`)), want: "C7", reason: rcEOFReason},
+		{name: "c7/array-arguments", setup: rcH2(rcSingleCall("call_PRIVATE_I1", "read_PRIVATE_I1", `["PRIVATE_I1.txt"]`)), want: "C7", reason: rcEOFReason},
+		{name: "c7/broken-arguments", setup: rcH2(rcSingleCall("call_PRIVATE_I1", "read_PRIVATE_I1", `{"path":"PRIVATE_I1.txt"`)), want: "C7", reason: rcEOFReason},
+		{name: "c7/finish-without-call", setup: rcH2(rcText + rcFinish + rcUsage), want: "C7", reason: "tool call finish reason without a tool call"},
+
+		// C8 declared tools and argument schema.
+		{name: "c8/unknown-tool", setup: rcH2(rcSingleCall("call_PRIVATE_I1", "write_PRIVATE_I1", `{"path":"PRIVATE_I1.txt"}`)), want: "C8", reason: rcEOFReason},
+		{name: "c8/no-tools-declared", setup: func(t *testing.T) rcSetup {
+			s := rcH2(rcStream)(t)
+			s.tools = []ToolDecl{}
+			return s
+		}, want: "C8", reason: rcEOFReason},
+		{name: "c8/missing-required", setup: rcH2(rcSingleCall("call_PRIVATE_I1", "read_PRIVATE_I1", `{}`)), want: "C8", reason: rcEOFReason},
+		{name: "c8/blank-required", setup: rcH2(rcSingleCall("call_PRIVATE_I1", "read_PRIVATE_I1", `{"path":" "}`)), want: "C8", reason: rcEOFReason},
+		{name: "c8/wrong-property-type", setup: rcH2(rcSingleCall("call_PRIVATE_I1", "read_PRIVATE_I1", `{"path":7}`)), want: "C8", reason: rcEOFReason},
+		{name: "c8/unknown-argument", setup: rcH2(rcSingleCall("call_PRIVATE_I1", "read_PRIVATE_I1", `{"path":"a","PRIVATE":1}`)), want: "C8", reason: rcEOFReason},
+
+		// C9 tail event.
+		{name: "c9/comment-tail", setup: rcH2(rcStream + ": PRIVATE_keepalive\n\n"), want: "C9", reason: rcEOFReason},
+	}
+}
+
+func rcKnownLength(stream string) func(*testing.T) rcSetup {
+	return func(t *testing.T) rcSetup {
+		s := rcTLS1(t, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Set("Content-Type", "text/event-stream")
+			w.Header().Set("Content-Length", strconv.Itoa(len(stream)))
+			_, _ = io.WriteString(w, stream)
+		}))
+		return rcSetup{client: rcClientFor(t, s), contract: rcContract(rcModel, s.URL)}
+	}
+}
+
+func TestRouteContractEOFMatrix(t *testing.T) {
+	for _, tc := range rcCases() {
+		t.Run(tc.name, func(t *testing.T) {
+			s := tc.setup(t)
+			tools := s.tools
+			if tools == nil {
+				tools = rcTools
+			}
+			wantCalls := tc.calls
+			if wantCalls == nil {
+				wantCalls = []ToolCall{rcCall}
+			}
+			wantUsage := 7
+			if tc.noUsage {
+				wantUsage = 0
+			}
+			off := rcRun(t, context.Background(), s.client, nil, tools, s.opts, nil)
+			on := rcRun(t, context.Background(), s.client, s.contract, tools, s.opts, nil)
+			for _, r := range []rcResult{off, on} {
+				if r.end.Usage.TotalTokens != wantUsage {
+					t.Fatalf("usage = %+v, want total %d", r.end.Usage, wantUsage)
+				}
+			}
+			if off.end.TerminalObservation.ContractCheck != "" {
+				t.Fatalf("contract-off stream carried a contract check: %+v", off.end.TerminalObservation)
+			}
+			if tc.reason != "" && off.end.ErrorMessage != tc.reason {
+				t.Fatalf("contract-off failure = %q, want %q", off.end.ErrorMessage, tc.reason)
+			}
+
+			switch tc.want {
+			case CompletionDoneMarker:
+				if !reflect.DeepEqual(on.end, off.end) {
+					t.Fatalf("contract changed a [DONE] terminal:\n on=%#v\noff=%#v", on.end, off.end)
+				}
+				if on.end.Err != nil || !on.end.StreamComplete || on.end.CompletionBasis != CompletionDoneMarker ||
+					on.end.TerminalObservation.ContractCheck != "" || on.end.TerminalObservation.ReadOutcome != "done_marker" {
+					t.Fatalf("[DONE] terminal not marked done_marker: %#v", on.end)
+				}
+				rcRequireReleased(t, on, wantCalls)
+			case CompletionRouteContractEOF:
+				rcRequireRejected(t, off)
+				if off.end.CompletionBasis != "" || off.end.ErrorMessage != rcEOFReason {
+					t.Fatalf("contract-off stream was not rejected unchanged: %#v", off.end)
+				}
+				end := on.end
+				if end.Err != nil || end.StreamComplete || end.CompletionBasis != CompletionRouteContractEOF ||
+					end.TerminalObservation.ContractCheck != "" || end.TerminalObservation.ReadOutcome != "clean_eof" ||
+					end.Message.StopReason != StopToolCalls || end.FinishReason != "tool_calls" || end.HTTPStatus != http.StatusOK {
+					t.Fatalf("contract stream was not released: %#v obs=%+v", end, end.TerminalObservation)
+				}
+				if end.Message.Content != off.end.Message.Content || !reflect.DeepEqual(end.Message.Thinking, off.end.Message.Thinking) {
+					t.Fatalf("released message changed content: %#v vs %#v", end.Message, off.end.Message)
+				}
+				rcRequireReleased(t, on, wantCalls)
+			case "off":
+				if !reflect.DeepEqual(on.end, off.end) {
+					t.Fatalf("zero contract changed the terminal:\n on=%#v\noff=%#v", on.end, off.end)
+				}
+				rcRequireRejected(t, on)
+			default:
+				rcRequireRejected(t, off)
+				rcRequireRejected(t, on)
+				if got := on.end.TerminalObservation.ContractCheck; got != tc.want {
+					t.Fatalf("contract check = %q, want %q (obs=%+v)", got, tc.want, on.end.TerminalObservation)
+				}
+				stripped := on.end
+				obs := *on.end.TerminalObservation
+				obs.ContractCheck = ""
+				stripped.TerminalObservation = &obs
+				if !reflect.DeepEqual(stripped, off.end) {
+					t.Fatalf("rejection differs from contract-off beyond contractCheck:\n on=%#v %+v\noff=%#v %+v",
+						stripped, stripped.TerminalObservation, off.end, off.end.TerminalObservation)
+				}
+			}
+		})
+	}
+}
+
+func rcRequireReleased(t *testing.T, r rcResult, calls []ToolCall) {
+	t.Helper()
+	if r.releasedMessages != 1 || r.releasedCalls != len(calls) || !reflect.DeepEqual(r.end.Message.ToolCalls, calls) {
+		t.Fatalf("released %d messages / %d calls %#v, want 1 / %#v", r.releasedMessages, r.releasedCalls, r.end.Message.ToolCalls, calls)
+	}
+}
+
+func rcRequireRejected(t *testing.T, r rcResult) {
+	t.Helper()
+	end := r.end
+	if r.releasedMessages != 0 || r.releasedCalls != 0 || len(end.Message.ToolCalls) != 0 || end.Err == nil ||
+		end.StreamComplete || end.CompletionBasis != "" || end.TerminalObservation.CompletionBasis != "" {
+		t.Fatalf("stream was released: %#v", end)
+	}
+}
+
+func TestRouteContractEOFCancelDuringReadAborts(t *testing.T) {
+	server := rcHTTP2(t, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		rcWrite(rcText+rcCall1+rcCall2+rcFinish+rcUsage)(w, r)
+		<-r.Context().Done()
+	}))
+	client := rcClientFor(t, server)
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	res := rcRun(t, ctx, client, rcContract(rcModel, server.URL), rcTools, StreamOptions{}, func(ev Event) {
+		if ev.Kind == KindToolCallDelta {
+			cancel()
+		}
+	})
+	end := res.end
+	if end.Kind != KindError || end.Message.StopReason != StopAborted || end.TerminalObservation.ReadOutcome != "cancelled" ||
+		end.TerminalObservation.ContractCheck != "" || end.CompletionBasis != "" || res.releasedMessages != 0 ||
+		res.releasedCalls != 0 || len(end.Message.ToolCalls) != 0 {
+		t.Fatalf("cancelled contract stream was not aborted: %#v obs=%+v", end, end.TerminalObservation)
+	}
+}
+
+func TestParseSSEUnchangedWithoutDone(t *testing.T) {
+	var end Event
+	for ev := range ParseSSE(context.Background(), strings.NewReader(rcStream)) {
+		end = ev
+	}
+	if end.Kind != KindMessageEnd || end.ErrorMessage != rcEOFReason || len(end.Message.ToolCalls) != 0 ||
+		end.StreamComplete || end.CompletionBasis != "" || end.Usage.TotalTokens != 7 ||
+		end.TerminalObservation == nil || end.TerminalObservation.CompletionBasis != "" ||
+		end.TerminalObservation.ContractCheck != "" || end.TerminalObservation.BodyBoundary != nil {
+		t.Fatalf("ParseSSE changed without [DONE]: %#v", end)
+	}
+	raw, err := json.Marshal(end.TerminalObservation)
+	if err != nil || strings.Contains(string(raw), "completionBasis") || strings.Contains(string(raw), "contractCheck") {
+		t.Fatalf("ParseSSE observation JSON changed: %s err=%v", raw, err)
+	}
+	var done Event
+	for ev := range ParseSSE(context.Background(), strings.NewReader(rcStream+rcDone)) {
+		done = ev
+	}
+	if done.Err != nil || !done.StreamComplete || done.CompletionBasis != "" || done.TerminalObservation.CompletionBasis != "" ||
+		!reflect.DeepEqual(done.Message.ToolCalls, []ToolCall{rcCall}) {
+		t.Fatalf("ParseSSE changed with [DONE]: %#v", done)
+	}
+}
+
+func TestRouteContractIdentity(t *testing.T) {
+	sum := sha256.Sum256([]byte("openai-chat\nm\nhttps://api.example.com/v1"))
+	if got, want := RouteContractIdentity("m", "https://api.example.com/v1"), hex.EncodeToString(sum[:]); got != want {
+		t.Fatalf("identity = %s, want %s", got, want)
+	}
+	if got := RouteContractIdentity("m", "https://api.example.com/v1"); got != strings.ToLower(got) || len(got) != 64 {
+		t.Fatalf("identity is not lowercase hex: %s", got)
+	}
+}
+
+func TestNormalizeRouteBaseURL(t *testing.T) {
+	tests := []struct {
+		raw, want string
+		ok        bool
+	}{
+		{"https://api.example.com/v1", "https://api.example.com/v1", true},
+		{"HTTPS://API.Example.COM/v1/", "https://api.example.com/v1", true},
+		{"https://api.example.com:8443/v1//", "https://api.example.com:8443/v1", true},
+		{"https://api.example.com", "https://api.example.com", true},
+		{"https://api.example.com/V1", "https://api.example.com/V1", true},
+		{"http://api.example.com/v1", "", false},
+		{"https://user@api.example.com/v1", "", false},
+		{"https://user:pw@api.example.com/v1", "", false},
+		{"https://api.example.com/v1?x=1", "", false},
+		{"https://api.example.com/v1?", "", false},
+		{"https://api.example.com/v1#frag", "", false},
+		{"https://api.example.com/v1#", "", false},
+		{"https:api.example.com", "", false},
+		{"https:///v1", "", false},
+		{"", "", false},
+		{"://bad", "", false},
+	}
+	for _, tc := range tests {
+		got, ok := NormalizeRouteBaseURL(tc.raw)
+		if got != tc.want || ok != tc.ok {
+			t.Fatalf("NormalizeRouteBaseURL(%q) = %q, %v; want %q, %v", tc.raw, got, ok, tc.want, tc.ok)
+		}
+	}
+}
diff --git a/runtime/llm/sse.go b/runtime/llm/sse.go
index 7ae4c35..d278a37 100644
--- a/runtime/llm/sse.go
+++ b/runtime/llm/sse.go
@@ -46,18 +46,49 @@ const (
 	maxObservedTailEvents        = 10000
 )
 
+// sseFacts are structural stream facts the route contract needs. They are
+// written by the parser goroutine before it sends the terminal event.
+type sseFacts struct {
+	// finishChunks counts chunks with a non-empty finish_reason.
+	finishChunks int
+	finishReason string
+	// multiChoice is set when any chunk carried more than one choice.
+	multiChoice bool
+	// fragmentAfterFinish is set when a tool-call fragment arrived in a chunk
+	// after the one carrying finish_reason.
+	fragmentAfterFinish bool
+}
+
+// sseHooks are internal parser options. The zero value is ParseSSE.
+type sseHooks struct {
+	facts *sseFacts
+	// decideEOF, when set, receives a tool stream whose terminal would be
+	// "tool call stream ended before [DONE]": success is the message_end the
+	// stream would end with had [DONE] arrived, failure is the event emitted
+	// today. It returns the event to send.
+	decideEOF func(success, failure Event) Event
+}
+
 // ParseSSE reads an OpenAI-compatible server-sent event body and emits
 // deltas plus one terminal message_end or error event.
 func ParseSSE(ctx context.Context, r io.Reader) <-chan Event {
+	return parseSSE(ctx, r, sseHooks{})
+}
+
+func parseSSE(ctx context.Context, r io.Reader, hooks sseHooks) <-chan Event {
 	out := make(chan Event)
 	go func() {
 		defer close(out)
-		emitParsed(ctx, r, out)
+		emitParsed(ctx, r, out, hooks)
 	}()
 	return out
 }
 
-func emitParsed(ctx context.Context, r io.Reader, out chan<- Event) {
+func emitParsed(ctx context.Context, r io.Reader, out chan<- Event, hooks sseHooks) {
+	facts := hooks.facts
+	if facts == nil {
+		facts = &sseFacts{}
+	}
 	var content strings.Builder
 	var reasoning strings.Builder
 	calls := map[int]*ToolCall{}
@@ -93,20 +124,39 @@ func emitParsed(ctx context.Context, r io.Reader, out chan<- Event) {
 			TailEventKind: tailKind, TailEventCount: reader.tailCount,
 		}
 	}
-	sendTerminalFailure := func(why string) {
+	buildTerminalFailure := func(why string) Event {
 		message := Message{Role: RoleAssistant, Content: content.String(), StopReason: StopError}
 		if reasoning.Len() > 0 {
 			message.Thinking = []ThinkingBlock{{Thinking: reasoning.String()}}
 		}
 		failed := terminalStreamFailure(message, usage, finished, sawDone, why)
 		failed.TerminalObservation = observation()
+		return failed
+	}
+	sendTerminal := func(ev Event) {
 		select {
 		case <-ctx.Done():
 			readOutcome = "cancelled"
 			emitAbort(out, content.String(), ctx.Err(), observation())
-		case out <- failed:
+		case out <- ev:
 		}
 	}
+	sendTerminalFailure := func(why string) {
+		sendTerminal(buildTerminalFailure(why))
+	}
+	buildMessageEnd := func() Event {
+		msg := Message{Role: RoleAssistant, Content: content.String(), StopReason: mapFinish(finished, len(order) > 0)}
+		if reasoning.Len() > 0 {
+			msg.Thinking = []ThinkingBlock{{Thinking: reasoning.String()}}
+		}
+		for _, idx := range order {
+			msg.ToolCalls = append(msg.ToolCalls, *calls[idx])
+		}
+		if msg.StopReason == StopToolCalls && len(msg.ToolCalls) == 0 {
+			msg.StopReason = StopEnd
+		}
+		return Event{Kind: KindMessageEnd, Message: msg, Usage: usage, FinishReason: finished, StreamComplete: sawDone, TerminalObservation: observation()}
+	}
 	for {
 		data, ok := reader.next()
 		if !ok {
@@ -155,12 +205,28 @@ func emitParsed(ctx context.Context, r io.Reader, out chan<- Event) {
 				usage.CacheReadTokens = chunk.Usage.Details.Cached
 			}
 		}
+		if len(chunk.Choices) > 1 {
+			facts.multiChoice = true
+		}
+		finishedBefore := facts.finishChunks > 0
+		for _, c := range chunk.Choices {
+			if c.FinishReason != "" {
+				if facts.finishChunks < maxObservedTailEvents {
+					facts.finishChunks++
+				}
+				break
+			}
+		}
 		if len(chunk.Choices) == 0 {
 			continue
 		}
 		choice := chunk.Choices[0]
 		if choice.FinishReason != "" {
 			finished = choice.FinishReason
+			facts.finishReason = finished
+		}
+		if finishedBefore && len(choice.Delta.ToolCalls) > 0 {
+			facts.fragmentAfterFinish = true
 		}
 		if choice.Delta.Content != "" {
 			content.WriteString(choice.Delta.Content)
@@ -279,26 +345,15 @@ func emitParsed(ctx context.Context, r io.Reader, out chan<- Event) {
 			}
 		}
 		if problem != "" {
+			if !sawDone && hooks.decideEOF != nil {
+				sendTerminal(hooks.decideEOF(buildMessageEnd(), buildTerminalFailure(problem)))
+				return
+			}
 			sendTerminalFailure(problem)
 			return
 		}
 	}
-	msg := Message{Role: RoleAssistant, Content: content.String(), StopReason: mapFinish(finished, len(order) > 0)}
-	if reasoning.Len() > 0 {
-		msg.Thinking = []ThinkingBlock{{Thinking: reasoning.String()}}
-	}
-	for _, idx := range order {
-		msg.ToolCalls = append(msg.ToolCalls, *calls[idx])
-	}
-	if msg.StopReason == StopToolCalls && len(msg.ToolCalls) == 0 {
-		msg.StopReason = StopEnd
-	}
-	select {
-	case <-ctx.Done():
-		readOutcome = "cancelled"
-		emitAbort(out, content.String(), ctx.Err(), observation())
-	case out <- Event{Kind: KindMessageEnd, Message: msg, Usage: usage, FinishReason: finished, StreamComplete: sawDone, TerminalObservation: observation()}:
-	}
+	sendTerminal(buildMessageEnd())
 }
 
 func terminalStreamFailure(message Message, usage Usage, reason string, complete bool, why string) Event {
diff --git a/runtime/llm/types.go b/runtime/llm/types.go
index 1499deb..4dd1b4d 100644
--- a/runtime/llm/types.go
+++ b/runtime/llm/types.go
@@ -117,6 +117,12 @@ type TerminalObservation struct {
 	// BodyBoundary is set only by Client on a response it received; a bare
 	// ParseSSE call leaves it nil.
 	BodyBoundary *BodyBoundaryObservation `json:"bodyBoundary,omitempty"`
+	// CompletionBasis mirrors Event.CompletionBasis.
+	CompletionBasis string `json:"completionBasis,omitempty"`
+	// ContractCheck is the first route-contract condition, C1 through C9, that
+	// failed when a configured RouteContractEOF did not release a stream that
+	// ended without [DONE]. Empty when no contract evaluated the stream.
+	ContractCheck string `json:"contractCheck,omitempty"`
 }
 
 // BodyBoundaryObservation records how the client read one HTTP response body.
@@ -152,8 +158,13 @@ type Event struct {
 	// 空表示这条事件不携带结束原因。StopReason 的映射不受此字段影响。
 	FinishReason string
 	// StreamComplete records whether the OpenAI-compatible SSE stream supplied
-	// its explicit [DONE] marker. Tool calls require this before execution.
+	// its explicit [DONE] marker. Tool calls require this before execution
+	// unless CompletionBasis is route_contract_eof.
 	StreamComplete bool
+	// CompletionBasis is set by Client on a successful OpenAI-chat message_end:
+	// done_marker when [DONE] arrived, route_contract_eof when RouteContractEOF
+	// released tool calls without it. Empty otherwise.
+	CompletionBasis string
 	// TerminalObservation is present only on a terminal/error event. It does
 	// not change StreamComplete or the tool-execution safety gate.
 	TerminalObservation *TerminalObservation
diff --git a/runtime/tools/registry.go b/runtime/tools/registry.go
index 563acae..e9ab4ba 100644
--- a/runtime/tools/registry.go
+++ b/runtime/tools/registry.go
@@ -9,6 +9,7 @@ import (
 	"sync"
 	"time"
 
+	"agent-native/runtime/argschema"
 	"agent-native/runtime/checkpoint"
 	"agent-native/runtime/filestate"
 )
@@ -286,74 +287,7 @@ func (r *Registry) audit(name string, blocked, isError bool, note string) {
 }
 
 func validateArgs(schema, args json.RawMessage) error {
-	var spec struct {
-		Type       string                     `json:"type"`
-		Required   []string                   `json:"required"`
-		Properties map[string]json.RawMessage `json:"properties"`
-	}
-	if len(schema) > 0 {
-		if err := json.Unmarshal(schema, &spec); err != nil {
-			return fmt.Errorf("invalid tool schema")
-		}
-	}
-	var obj map[string]any
-	if err := json.Unmarshal(args, &obj); err != nil {
-		return fmt.Errorf("arguments must be a JSON object")
-	}
-	if spec.Type != "" && spec.Type != "object" {
-		return fmt.Errorf("unsupported schema type %s", spec.Type)
-	}
-	for _, req := range spec.Required {
-		v, ok := obj[req]
-		if !ok || v == nil {
-			return fmt.Errorf("missing required argument %s", req)
-		}
-		if s, ok := v.(string); ok && strings.TrimSpace(s) == "" {
-			return fmt.Errorf("missing required argument %s", req)
-		}
-	}
-	for key, raw := range spec.Properties {
-		v, ok := obj[key]
-		if !ok {
-			continue
-		}
-		var prop struct {
-			Type string `json:"type"`
-		}
-		if err := json.Unmarshal(raw, &prop); err != nil || prop.Type == "" {
-			continue
-		}
-		if !matchesType(prop.Type, v) {
-			return fmt.Errorf("argument %s must be %s", key, prop.Type)
-		}
-	}
-	if len(spec.Properties) > 0 {
-		for key := range obj {
-			if _, ok := spec.Properties[key]; !ok {
-				return fmt.Errorf("unknown argument %s", key)
-			}
-		}
-	}
-	return nil
-}
-
-func matchesType(kind string, v any) bool {
-	switch kind {
-	case "string":
-		_, ok := v.(string)
-		return ok
-	case "number":
-		_, ok := v.(float64)
-		return ok
-	case "integer":
-		f, ok := v.(float64)
-		return ok && f == float64(int64(f))
-	case "boolean":
-		_, ok := v.(bool)
-		return ok
-	default:
-		return true
-	}
+	return argschema.Validate(schema, args)
 }
 
 // WorkspaceTools registers the document workspace tool set.
diff --git a/runtime/tools/registry_test.go b/runtime/tools/registry_test.go
new file mode 100644
index 0000000..7de03b7
--- /dev/null
+++ b/runtime/tools/registry_test.go
@@ -0,0 +1,18 @@
+package tools
+
+import (
+	"encoding/json"
+	"testing"
+
+	"agent-native/runtime/argschema"
+)
+
+func TestValidateArgsDelegatesToArgschema(t *testing.T) {
+	schema := json.RawMessage(`{"type":"object","required":["path"],"properties":{"path":{"type":"string"}}}`)
+	for _, args := range []string{`{"path":"a"}`, `{}`, `{"path":" "}`, `{"path":1}`, `{"path":"a","x":1}`, `[1]`} {
+		got, want := validateArgs(schema, json.RawMessage(args)), argschema.Validate(schema, json.RawMessage(args))
+		if (got == nil) != (want == nil) || (got != nil && got.Error() != want.Error()) {
+			t.Fatalf("validateArgs(%s) = %v, argschema.Validate = %v", args, got, want)
+		}
+	}
+}