feat(agents): resolve unique advertised model variations (#3472)

.github/scripts/pr-walkthrough-workflow-contract_test.py

@@ -129,7 +129,7 @@ class PRWalkthroughWorkflowContractTest(unittest.TestCase):
             'PUBLIC_URL="${WALKTHROUGH_BASE_URL%/}/pr/${PR_NUMBER}/${SHORT_HEAD_SHA}.html"',
             "RESPONSE_META_PATH=pr-walkthrough-public.response",
             "curl --fail",
-            "--write-out '%{http_code}\\t%{content_type}\\t%{url_effective}'",
+            "--write-out '%{http_code}\\t%{content_type}\\t%{url_effective}\\n'",
             "response_status",
             'response_effective_url" != "$PUBLIC_URL"',
             "response_content_type",

.github/workflows/pr-walkthrough-reconcile.yml

@@ -69,7 +69,7 @@ jobs:
           if ! curl --fail --silent --show-error --location --max-time 30 \
             --retry 3 --retry-all-errors --retry-delay 2 --retry-max-time 30 \
             --output "$PUBLIC_HTML_PATH" \
-            --write-out '%{http_code}\t%{content_type}\t%{url_effective}' \
+            --write-out '%{http_code}\t%{content_type}\t%{url_effective}\n' \
             > "$RESPONSE_META_PATH" \
             "$PUBLIC_URL"; then
             echo "Canonical walkthrough is not publicly available; skipping repair." >> "$GITHUB_STEP_SUMMARY"

apps/backend/cmd/mock-agent/main.go

@@ -24,6 +24,9 @@ const (
 	modelFast           = "mock-fast"
 	modelSmart          = "mock-smart"
 	modelSlow           = "mock-slow"
+	modelUnique         = "opus[1m]"
+	modelAmbiguousFirst = "opus[270k]"
+	modelAmbiguousLast  = "opus[1m, fast]"
 	reasoningEffortLow  = "low"
 	reasoningEffortMed  = "medium"
 	reasoningEffortHigh = "high"
@@ -207,22 +210,24 @@ func mockSessionConfigOptionsForModel(model string) []acp.SessionConfigOption {
 			{Value: "max", Name: "Max", Description: ptr("Use maximum reasoning")},
 		}
 	}
+	modelOptions := acp.SessionConfigSelectOptionsUngrouped{
+		{Value: modelFast, Name: "Mock Fast", Description: ptr("Fast mock model for testing")},
+		{Value: modelSmart, Name: "Mock Smart", Description: ptr("Smart mock model for testing")},
+		// E2E fixtures use "mock-slow" for the slow-response delay tier.
+		// It must be advertised so the no-silent-model-fallback strict
+		// policy (which fails session start when the profile model is
+		// absent from the advertised list) does not reject it.
+		{Value: modelSlow, Name: "Mock Slow", Description: ptr("Slow mock model for testing")},
+	}
+	modelOptions = append(modelOptions, mockModelVariationOptions()...)
 	return []acp.SessionConfigOption{
 		{Select: &acp.SessionConfigOptionSelect{
 			Category:     &modelCat,
 			CurrentValue: acp.SessionConfigValueId(model),
 			Id:           "model",
 			Name:         "Model",
-			Options: acp.SessionConfigSelectOptions{Ungrouped: &acp.SessionConfigSelectOptionsUngrouped{
+			Options:      acp.SessionConfigSelectOptions{Ungrouped: &modelOptions},
-				{Value: modelFast, Name: "Mock Fast", Description: ptr("Fast mock model for testing")},
+			Type:         "select",
-				{Value: modelSmart, Name: "Mock Smart", Description: ptr("Smart mock model for testing")},
-				// E2E fixtures use "mock-slow" for the slow-response delay tier.
-				// It must be advertised so the no-silent-model-fallback strict
-				// policy (which fails session start when the profile model is
-				// absent from the advertised list) does not reject it.
-				{Value: modelSlow, Name: "Mock Slow", Description: ptr("Slow mock model for testing")},
-			}},
-			Type: "select",
 		}},
 		{Select: &acp.SessionConfigOptionSelect{
 			Category:     &modeCat,
@@ -247,6 +252,22 @@ func mockSessionConfigOptionsForModel(model string) []acp.SessionConfigOption {
 	}
 }
 
+func mockModelVariationOptions() []acp.SessionConfigSelectOption {
+	catalog := strings.ToLower(strings.TrimSpace(os.Getenv("MOCK_AGENT_MODEL_CATALOG")))
+	if catalog == "ambiguous" {
+		return []acp.SessionConfigSelectOption{
+			{Value: modelAmbiguousFirst, Name: "Opus (270k)", Description: ptr("Ambiguous variation fixture")},
+			{Value: modelAmbiguousLast, Name: "Opus (1m, fast)", Description: ptr("Ambiguous variation fixture")},
+		}
+	}
+	if catalog == "unique" || (catalog == "" && strings.EqualFold(os.Getenv("KANDEV_E2E_MOCK"), "true")) {
+		return []acp.SessionConfigSelectOption{
+			{Value: modelUnique, Name: "Opus (1m)", Description: ptr("Unique variation fixture")},
+		}
+	}
+	return nil
+}
+
 func cloneSessionConfigOptions(options []acp.SessionConfigOption) []acp.SessionConfigOption {
 	cloned := make([]acp.SessionConfigOption, len(options))
 	copy(cloned, options)

apps/backend/cmd/mock-agent/session_config_test.go

@@ -224,6 +224,26 @@ func TestMockSessionConfigOptionsForModelAdvertisesSlowModel(t *testing.T) {
 	}
 }
 
+func TestMockSessionConfigOptionsVariationCatalogs(t *testing.T) {
+	t.Setenv("KANDEV_E2E_MOCK", "true")
+	t.Setenv("MOCK_AGENT_MODEL_CATALOG", "")
+	unique := modelIDs(findModelOption(t))
+	if !containsString(unique, modelUnique) {
+		t.Fatalf("unique catalog = %v, missing %s", unique, modelUnique)
+	}
+	if containsString(unique, modelAmbiguousFirst) || containsString(unique, modelAmbiguousLast) {
+		t.Fatalf("unique catalog = %v, must not include ambiguous variations", unique)
+	}
+
+	t.Setenv("MOCK_AGENT_MODEL_CATALOG", "ambiguous")
+	ambiguous := modelIDs(findModelOption(t))
+	for _, want := range []string{modelAmbiguousFirst, modelAmbiguousLast} {
+		if !containsString(ambiguous, want) {
+			t.Errorf("ambiguous catalog = %v, missing %s", ambiguous, want)
+		}
+	}
+}
+
 func findModelOption(t *testing.T) acp.SessionConfigOption {
 	t.Helper()
 	for _, option := range mockSessionConfigOptionsForModel(modelFast) {
@@ -235,6 +255,17 @@ func findModelOption(t *testing.T) acp.SessionConfigOption {
 	return acp.SessionConfigOption{}
 }
 
+func modelIDs(option acp.SessionConfigOption) []string {
+	if option.Select == nil || option.Select.Options.Ungrouped == nil {
+		return nil
+	}
+	ids := make([]string, 0, len(*option.Select.Options.Ungrouped))
+	for _, model := range *option.Select.Options.Ungrouped {
+		ids = append(ids, string(model.Value))
+	}
+	return ids
+}
+
 func containsString(values []string, want string) bool {
 	for _, v := range values {
 		if v == want {

apps/backend/internal/agent/runtime/lifecycle/manager_interaction.go

@@ -543,7 +543,9 @@ func (m *Manager) reapplySessionModelAfterReset(
 		m.sessionManager.publishModelSelectionWarningEvent(execution, newSessionID, decision)
 	}
 	if decision.EffectiveModel != "" &&
-		(decision.Outcome == ModelSelectionOutcomeApplied || decision.Outcome == ModelSelectionOutcomeExplicitFallback) {
+		(decision.Outcome == ModelSelectionOutcomeApplied ||
+			decision.Outcome == ModelSelectionOutcomeExplicitFallback ||
+			decision.Outcome == ModelSelectionOutcomeUniqueVariation) {
 		m.logger.Info("re-applied session model after context reset",
 			zap.String("execution_id", execution.ID),
 			zap.String("session_id", execution.SessionID),

apps/backend/internal/agent/runtime/lifecycle/manager_interaction_runtime_config_reset_test.go

@@ -99,6 +99,51 @@ func TestManager_ResetAgentContext_ReappliesSessionRuntimeConfig(t *testing.T) {
 	require.Equal(t, v1.AgentStatusReady, exec.Status)
 }
 
+func TestReapplySessionModel_UsesUniqueAdvertisedVariation(t *testing.T) {
+	mgr := newTestManager(t)
+	mock := newRestartMockAgentctlServer(t, false, false)
+	client := createTestClient(t, mock.server.URL)
+	t.Cleanup(client.Close)
+	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
+	t.Cleanup(cancel)
+	require.NoError(t, client.StreamUpdates(ctx, func(agentctl.AgentEvent) {}, nil, nil))
+
+	exec := runtimeConfigResetExecution(client, true)
+	exec.SetModelState(&CachedModelState{
+		CurrentModelID: "provider-default",
+		Models:         []streams.SessionModelInfo{{ModelID: "opus[1m]"}},
+	})
+
+	require.NoError(t, mgr.reapplySessionModelAfterReset(ctx, exec, "reset-session", "opus"))
+	require.Equal(t, []string{"opus[1m]"}, mock.getSetModelIDs())
+}
+
+func TestWorkspaceRebindModel_UsesUniqueAdvertisedVariation(t *testing.T) {
+	mgr := newTestManager(t)
+	mock := newRestartMockAgentctlServer(t, false, false)
+	client := createTestClient(t, mock.server.URL)
+	t.Cleanup(client.Close)
+	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
+	t.Cleanup(cancel)
+	require.NoError(t, client.StreamUpdates(ctx, func(agentctl.AgentEvent) {}, nil, nil))
+
+	exec := runtimeConfigResetExecution(client, true)
+	exec.SetModelState(&CachedModelState{
+		CurrentModelID: "provider-default",
+		Models:         []streams.SessionModelInfo{{ModelID: "opus[1m]"}},
+	})
+
+	require.NoError(t, mgr.reapplyReboundSessionConfig(
+		ctx,
+		exec,
+		"rebind-session",
+		&CachedModelState{},
+		"opus",
+		nil,
+	))
+	require.Equal(t, []string{"opus[1m]"}, mock.getSetModelIDs())
+}
+
 func TestManager_RestartAgentProcess_ReappliesSessionRuntimeConfig(t *testing.T) {
 	mgr := newTestManager(t)
 	provider := runtimeConfigResetWorkspaceInfo()

apps/backend/internal/agent/runtime/lifecycle/session.go

@@ -513,10 +513,12 @@ func (sm *SessionManager) applyStartModelPolicyToEffectiveModel(
 	}
 	effective.decision = decision
 	if decision.Outcome == ModelSelectionOutcomeApplied ||
-		decision.Outcome == ModelSelectionOutcomeExplicitFallback {
+		decision.Outcome == ModelSelectionOutcomeExplicitFallback ||
+		decision.Outcome == ModelSelectionOutcomeUniqueVariation {
 		effective.appliedModel = decision.EffectiveModel
 	}
-	if decision.Outcome == ModelSelectionOutcomeExplicitFallback {
+	if decision.Outcome == ModelSelectionOutcomeExplicitFallback ||
+		decision.Outcome == ModelSelectionOutcomeUniqueVariation {
 		effective.model = decision.EffectiveModel
 	}
 	return effective

apps/backend/internal/agent/runtime/lifecycle/session_model_selection_warning_test.go

@@ -0,0 +1,100 @@
+package lifecycle
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/kandev/kandev/internal/agent/agents"
+	agentctl "github.com/kandev/kandev/internal/agent/runtime/agentctl"
+	"github.com/kandev/kandev/internal/agentctl/types/streams"
+	"github.com/kandev/kandev/pkg/agent"
+)
+
+func TestInitializeAndPrompt_UniqueVariationPublishesProviderNeutralWarning(t *testing.T) {
+	mock := newMockAgentServer(t)
+	defer mock.Close()
+
+	log := newSessionTestLogger()
+	stopCh := newTestStopCh(t)
+	sm := NewSessionManager(log, stopCh)
+	streamMgr := NewStreamManager(log, StreamCallbacks{
+		OnAgentEvent: func(execution *AgentExecution, event agentctl.AgentEvent) {},
+	}, nil, stopCh)
+	cleanupStreamManager(t, stopCh, streamMgr)
+	eventBus := &MockEventBusWithTracking{}
+	sm.SetDependencies(NewEventPublisher(eventBus, log), streamMgr, nil, nil)
+
+	client := createTestClient(t, mock.server.URL)
+	defer client.Close()
+	execution := &AgentExecution{
+		ID:            "exec-unique-variation",
+		TaskID:        "task-1",
+		SessionID:     "session-1",
+		WorkspacePath: "/workspace",
+		agentctl:      client,
+		promptDoneCh:  make(chan PromptCompletionSignal, 1),
+	}
+	execution.SetModelState(modelState("opus[1m]"))
+	agentConfig := &testAgent{
+		id:      "test-agent",
+		enabled: true,
+		runtimeConfig: &agents.RuntimeConfig{
+			Cmd:            agents.NewCommand("test-agent"),
+			Protocol:       agent.ProtocolACP,
+			SessionConfig:  agents.SessionConfig{},
+			ResourceLimits: agents.ResourceLimits{MemoryMB: 512, CPUCores: 0.5, Timeout: time.Hour},
+		},
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
+	defer cancel()
+	err := sm.InitializeAndPrompt(ctx, execution, agentConfig, "", nil, nil,
+		func(executionID string) error { return nil },
+		StartModelPolicy{Model: "opus"}, "plan", nil)
+	if err != nil {
+		t.Fatalf("InitializeAndPrompt failed: %v", err)
+	}
+
+	setModelCalls := 0
+	for _, action := range mock.getActionLog() {
+		if action == "agent.session.set_model" {
+			setModelCalls++
+		}
+	}
+	if setModelCalls != 1 {
+		t.Fatalf("set_model calls = %d, want exactly 1", setModelCalls)
+	}
+
+	var warning *streams.ModelSelectionWarning
+	legacyFallbackEvents := 0
+	for _, event := range eventBus.getStreamEvents() {
+		if event.Data == nil {
+			continue
+		}
+		if event.Data.ModelSelectionWarning != nil {
+			warning = event.Data.ModelSelectionWarning
+		}
+		if event.Data.Type == streams.EventTypeSessionModelFallback {
+			legacyFallbackEvents++
+		}
+	}
+	if warning == nil {
+		t.Fatal("expected a model-selection warning event")
+	}
+	if warning.RequestedModel != "opus" {
+		t.Errorf("warning requested model = %q, want opus", warning.RequestedModel)
+	}
+	if warning.EffectiveModel != "opus[1m]" {
+		t.Errorf("warning effective model = %q, want opus[1m]", warning.EffectiveModel)
+	}
+	if warning.FallbackModel != "" {
+		t.Errorf("warning fallback model = %q, want empty", warning.FallbackModel)
+	}
+	if warning.Reason != ModelSelectionReasonUniqueVariationApplied {
+		t.Errorf("warning reason = %q, want %q", warning.Reason, ModelSelectionReasonUniqueVariationApplied)
+	}
+	if legacyFallbackEvents != 0 {
+		t.Fatalf("legacy fallback events = %d, want zero for unique variation", legacyFallbackEvents)
+	}
+}

apps/backend/internal/agent/runtime/lifecycle/start_model.go

@@ -3,6 +3,7 @@ package lifecycle
 import (
 	"context"
 	"fmt"
+	"strings"
 
 	"github.com/kandev/kandev/internal/agentctl/sessionmodel"
 	"github.com/kandev/kandev/internal/common/logger"
@@ -31,6 +32,7 @@ const (
 	ModelSelectionOutcomeNone             ModelSelectionOutcome = ""
 	ModelSelectionOutcomeApplied          ModelSelectionOutcome = "applied"
 	ModelSelectionOutcomeExplicitFallback ModelSelectionOutcome = "explicit_fallback"
+	ModelSelectionOutcomeUniqueVariation  ModelSelectionOutcome = "unique_variation"
 	ModelSelectionOutcomeProviderDefault  ModelSelectionOutcome = "provider_default"
 )
 
@@ -42,6 +44,7 @@ const (
 	ModelSelectionReasonCatalogEmpty                = "catalog_empty"
 	ModelSelectionReasonSelectionUnsupported        = "selection_unsupported"
 	ModelSelectionReasonSelectionFailedAutoFallback = "selection_failed_auto_fallback"
+	ModelSelectionReasonUniqueVariationApplied      = "unique_variation_applied"
 )
 
 // ModelSelectionDecision is the single model-selection result shared by
@@ -84,6 +87,32 @@ func containsModel(ids []string, id string) bool {
 	return false
 }
 
+func uniqueAdvertisedModelVariation(requested string, advertised []string) string {
+	if requested == "" || strings.ContainsAny(requested, "[]") {
+		return ""
+	}
+
+	prefix := requested + "["
+	candidates := make(map[string]struct{})
+	for _, id := range advertised {
+		if !strings.HasPrefix(id, prefix) || !strings.HasSuffix(id, "]") {
+			continue
+		}
+		variant := strings.TrimSuffix(strings.TrimPrefix(id, prefix), "]")
+		if variant == "" || strings.ContainsAny(variant, "[]") {
+			continue
+		}
+		candidates[id] = struct{}{}
+		if len(candidates) > 1 {
+			return ""
+		}
+	}
+	for candidate := range candidates {
+		return candidate
+	}
+	return ""
+}
+
 func providerDefaultDecision(state *CachedModelState, policy StartModelPolicy, reason string) ModelSelectionDecision {
 	decision := ModelSelectionDecision{
 		RequestedModel: policy.Model,
@@ -114,6 +143,9 @@ func applyStartModelPolicy(
 	if policy.Model == "" {
 		return ModelSelectionDecision{Outcome: ModelSelectionOutcomeNone}, nil
 	}
+	if policy.AutoFallback {
+		policy.FallbackModel = ""
+	}
 
 	decision := ModelSelectionDecision{
 		RequestedModel: policy.Model,
@@ -125,9 +157,15 @@ func applyStartModelPolicy(
 	}
 
 	if !containsModel(advertised, policy.Model) {
+		if policy.AutoFallback {
+			return providerDefaultDecision(state, policy, ModelSelectionReasonRequestedNotAdvertised), nil
+		}
 		if policy.FallbackModel != "" && containsModel(advertised, policy.FallbackModel) {
 			return applyAdvertisedFallback(ctx, log, applier, state, policy, decision)
 		}
+		if variation := uniqueAdvertisedModelVariation(policy.Model, advertised); variation != "" {
+			return applyUniqueAdvertisedVariation(ctx, log, applier, state, policy, decision, variation)
+		}
 		reason := ModelSelectionReasonRequestedNotAdvertised
 		if policy.FallbackModel != "" {
 			reason = ModelSelectionReasonFallbackNotAdvertised
@@ -159,6 +197,41 @@ func applyStartModelPolicy(
 	return decision, nil
 }
 
+func applyUniqueAdvertisedVariation(
+	ctx context.Context,
+	log *logger.Logger,
+	applier modelApplier,
+	state *CachedModelState,
+	policy StartModelPolicy,
+	decision ModelSelectionDecision,
+	variation string,
+) (ModelSelectionDecision, error) {
+	decision.FallbackModel = ""
+	policy.FallbackModel = ""
+	decision.SetModelCalled = true
+	if err := applier.SetModel(ctx, variation); err != nil {
+		if sessionmodel.IsMethodNotFound(err) {
+			decision = providerDefaultDecision(state, policy, ModelSelectionReasonSelectionUnsupported)
+			decision.SetModelCalled = true
+			return decision, nil
+		}
+		if policy.AutoFallback {
+			decision = providerDefaultDecision(state, policy, ModelSelectionReasonSelectionFailedAutoFallback)
+			decision.SetModelCalled = true
+			return decision, nil
+		}
+		return decision, fmt.Errorf("failed to set unique model variation %q: %w", variation, err)
+	}
+	decision.EffectiveModel = variation
+	decision.Outcome = ModelSelectionOutcomeUniqueVariation
+	decision.Reason = ModelSelectionReasonUniqueVariationApplied
+	decision.Warning = true
+	log.Info("start model unavailable, using unique advertised variation",
+		zap.String("start_model", policy.Model),
+		zap.String("variation_model", variation))
+	return decision, nil
+}
+
 func applyAdvertisedFallback(
 	ctx context.Context,
 	log *logger.Logger,

apps/backend/internal/agent/runtime/lifecycle/start_model_executor_authority_test.go

@@ -47,6 +47,104 @@ func TestApplyStartModelPolicyExecutorAuthority(t *testing.T) {
 			wantEffective: "fallback",
 			wantWarning:   true,
 		},
+		{
+			name:          "unique variation is applied when fallback is absent",
+			state:         modelState("opus[1m]"),
+			policy:        StartModelPolicy{Model: "opus"},
+			wantCalls:     []string{"opus[1m]"},
+			wantOutcome:   ModelSelectionOutcomeUniqueVariation,
+			wantReason:    ModelSelectionReasonUniqueVariationApplied,
+			wantEffective: "opus[1m]",
+			wantWarning:   true,
+		},
+		{
+			name:          "advertised fallback takes precedence over unique variation",
+			state:         modelState("fallback", "opus[1m]"),
+			policy:        StartModelPolicy{Model: "opus", FallbackModel: "fallback"},
+			wantCalls:     []string{"fallback"},
+			wantOutcome:   ModelSelectionOutcomeExplicitFallback,
+			wantReason:    ModelSelectionReasonRequestedNotAdvertised,
+			wantEffective: "fallback",
+			wantWarning:   true,
+		},
+		{
+			name:          "unadvertised fallback does not block unique variation",
+			state:         modelState("opus[1m]"),
+			policy:        StartModelPolicy{Model: "opus", FallbackModel: "fallback"},
+			wantCalls:     []string{"opus[1m]"},
+			wantOutcome:   ModelSelectionOutcomeUniqueVariation,
+			wantReason:    ModelSelectionReasonUniqueVariationApplied,
+			wantEffective: "opus[1m]",
+			wantWarning:   true,
+		},
+		{
+			name:        "auto fallback keeps unavailable model on provider default",
+			state:       modelState("fallback", "opus[1m]"),
+			policy:      StartModelPolicy{Model: "opus", FallbackModel: "fallback", AutoFallback: true},
+			wantOutcome: ModelSelectionOutcomeProviderDefault,
+			wantReason:  ModelSelectionReasonRequestedNotAdvertised,
+			wantWarning: true,
+		},
+		{
+			name:          "duplicate unique variation is one candidate",
+			state:         modelState("opus[1m]", "opus[1m]"),
+			policy:        StartModelPolicy{Model: "opus"},
+			wantCalls:     []string{"opus[1m]"},
+			wantOutcome:   ModelSelectionOutcomeUniqueVariation,
+			wantReason:    ModelSelectionReasonUniqueVariationApplied,
+			wantEffective: "opus[1m]",
+			wantWarning:   true,
+		},
+		{
+			name:        "multiple variations keep provider default",
+			state:       modelState("opus[1m]", "opus[270k]"),
+			policy:      StartModelPolicy{Model: "opus"},
+			wantOutcome: ModelSelectionOutcomeProviderDefault,
+			wantReason:  ModelSelectionReasonRequestedNotAdvertised,
+			wantWarning: true,
+		},
+		{
+			name:        "malformed variations keep provider default",
+			state:       modelState("opus[]", "opus[1m", "opus[1m][fast]", "opus-pro[1m]"),
+			policy:      StartModelPolicy{Model: "opus"},
+			wantOutcome: ModelSelectionOutcomeProviderDefault,
+			wantReason:  ModelSelectionReasonRequestedNotAdvertised,
+			wantWarning: true,
+		},
+		{
+			name:          "variation text remains opaque",
+			state:         modelState("opus[1m, fast]"),
+			policy:        StartModelPolicy{Model: "opus"},
+			wantCalls:     []string{"opus[1m, fast]"},
+			wantOutcome:   ModelSelectionOutcomeUniqueVariation,
+			wantReason:    ModelSelectionReasonUniqueVariationApplied,
+			wantEffective: "opus[1m, fast]",
+			wantWarning:   true,
+		},
+		{
+			name:        "case-sensitive variation matching keeps provider default",
+			state:       modelState("Opus[1m]"),
+			policy:      StartModelPolicy{Model: "opus"},
+			wantOutcome: ModelSelectionOutcomeProviderDefault,
+			wantReason:  ModelSelectionReasonRequestedNotAdvertised,
+			wantWarning: true,
+		},
+		{
+			name:        "bracketed request does not infer another variation",
+			state:       modelState("opus[2m]"),
+			policy:      StartModelPolicy{Model: "opus[1m]"},
+			wantOutcome: ModelSelectionOutcomeProviderDefault,
+			wantReason:  ModelSelectionReasonRequestedNotAdvertised,
+			wantWarning: true,
+		},
+		{
+			name:          "exact bracketed request remains exact",
+			state:         modelState("opus[1m]", "opus[2m]"),
+			policy:        StartModelPolicy{Model: "opus[1m]"},
+			wantCalls:     []string{"opus[1m]"},
+			wantOutcome:   ModelSelectionOutcomeApplied,
+			wantEffective: "opus[1m]",
+		},
 		{
 			name:          "advertised fallback method not supported keeps provider default",
 			state:         modelState("fallback"),
@@ -57,6 +155,16 @@ func TestApplyStartModelPolicyExecutorAuthority(t *testing.T) {
 			wantReason:    ModelSelectionReasonSelectionUnsupported,
 			wantWarning:   true,
 		},
+		{
+			name:          "unique variation method not supported keeps provider default",
+			state:         modelState("opus[1m]"),
+			policy:        StartModelPolicy{Model: "opus", FallbackModel: "fallback"},
+			applierErrors: []error{methodNotFoundErr()},
+			wantCalls:     []string{"opus[1m]"},
+			wantOutcome:   ModelSelectionOutcomeProviderDefault,
+			wantReason:    ModelSelectionReasonSelectionUnsupported,
+			wantWarning:   true,
+		},
 		{
 			name:        "unadvertised fallback keeps provider default",
 			state:       modelState("executor-default"),
@@ -132,6 +240,12 @@ func TestApplyStartModelPolicyExecutorAuthority(t *testing.T) {
 			if decision.Warning != tt.wantWarning {
 				t.Errorf("warning = %v, want %v", decision.Warning, tt.wantWarning)
 			}
+			if decision.Outcome == ModelSelectionOutcomeUniqueVariation && decision.FallbackModel != "" {
+				t.Errorf("unique variation fallback model = %q, want empty", decision.FallbackModel)
+			}
+			if tt.policy.AutoFallback && decision.FallbackModel != "" {
+				t.Errorf("auto-fallback fallback model = %q, want empty", decision.FallbackModel)
+			}
 		})
 	}
 }

apps/web/components/settings/profile-form-fields.test.tsx

@@ -150,6 +150,20 @@ describe("ProfileFormFields no-silent-model-fallback rows", () => {
     expect(trigger.textContent).toContain("claude-gone");
   });
 
+  it("names a unique advertised variation while preserving the saved model", () => {
+    renderForm(formData({ model: "opus" }), {
+      ...modelConfig,
+      available_models: [{ id: "opus[1m]", name: "Opus (1m)" }],
+    });
+
+    const advisory = screen.getByTestId("profile-model-variation-advisory");
+    expect(advisory.textContent).toContain("opus[1m]");
+    expect(advisory.textContent).toContain("opus");
+    expect(
+      screen.getByRole("button", { name: profileStartModelSettingsLabel }).textContent,
+    ).toContain("opus");
+  });
+
   it("shows the agent fallback row when auto-fallback is off", () => {
     renderForm(formData({ auto_fallback: false }));
     expandFallbackSettings();

apps/web/components/settings/profile-model-fields.tsx

@@ -23,6 +23,7 @@ import {
 import type { ModelConfig, ModeEntry, ModelEntry } from "@/lib/types/http";
 import type { PermissionKey } from "@/lib/agent-permissions";
 import type { CLIFlag } from "@/lib/types/http";
+import { findUniqueModelVariation } from "@/lib/model-variation";
 import {
   SettingsFieldDescription,
   SettingsFieldLabel,
@@ -83,6 +84,12 @@ export function ModelPicker({
   // in the list, greyed out and unselectable, so the user sees what was
   // configured instead of it silently vanishing.
   const modelIsGone = Boolean(profile.model && !modelOptions.some((m) => m.id === profile.model));
+  const uniqueVariation = modelIsGone
+    ? findUniqueModelVariation(
+        profile.model,
+        modelOptions.map((model) => model.id),
+      )
+    : null;
   if (modelIsGone) {
     modelOptions.unshift({
       id: profile.model!,
@@ -99,22 +106,32 @@ export function ModelPicker({
   }));
 
   return (
-    <ModelConfigSelector
+    <div className="space-y-1.5">
-      modelOptions={modelOptions}
+      <ModelConfigSelector
-      currentModel={currentModel}
+        modelOptions={modelOptions}
-      configOptions={selectedConfigOptions}
+        currentModel={currentModel}
-      onModelChange={(value) => onChange({ model: value })}
+        configOptions={selectedConfigOptions}
-      onConfigChange={(configId, value) =>
+        onModelChange={(value) => onChange({ model: value })}
-        onChange({ config_options: { ...(profile.config_options ?? {}), [configId]: value } })
+        onConfigChange={(configId, value) =>
-      }
+          onChange({ config_options: { ...(profile.config_options ?? {}), [configId]: value } })
-      placeholder={placeholder ?? t("settings:selectAModel")}
+        }
-      ariaLabel={ariaLabel}
+        placeholder={placeholder ?? t("settings:selectAModel")}
-      popoverAlign="start"
+        ariaLabel={ariaLabel}
-      disabled={disabled}
+        popoverAlign="start"
-      configOptionsLoading={configOptionsLoading}
+        disabled={disabled}
-      keepOpenOnModelChange={keepOpenOnModelChange}
+        configOptionsLoading={configOptionsLoading}
-      triggerClassName={modelIsGone ? "text-destructive" : undefined}
+        keepOpenOnModelChange={keepOpenOnModelChange}
-    />
+        triggerClassName={modelIsGone ? "text-destructive" : undefined}
+      />
+      {uniqueVariation && (
+        <p className="text-xs text-muted-foreground" data-testid="profile-model-variation-advisory">
+          {t("settings:modelVariationAdvisory", {
+            model: profile.model,
+            variation: uniqueVariation,
+          })}
+        </p>
+      )}
+    </div>
   );
 }
 

apps/web/components/task-create-dialog-options.test.tsx

@@ -58,6 +58,19 @@ const AGENT_WITH_GPT: AvailableAgent = {
   },
 } as unknown as AvailableAgent;
 
+const AGENT_WITH_OPUS_VARIATION: AvailableAgent = {
+  name: "omp-acp",
+  available: true,
+  model_config: {
+    default_model: "opus[1m]",
+    available_models: [{ id: "opus[1m]", name: "Opus (1m)" }],
+    current_model_id: "opus[1m]",
+    available_modes: [],
+    supports_dynamic_models: false,
+    status: "ok",
+  },
+} as unknown as AvailableAgent;
+
 const GONE_MODEL = "claude-gone";
 const DATA_DISABLED = "data-disabled";
 const MODEL_PROBE_WARNING_TEST_ID = "agent-profile-model-probe-warning";
@@ -225,6 +238,14 @@ describe("useAgentProfileOptions executor-authoritative model hint", () => {
     expect(option.getAttribute(DATA_DISABLED)).toBeNull();
   });
 
+  it("names a unique advertised variation without disabling the profile", () => {
+    setAvailableAgents([AGENT_WITH_OPUS_VARIATION]);
+    const option = renderOptions([profileOption({ model: "opus" })]);
+
+    expect(option.getAttribute(DATA_DISABLED)).toBeNull();
+    expect(getModelProbeWarningLabel()).toContain("opus[1m]");
+  });
+
   it("keeps a profile with an empty (agent default) model selectable", () => {
     const option = renderOptions([profileOption({ model: "" })]);
     expect(option.getAttribute(DATA_DISABLED)).toBeNull();

apps/web/components/task-create-dialog-options.tsx

@@ -32,6 +32,7 @@ import { formatUserHomePath, truncateRepoPath } from "@/lib/utils";
 import { getExecutorIcon } from "@/lib/executor-icons";
 import { AgentLogo } from "@/components/agent-logo";
 import { getCapabilityWarning } from "@/lib/capability-warning";
+import { findUniqueModelVariation } from "@/lib/model-variation";
 import { useTouchDrawer } from "@/hooks/use-compact-task-chrome";
 import { buildBranchKeywords } from "./branch-picker-options";
 import {
@@ -229,9 +230,18 @@ export function useAgentProfileOptions(
       const startModelGone = Boolean(
         profile.model && advertised.length > 0 && !advertised.includes(profile.model),
       );
-      const modelProbeNote = startModelGone
+      const uniqueVariation = startModelGone
-        ? t("settings:profileStartModelNotAdvertisedOnHost", { model: profile.model })
+        ? findUniqueModelVariation(profile.model ?? "", advertised)
-        : undefined;
+        : null;
+      let modelProbeNote: string | undefined;
+      if (startModelGone) {
+        modelProbeNote = uniqueVariation
+          ? t("settings:profileStartModelUniqueVariationOnHost", {
+              model: profile.model,
+              variation: uniqueVariation,
+            })
+          : t("settings:profileStartModelNotAdvertisedOnHost", { model: profile.model });
+      }
       const renderProfileLabel = (modelProbeWarning: React.ReactNode) => (
         <span className="flex min-w-0 flex-1 flex-col gap-1">
           <span className="flex shrink-0 items-center justify-between gap-2">

apps/web/components/task/chat/messages/status-message.test.tsx

@@ -42,6 +42,23 @@ describe("StatusMessage model selection warnings", () => {
     expect(screen.getByText("Check the agent version in the executor.")).toBeTruthy();
     expect(screen.getByText("The saved model was not advertised by the executor.")).toBeTruthy();
   });
+
+  it("explains when the executor applied the only advertised variation", () => {
+    const comment = modelSelectionWarningMessage();
+    comment.metadata = {
+      ...comment.metadata,
+      reason: "unique_variation_applied",
+      effective_model: "opus[1m]",
+      fallback_model: undefined,
+    };
+
+    render(<StatusMessage comment={comment} />);
+
+    expect(
+      screen.getByText("The executor applied the only advertised variation of the saved model."),
+    ).toBeTruthy();
+    expect(screen.queryByText(/fallback model/i)).toBeNull();
+  });
 });
 
 describe("StatusMessage branch replacement warnings", () => {

apps/web/components/task/chat/messages/status-message.tsx

@@ -180,6 +180,7 @@ function modelSelectionReasonLabel(reason: string | undefined): string {
   const keyByReason: Record<string, string> = {
     requested_not_advertised: "task:modelSelectionReasonRequestedNotAdvertised",
     fallback_not_advertised: "task:modelSelectionReasonFallbackNotAdvertised",
+    unique_variation_applied: "task:modelSelectionReasonUniqueVariation",
     catalog_empty: "task:modelSelectionReasonCatalogEmpty",
     selection_unsupported: "task:modelSelectionReasonUnsupported",
     selection_failed_auto_fallback: "task:modelSelectionReasonAutoFallback",

apps/web/e2e/tests/session/model-mismatch-warning-helpers.ts

@@ -2,6 +2,10 @@ import type { AgentProfile } from "../../../lib/types/http-agents";
 import type { ApiClient } from "../../helpers/api-client";
 
 export const UNADVERTISED_MODEL = "host-only-model";
+export const MODEL_VARIATION_BASE = "opus";
+export const UNIQUE_MODEL_VARIATION = "opus[1m]";
+export const AMBIGUOUS_MODEL_VARIATIONS = ["opus[270k]", "opus[1m, fast]"] as const;
+const MODEL_CATALOG_ENV = "MOCK_AGENT_MODEL_CATALOG";
 
 export async function createMismatchedProfile(
   apiClient: ApiClient,
@@ -13,6 +17,20 @@ export async function createMismatchedProfile(
   return apiClient.createAgentProfile(agent.id, name, { model: UNADVERTISED_MODEL });
 }
 
+export async function createModelVariationProfile(
+  apiClient: ApiClient,
+  name: string,
+  catalog: "unique" | "ambiguous",
+): Promise<AgentProfile> {
+  const { agents } = await apiClient.listAgents();
+  const agent = agents.find((item) => item.name === "mock-agent") ?? agents[0];
+  if (!agent) throw new Error("The E2E fixture must provide a mock agent");
+  return apiClient.createAgentProfile(agent.id, name, {
+    model: MODEL_VARIATION_BASE,
+    env_vars: [{ key: MODEL_CATALOG_ENV, value: catalog }],
+  });
+}
+
 export async function readModelSelectionWarnings(
   apiClient: ApiClient,
   sessionId: string,

apps/web/e2e/tests/session/model-mismatch-warning.spec.ts

@@ -2,7 +2,10 @@ import { expect, test } from "../../fixtures/test-base";
 import { waitForSessionDone } from "../../helpers/session";
 import { SessionPage } from "../../pages/session-page";
 import {
+  createModelVariationProfile,
   createMismatchedProfile,
+  MODEL_VARIATION_BASE,
+  UNIQUE_MODEL_VARIATION,
   readModelSelectionWarnings,
   UNADVERTISED_MODEL,
 } from "./model-mismatch-warning-helpers";
@@ -73,4 +76,124 @@ test.describe("model mismatch warning", () => {
       await apiClient.deleteAgentProfile(profile.id, true).catch(() => {});
     }
   });
+
+  test("applies one unique advertised variation and persists its warning", async ({
+    testPage,
+    apiClient,
+    seedData,
+  }) => {
+    test.setTimeout(120_000);
+    const profile = await createModelVariationProfile(
+      apiClient,
+      "Unique model variation profile",
+      "unique",
+    );
+    try {
+      const task = await apiClient.createTaskWithAgent(
+        seedData.workspaceId,
+        "Unique model variation warning",
+        profile.id,
+        {
+          description: "/e2e:simple-message",
+          workflow_id: seedData.workflowId,
+          workflow_step_id: seedData.startStepId,
+          repository_ids: [seedData.repositoryId],
+        },
+      );
+      expect(task.session_id).toBeTruthy();
+      await waitForSessionDone(
+        apiClient,
+        task.id,
+        task.session_id!,
+        "Waiting for unique model variation task continuation",
+      );
+
+      await expect
+        .poll(() => readModelSelectionWarnings(apiClient, task.session_id!), {
+          timeout: 15_000,
+          message: "Waiting for the unique model variation warning",
+        })
+        .toHaveLength(1);
+      const warnings = await readModelSelectionWarnings(apiClient, task.session_id!);
+      expect(warnings[0]?.metadata).toMatchObject({
+        kind: "model_selection_warning",
+        reason: "unique_variation_applied",
+        requested_model: MODEL_VARIATION_BASE,
+        effective_model: UNIQUE_MODEL_VARIATION,
+        agent_id: "mock-agent",
+      });
+      expect(warnings[0]?.metadata?.fallback_model).toBeUndefined();
+      expect((await apiClient.getAgentProfile(profile.id)).model).toBe(MODEL_VARIATION_BASE);
+
+      await testPage.goto(`/t/${task.id}`);
+      const session = new SessionPage(testPage);
+      await session.waitForLoad();
+      await expect(
+        session.activeChat().getByText("The executor could not use the saved model selection."),
+      ).toBeVisible({ timeout: 15_000 });
+      await expect(session.activeChat()).toContainText(UNIQUE_MODEL_VARIATION);
+
+      await testPage.reload();
+      await session.waitForLoad();
+      await expect(
+        session.activeChat().getByText("The executor could not use the saved model selection."),
+      ).toBeVisible({ timeout: 15_000 });
+      await expect(session.activeChat()).toContainText(UNIQUE_MODEL_VARIATION);
+      await expect
+        .poll(() => readModelSelectionWarnings(apiClient, task.session_id!))
+        .toHaveLength(1);
+    } finally {
+      await apiClient.deleteAgentProfile(profile.id, true).catch(() => {});
+    }
+  });
+
+  test("does not infer a model when the executor advertises multiple variations", async ({
+    apiClient,
+    seedData,
+  }) => {
+    test.setTimeout(120_000);
+    const profile = await createModelVariationProfile(
+      apiClient,
+      "Ambiguous model variation profile",
+      "ambiguous",
+    );
+    try {
+      const task = await apiClient.createTaskWithAgent(
+        seedData.workspaceId,
+        "Ambiguous model variation warning",
+        profile.id,
+        {
+          description: "/e2e:simple-message",
+          workflow_id: seedData.workflowId,
+          workflow_step_id: seedData.startStepId,
+          repository_ids: [seedData.repositoryId],
+        },
+      );
+      expect(task.session_id).toBeTruthy();
+      await waitForSessionDone(
+        apiClient,
+        task.id,
+        task.session_id!,
+        "Waiting for ambiguous model variation task continuation",
+      );
+
+      await expect
+        .poll(() => readModelSelectionWarnings(apiClient, task.session_id!), {
+          timeout: 15_000,
+          message: "Waiting for the ambiguous model variation warning",
+        })
+        .toHaveLength(1);
+      const warnings = await readModelSelectionWarnings(apiClient, task.session_id!);
+      expect(warnings[0]?.metadata).toMatchObject({
+        kind: "model_selection_warning",
+        reason: "requested_not_advertised",
+        requested_model: MODEL_VARIATION_BASE,
+        effective_model: "mock-fast",
+        agent_id: "mock-agent",
+      });
+      expect((await apiClient.getAgentProfile(profile.id)).model).toBe(MODEL_VARIATION_BASE);
+    } finally {
+      await apiClient.deleteAgentProfile(profile.id, true).catch(() => {});
+    }
+  });
 });

apps/web/e2e/tests/settings/mobile-no-silent-model-fallback.spec.ts

@@ -2,7 +2,10 @@ import { expect, test } from "../../fixtures/test-base";
 import { KanbanPage } from "../../pages/kanban-page";
 import { assertNoDocumentHorizontalOverflow } from "../../helpers/layout-assertions";
 import {
+  createModelVariationProfile,
   createMismatchedProfile,
+  MODEL_VARIATION_BASE,
+  UNIQUE_MODEL_VARIATION,
   UNADVERTISED_MODEL,
 } from "../session/model-mismatch-warning-helpers";
 
@@ -41,4 +44,44 @@ test.describe("executor-authoritative model selection on mobile", () => {
       await apiClient.deleteAgentProfile(profile.id, true).catch(() => {});
     }
   });
+
+  test("opens the unique variation advisory by touch without overflow", async ({
+    testPage,
+    apiClient,
+  }) => {
+    const profile = await createModelVariationProfile(
+      apiClient,
+      "Mobile unique host variation profile",
+      "unique",
+    );
+    try {
+      const kanban = new KanbanPage(testPage);
+      await kanban.goto();
+      await testPage.reload({ waitUntil: "networkidle" });
+      await testPage.getByRole("button", { name: "Add task" }).tap();
+
+      const dialog = testPage.getByTestId("create-task-dialog");
+      await expect(dialog).toBeVisible();
+      const selector = dialog.getByTestId("agent-profile-selector");
+      await selector.tap();
+
+      const option = testPage
+        .getByRole("listbox")
+        .getByRole("option", { name: profile.name, exact: false });
+      await expect(option).toBeVisible();
+      await expect(option).toBeEnabled();
+      const warning = option.getByTestId("agent-profile-model-probe-warning");
+      await expect(warning).toBeVisible();
+      const warningText = `The host probe found one possible variation of ${MODEL_VARIATION_BASE}: ${UNIQUE_MODEL_VARIATION}. The selected executor will decide the model at launch.`;
+      await warning.tap();
+      await expect(
+        testPage
+          .locator('[data-slot="drawer-content"][data-state="open"]')
+          .filter({ hasText: warningText }),
+      ).toBeVisible();
+      await assertNoDocumentHorizontalOverflow(testPage, "mobile unique variation advisory");
+    } finally {
+      await apiClient.deleteAgentProfile(profile.id, true).catch(() => {});
+    }
+  });
 });

apps/web/e2e/tests/settings/no-silent-model-fallback.spec.ts

@@ -1,7 +1,10 @@
 import { expect, test } from "../../fixtures/test-base";
 import { KanbanPage } from "../../pages/kanban-page";
 import {
+  createModelVariationProfile,
   createMismatchedProfile,
+  MODEL_VARIATION_BASE,
+  UNIQUE_MODEL_VARIATION,
   UNADVERTISED_MODEL,
 } from "../session/model-mismatch-warning-helpers";
 
@@ -41,4 +44,44 @@ test.describe("executor-authoritative model selection", () => {
       await apiClient.deleteAgentProfile(profile.id, true).catch(() => {});
     }
   });
+
+  test("names one host-advertised variation while keeping the profile selectable", async ({
+    testPage,
+    apiClient,
+  }) => {
+    const profile = await createModelVariationProfile(
+      apiClient,
+      "Unique host variation selectable profile",
+      "unique",
+    );
+    try {
+      const kanban = new KanbanPage(testPage);
+      await kanban.goto();
+      await testPage.reload({ waitUntil: "networkidle" });
+      await kanban.createTaskButton.first().click();
+
+      const dialog = testPage.getByTestId("create-task-dialog");
+      await expect(dialog).toBeVisible();
+      const selector = dialog.getByTestId("agent-profile-selector");
+      await selector.click();
+
+      const option = testPage
+        .getByRole("listbox")
+        .getByRole("option", { name: profile.name, exact: false });
+      await expect(option).toBeVisible();
+      await expect(option).toBeEnabled();
+      const warning = option.getByTestId("agent-profile-model-probe-warning");
+      await expect(warning).toBeVisible();
+      const warningText = `The host probe found one possible variation of ${MODEL_VARIATION_BASE}: ${UNIQUE_MODEL_VARIATION}. The selected executor will decide the model at launch.`;
+      await warning.hover();
+      await expect(
+        testPage
+          .locator('[data-slot="tooltip-content"]:not([data-state="closed"])')
+          .filter({ hasText: warningText }),
+      ).toBeVisible();
+      await option.click();
+    } finally {
+      await apiClient.deleteAgentProfile(profile.id, true).catch(() => {});
+    }
+  });
 });

apps/web/lib/model-variation.test.ts

@@ -0,0 +1,57 @@
+import { describe, expect, it } from "vitest";
+import { findUniqueModelVariation } from "./model-variation";
+
+describe("findUniqueModelVariation", () => {
+  it.each([
+    {
+      name: "finds one bracketed variation",
+      requested: "opus",
+      advertised: ["opus[1m]"],
+      expected: "opus[1m]",
+    },
+    {
+      name: "deduplicates the same variation",
+      requested: "opus",
+      advertised: ["opus[1m]", "opus[1m]"],
+      expected: "opus[1m]",
+    },
+    {
+      name: "keeps opaque variation text",
+      requested: "opus",
+      advertised: ["opus[1m, fast]"],
+      expected: "opus[1m, fast]",
+    },
+  ])("$name", ({ requested, advertised, expected }) => {
+    expect(findUniqueModelVariation(requested, advertised)).toBe(expected);
+  });
+
+  it.each([
+    {
+      name: "returns no candidate for an empty catalog",
+      requested: "opus",
+      advertised: [],
+    },
+    {
+      name: "returns no candidate for ambiguous variations",
+      requested: "opus",
+      advertised: ["opus[1m]", "opus[270k]"],
+    },
+    {
+      name: "returns no candidate for case differences",
+      requested: "opus",
+      advertised: ["Opus[1m]"],
+    },
+    {
+      name: "returns no candidate for a bracketed request",
+      requested: "opus[1m]",
+      advertised: ["opus[2m]"],
+    },
+    {
+      name: "returns no candidate for malformed IDs",
+      requested: "opus",
+      advertised: ["opus[]", "opus[1m", "opus[1m][fast]", "opus-pro[1m]"],
+    },
+  ])("$name", ({ requested, advertised }) => {
+    expect(findUniqueModelVariation(requested, advertised)).toBeNull();
+  });
+});

apps/web/lib/model-variation.ts

@@ -0,0 +1,17 @@
+function isModelVariation(requested: string, advertised: string): boolean {
+  const prefix = `${requested}[`;
+  if (!advertised.startsWith(prefix) || !advertised.endsWith("]")) return false;
+
+  const variant = advertised.slice(prefix.length, -1);
+  return variant.length > 0 && !variant.includes("[") && !variant.includes("]");
+}
+
+export function findUniqueModelVariation(
+  requested: string,
+  advertised: readonly string[],
+): string | null {
+  if (!requested || requested.includes("[") || requested.includes("]")) return null;
+
+  const candidates = new Set(advertised.filter((model) => isModelVariation(requested, model)));
+  return candidates.size === 1 ? ([...candidates][0] ?? null) : null;
+}

apps/web/src/locales/en/settings.json

@@ -504,6 +504,8 @@
   "profileForTasksCreatedByAgents": "Profile for Tasks Created by Agents",
   "programming": "Programming",
   "profileStartModelNotAdvertisedOnHost": "The host probe did not advertise {{model}}. The selected executor will decide the model at launch.",
+  "profileStartModelUniqueVariationOnHost": "The host probe found one possible variation of {{model}}: {{variation}}. The selected executor will decide the model at launch.",
+  "modelVariationAdvisory": "The host catalog has one possible variation of {{model}}: {{variation}}. The saved model remains unchanged until launch.",
   "promptAdd": "Add prompt",
   "promptEditorAriaLabel": "Prompt editor",
   "promptEditorBothHint": "Type {{placeholder}} for available placeholders or {{mention}} for saved prompts.",

apps/web/src/locales/en/task.json

@@ -883,6 +883,7 @@
   "modelSelectionReasonCatalogEmpty": "The executor did not advertise a model catalog.",
   "modelSelectionReasonFallbackNotAdvertised": "The saved fallback model was not advertised by the executor.",
   "modelSelectionReasonRequestedNotAdvertised": "The saved model was not advertised by the executor.",
+  "modelSelectionReasonUniqueVariation": "The executor applied the only advertised variation of the saved model.",
   "modelSelectionReasonUnknown": "{{reason}}",
   "modelSelectionReasonUnsupported": "The executor does not support model selection.",
   "modelSelectionRemediationAgentVersion": "Check the agent version in the executor.",

apps/web/src/locales/pseudo/settings.json

@@ -504,6 +504,8 @@
   "profileForTasksCreatedByAgents": "Ƥŕōƒĩĺē ƒōŕ Ţàśķś Ćŕēàţēď ƀŷ Àĝēńţś",
   "programming": "Ƥŕōĝŕàḿḿĩńĝ",
   "profileStartModelNotAdvertisedOnHost": "Ţĥē ĥōśţ ƥŕōƀē ďĩď ńōţ àďvēŕţĩśē {{model}}. Ţĥē śēĺēćţēď ēxēćũţōŕ ŵĩĺĺ ďēćĩďē ţĥē ḿōďēĺ àţ ĺàũńćĥ.",
+  "profileStartModelUniqueVariationOnHost": "Ţĥē ĥōśţ ƥŕōƀē ƒōũńď ōńē ƥōśśĩƀĺē vàŕĩàţĩōń ōƒ {{model}}: {{variation}}. Ţĥē śēĺēćţēď ēxēćũţōŕ ŵĩĺĺ ďēćĩďē ţĥē ḿōďēĺ àţ ĺàũńćĥ.",
+  "modelVariationAdvisory": "Ţĥē ĥōśţ ćàţàĺōĝ ĥàś ōńē ƥōśśĩƀĺē vàŕĩàţĩōń ōƒ {{model}}: {{variation}}. Ţĥē śàvēď ḿōďēĺ ŕēḿàĩńś ũńćĥàńĝēď ũńţĩĺ ĺàũńćĥ.",
   "promptAdd": "Àďď ƥŕōḿƥţ",
   "promptEditorAriaLabel": "Ƥŕōḿƥţ ēďĩţōŕ",
   "promptEditorBothHint": "Ţŷƥē {{placeholder}} ƒōŕ àvàĩĺàƀĺē ƥĺàćēĥōĺďēŕś ōŕ {{mention}} ƒōŕ śàvēď ƥŕōḿƥţś.",

apps/web/src/locales/pseudo/task.json

@@ -883,6 +883,7 @@
   "modelSelectionReasonCatalogEmpty": "Ţĥē ēxēćũţōŕ ďĩď ńōţ àďvēŕţĩśē à ḿōďēĺ ćàţàĺōĝ.",
   "modelSelectionReasonFallbackNotAdvertised": "Ţĥē śàvēď ƒàĺĺƀàćķ ḿōďēĺ ŵàś ńōţ àďvēŕţĩśēď ƀŷ ţĥē ēxēćũţōŕ.",
   "modelSelectionReasonRequestedNotAdvertised": "Ţĥē śàvēď ḿōďēĺ ŵàś ńōţ àďvēŕţĩśēď ƀŷ ţĥē ēxēćũţōŕ.",
+  "modelSelectionReasonUniqueVariation": "Ţĥē ēxēćũţōŕ àƥƥĺĩēď ţĥē ōńĺŷ àďvēŕţĩśēď vàŕĩàţĩōń ōƒ ţĥē śàvēď ḿōďēĺ.",
   "modelSelectionReasonUnknown": "{{reason}}",
   "modelSelectionReasonUnsupported": "Ţĥē ēxēćũţōŕ ďōēś ńōţ śũƥƥōŕţ ḿōďēĺ śēĺēćţĩōń.",
   "modelSelectionRemediationAgentVersion": "Ćĥēćķ ţĥē àĝēńţ vēŕśĩōń ĩń ţĥē ēxēćũţōŕ.",

apps/web/src/locales/pt-pt/settings.json

@@ -751,6 +751,8 @@
   "terminalAndEditors": "Terminal e editores",
   "workspacesAndAccess": "Workspaces e acesso",
   "profileStartModelNotAdvertisedOnHost": "A sondagem do anfitrião não anunciou {{model}}. O executor selecionado decidirá o modelo no arranque.",
+  "profileStartModelUniqueVariationOnHost": "A sondagem do anfitrião encontrou uma única variação possível de {{model}}: {{variation}}. O executor selecionado decidirá o modelo no arranque.",
+  "modelVariationAdvisory": "O catálogo do anfitrião tem uma única variação possível de {{model}}: {{variation}}. O modelo guardado permanece inalterado até ao arranque.",
   "navUnits": "Unidades da organização",
   "unitsTitle": "Unidades da organização",
   "unitsDescription": "Uma unidade contém equipas, áreas de trabalho e pessoas. Pertencer a uma unidade dá acesso a todas as áreas de trabalho abaixo dela, incluindo as criadas depois.",

apps/web/src/locales/pt-pt/task.json

@@ -1958,6 +1958,7 @@
   "modelSelectionReasonCatalogEmpty": "O executor não anunciou um catálogo de modelos.",
   "modelSelectionReasonFallbackNotAdvertised": "O modelo alternativo guardado não foi anunciado pelo executor.",
   "modelSelectionReasonRequestedNotAdvertised": "O modelo guardado não foi anunciado pelo executor.",
+  "modelSelectionReasonUniqueVariation": "O executor aplicou a única variação anunciada do modelo guardado.",
   "modelSelectionReasonUnknown": "{{reason}}",
   "modelSelectionReasonUnsupported": "O executor não suporta seleção de modelo.",
   "modelSelectionRemediationAgentVersion": "Verifique a versão do agente no executor.",

apps/web/src/locales/zh-cn/settings.json

@@ -751,6 +751,8 @@
   "keyValueKeyPlaceholder": "键",
   "keyValueValuePlaceholder": "值",
   "profileStartModelNotAdvertisedOnHost": "主机探测未公布 {{model}}。所选执行器将在启动时决定使用的模型。",
+  "profileStartModelUniqueVariationOnHost": "主机探测发现 {{model}} 的一个可能变体：{{variation}}。所选执行器将在启动时决定使用的模型。",
+  "modelVariationAdvisory": "主机目录中有一个可能的 {{model}} 变体：{{variation}}。保存的模型在启动前保持不变。",
   "navUnits": "组织单元",
   "unitsTitle": "组织单元",
   "unitsDescription": "单元包含团队、工作区和成员。加入某个单元即可访问其下的所有工作区，包括之后创建的。",

apps/web/src/locales/zh-cn/task.json

@@ -1958,6 +1958,7 @@
   "modelSelectionReasonCatalogEmpty": "执行器未公布模型目录。",
   "modelSelectionReasonFallbackNotAdvertised": "执行器未公布已保存的备选模型。",
   "modelSelectionReasonRequestedNotAdvertised": "执行器未公布已保存的模型。",
+  "modelSelectionReasonUniqueVariation": "执行器应用了已保存模型唯一公布的变体。",
   "modelSelectionReasonUnknown": "{{reason}}",
   "modelSelectionReasonUnsupported": "该执行器不支持选择模型。",
   "modelSelectionRemediationAgentVersion": "请检查执行器中的智能体版本。",

apps/web/src/locales/zh-hk/settings.json

@@ -751,6 +751,8 @@
   "keyValueKeyPlaceholder": "鍵",
   "keyValueValuePlaceholder": "值",
   "profileStartModelNotAdvertisedOnHost": "主機探測未公佈 {{model}}。所選執行器將在啓動時決定使用的模型。",
+  "profileStartModelUniqueVariationOnHost": "主機探測發現 {{model}} 的一個可能變體：{{variation}}。所選執行器將在啓動時決定使用的模型。",
+  "modelVariationAdvisory": "主機目錄中有一個可能的 {{model}} 變體：{{variation}}。已儲存的模型在啟動前保持不變。",
   "navUnits": "組織單元",
   "unitsTitle": "組織單元",
   "unitsDescription": "單元包含團隊、工作區和成員。加入某個單元即可存取其下的所有工作區，包括之後建立的。",

apps/web/src/locales/zh-hk/task.json

@@ -1958,6 +1958,7 @@
   "modelSelectionReasonCatalogEmpty": "執行器未公佈模型目錄。",
   "modelSelectionReasonFallbackNotAdvertised": "執行器未公佈已儲存的備選模型。",
   "modelSelectionReasonRequestedNotAdvertised": "執行器未公佈已儲存的模型。",
+  "modelSelectionReasonUniqueVariation": "執行器套用了已儲存模型唯一公佈的變體。",
   "modelSelectionReasonUnknown": "{{reason}}",
   "modelSelectionReasonUnsupported": "該執行器不支援選擇模型。",
   "modelSelectionRemediationAgentVersion": "請檢查執行器中的代理程式版本。",

apps/web/src/locales/zh-tw/settings.json

@@ -751,6 +751,8 @@
   "keyValueKeyPlaceholder": "鍵",
   "keyValueValuePlaceholder": "值",
   "profileStartModelNotAdvertisedOnHost": "主機探測未公佈 {{model}}。所選執行器將在啟動時決定使用的模型。",
+  "profileStartModelUniqueVariationOnHost": "主機探測發現 {{model}} 的一個可能變體：{{variation}}。所選執行器將在啟動時決定使用的模型。",
+  "modelVariationAdvisory": "主機目錄中有一個可能的 {{model}} 變體：{{variation}}。已儲存的模型在啟動前保持不變。",
   "navUnits": "組織單元",
   "unitsTitle": "組織單元",
   "unitsDescription": "單元包含團隊、工作區和成員。加入某個單元即可存取其下的所有工作區，包括之後建立的。",

apps/web/src/locales/zh-tw/task.json

@@ -1958,6 +1958,7 @@
   "modelSelectionReasonCatalogEmpty": "執行器未公佈模型目錄。",
   "modelSelectionReasonFallbackNotAdvertised": "執行器未公佈已儲存的備選模型。",
   "modelSelectionReasonRequestedNotAdvertised": "執行器未公佈已儲存的模型。",
+  "modelSelectionReasonUniqueVariation": "執行器套用了已儲存模型唯一公佈的變體。",
   "modelSelectionReasonUnknown": "{{reason}}",
   "modelSelectionReasonUnsupported": "該執行器不支援選擇模型。",
   "modelSelectionRemediationAgentVersion": "請檢查執行器中的代理程式版本。",

docs/decisions/2026-09-07-unique-model-variation-resolution.md

@@ -0,0 +1,84 @@
+# ADR-2026-09-07: Resolve Only One Advertised Model Variation
+
+**Status:** proposed
+**Date:** 2026-09-07
+**Area:** backend, frontend, protocol
+**Amends:** `2026-08-15-executor-authoritative-model-selection`
+
+## Context
+
+An agent CLI can replace a bare model ID with bracketed variations. A profile
+can keep `opus` while the executor later advertises only `opus[1m]`.
+
+The current executor-authoritative policy treats the saved ID as absent. It
+uses an explicit fallback when available. Otherwise, it continues with the
+provider current or default model and records a warning. This result can move a
+session to an unrelated model even when the catalog has one clear variation of
+the requested model.
+
+Variation text is provider-owned. Kandev cannot safely rank `270k`, `1m`,
+`fast`, or future labels. Catalog order and the current-model marker do not
+express user intent.
+
+## Decision
+
+Kandev recognizes a model variation only by a narrow bracketed ID shape. A bare
+requested ID `x` matches an advertised ID `x[v]` when `v` is non-empty and
+contains no bracket. Matching is exact and case-sensitive. Kandev treats `v` as
+opaque text.
+
+For profiles with `auto_fallback = false`, the executor-authoritative resolution
+order is:
+
+1. Exact requested model.
+2. Advertised explicit fallback from the profile.
+3. One distinct advertised variation of the requested bare model.
+4. Provider current or default model, with no speculative model-selection call.
+
+Kandev applies step 3 only when exactly one distinct candidate exists. Zero or
+multiple candidates produce no inferred selection. An unadvertised explicit
+fallback does not block step 3.
+
+A requested ID that contains a bracket is an exact ID only. Kandev does not
+infer another variation from it.
+
+Profiles with `auto_fallback = true` retain the legacy path when the requested
+model is absent. Kandev ignores the configured explicit fallback, does not
+infer a variation, and continues with the provider current or default model.
+Apply errors for an advertised model remain best-effort in that mode.
+
+The lifecycle stores `unique_variation` as the decision outcome and
+`unique_variation_applied` as the warning reason. The effective model contains
+the advertised variation. The explicit fallback field keeps its existing
+meaning and stays empty when Kandev infers a variation.
+
+The saved profile model does not change. The rule runs for initial launch,
+context reset, and workspace rebind. The executor catalog remains authoritative.
+Any host-catalog result remains an advisory.
+
+## Consequences
+
+- A profile with `opus` follows `opus[1m]` when it is the only advertised
+  variation.
+- A catalog with `opus[270k]` and `opus[1m, fast]` remains ambiguous and uses
+  the existing provider-default path.
+- An explicit advertised fallback remains stronger than inference.
+- Kandev never sends a model ID that the executor did not advertise.
+- Users receive a durable warning because the effective model differs from the
+  saved request.
+- Provider-specific ranking logic does not enter the lifecycle policy.
+- Backend and frontend helpers need mirrored contract tests. The backend result
+  remains authoritative when their input catalogs differ.
+
+## Alternatives Considered
+
+1. **Always choose the first variation.** Rejected because catalog order is not
+   a user preference or a stable provider contract.
+2. **Prefer the provider current model.** Rejected because current state can
+   reflect a default or an earlier session, not the saved profile intent.
+3. **Rank known labels such as context size or fast mode.** Rejected because
+   labels are provider-owned and can change without a Kandev release.
+4. **Rewrite the saved profile to the inferred model.** Rejected because one
+   executor observation must not change behavior for every executor.
+5. **Infer from an already bracketed request.** Rejected because it can replace
+   one explicit variation with another without user intent.

docs/decisions/INDEX.md

@@ -95,6 +95,7 @@ Read individual ADRs for full context. Create new ones via `/record decision` or
 | 2026-08-15-subagent-context-schema-boundary | [Start with the execution-aware subagent schema](2026-08-15-subagent-context-schema-boundary.md) | accepted | backend | 2026-08-15 |
 | 2026-08-15-portable-agent-configuration-bundles | [Use Explicit Portable Agent Configuration Bundles](2026-08-15-portable-agent-configuration-bundles.md) | accepted | backend, frontend, protocol, security | 2026-08-15 |
 | 2026-08-15-executor-authoritative-model-selection | [Let the Executor Own Model Selection](2026-08-15-executor-authoritative-model-selection.md) | accepted | backend, frontend, protocol, persistence | 2026-08-15 |
+| 2026-09-07-unique-model-variation-resolution | [Resolve Only One Advertised Model Variation](2026-09-07-unique-model-variation-resolution.md) | proposed | backend, frontend, protocol | 2026-09-07 |
 | 2026-08-18-context-reset-preserves-runtime-configuration | [Preserve ACP Runtime Configuration Across Context Reset](2026-08-18-context-reset-preserves-runtime-configuration.md) | accepted | backend, protocol, workflow | 2026-08-18 |
 | 2026-08-19-parent-authorized-child-workspace-sources | [Parent-authorized child workspace sources](2026-08-19-parent-authorized-child-workspace-sources.md) | accepted | backend, protocol, security | 2026-08-19 |
 | 2026-08-24-task-snapshotted-branch-policies | [Snapshot Repository Branch Policies on Tasks](2026-08-24-task-snapshotted-branch-policies.md) | proposed | backend, frontend, persistence | 2026-08-24 |

docs/plans/unique-model-variation-fallback/plan.md

@@ -0,0 +1,129 @@
+---
+created: 2026-09-07
+status: complete
+requirements:
+  - REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001
+  - REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002
+system_design:
+  - ../../specs/agents/system-design/no-silent-model-fallback-01.md
+  - ../../specs/agents/system-design/no-silent-model-fallback-02.md
+legacy_specs: []
+---
+
+# Implementation Plan: Unique Model Variation Fallback
+
+## Overview
+
+Extend the central executor-authoritative model policy with one deterministic
+inference step. Implement the runtime contract first, expose its stable decision
+in the existing frontend surfaces, then prove and document the user outcome.
+
+## Scope
+
+### In scope
+
+- Resolve a missing bare model to its only distinct advertised bracketed
+  variation.
+- Keep exact models and advertised explicit fallbacks at higher precedence.
+- Persist a distinct warning outcome and reason without rewriting the profile.
+- Present host results as advisory on desktop and touch interfaces.
+- Test and document unique and ambiguous catalogs.
+
+### Out of scope
+
+- Provider-specific ranking of variation labels.
+- Selection among multiple variations.
+- Profile schema changes or saved-model migration.
+- Office post-start route changes or mid-turn model switching.
+
+## Technical approach
+
+### Runtime policy
+
+Add a pure unique-candidate helper in
+`apps/backend/internal/agent/runtime/lifecycle/start_model.go`. It accepts the
+requested ID and executor model IDs. It returns one distinct advertised ID only
+when the structural contract matches.
+
+For profiles with automatic fallback disabled, extend `applyStartModelPolicy`
+with this order: exact request, advertised explicit fallback, unique variation,
+provider current or default. Automatic-fallback profiles retain their legacy
+no-selection behavior when the requested model is absent. Add
+`unique_variation` to `ModelSelectionOutcome` and
+`unique_variation_applied` to stable warning reasons.
+
+Keep `EffectiveModel` as the inferred ID. Do not set `FallbackModel` for this
+outcome. `publishModelSelectionWarningEvent` must therefore emit the new reason
+without the legacy `session_model_fallback` compatibility event.
+
+Initial launch, context reset, and workspace rebind already use this policy.
+Targeted tests must prove that no separate path bypasses the new order.
+
+### Frontend advisory
+
+Add the mirrored pure matcher under `apps/web/lib/`. Its table tests use the
+same contract cases as the Go helper. Backend lifecycle data remains the launch
+authority.
+
+Use the helper in `task-create-dialog-options.tsx` and
+`settings/profile-model-fields.tsx`. One host variation names the possible
+target while keeping the saved value and selectable profile. Zero or multiple
+variations keep the current missing-model presentation.
+
+Map `unique_variation_applied` in `status-message.tsx`. Add localized copy to
+all required `settings` and `task` catalogs. Reuse the existing desktop tooltip,
+touch drawer, responsive model selector, and task-chat status layout.
+
+### Documentation
+
+Update `docs/public/agents-and-profiles.md` and `docs/public/executors.md` with
+the four-step order, one unique example, one ambiguous example, and the
+unchanged saved-profile rule.
+
+## Tests
+
+- AC-002.1 and AC-002.2: Go policy tests prove exact and explicit-fallback
+  precedence before one inferred variation, including the legacy
+  auto-fallback path.
+- AC-002.3 through AC-002.5: mirrored Go and TypeScript table tests prove zero,
+  duplicate, multiple, case-different, bracketed, prefix, and malformed cases.
+- AC-002.6: lifecycle event and React status-message tests prove the distinct
+  outcome, effective model, absent explicit-fallback field, and durable copy.
+- AC-002.7: task picker and profile editor tests prove advisory host behavior.
+- AC-002.8: lifecycle integration tests prove launch, reset, and rebind parity.
+
+## E2E tests
+
+- AC-002.2 and AC-002.6: extend
+  `apps/web/e2e/tests/session/model-mismatch-warning.spec.ts` to launch `opus`
+  against one `opus[1m]`, show the effective model, and retain one warning after
+  reload.
+- AC-002.3: add an ambiguous catalog with `opus[270k]` and
+  `opus[1m, fast]`; prove that Kandev does not select either variation.
+- AC-002.7: extend the desktop and mobile settings mismatch specs. Prove that
+  the profile remains selectable, the advisory is keyboard or tap accessible,
+  and mobile has no horizontal document overflow.
+
+## Work orders
+
+- [x] [Task 01: Resolve one executor variation](task-01-runtime-resolution.md)
+- [x] [Task 02: Present variation decisions](task-02-frontend-advisory.md)
+- [x] [Task 03: Prove variation workflows](task-03-e2e-verification.md)
+- [x] [Task 04: Document variation fallback](task-04-public-docs.md)
+
+## Verification results
+
+Backend verification passed: 2,364 lifecycle tests, 29 focused model-policy
+tests, and 212 mock-agent tests. Frontend verification passed: 51 focused
+unit tests, typecheck, lint, `i18n:check`, and `i18n:ratchet`. Desktop E2E
+passed 5 tests and mobile E2E passed 3 tests. Public-document validation
+passed 61 tests and validated 46 published pages. Specification lint passed.
+
+## Risks
+
+- Provider variation labels can change. Kandev must keep their content opaque.
+- Host and executor catalogs can differ. Host preview logic cannot become a
+  launch gate.
+- Older frontends can render the new reason as unknown during mixed-version
+  use. Requested and effective fields must remain useful.
+- Duplicate or malformed catalog rows can make a naive candidate count unstable.

docs/plans/unique-model-variation-fallback/task-01-runtime-resolution.md

@@ -0,0 +1,100 @@
+---
+id: "01-runtime-resolution"
+title: "Resolve one executor variation"
+status: done
+wave: 1
+depends_on: []
+plan: "plan.md"
+requirements:
+  - REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001
+  - REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002
+acceptance_criteria:
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.1
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.2
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.3
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.4
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.5
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.6
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.8
+system_design:
+  - ../../specs/agents/system-design/no-silent-model-fallback-01.md
+  - ../../specs/agents/system-design/no-silent-model-fallback-02.md
+---
+
+# Task 01: Resolve One Executor Variation
+
+## Summary
+
+Extend the single lifecycle model policy with safe unique-variation inference.
+Expose a distinct decision without changing explicit fallback semantics.
+
+## In scope
+
+- Add the pure backend candidate matcher.
+- Apply the defined four-step precedence order.
+- Extend decision, logging, and warning metadata behavior.
+- Cover initial launch, context reset, and workspace rebind.
+
+## Out of scope
+
+- Host advisory UI and translations.
+- Provider-specific variation parsing or ranking.
+- Profile persistence changes.
+
+## Acceptance
+
+- One valid distinct variation is the only inferred model-selection call.
+- Exact and advertised explicit fallback models remain higher priority; zero or
+  multiple variations cause no inference.
+- Automatic-fallback profiles keep the legacy no-selection behavior when the
+  requested model is absent.
+- The warning records the unique outcome and effective model without setting
+  the explicit fallback field or compatibility fallback event.
+
+## Verification
+
+```bash
+(
+  cd apps/backend
+  go test -tags fts5 -run 'TestApplyStartModelPolicy|TestInitializeAndPrompt.*Model|TestReapplySessionModel|TestWorkspaceRebind.*Model|Test.*ModelSelectionWarning' ./internal/agent/runtime/lifecycle
+  go test -tags fts5 ./internal/agent/runtime/lifecycle
+)
+git diff --check
+```
+
+## Files likely touched
+
+- `apps/backend/internal/agent/runtime/lifecycle/start_model.go`
+- `apps/backend/internal/agent/runtime/lifecycle/start_model_executor_authority_test.go`
+- `apps/backend/internal/agent/runtime/lifecycle/session.go`
+- `apps/backend/internal/agent/runtime/lifecycle/session_model_selection_warning_test.go`
+- `apps/backend/internal/agentctl/types/streams/agent.go`
+
+## Dependencies
+
+None.
+
+## Risks
+
+- The Cursor-specific configuration parser rejects labels such as `1m`. This
+  matcher must remain a separate model-ID helper.
+- A special inferred-model apply path can weaken existing error handling.
+
+## Parallelism
+
+`sequential`
+
+## Inputs
+
+- Requirement 002 and its matching examples.
+- The unique-variation ADR.
+- Existing `applyStartModelPolicy` and warning publication tests.
+
+## Results
+
+Implemented the executor-authoritative unique-variation policy in
+`start_model.go`, including explicit-fallback precedence, opaque and
+case-sensitive matching, the legacy automatic-fallback path, and distinct
+warning metadata without a legacy fallback event. Initial launch, context
+reset, and workspace rebind all use the same policy. Focused model-policy
+tests passed (29), and the full lifecycle suite passed (2,364).

docs/plans/unique-model-variation-fallback/task-02-frontend-advisory.md

@@ -0,0 +1,102 @@
+---
+id: "02-frontend-advisory"
+title: "Present variation decisions"
+status: done
+wave: 2
+depends_on: ["01-runtime-resolution"]
+plan: "plan.md"
+requirements:
+  - REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002
+acceptance_criteria:
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.3
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.4
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.5
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.6
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.7
+system_design:
+  - ../../specs/agents/system-design/no-silent-model-fallback-01.md
+---
+
+# Task 02: Present Variation Decisions
+
+## Summary
+
+Present one host variation as an advisory and render the runtime decision in
+task chat. Keep the host probe non-authoritative on every viewport.
+
+## In scope
+
+- Add the mirrored frontend matcher and table tests.
+- Update task-create and profile-editor missing-model states.
+- Render the new warning reason with requested and effective models.
+- Add all required localized copy.
+
+## Out of scope
+
+- Runtime model selection.
+- New dialog, drawer, or navigation patterns.
+- Changes to the saved profile model.
+
+## Acceptance
+
+- One host variation names a possible target and keeps the profile selectable.
+- Zero or multiple host variations keep the existing missing-model state.
+- Desktop, keyboard, and touch users can reach the advisory and durable warning.
+
+## Verification
+
+```bash
+(
+  cd apps
+  pnpm --filter @kandev/web test -- --run components/task-create-dialog-options components/settings/profile-form-fields components/task/chat/messages/status-message lib/model-variation
+  pnpm --filter @kandev/web lint
+)
+(
+  cd apps/web
+  pnpm run typecheck
+  pnpm run i18n:check
+  pnpm run i18n:ratchet
+)
+git diff --check
+```
+
+## Files likely touched
+
+- `apps/web/lib/model-variation.ts`
+- `apps/web/lib/model-variation.test.ts`
+- `apps/web/components/task-create-dialog-options.tsx`
+- `apps/web/components/task-create-dialog-options.test.tsx`
+- `apps/web/components/settings/profile-model-fields.tsx`
+- `apps/web/components/settings/profile-form-fields.test.tsx`
+- `apps/web/components/task/chat/messages/status-message.tsx`
+- `apps/web/components/task/chat/messages/status-message.test.tsx`
+- `apps/web/src/locales/*/settings.json`
+- `apps/web/src/locales/*/task.json`
+
+## Dependencies
+
+Task 01.
+
+## Risks
+
+- Host preview text can sound authoritative when another executor can advertise
+  a different catalog.
+- Missing and resolvable states must be mutually exclusive in the profile row.
+
+## Parallelism
+
+`sequential`
+
+## Inputs
+
+- Task 01 warning reason and payload fields.
+- Existing host warning tooltip, touch drawer, profile selector, and status
+  message patterns.
+
+## Results
+
+Added the mirrored structural matcher, host advisory states, and the task-chat
+warning reason while preserving the saved profile model. Added localized copy
+for all required catalogs and retained the existing desktop tooltip and mobile
+touch-drawer patterns. Focused frontend tests passed (51), typecheck and lint
+passed, and both i18n checks passed.

docs/plans/unique-model-variation-fallback/task-03-e2e-verification.md

@@ -0,0 +1,84 @@
+---
+id: "03-e2e-verification"
+title: "Prove variation workflows"
+status: done
+wave: 3
+depends_on: ["01-runtime-resolution", "02-frontend-advisory"]
+plan: "plan.md"
+requirements:
+  - REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002
+acceptance_criteria:
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.2
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.3
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.6
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.7
+system_design:
+  - ../../specs/agents/system-design/no-silent-model-fallback-01.md
+---
+
+# Task 03: Prove Variation Workflows
+
+## Summary
+
+Extend the existing model-mismatch browser flows with unique and ambiguous
+catalogs. Prove the launch result, durable warning, and touch interaction.
+
+## In scope
+
+- Desktop launch and reload coverage for one variation.
+- Desktop no-inference coverage for multiple variations.
+- Mobile advisory and warning access through tap.
+- Horizontal overflow checks for the changed mobile states.
+
+## Out of scope
+
+- New browser fixtures unrelated to model catalogs.
+- Full E2E suite execution.
+- Public documentation.
+
+## Acceptance
+
+- `opus` launches as `opus[1m]` only when that is the sole distinct variation.
+- Two variations do not select either candidate.
+- The warning survives reload and the mobile flow needs no hover interaction.
+
+## Verification
+
+```bash
+cd apps/web && pnpm e2e:run tests/settings/no-silent-model-fallback.spec.ts tests/session/model-mismatch-warning.spec.ts
+cd apps/web && pnpm e2e:run --project mobile-chrome --no-build tests/settings/mobile-no-silent-model-fallback.spec.ts tests/session/mobile-model-mismatch-warning.spec.ts
+git diff --check
+```
+
+## Files likely touched
+
+- `apps/web/e2e/tests/settings/no-silent-model-fallback.spec.ts`
+- `apps/web/e2e/tests/settings/mobile-no-silent-model-fallback.spec.ts`
+- `apps/web/e2e/tests/session/model-mismatch-warning.spec.ts`
+- `apps/web/e2e/tests/session/mobile-model-mismatch-warning.spec.ts`
+- `apps/web/e2e/tests/session/model-mismatch-warning-helpers.ts`
+
+## Dependencies
+
+Tasks 01 and 02.
+
+## Risks
+
+- Mock catalogs must prove the executor decision, not only the host advisory.
+- Each scenario needs isolated profile data so another catalog does not change
+  the distinct candidate count.
+
+## Parallelism
+
+`parallel-safe` with Task 04 after Tasks 01 and 02.
+
+## Inputs
+
+- Completed runtime and frontend work.
+- Existing desktop and mobile model-mismatch fixtures.
+
+## Results
+
+Added unique and ambiguous mock-agent catalogs and covered launch, reload,
+profile persistence, host advisory access, and mobile overflow. The focused
+desktop E2E run passed 5 tests; the focused mobile E2E run passed 3 tests.

docs/plans/unique-model-variation-fallback/task-04-public-docs.md

@@ -0,0 +1,83 @@
+---
+id: "04-public-docs"
+title: "Document variation fallback"
+status: done
+wave: 3
+depends_on: ["01-runtime-resolution", "02-frontend-advisory"]
+plan: "plan.md"
+requirements:
+  - REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002
+acceptance_criteria:
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.1
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.2
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.3
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.5
+  - AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.6
+system_design:
+  - ../../specs/agents/system-design/no-silent-model-fallback-01.md
+---
+
+# Task 04: Document Variation Fallback
+
+## Summary
+
+Update the public profile and executor guides with the unique-variation rule.
+Give users enough detail to predict unique and ambiguous results.
+
+## In scope
+
+- Document the four-step launch order.
+- Add one unique and one ambiguous example.
+- State that labels remain opaque and saved profiles do not change.
+- Run the public-doc validation commands.
+
+## Out of scope
+
+- Release notes and changelog generation.
+- Internal implementation detail beyond user-visible behavior.
+- New screenshots or media.
+
+## Acceptance
+
+- Both guides describe the same precedence and ambiguity rule.
+- The docs state that the executor is authoritative and the profile stays
+  unchanged.
+- Public-doc validators pass.
+
+## Verification
+
+```bash
+node --test scripts/validate-public-docs.test.mjs
+node scripts/validate-public-docs.mjs
+git diff --check
+```
+
+## Files likely touched
+
+- `docs/public/agents-and-profiles.md`
+- `docs/public/executors.md`
+
+## Dependencies
+
+Tasks 01 and 02.
+
+## Risks
+
+- Examples can imply that Kandev understands `1m` or `fast`. The docs must state
+  that it compares only the ID shape and candidate count.
+
+## Parallelism
+
+`parallel-safe` with Task 03 after Tasks 01 and 02.
+
+## Inputs
+
+- Final runtime precedence and warning behavior.
+- Existing host-probe and remote-executor guide sections.
+
+## Results
+
+Updated the public agent-profile and executor guides with the four-step
+resolution order, unique and ambiguous examples, opaque variation matching,
+and the unchanged saved-profile rule. Public-document tests passed (61) and
+the validator checked 46 published pages.

docs/public/agents-and-profiles.md

@@ -171,6 +171,31 @@ change makes a saved option value unsupported, Kandev removes that value after
 a successful resolution; a failed resolution keeps the draft unchanged so you
 can retry it.
 
+### Model IDs and executor catalogs
+
+The host model probe is an editing hint. The selected executor owns the model
+catalog at launch. Kandev resolves a saved model in this order:
+
+1. Use the exact requested model when the executor advertises it.
+2. Use the advertised explicit fallback when the requested model is absent.
+3. Use one unique bracketed variation when the requested model is absent and
+   the executor advertises exactly one matching ID.
+4. Use the agent's current or default model when no earlier choice applies.
+
+Profiles with automatic fallback enabled keep the legacy behavior when the
+saved model is absent: Kandev ignores the explicit fallback and does not infer
+a variation. It uses the agent's current or default model instead.
+
+For example, a saved `opus` model can launch as `opus[1m]` when that is the
+only advertised `opus[...]` ID. If the executor advertises both
+`opus[270k]` and `opus[1m, fast]`, Kandev does not choose either variation.
+Variation text is opaque and model IDs remain case-sensitive.
+
+Kandev shows a warning when the launch result differs from the saved model.
+The saved profile remains `opus`; Kandev does not rewrite it after applying a
+unique variation or using the agent default. Recheck the executor catalog when
+the warning repeats after credentials, copied configuration, or agent updates.
+
 ### Use a dynamic profile
 
 > [!EXPERIMENTAL]
@@ -228,13 +253,13 @@ The model list shown while editing a profile comes from a host probe. It is an
 editing hint, not a launch gate. A profile remains selectable when its saved
 model is missing from that host list.
 
-At task launch, the selected executor's ACP catalog is authoritative. Kandev
+At task launch, the selected executor's ACP catalog is authoritative. For
-sends the requested model only when the executor advertises it. If it does
+profiles without automatic fallback, Kandev follows the four-step order above.
-not, Kandev uses an advertised fallback when available, or sends no model
+For profiles with automatic fallback enabled, an absent saved model causes no
-request and continues with the agent's current or default model. Kandev stores
+model request, and Kandev ignores the explicit fallback and any variation.
-one warning in task chat with the requested model and the effective model when
+Kandev stores one warning in task chat with the requested model and the
-known. The warning also identifies the agent and executor and asks you to
+effective model when known. The warning also identifies the agent and executor
-check credentials, copied configuration, and the agent version.
+and asks you to check credentials, copied configuration, and the agent version.
 
 The saved profile model is not changed. Optional portable configuration can
 copy selected allowlisted files into a remote executor, but it cannot guarantee

docs/public/executors.md

@@ -101,15 +101,30 @@ Review the selected bundles before saving the profile.
 ### Model selection in remote executors
 
 The host model probe helps edit a profile, but it is not the launch authority.
-At launch, the selected executor's advertised ACP catalog decides whether
+At launch, the selected executor's advertised ACP catalog decides the model.
-Kandev sends the saved model. If the executor does not advertise that model,
+For profiles without automatic fallback, Kandev applies this deterministic
-Kandev sends no request for it. It uses an advertised fallback only when one
+order:
-exists; otherwise the agent uses its current or default model.
 
-Kandev writes one warning to task chat when this happens. The warning can list
+1. An exact advertised model ID.
-the requested model, effective model, agent, executor, and executor profile.
+2. An advertised explicit fallback.
-It also tells you to check executor credentials, copied agent configuration,
+3. One unique advertised bracketed variation of the saved model.
-and the agent version. Kandev does not rewrite the saved profile model.
+4. The agent's current or default model.
+
+For profiles with automatic fallback enabled, an absent saved model keeps the
+legacy behavior: Kandev ignores the explicit fallback and does not infer a
+variation. It uses the agent's current or default model instead.
+
+For example, a saved `opus` model uses `opus[1m]` when that is the only
+advertised variation. With both `opus[270k]` and `opus[1m, fast]`, Kandev
+does not infer a choice and uses the agent's current or default model instead.
+It treats model IDs as case-sensitive and variation text as opaque.
+
+Kandev writes one warning to task chat when the effective model differs from
+the saved model. The warning can list the requested model, effective model,
+agent, executor, and executor profile. It also tells you to check executor
+credentials, copied agent configuration, and the agent version. Kandev does
+not rewrite the saved profile model, including after applying a unique
+variation.
 Portable configuration can improve parity, but it does not guarantee equal
 host and executor model catalogs.
 

docs/specs/agents/requirements/no-silent-model-fallback.md

@@ -1,26 +1,101 @@
 ---
-status: draft
+status: active
 system: agents
 created: 2026-08-23
 owners:
   - kandev
 ---
+
 # No Silent Model Fallback Requirements
 
 ## Overview
 
-**Status**: implemented (executor-authority amendment 2026-08-15) **Date**: 2026-08-04 **Slug**: `no-silent-model-fallback`
+Kandev applies an agent profile model against the model catalog from the
+selected executor. A different effective model must be deterministic and
+visible to the user. The agent system owns this contract because it owns
+profiles, ACP session startup, and model-selection warnings.
+
+## Terminology
+
+- **Requested model:** The model ID stored in the agent profile.
+- **Explicit fallback:** The optional fallback model ID stored in the profile.
+- **Bare model ID:** A model ID that contains no `[` or `]` character.
+- **Model variation:** An advertised model ID with the exact form
+  `<bare-model-id>[<non-empty-variant>]`. The variant contains no bracket
+  character. Its content is otherwise opaque.
+- **Unique variation:** The only distinct advertised variation for a requested
+  bare model ID.
 
 ## Requirements
 
-### REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001: No Silent Model Fallback
+### REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001: Use executor-authoritative model selection
 
-**Intent:** **Status**: implemented (executor-authority amendment 2026-08-15) **Date**: 2026-08-04 **Slug**: `no-silent-model-fallback`
+**Intent:** Keep task launch operational without hiding a difference between
+the saved model and the effective executor model.
+
+**User story:** As a user, I want Kandev to use the selected executor's model
+catalog and report any fallback, so that I can understand which model runs.
 
 #### Acceptance criteria
 
-- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-001.1:** When a consumer uses **Status**: implemented (executor-authority amendment 2026-08-15), the system shall provide the documented behavior.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-001.1:** When the executor advertises
+  the requested model, the system shall apply that exact model.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-001.2:** When the requested model is
+  absent and the executor advertises the configured explicit fallback, the
+  system shall apply the explicit fallback.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-001.3:** When no permitted advertised
+  model applies, the system shall make no speculative model-selection call and
+  shall continue with the provider current or default model.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-001.4:** When the effective model differs
+  from the requested model, the system shall persist one structured warning
+  that identifies the requested and effective models when known.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-001.5:** The system shall not rewrite the
+  saved profile model from an executor model-selection decision.
+
+### REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002: Resolve one advertised model variation
+
+**Intent:** Preserve a user's bare model choice when a CLI replaces that model
+ID with one unambiguous bracketed variation.
+
+**User story:** As a user, I want `opus` to resolve to `opus[1m]` when that is
+the only advertised variation, so that a provider catalog change does not move
+my session to an unrelated default model.
+
+#### Acceptance criteria
+
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.1:** When automatic fallback is
+  disabled, the exact requested model is absent, and an advertised explicit
+  fallback exists, the system shall apply the explicit fallback before it
+  considers an inferred variation. Automatic-fallback profiles shall retain
+  their legacy no-selection behavior for an absent requested model.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.2:** When no advertised explicit
+  fallback exists and the catalog contains exactly one distinct variation of a
+  requested bare model ID, the system shall apply that advertised variation.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.3:** When the catalog contains zero
+  or more than one distinct variation, the system shall not infer a model.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.4:** When the requested ID contains a
+  bracket, the system shall treat it as an exact ID and shall not infer another
+  variation.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.5:** Matching shall be case-sensitive
+  and shall not parse, rank, or assign meaning to variation text.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.6:** When Kandev applies a unique
+  variation, it shall keep the saved model unchanged and shall persist a
+  warning that identifies the inferred effective model.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.7:** The host profile probe shall
+  present unique-variation resolution as an advisory. It shall not become the
+  launch authority or disable the profile.
+- **AC-AGENTS-NO-SILENT-MODEL-FALLBACK-002.8:** The same resolution order shall
+  apply at initial launch, context reset, and workspace rebind.
+
+## Out of scope
+
+- Ranking multiple variations by context size, speed, price, or display order.
+- Parsing provider-specific variation syntax beyond the bracketed ID shape.
+- Inferring a base model from an already bracketed request.
+- Rewriting the profile model to the current executor's advertised variation.
+- Changing Office post-start provider routing or mid-turn model switching.
 
 ## System design
 
-The migrated technical source is split into [part 1](../system-design/no-silent-model-fallback-01.md), [part 2](../system-design/no-silent-model-fallback-02.md).
+The technical source is split into [part 1](../system-design/no-silent-model-fallback-01.md)
+and [part 2](../system-design/no-silent-model-fallback-02.md).

docs/specs/agents/system-design/no-silent-model-fallback-01.md

@@ -1,8 +1,9 @@
 ---
-status: draft
+status: current
 system: agents
 requirements:
   - REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001
+  - REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002
 created: 2026-08-23
 owners:
   - kandev
@@ -11,13 +12,15 @@ owners:
 
 ## Purpose and boundaries
 
-This design preserves the technical source detail for `REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001` during migration.
+This design defines executor-authoritative model fallback, including safe
+resolution from a bare requested model to one advertised bracketed variation.
 
 ## Requirement mapping
 
 | Requirement | Design section |
 | --- | --- |
 | `REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001` | [Migrated source detail](#migrated-source-detail) |
+| `REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002` | [Unique model-variation resolution](#unique-model-variation-resolution) |
 
 ## Migrated source detail
 
@@ -146,6 +149,121 @@ the launch. The agent uses its default and Kandev persists a warning.
 The executor ACP catalog is authoritative for launch.
 The host probe remains an editing hint and does not block profile selection.
 
+## Unique model-variation resolution
+
+### Matching contract
+
+ACP model IDs remain opaque and case-sensitive. Kandev recognizes only this
+structural relationship:
+
+```text
+<requested>[<variant>]
+```
+
+The requested ID must contain no `[` or `]` character. The advertised ID must
+start with the complete requested ID followed by `[`, end with `]`, and contain
+a non-empty variant with no bracket character. Kandev does not trim, parse, or
+rank the variant.
+
+Examples:
+
+| Requested | Advertised candidates | Result |
+| --- | --- | --- |
+| `opus` | `opus[1m]` | Apply `opus[1m]`. |
+| `opus` | `opus[270k]`, `opus[1m, fast]` | Do not infer. |
+| `opus[1m]` | `opus[270k]` | Do not infer. |
+| `opus` | `myopus[1m]`, `opus-extra[1m]` | Do not infer. |
+| `opus` | `opus[]`, `opus[1m][fast]` | Do not infer. |
+
+Duplicate catalog rows with the same model ID count as one distinct candidate.
+This rule keeps the outcome stable when an agent repeats a catalog entry.
+
+### Resolution order
+
+For profiles with `auto_fallback = false`, the lifecycle applies this order
+after ACP initialization:
+
+1. Apply the exact requested model when advertised.
+2. Apply the configured explicit fallback when advertised.
+3. Apply the requested model's unique advertised variation when one exists.
+4. Otherwise, make no model-selection call and keep the provider current or
+   default model.
+
+An unadvertised explicit fallback does not block step 3. More than one distinct
+variation blocks inference even when one candidate appears first or is the
+provider current model.
+
+When `auto_fallback = true`, the legacy path takes precedence when the
+requested model is absent: Kandev ignores the explicit fallback and does not
+infer a variation. It makes no model-selection call and continues on the
+provider current or default model with a warning. Apply errors for an
+advertised model remain best-effort in that mode.
+
+`applyStartModelPolicy` remains the single runtime owner. A pure helper returns
+the unique candidate or no candidate. Initial launch, context reset, and
+workspace rebind continue to call the same policy.
+
+### Decision and warning contract
+
+The typed decision adds the outcome `unique_variation` and the stable reason
+`unique_variation_applied`. `EffectiveModel` contains the advertised variation.
+`FallbackModel` remains reserved for a configured explicit fallback and is not
+overloaded with an inferred value.
+
+Kandev calls `SetModel` only with the candidate's exact advertised ID. A failed
+call follows the existing advertised-model rule: fail the operation unless
+legacy `auto_fallback` permits provider-default continuation. A
+method-not-supported response also follows the current provider-default path.
+
+The persisted `model_selection_warning` event uses the new reason and existing
+requested and effective model fields. The profile remains unchanged. The
+decision ID continues to include the requested model, reason, and effective
+model, so the warning stays idempotent for one session decision.
+
+### Host advisory and mobile behavior
+
+The frontend uses a small pure helper with the same case-sensitive matching
+table. This calculation is advisory because the host catalog can differ from
+the selected executor catalog.
+
+When the host advertises one variation, the task profile option remains
+selectable and identifies the possible target in its existing amber advisory.
+The profile editor keeps the saved bare ID visible and describes the unique
+host variation instead of reporting that the model is simply gone. Selecting
+the advertised variation remains an explicit way to update the profile.
+
+When the host advertises zero or multiple variations, the current missing-model
+presentation remains. The runtime can still reach a different decision from
+the selected executor catalog.
+
+The task-create advisory keeps its existing desktop tooltip and coarse-pointer
+drawer. The profile editor uses its existing responsive selector. The durable
+chat warning uses the existing status-message layout on desktop and mobile.
+This change adds no nested scroll area or hover-only information.
+
+### Tests and operational evidence
+
+Backend table tests cover exact precedence, explicit-fallback precedence,
+one variation, duplicate rows, multiple variations, bracketed requests,
+case differences, malformed IDs, method-not-supported, and apply errors.
+Existing launch, reset, rebind, warning persistence, and reload tests cover the
+new decision outcome.
+
+Frontend unit tests mirror the matching table and cover the task picker,
+profile editor, and localized status warning. Existing desktop and mobile model
+mismatch E2E flows add the unique and ambiguous catalog cases.
+
+Structured lifecycle logs record the requested model, effective model, outcome,
+and distinct candidate count. They do not record credentials or configuration
+file contents.
+
+No database migration is required.
+
+## Related decisions
+
+- [Let the Executor Own Model Selection](../../../decisions/2026-08-15-executor-authoritative-model-selection.md)
+- [Resolve Only One Advertised Model Variation](../../../decisions/2026-09-07-unique-model-variation-resolution.md)
+
 ## Backend Changes
 
 ### 1. Agent profile schema (new columns)

docs/specs/agents/system-design/no-silent-model-fallback-02.md

@@ -1,8 +1,9 @@
 ---
-status: draft
+status: current
 system: agents
 requirements:
   - REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001
+  - REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002
 created: 2026-08-23
 owners:
   - kandev
@@ -11,13 +12,15 @@ owners:
 
 ## Purpose and boundaries
 
-This design preserves the technical source detail for `REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001` during migration.
+This design records risks for executor-authoritative model fallback and unique
+variation resolution.
 
 ## Requirement mapping
 
 | Requirement | Design section |
 | --- | --- |
 | `REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-001` | [Migrated source detail](#migrated-source-detail) |
+| `REQ-AGENTS-NO-SILENT-MODEL-FALLBACK-002` | [Risks & Open Questions](#risks--open-questions) |
 
 ## Migrated source detail
 
@@ -51,3 +54,14 @@ This design preserves the technical source detail for `REQ-AGENTS-NO-SILENT-MODE
 - **Hover is supplementary**: every info icon is focusable, and coarse-pointer
   devices receive the same content in a drawer. The visible option helper copy
   remains the baseline explanation.
+- **Provider-specific labels remain opaque**: `1m`, `270k`, and `fast` have no
+  Kandev-defined order. More than one variation therefore fails closed to the
+  existing provider-default path.
+- **Host and executor decisions can differ**: a unique host variation is only
+  an advisory. The selected executor can advertise zero, one, or multiple
+  variations at launch.
+- **Bracketed requests do not drift sideways**: a request such as `opus[1m]`
+  does not infer `opus[270k]`. The user must select another explicit model.
+- **Legacy automatic fallback remains unchanged**: when `auto_fallback` is
+  enabled and the requested model is absent, Kandev does not apply an explicit
+  fallback or infer a variation. It continues with the provider default.