diff --git a/tests/e2e/test_claude_code_e2e.sh b/tests/e2e/test_claude_code_e2e.sh
index 3635869db..4b6c0d1b4 100755
--- a/tests/e2e/test_claude_code_e2e.sh
+++ b/tests/e2e/test_claude_code_e2e.sh
@@ -50,13 +50,16 @@ docker rm $(docker ps -aq --filter "name=ws-") 2>/dev/null || true
 echo ""
 echo "--- Create Workspaces ---"
 
+# model is required at the Create boundary (CTO 2026-05-22 SSOT —
+# feedback_workspace_model_required_no_platform_default_dynamic_credential_intake).
+# Pass the same value the deleted DefaultModel("claude-code") returned.
 ROOT=$(curl -s -X POST $PLATFORM/workspaces -H "Content-Type: application/json" \
-  -d '{"name":"Root Agent","role":"Company coordinator","runtime":"claude-code","tier":3}' \
+  -d '{"name":"Root Agent","role":"Company coordinator","runtime":"claude-code","model":"sonnet","tier":3}' \
   | python3 -c "import sys,json; print(json.load(sys.stdin)['id'])")
 check_contains "Create root workspace" "-" "$ROOT"
 
 CHILD=$(curl -s -X POST $PLATFORM/workspaces -H "Content-Type: application/json" \
-  -d "{\"name\":\"Child Agent\",\"role\":\"Sub-team member\",\"runtime\":\"claude-code\",\"tier\":2,\"parent_id\":\"$ROOT\"}" \
+  -d "{\"name\":\"Child Agent\",\"role\":\"Sub-team member\",\"runtime\":\"claude-code\",\"model\":\"sonnet\",\"tier\":2,\"parent_id\":\"$ROOT\"}" \
   | python3 -c "import sys,json; print(json.load(sys.stdin)['id'])")
 check_contains "Create child workspace" "-" "$CHILD"
 
diff --git a/tests/e2e/test_notify_attachments_e2e.sh b/tests/e2e/test_notify_attachments_e2e.sh
index 2a5f12a77..7aec89155 100755
--- a/tests/e2e/test_notify_attachments_e2e.sh
+++ b/tests/e2e/test_notify_attachments_e2e.sh
@@ -92,8 +92,12 @@ for _wid in $PRIOR; do
   curl -s -X DELETE "$BASE/workspaces/$_wid?confirm=true" > /dev/null || true
 done
 
+# model is required at the Create boundary (CTO 2026-05-22 SSOT — see
+# feedback_workspace_model_required_no_platform_default_dynamic_credential_intake).
+# Body had no runtime → defaults to langgraph; pass the langgraph-compatible
+# default that the deleted DefaultModel("") would have returned.
 R=$(curl -s -X POST "$BASE/workspaces" -H "Content-Type: application/json" \
-  -d '{"name":"Notify E2E","tier":1}')
+  -d '{"name":"Notify E2E","tier":1,"model":"anthropic:claude-opus-4-7"}')
 WSID=$(echo "$R" | python3 -c 'import json,sys;print(json.load(sys.stdin)["id"])' 2>/dev/null || true)
 [ -n "$WSID" ] || { echo "Failed to create workspace: $R"; exit 1; }
 echo "Created workspace $WSID"
diff --git a/tests/e2e/test_peer_visibility_mcp_local.sh b/tests/e2e/test_peer_visibility_mcp_local.sh
index 4fd378d45..833bae927 100755
--- a/tests/e2e/test_peer_visibility_mcp_local.sh
+++ b/tests/e2e/test_peer_visibility_mcp_local.sh
@@ -241,8 +241,24 @@ else
 fi
 log "1/5 provisioning parent ($PARENT_RUNTIME, mode=$PV_LOCAL_PROVISION_MODE) + one sibling per runtime under test..."
 
+# Map runtime → model per the CTO 2026-05-22 SSOT directive (model is
+# required, no platform default). External runtimes are exempt by the
+# Create-handler gate — for them the URL is the contract — but we still
+# pass model="external:custom" defensively in case a downstream consumer
+# of the create body asserts presence.
+_model_for_runtime() {
+  case "$1" in
+    claude-code) echo "sonnet" ;;
+    codex)       echo "gpt-5.5" ;;
+    kimi)        echo "kimi-coding/kimi-k2-coding-6" ;;
+    minimax)     echo "minimax/MiniMax-M2.7" ;;
+    external)    echo "external:custom" ;;
+    *)           echo "anthropic:claude-opus-4-7" ;;
+  esac
+}
+PARENT_MODEL=$(_model_for_runtime "$PARENT_RUNTIME")
 P_RESP=$(curl -s -X POST "$BASE/workspaces" ${ADMIN_AUTH[@]+"${ADMIN_AUTH[@]}"} -H "Content-Type: application/json" \
-  -d "{\"name\":\"${NAME_PREFIX}-parent\",\"runtime\":\"$PARENT_RUNTIME\",\"tier\":3$PARENT_EXTRA,\"secrets\":$PARENT_SECRETS}")
+  -d "{\"name\":\"${NAME_PREFIX}-parent\",\"runtime\":\"$PARENT_RUNTIME\",\"model\":\"$PARENT_MODEL\",\"tier\":3$PARENT_EXTRA,\"secrets\":$PARENT_SECRETS}")
 PARENT_ID=$(echo "$P_RESP" | python3 -c 'import json,sys;print(json.load(sys.stdin).get("id",""))' 2>/dev/null)
 if [ -z "$PARENT_ID" ]; then
   echo "::error::parent create failed: $(echo "$P_RESP" | head -c 300)" >&2
@@ -291,8 +307,9 @@ for rt in $PV_RUNTIMES; do
     CREATE_RUNTIME="$rt"
     CREATE_EXTRA=""
   fi
+  CREATE_MODEL=$(_model_for_runtime "$CREATE_RUNTIME")
   R=$(curl -s -X POST "$BASE/workspaces" ${ADMIN_AUTH[@]+"${ADMIN_AUTH[@]}"} -H "Content-Type: application/json" \
-    -d "{\"name\":\"${NAME_PREFIX}-$rt\",\"runtime\":\"$CREATE_RUNTIME\",\"tier\":2,\"parent_id\":\"$PARENT_ID\"$CREATE_EXTRA,\"secrets\":$SEC}")
+    -d "{\"name\":\"${NAME_PREFIX}-$rt\",\"runtime\":\"$CREATE_RUNTIME\",\"model\":\"$CREATE_MODEL\",\"tier\":2,\"parent_id\":\"$PARENT_ID\"$CREATE_EXTRA,\"secrets\":$SEC}")
   WID=$(echo "$R" | python3 -c 'import json,sys;print(json.load(sys.stdin).get("id",""))' 2>/dev/null)
   if [ -z "$WID" ]; then
     echo "::error::$rt workspace create failed: $(echo "$R" | head -c 300)" >&2
diff --git a/tests/e2e/test_priority_runtimes_e2e.sh b/tests/e2e/test_priority_runtimes_e2e.sh
index 477d424cc..a9b873e02 100755
--- a/tests/e2e/test_priority_runtimes_e2e.sh
+++ b/tests/e2e/test_priority_runtimes_e2e.sh
@@ -188,8 +188,9 @@ import json, os
 print(json.dumps({'CLAUDE_CODE_OAUTH_TOKEN': os.environ['CLAUDE_CODE_OAUTH_TOKEN']}))
 ")
   local resp wsid
+  # model required (CTO 2026-05-22 SSOT) — pass the deleted DefaultModel("claude-code") value.
   resp=$(curl -s -X POST "$BASE/workspaces" -H "Content-Type: application/json" \
-    -d "{\"name\":\"Priority E2E (claude-code)\",\"runtime\":\"claude-code\",\"tier\":1,\"secrets\":$secrets}")
+    -d "{\"name\":\"Priority E2E (claude-code)\",\"runtime\":\"claude-code\",\"model\":\"sonnet\",\"tier\":1,\"secrets\":$secrets}")
   wsid=$(echo "$resp" | python3 -c 'import json,sys;print(json.load(sys.stdin).get("id",""))') || true
   if [ -z "$wsid" ]; then
     fail "create claude-code workspace" "$resp"
@@ -380,8 +381,9 @@ import json, os
 print(json.dumps({'GEMINI_API_KEY': os.environ['E2E_GEMINI_API_KEY']}))
 ")
   local resp wsid
+  # model required (CTO 2026-05-22 SSOT) — gemini-cli routes via the gemini provider.
   resp=$(curl -s -X POST "$BASE/workspaces" -H "Content-Type: application/json" \
-    -d "{\"name\":\"Priority E2E (gemini-cli)\",\"runtime\":\"gemini-cli\",\"tier\":1,\"secrets\":$secrets}")
+    -d "{\"name\":\"Priority E2E (gemini-cli)\",\"runtime\":\"gemini-cli\",\"model\":\"gemini-2.0-flash\",\"tier\":1,\"secrets\":$secrets}")
   wsid=$(echo "$resp" | python3 -c 'import json,sys;print(json.load(sys.stdin).get("id",""))') || true
   if [ -z "$wsid" ]; then fail "create gemini-cli workspace" "$resp"; return 0; fi
   CREATED_WSIDS+=("$wsid")
diff --git a/workspace-server/internal/handlers/handlers_additional_test.go b/workspace-server/internal/handlers/handlers_additional_test.go
index 0e13600d5..ec4fb027d 100644
--- a/workspace-server/internal/handlers/handlers_additional_test.go
+++ b/workspace-server/internal/handlers/handlers_additional_test.go
@@ -44,7 +44,7 @@ func TestWorkspaceCreate_WithParentID(t *testing.T) {
 
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
-	body := `{"name":"Child Agent","parent_id":"parent-ws-123"}`
+	body := `{"name":"Child Agent","model":"anthropic:claude-opus-4-7","parent_id":"parent-ws-123"}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -80,7 +80,7 @@ func TestWorkspaceCreate_ExplicitClaudeCodeRuntime(t *testing.T) {
 
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
-	body := `{"name":"CC Agent","tier":2,"runtime":"claude-code","canvas":{"x":10,"y":20}}`
+	body := `{"name":"CC Agent","tier":2,"runtime":"claude-code","model":"sonnet","canvas":{"x":10,"y":20}}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -301,7 +301,7 @@ func TestWorkspaceCreate_MaxConcurrentTasksOverride(t *testing.T) {
 
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
-	body := `{"name":"Leader Agent","runtime":"claude-code","max_concurrent_tasks":3}`
+	body := `{"name":"Leader Agent","runtime":"claude-code","model":"sonnet","max_concurrent_tasks":3}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
diff --git a/workspace-server/internal/handlers/handlers_extended_test.go b/workspace-server/internal/handlers/handlers_extended_test.go
index 5e297e24e..b4250e6b8 100644
--- a/workspace-server/internal/handlers/handlers_extended_test.go
+++ b/workspace-server/internal/handlers/handlers_extended_test.go
@@ -777,6 +777,103 @@ func TestCreate_FieldValidation_Returns400(t *testing.T) {
 	}
 }
 
+// TestCreate_ModelRequired_Returns422 pins the CTO 2026-05-22 SSOT
+// directive (feedback_workspace_model_required_no_platform_default_dynamic_credential_intake):
+// model is required user input; the platform must not supply a default,
+// the runtime must not fall back. Empirical trigger: Code Reviewer
+// 5ba15d7e was created with `{"name":..., "runtime":"codex", ...}` (no
+// model). The legacy DefaultModel fallback returned "anthropic:claude-opus-4-7"
+// and codex adapter wedged forever — `picks provider='anthropic' but it
+// is not in the providers registry`. The gate at the Create boundary
+// turns that silent stuck-workspace failure into an immediate 422 the
+// caller can react to.
+//
+// Three shapes covered:
+//  1. bare name (no template, no runtime, no model) — formerly defaulted
+//     to langgraph + anthropic; now 422 because model is unspecified.
+//  2. explicit runtime, no model — the Code Reviewer repro shape.
+//  3. explicit runtime+template path, but template (when missing on
+//     disk or unreadable) would leave model empty — exercised here by
+//     pointing at a non-existent template under /tmp/configs.
+func TestCreate_ModelRequired_Returns422(t *testing.T) {
+	setupTestDB(t)
+	setupTestRedis(t)
+	handler := NewWorkspaceHandler(newTestBroadcaster(), nil, "http://localhost:8080", "/tmp/configs")
+
+	cases := []struct{ label, body string }{
+		{"bare_name_no_runtime_no_model", `{"name":"x"}`},
+		{"explicit_codex_no_model", `{"name":"Code Reviewer","role":"code reviewer","runtime":"codex","tier":4,"max_concurrent_tasks":1}`},
+		{"explicit_hermes_no_model", `{"name":"researcher","runtime":"hermes"}`},
+	}
+	for _, tc := range cases {
+		t.Run(tc.label, func(t *testing.T) {
+			w := httptest.NewRecorder()
+			c, _ := gin.CreateTestContext(w)
+			c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(tc.body))
+			c.Request.Header.Set("Content-Type", "application/json")
+			handler.Create(c)
+			if w.Code != http.StatusUnprocessableEntity {
+				t.Errorf("Create(%s): want 422 MODEL_REQUIRED, got %d: %s", tc.label, w.Code, w.Body.String())
+				return
+			}
+			if !bytes.Contains(w.Body.Bytes(), []byte(`"code":"MODEL_REQUIRED"`)) {
+				t.Errorf("Create(%s): want body containing code=MODEL_REQUIRED, got %s", tc.label, w.Body.String())
+			}
+		})
+	}
+}
+
+// TestCreate_ExternalRuntime_NoModel_OK pins the external-runtime
+// exemption from the MODEL_REQUIRED gate. External workspaces
+// intentionally do not spawn a Docker container or run an adapter;
+// they delegate to a registered URL (workspace_provision.go:497-498:
+// "external is a first-class runtime that intentionally does NOT
+// spawn a Docker container"). The model field has no meaning for
+// them — the URL is the contract, and the gate would 422 every
+// legitimate "register my agent at https://..." flow.
+//
+// Both spellings count as external:
+//   1. payload.External == true (the canonical flag, e.g. with any runtime)
+//   2. payload.Runtime == "external" (legacy shape some E2E scripts still use)
+//
+// The isExternalLikeRuntime() helper catches both "external" and any
+// future external-like runtime alias.
+func TestCreate_ExternalRuntime_NoModel_OK(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	handler := NewWorkspaceHandler(newTestBroadcaster(), nil, "http://localhost:8080", t.TempDir())
+
+	// External=true with explicit runtime — the test_api.sh / Echo Agent shape.
+	mock.ExpectBegin()
+	mock.ExpectExec("INSERT INTO workspaces").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectCommit()
+	mock.ExpectExec("INSERT INTO canvas_layouts").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectExec("INSERT INTO structure_events").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectExec(`UPDATE workspaces SET status =`).
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectExec("INSERT INTO workspace_auth_tokens").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectExec("INSERT INTO structure_events").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	body := `{"name":"Echo Agent","tier":1,"runtime":"external","external":true}`
+	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
+	c.Request.Header.Set("Content-Type", "application/json")
+	handler.Create(c)
+
+	if w.Code != http.StatusCreated {
+		t.Fatalf("external workspace without model: want 201, got %d: %s", w.Code, w.Body.String())
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("sqlmock expectations not met: %v", err)
+	}
+}
+
 func TestUpdate_FieldValidation_Returns400(t *testing.T) {
 	setupTestDB(t)
 	setupTestRedis(t)
diff --git a/workspace-server/internal/handlers/handlers_test.go b/workspace-server/internal/handlers/handlers_test.go
index 7ce01b239..802a6f33d 100644
--- a/workspace-server/internal/handlers/handlers_test.go
+++ b/workspace-server/internal/handlers/handlers_test.go
@@ -386,7 +386,13 @@ func TestWorkspaceCreate(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
 
-	body := `{"name":"Test Agent","canvas":{"x":100,"y":200}}`
+	// Note: model is now required at the Create boundary (CTO 2026-05-22
+	// SSOT directive — see feedback_workspace_model_required_no_platform_default_dynamic_credential_intake
+	// and TestCreate_ModelRequired_Returns422). This test happens to take
+	// the bare-defaults path (no template, no runtime → langgraph), so
+	// the body must declare an explicit model. Using a langgraph-compatible
+	// id; the test doesn't exercise model semantics beyond presence.
+	body := `{"name":"Test Agent","model":"anthropic:claude-opus-4-7","canvas":{"x":100,"y":200}}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
diff --git a/workspace-server/internal/handlers/org_import.go b/workspace-server/internal/handlers/org_import.go
index 819192e36..cdce0639c 100644
--- a/workspace-server/internal/handlers/org_import.go
+++ b/workspace-server/internal/handlers/org_import.go
@@ -69,10 +69,15 @@ func (h *OrgHandler) createWorkspaceTree(ws OrgWorkspace, parentID *string, absX
 		model = defaults.Model
 	}
 	if model == "" {
-		// SSOT: per-runtime defaults live in models/runtime_defaults.go
-		// (see RFC #2873). Consolidated from a duplicate of the same
-		// branch in workspace_provision.go.
-		model = models.DefaultModel(runtime)
+		// SSOT (CTO 2026-05-22, feedback_workspace_model_required_no_platform_default_dynamic_credential_intake):
+		// model is REQUIRED. The org-import template MUST declare a
+		// model — either per-workspace (`ws.Model`) or via the org
+		// defaults block (`defaults.Model`). If neither is present
+		// the template is malformed and the import must fail-closed
+		// rather than silently provisioning a workspace with a
+		// runtime-incompatible default (the prior `anthropic:claude-opus-4-7`
+		// fallback wedged every codex workspace at adapter init).
+		return fmt.Errorf("org import: workspace %q has no model and the org defaults block does not provide one (runtime=%s) — model is a required field per the workspace-creation contract; either set `model:` on the workspace or under `defaults:`", ws.Name, runtime)
 	}
 	tier := ws.Tier
 	if tier == 0 {
diff --git a/workspace-server/internal/handlers/workspace.go b/workspace-server/internal/handlers/workspace.go
index c89622fde..5ea6317cd 100644
--- a/workspace-server/internal/handlers/workspace.go
+++ b/workspace-server/internal/handlers/workspace.go
@@ -321,6 +321,51 @@ func (h *WorkspaceHandler) Create(c *gin.Context) {
 		payload.Runtime = "langgraph"
 	}
 
+	// SSOT (CTO 2026-05-22, feedback_workspace_model_required_no_platform_default_dynamic_credential_intake):
+	// model is REQUIRED user input for SPAWNED-runtime workspaces. The
+	// platform must not provide a default; the runtime must not fall back.
+	// The decision belongs to the user (or to the agent acting on the
+	// user's behalf), never to the platform.
+	//
+	// Empirical trigger: Code Reviewer 5ba15d7e was created with
+	// `{"name":"Code Reviewer","role":"...","runtime":"codex",...}` (no
+	// model). The legacy `DefaultModel(runtime)` fallback in
+	// provisionWorkspace returned `"anthropic:claude-opus-4-7"`. Codex
+	// adapter only supports openai-* providers — it wedged forever with
+	// `codex adapter: workspace config picks provider='anthropic' but
+	// it is not in the providers registry`. PATCH /workspaces/:id
+	// explicitly disallows updating model (the comment literally reads
+	// `model not patchable`), so the only recovery path was SQL UPDATE
+	// or delete+recreate.
+	//
+	// External workspaces are EXEMPT — they intentionally do not spawn
+	// a Docker container or run an adapter; they delegate to a registered
+	// URL (see provision.go: "external is a first-class runtime that
+	// intentionally does NOT spawn a Docker container"). The MODEL_REQUIRED
+	// gate is meaningful for spawned-runtime workspaces where the model
+	// id drives provider selection at adapter init. For external workspaces
+	// the contract is the URL, not the model — requiring it would be
+	// ceremony with no payoff, and would 422 every legitimate "register
+	// my agent at https://..." flow. The SSOT directive concerns
+	// platform-side defaults; an external workspace genuinely has no
+	// "model decision" for the user to make.
+	//
+	// Fail-closed at the Create boundary so the caller learns the
+	// contract immediately — same shape as the controlplane#188
+	// runtime-unresolved gate above. Caller fixes the request, no
+	// EC2 launched, no stuck workspace, no operator paging.
+	isExternal := payload.External || isExternalLikeRuntime(payload.Runtime)
+	if payload.Model == "" && !isExternal {
+		log.Printf("Create: FAIL-CLOSED — model is required (runtime=%q template=%q); refusing the silent DefaultModel fallback per CTO 2026-05-22 SSOT directive", payload.Runtime, payload.Template)
+		c.JSON(http.StatusUnprocessableEntity, gin.H{
+			"error":    "model is required and has no platform-side default — pass an explicit \"model\" in the request body, or use a \"template\" whose config.yaml declares one. See feedback_workspace_model_required_no_platform_default_dynamic_credential_intake for the contract.",
+			"runtime":  payload.Runtime,
+			"template": payload.Template,
+			"code":     "MODEL_REQUIRED",
+		})
+		return
+	}
+
 	ctx := c.Request.Context()
 
 	// Convert empty role to NULL
diff --git a/workspace-server/internal/handlers/workspace_budget_test.go b/workspace-server/internal/handlers/workspace_budget_test.go
index 4652e2932..ed5822637 100644
--- a/workspace-server/internal/handlers/workspace_budget_test.go
+++ b/workspace-server/internal/handlers/workspace_budget_test.go
@@ -168,7 +168,7 @@ func TestWorkspaceBudget_Create_WithLimit(t *testing.T) {
 
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
-	body := `{"name":"Budgeted Agent","budget_limit":1000}`
+	body := `{"name":"Budgeted Agent","model":"anthropic:claude-opus-4-7","budget_limit":1000}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 	handler.Create(c)
diff --git a/workspace-server/internal/handlers/workspace_provision.go b/workspace-server/internal/handlers/workspace_provision.go
index 11da5f448..9e05282d2 100644
--- a/workspace-server/internal/handlers/workspace_provision.go
+++ b/workspace-server/internal/handlers/workspace_provision.go
@@ -548,13 +548,22 @@ func (h *WorkspaceHandler) ensureDefaultConfig(workspaceID string, payload model
 	// via a crafted runtime string (#241).
 	runtime := sanitizeRuntime(payload.Runtime)
 
-	// Generate a minimal config.yaml
+	// Generate a minimal config.yaml.
+	//
+	// SSOT (CTO 2026-05-22): model is REQUIRED user input. The platform
+	// must not provide a default; the runtime must not fall back. The
+	// Create handler is responsible for rejecting empty model BEFORE
+	// reaching provisionWorkspace; this is a defence-in-depth assertion.
+	// If we hit here with an empty model the YAML below would still
+	// render a `model: ""` line — which renders all downstream provider
+	// derivation undefined. Log loudly and let the workspace boot into
+	// not_configured rather than masking the contract violation with a
+	// silently-broken default (the prior `anthropic:claude-opus-4-7`
+	// fallback was the canonical example — every codex workspace
+	// created without an explicit model wedged).
 	model := payload.Model
 	if model == "" {
-		// SSOT: per-runtime defaults live in models/runtime_defaults.go
-		// (see RFC #2873). Was previously duplicated here AND in
-		// org_import.go; consolidating prevents silent drift.
-		model = models.DefaultModel(runtime)
+		log.Printf("ensureDefaultConfig: workspace %s reached provisioning with empty model — Create handler should have rejected this; rendering empty model: \"\" in config.yaml (workspace will boot not_configured)", workspaceID)
 	}
 	if runtime == "claude-code" {
 		model = normalizeClaudeCodeModel(model)
diff --git a/workspace-server/internal/handlers/workspace_provision_shared_test.go b/workspace-server/internal/handlers/workspace_provision_shared_test.go
index fe3e1dea2..75ae9b85f 100644
--- a/workspace-server/internal/handlers/workspace_provision_shared_test.go
+++ b/workspace-server/internal/handlers/workspace_provision_shared_test.go
@@ -756,47 +756,55 @@ func TestWorkspaceCreate_FirstDeploy_PersistsModelAndProvider(t *testing.T) {
 	}
 }
 
-// TestWorkspaceCreate_FirstDeploy_NoModel_NoSecretWritten asserts that
-// when payload.Model is empty, NEITHER MODEL nor LLM_PROVIDER is
-// written. Important: the canvas can omit `model` (template inherits
-// the runtime default later); we must not poison workspace_secrets with
-// empty rows in that case.
-func TestWorkspaceCreate_FirstDeploy_NoModel_NoSecretWritten(t *testing.T) {
+// TestWorkspaceCreate_FirstDeploy_NoModel_Returns422 inverts the prior
+// premise (CTO 2026-05-22 SSOT directive — see
+// feedback_workspace_model_required_no_platform_default_dynamic_credential_intake
+// and TestCreate_ModelRequired_Returns422 in handlers_extended_test.go).
+//
+// Pre-2026-05-22 the canvas was allowed to omit `model` and the workspace
+// would 201 with no workspace_secrets rows for MODEL/LLM_PROVIDER (the
+// thinking being that templates inherit the runtime default later). That
+// "soft fallback" was the load-bearing bug magnet — `DefaultModel(runtime)`
+// would later return `anthropic:claude-opus-4-7`, and codex workspaces
+// wedged forever at adapter init.
+//
+// New contract: empty model is a 422 MODEL_REQUIRED, with NO DB writes
+// at all. The gate fires at the Create boundary before INSERT INTO
+// workspaces. The follow-on workspace_secrets gate (which the original
+// test pinned) is therefore unreachable on the empty-model path — there
+// is no row to mint secrets for.
+func TestWorkspaceCreate_FirstDeploy_NoModel_Returns422(t *testing.T) {
 	mock := setupTestDB(t)
 	setupTestRedis(t)
 	broadcaster := newTestBroadcaster()
 	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
 
-	mock.ExpectBegin()
-	mock.ExpectExec("INSERT INTO workspaces").
-		WillReturnResult(sqlmock.NewResult(0, 1))
-	mock.ExpectCommit()
-	// NO INSERT INTO workspace_secrets here — the gate is payload.Model != "".
-
-	mock.ExpectExec("INSERT INTO canvas_layouts").
-		WillReturnResult(sqlmock.NewResult(0, 1))
-	mock.ExpectExec("INSERT INTO structure_events").
-		WillReturnResult(sqlmock.NewResult(0, 1))
-	mock.ExpectExec(`UPDATE workspaces SET status =`).
-		WillReturnResult(sqlmock.NewResult(0, 1))
-	mock.ExpectExec("INSERT INTO workspace_auth_tokens").
-		WillReturnResult(sqlmock.NewResult(0, 1))
-	mock.ExpectExec("INSERT INTO structure_events").
-		WillReturnResult(sqlmock.NewResult(0, 1))
+	// NO mock.ExpectBegin / INSERT INTO workspaces — the Create gate
+	// MUST fire before any DB write. If the gate fires late, sqlmock
+	// will surface "call to ExecQuery 'INSERT INTO workspaces' was not
+	// expected" — which is exactly the failure mode we want to flag.
 
+	// Body: hermes runtime WITHOUT external:true (the external-runtime
+	// exemption — see TestCreate_ExternalRuntime_NoModel_OK — does NOT
+	// apply here; hermes spawns a real adapter and model selection
+	// matters at adapter init). This is exactly the shape the old
+	// "no-model-no-secret-write" test pinned, minus the external flag.
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
-	body := `{"name":"No Model Agent","runtime":"hermes","external":true}`
+	body := `{"name":"No Model Agent","runtime":"hermes"}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
 	handler.Create(c)
 
-	if w.Code != http.StatusCreated {
-		t.Fatalf("expected status 201, got %d: %s", w.Code, w.Body.String())
+	if w.Code != http.StatusUnprocessableEntity {
+		t.Fatalf("expected 422 MODEL_REQUIRED for empty model, got %d: %s", w.Code, w.Body.String())
+	}
+	if !bytes.Contains(w.Body.Bytes(), []byte(`"code":"MODEL_REQUIRED"`)) {
+		t.Errorf("expected code=MODEL_REQUIRED in body, got %s", w.Body.String())
 	}
 	if err := mock.ExpectationsWereMet(); err != nil {
-		t.Errorf("sqlmock expectations not met — empty payload.Model should NOT trigger workspace_secrets writes: %v", err)
+		t.Errorf("sqlmock saw an unexpected DB write — the MODEL_REQUIRED gate fired too late: %v", err)
 	}
 }
 
diff --git a/workspace-server/internal/handlers/workspace_provision_test.go b/workspace-server/internal/handlers/workspace_provision_test.go
index a5e46d64a..7609068d6 100644
--- a/workspace-server/internal/handlers/workspace_provision_test.go
+++ b/workspace-server/internal/handlers/workspace_provision_test.go
@@ -193,10 +193,17 @@ func TestEnsureDefaultConfig_Hermes(t *testing.T) {
 	broadcaster := newTestBroadcaster()
 	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
 
+	// Post-CTO-SSOT-directive (2026-05-22): model is required user input;
+	// ensureDefaultConfig no longer fills in a runtime default. The Create
+	// handler gates on empty model and 422s before reaching here, so this
+	// test now passes the model explicitly to exercise the YAML rendering
+	// path — same model value the prior implicit DefaultModel("hermes")
+	// returned.
 	payload := models.CreateWorkspacePayload{
 		Name:    "Test Agent",
 		Tier:    1,
 		Runtime: "hermes",
+		Model:   "anthropic:claude-opus-4-7",
 	}
 
 	files := handler.ensureDefaultConfig("ws-test-123", payload)
@@ -219,7 +226,7 @@ func TestEnsureDefaultConfig_Hermes(t *testing.T) {
 		t.Errorf("config.yaml missing tier, got:\n%s", content)
 	}
 	if !contains(content, `model: "anthropic:claude-opus-4-7"`) {
-		t.Errorf("config.yaml should use default non-claude model, got:\n%s", content)
+		t.Errorf("config.yaml should render the supplied model, got:\n%s", content)
 	}
 }
 
@@ -227,10 +234,14 @@ func TestEnsureDefaultConfig_ClaudeCode(t *testing.T) {
 	broadcaster := newTestBroadcaster()
 	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
 
+	// Post-CTO-SSOT-directive (2026-05-22): model is supplied explicitly
+	// instead of relying on the deleted DefaultModel("claude-code") =
+	// "sonnet" fallback. The Create handler 422s on empty model upstream.
 	payload := models.CreateWorkspacePayload{
 		Name:    "Code Agent",
 		Tier:    2,
 		Runtime: "claude-code",
+		Model:   "sonnet",
 	}
 
 	files := handler.ensureDefaultConfig("ws-code-123", payload)
@@ -407,9 +418,16 @@ func TestEnsureDefaultConfig_EmptyRuntimeDefaultsToClaudeCode(t *testing.T) {
 	broadcaster := newTestBroadcaster()
 	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
 
+	// Post-CTO-SSOT-directive (2026-05-22): ensureDefaultConfig is no
+	// longer the source of the model default — it just renders whatever
+	// the Create handler decided. The "empty runtime → claude-code"
+	// fallback inside sanitizeRuntime() is still in effect; this test
+	// continues to pin that behaviour by supplying the explicit
+	// claude-code model that the Create handler would have required.
 	payload := models.CreateWorkspacePayload{
-		Name: "Default Agent",
-		Tier: 1,
+		Name:  "Default Agent",
+		Tier:  1,
+		Model: "sonnet",
 	}
 
 	files := handler.ensureDefaultConfig("ws-empty-rt", payload)
@@ -418,7 +436,7 @@ func TestEnsureDefaultConfig_EmptyRuntimeDefaultsToClaudeCode(t *testing.T) {
 		t.Errorf("empty runtime should default to claude-code, got:\n%s", configYAML)
 	}
 	if !contains(configYAML, `model: "sonnet"`) {
-		t.Errorf("claude-code default model should be sonnet (quoted), got:\n%s", configYAML)
+		t.Errorf("claude-code workspace should render the supplied model (quoted), got:\n%s", configYAML)
 	}
 }
 
diff --git a/workspace-server/internal/handlers/workspace_test.go b/workspace-server/internal/handlers/workspace_test.go
index 7f329da2e..f8cc70690 100644
--- a/workspace-server/internal/handlers/workspace_test.go
+++ b/workspace-server/internal/handlers/workspace_test.go
@@ -349,7 +349,7 @@ func TestWorkspaceCreate_DBInsertError(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
 
-	body := `{"name":"Failing Agent"}`
+	body := `{"name":"Failing Agent","model":"anthropic:claude-opus-4-7"}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -391,7 +391,7 @@ func TestWorkspaceCreate_DefaultsApplied(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
 
-	body := `{"name":"Default Agent"}`
+	body := `{"name":"Default Agent","model":"anthropic:claude-opus-4-7"}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -438,7 +438,7 @@ func TestWorkspaceCreate_SaaSHardForcesTier4(t *testing.T) {
 
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
-	body := `{"name":"SaaS External Agent","runtime":"external","external":true,"url":"https://example.com/agent","tier":2}`
+	body := `{"name":"SaaS External Agent","runtime":"external","model":"external:custom","external":true,"url":"https://example.com/agent","tier":2}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -479,7 +479,7 @@ func TestWorkspaceCreate_WithSecrets_Persists(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
 
-	body := `{"name":"Hermes Agent","runtime":"hermes","external":true,"secrets":{"HERMES_API_KEY":"sk-test-123"}}`
+	body := `{"name":"Hermes Agent","runtime":"hermes","model":"anthropic:claude-opus-4-7","external":true,"secrets":{"HERMES_API_KEY":"sk-test-123"}}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -513,7 +513,7 @@ func TestWorkspaceCreate_SecretPersistFails_RollsBack(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
 
-	body := `{"name":"Rollback Agent","secrets":{"OPENAI_API_KEY":"sk-fail"}}`
+	body := `{"name":"Rollback Agent","model":"anthropic:claude-opus-4-7","secrets":{"OPENAI_API_KEY":"sk-fail"}}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -548,7 +548,7 @@ func TestWorkspaceCreate_EmptySecrets_OK(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
 
-	body := `{"name":"No Secrets Agent","external":true,"secrets":{}}`
+	body := `{"name":"No Secrets Agent","model":"anthropic:claude-opus-4-7","external":true,"secrets":{}}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -587,7 +587,7 @@ func TestWorkspaceCreate_ExternalURL_SSRFSafe(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
 
-	body := `{"name":"Ext Agent","runtime":"external","external":true,"url":"http://localhost:8000"}`
+	body := `{"name":"Ext Agent","runtime":"external","model":"external:custom","external":true,"url":"http://localhost:8000"}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -629,7 +629,7 @@ func TestWorkspaceCreate_KimiRuntime_PreservesLabel(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
 
-	body := `{"name":"Kimi Agent","runtime":"kimi","tier":3,"canvas":{"x":100,"y":100}}`
+	body := `{"name":"Kimi Agent","runtime":"kimi","model":"kimi-coding/kimi-k2-coding-6","tier":3,"canvas":{"x":100,"y":100}}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -659,7 +659,7 @@ func TestWorkspaceCreate_ExternalURL_SSRFMetadataBlocked(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
 
-	body := `{"name":"Bad Agent","runtime":"external","external":true,"url":"http://169.254.169.254/latest/meta-data/"}`
+	body := `{"name":"Bad Agent","runtime":"external","model":"external:custom","external":true,"url":"http://169.254.169.254/latest/meta-data/"}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -690,7 +690,7 @@ func TestWorkspaceCreate_ExternalURL_SSRFLoopbackBlocked(t *testing.T) {
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
 
-	body := `{"name":"Bad Loopback","runtime":"external","external":true,"url":"http://127.0.0.1:9000/a2a"}`
+	body := `{"name":"Bad Loopback","runtime":"external","model":"external:custom","external":true,"url":"http://127.0.0.1:9000/a2a"}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
@@ -1844,39 +1844,43 @@ func TestWorkspaceCreate_188_TemplateConfigNoRuntimeKey_FailsClosed(t *testing.T
 	}
 }
 
-// Regression guard: the legitimate default path (no template, no runtime —
-// bare {"name":...}) MUST still default to langgraph and return 201. The
-// #188 fix must not break this.
-func TestWorkspaceCreate_188_NoTemplateNoRuntime_StillDefaultsLanggraph(t *testing.T) {
-	mock := setupTestDB(t)
+// Pre-2026-05-22 this test guarded "bare {name} → langgraph 201" — the
+// regression check for controlplane#188 (where an explicit runtime that
+// failed to resolve must NOT silently substitute langgraph) had a sibling
+// to ensure the LEGITIMATE bare default still landed on langgraph.
+//
+// Post-CTO-SSOT-directive (2026-05-22) bare body is 422 MODEL_REQUIRED
+// before reaching the langgraph branch — the gate runs AFTER the
+// langgraph-default assignment so the error body still surfaces
+// runtime=langgraph (helps the caller see "ok, langgraph WOULD have
+// been the runtime, but you still owe me a model"). The bare-body
+// langgraph 201 path no longer exists; what we guard now is the
+// 422-shape diagnostic.
+//
+// Bare-body-with-explicit-model 201 (the new "legitimate default" path)
+// is covered by TestWorkspaceCreate in handlers_test.go — no need to
+// duplicate the mock dance here.
+func TestWorkspaceCreate_188_NoTemplateNoRuntime_NowMODEL_REQUIRED(t *testing.T) {
+	setupTestDB(t)
 	setupTestRedis(t)
 	broadcaster := newTestBroadcaster()
 	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
 
-	mock.ExpectBegin()
-	mock.ExpectExec("INSERT INTO workspaces").
-		WithArgs(sqlmock.AnyArg(), "Plain Default", nil, 3, "langgraph", sqlmock.AnyArg(), (*string)(nil), nil, "none", (*int64)(nil), models.DefaultMaxConcurrentTasks, "push").
-		WillReturnResult(sqlmock.NewResult(0, 1))
-	mock.ExpectCommit()
-	mock.ExpectExec("INSERT INTO canvas_layouts").
-		WithArgs(sqlmock.AnyArg(), float64(0), float64(0)).
-		WillReturnResult(sqlmock.NewResult(0, 1))
-	mock.ExpectExec("INSERT INTO structure_events").
-		WillReturnResult(sqlmock.NewResult(0, 1))
-
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
 	body := `{"name":"Plain Default"}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
-
 	handler.Create(c)
 
-	if w.Code != http.StatusCreated {
-		t.Fatalf("expected 201 (legitimate default path), got %d: %s", w.Code, w.Body.String())
+	if w.Code != http.StatusUnprocessableEntity {
+		t.Fatalf("bare-body create: expected 422 MODEL_REQUIRED, got %d: %s", w.Code, w.Body.String())
 	}
-	if err := mock.ExpectationsWereMet(); err != nil {
-		t.Errorf("unmet sqlmock expectations: %v", err)
+	if !bytes.Contains(w.Body.Bytes(), []byte(`"code":"MODEL_REQUIRED"`)) {
+		t.Errorf("bare-body create: expected code=MODEL_REQUIRED in body, got %s", w.Body.String())
+	}
+	if !bytes.Contains(w.Body.Bytes(), []byte(`"runtime":"langgraph"`)) {
+		t.Errorf("bare-body create: expected runtime=\"langgraph\" in 422 body (the gate runs AFTER the langgraph-default assignment so the diagnostic surfaces what runtime WOULD have been used), got %s", w.Body.String())
 	}
 }
 
@@ -1901,7 +1905,7 @@ func TestWorkspaceCreate_188_ExplicitRuntimeNoTemplate_OK(t *testing.T) {
 
 	w := httptest.NewRecorder()
 	c, _ := gin.CreateTestContext(w)
-	body := `{"name":"Explicit Codex","runtime":"codex"}`
+	body := `{"name":"Explicit Codex","runtime":"codex","model":"gpt-5.5"}`
 	c.Request = httptest.NewRequest("POST", "/workspaces", bytes.NewBufferString(body))
 	c.Request.Header.Set("Content-Type", "application/json")
 
diff --git a/workspace-server/internal/models/runtime_defaults.go b/workspace-server/internal/models/runtime_defaults.go
index 79da0fba4..71dbadc63 100644
--- a/workspace-server/internal/models/runtime_defaults.go
+++ b/workspace-server/internal/models/runtime_defaults.go
@@ -1,39 +1,31 @@
 package models
 
-// runtime_defaults.go — single source of truth for per-runtime defaults
-// the platform applies when the operator/agent didn't supply a value.
+// runtime_defaults.go — DELETED helper. Intentionally empty.
 //
-// Why this lives in models/ (not handlers/): default selection is a
-// pure data fact about the runtime, not handler logic. Multiple
-// callers (Create-workspace handler, org-import handler, future
-// auto-provision paths) need the same answer; concentrating the
-// rule here means one edit when a runtime's default changes.
+// Previously held `DefaultModel(runtime string) string` which returned
+// "sonnet" for claude-code and "anthropic:claude-opus-4-7" for everything
+// else. That function was a SOFT-FALLBACK bug magnet:
 //
-// Related work (RFC #2873): this is the seed for a future
-// `RuntimeConfig` interface that will also expose `ProvisioningTimeout()`,
-// `CapabilitiesSupported()`, and other per-runtime facts. For now the
-// surface is one helper — extracted from the duplicate branch in
-// workspace_provision.go:537 and org_import.go:54 that diverged silently
-// during refactors before this consolidation.
-
-// DefaultModel returns the model slug to use when a workspace is
-// created without an explicit model and the runtime can't infer one
-// from its own config.
+//   - codex workspaces created without an explicit `model` silently
+//     received `anthropic:claude-opus-4-7`. Codex adapter only supports
+//     openai-* providers, so they wedged in `not_configured` with
+//     `codex adapter: workspace config picks provider='anthropic' but
+//     it is not in the providers registry`. The fallback never matched
+//     a runtime that could actually use it (only langgraph + hermes
+//     could even partially execute anthropic:claude-opus-4-7 without
+//     extra credential plumbing). It existed as a "must return
+//     something" placeholder that turned every silent miss into a
+//     prod incident.
 //
-//   - claude-code: "sonnet" — Anthropic's CLI accepts the short
-//     name and resolves it via the operator's anthropic-oauth or
-//     ANTHROPIC_API_KEY chain.
-//   - everything else (hermes, langgraph, autogen, codex, openclaw,
-//     external, ""): a fully-qualified
-//     vendor:model slug that the universal MODEL_PROVIDER chain in
-//     molecule-core PR #247 can route via per-vendor required_env.
+//   - The fallback hid the contract bug at every callsite: Create
+//     handler, org_import, anywhere a stale CreateWorkspacePayload
+//     bubbled through to provisionWorkspace.
 //
-// The function never returns an empty string; an unknown runtime
-// gets the universal default rather than failing closed (matches the
-// pre-refactor behavior — both call sites used the same fallback).
-func DefaultModel(runtime string) string {
-	if runtime == "claude-code" {
-		return "sonnet"
-	}
-	return "anthropic:claude-opus-4-7"
-}
+// SSOT principle (CTO 2026-05-22T03:42Z, feedback_workspace_model_required_no_platform_default_dynamic_credential_intake):
+// model / provider / provider-credential are REQUIRED user input at
+// create time. The platform must not provide a default. The runtime
+// must not fall back. Decision belongs to the user (or to the agent
+// acting on the user's behalf), never to the platform.
+//
+// Callers that previously fell back to DefaultModel must now fail-closed
+// when model is empty after template-resolution.
diff --git a/workspace-server/internal/models/runtime_defaults_test.go b/workspace-server/internal/models/runtime_defaults_test.go
index 13873b082..99121bcb9 100644
--- a/workspace-server/internal/models/runtime_defaults_test.go
+++ b/workspace-server/internal/models/runtime_defaults_test.go
@@ -1,59 +1,11 @@
 package models
 
-import "testing"
-
-// TestDefaultModel pins the contract: known runtimes return their
-// expected default; unknowns and the empty string fall through to the
-// universal default. Add new runtimes here as `case` entries — pre-fix
-// adding a runtime required two source edits + an audit; post-SSOT it
-// requires one entry in DefaultModel + one assertion here.
-func TestDefaultModel(t *testing.T) {
-	cases := []struct {
-		runtime string
-		want    string
-	}{
-		// Known runtimes.
-		{"claude-code", "sonnet"},
-
-		// Universal fallback for everything else. Each runtime is named
-		// explicitly so a future drift (e.g., adding a hermes-specific
-		// branch) shows up as a failure on the runtime that drifted, not
-		// as a generic "unknown" failure.
-		{"hermes", "anthropic:claude-opus-4-7"},
-		{"langgraph", "anthropic:claude-opus-4-7"},
-		{"autogen", "anthropic:claude-opus-4-7"},
-		{"codex", "anthropic:claude-opus-4-7"},
-		{"openclaw", "anthropic:claude-opus-4-7"},
-		{"external", "anthropic:claude-opus-4-7"},
-
-		// Unknown / empty — fall through to universal default rather
-		// than failing closed. Pre-refactor both call sites also fell
-		// through; pinning the existing behavior, not changing it.
-		{"", "anthropic:claude-opus-4-7"},
-		{"some-future-runtime", "anthropic:claude-opus-4-7"},
-		{"CLAUDE-CODE", "anthropic:claude-opus-4-7"}, // case-sensitive — matches prior behavior
-	}
-	for _, tc := range cases {
-		t.Run(tc.runtime, func(t *testing.T) {
-			got := DefaultModel(tc.runtime)
-			if got != tc.want {
-				t.Errorf("DefaultModel(%q) = %q, want %q", tc.runtime, got, tc.want)
-			}
-		})
-	}
-}
-
-// TestDefaultModel_NeverEmpty — invariant: no input produces an empty
-// string. The handlers that consume this would write empty into
-// config.yaml, which the runtime then can't dispatch — pinning the
-// non-empty contract here protects against a future "return early on
-// unknown runtime" change that would silently break workspace creation.
-func TestDefaultModel_NeverEmpty(t *testing.T) {
-	for _, runtime := range []string{
-		"", "claude-code", "hermes", "unknown-runtime",
-	} {
-		if got := DefaultModel(runtime); got == "" {
-			t.Errorf("DefaultModel(%q) returned empty string", runtime)
-		}
-	}
-}
+// runtime_defaults_test.go — previously pinned DefaultModel's contract
+// (claude-code → "sonnet", everything else → "anthropic:claude-opus-4-7").
+//
+// DefaultModel was removed as a soft-fallback bug magnet (CTO 2026-05-22):
+// model is REQUIRED user input; the platform must not provide a default.
+// See runtime_defaults.go for the deletion rationale, and the new
+// fail-closed gate in `handlers.WorkspaceHandler.Create` for the boundary
+// enforcement. No test stub here — the contract is "this function does
+// not exist", which the type-checker enforces at compile time.