fix(cli): --tui -model reaches the TUI

cmd/harnesscli/main.go

@@ -176,7 +176,7 @@ func run(args []string) int {
 	workspacePath := resolveWorkspacePath(*workspace)
 
 	if *enableTUI {
-		if err := runTUI(*baseURL, workspacePath, *resume, *planMode); err != nil {
+		if err := runTUI(*baseURL, workspacePath, *resume, *model, *planMode); err != nil {
 			fmt.Fprintf(stderr, "harnesscli: tui: %v\n", err)
 			return exitClientError
 		}
@@ -535,7 +535,13 @@ func resolveWorkspacePath(workspace string) string {
 	return workspacePath
 }
 
-func newTUIConfig(baseURL, workspace, resumeConversationID string) tui.TUIConfig {
+// newTUIConfig assembles the TUI's configuration.
+//
+// model is the explicitly requested model (the -model flag) and may be empty.
+// Empty is meaningful: it lets the model remembered from the last session
+// (issue #1424) apply, and failing that the daemon default. A non-empty value
+// outranks both — a flag is an instruction, not a preference. Issue #1426.
+func newTUIConfig(baseURL, workspace, resumeConversationID, model string) tui.TUIConfig {
 	// Default to auto-detection; HARNESS_COLOR_PROFILE overrides (truecolor, 256,
 	// ansi, none). Resolved and applied in runTUI before the program starts.
 	colorProfile := strings.TrimSpace(os.Getenv("HARNESS_COLOR_PROFILE"))
@@ -568,14 +574,15 @@ func newTUIConfig(baseURL, workspace, resumeConversationID string) tui.TUIConfig
 		ResumeConversationID: resumeConversationID,
 		APIKey:               apiKey,
 		Theme:                themeName,
+		Model:                model,
 	}
 }
 
-func runTUI(baseURL, workspace, resumeConversationID string, planMode bool) error {
+func runTUI(baseURL, workspace, resumeConversationID, model string, planMode bool) error {
 	if !term.IsTerminal(int(os.Stdout.Fd())) {
 		return fmt.Errorf("--tui requires a terminal; pipe output or use without --tui for streaming mode")
 	}
-	tuiCfg := newTUIConfig(baseURL, workspace, resumeConversationID)
+	tuiCfg := newTUIConfig(baseURL, workspace, resumeConversationID, model)
 	tuiCfg.PlanMode = planMode
 	// Resolve and apply the color profile to the renderer before building the
 	// model, and store the effective profile back for accurate display.

cmd/harnesscli/main_test.go

@@ -184,7 +184,7 @@ func TestRunCreatesAndStreamsToCompletion(t *testing.T) {
 }
 
 func TestNewTUIConfigIncludesWorkspace(t *testing.T) {
-	cfg := newTUIConfig("http://127.0.0.1:8080", "/tmp/tui-project", "")
+	cfg := newTUIConfig("http://127.0.0.1:8080", "/tmp/tui-project", "", "")
 	if cfg.BaseURL != "http://127.0.0.1:8080" {
 		t.Fatalf("BaseURL = %q", cfg.BaseURL)
 	}
@@ -200,7 +200,7 @@ func TestNewTUIConfigIncludesWorkspace(t *testing.T) {
 }
 
 func TestNewTUIConfigIncludesResumeConversationID(t *testing.T) {
-	cfg := newTUIConfig("http://127.0.0.1:8080", "/tmp/tui-project", "conv-resume-42")
+	cfg := newTUIConfig("http://127.0.0.1:8080", "/tmp/tui-project", "conv-resume-42", "")
 	if cfg.ResumeConversationID != "conv-resume-42" {
 		t.Fatalf("ResumeConversationID = %q, want %q", cfg.ResumeConversationID, "conv-resume-42")
 	}
@@ -328,7 +328,7 @@ func TestNewTUIConfigLoadsSavedTheme(t *testing.T) {
 		t.Fatalf("config.Save: %v", err)
 	}
 
-	cfg := newTUIConfig("http://127.0.0.1:8080", "/tmp/tui-project", "")
+	cfg := newTUIConfig("http://127.0.0.1:8080", "/tmp/tui-project", "", "")
 	if cfg.Theme != "ocean" {
 		t.Errorf("TUIConfig.Theme = %q, want %q", cfg.Theme, "ocean")
 	}
@@ -339,8 +339,39 @@ func TestNewTUIConfigLoadsSavedTheme(t *testing.T) {
 func TestNewTUIConfigNoSavedThemeIsEmpty(t *testing.T) {
 	t.Setenv("HOME", t.TempDir())
 
-	cfg := newTUIConfig("http://127.0.0.1:8080", "/tmp/tui-project", "")
+	cfg := newTUIConfig("http://127.0.0.1:8080", "/tmp/tui-project", "", "")
 	if cfg.Theme != "" {
 		t.Errorf("TUIConfig.Theme = %q, want empty", cfg.Theme)
 	}
 }
+
+// TestNewTUIConfigCarriesExplicitModel pins issue #1426: an explicitly
+// requested model must reach the TUI.
+//
+// `harnesscli --tui -model X` parsed the flag and threw it away, so the TUI
+// started on the daemon default or — after #1424 — on the remembered model,
+// which is precisely the thing a user passing -model is trying to override.
+//
+// runTUI itself cannot be unit tested (it requires a terminal), so this is the
+// closest honest seam: the point where the flag's value becomes TUIConfig.Model.
+func TestNewTUIConfigCarriesExplicitModel(t *testing.T) {
+	cfg := newTUIConfig("http://127.0.0.1:8080", "/tmp/tui-project", "", "gpt-4.1-mini")
+
+	if cfg.Model != "gpt-4.1-mini" {
+		t.Fatalf("TUIConfig.Model = %q, want %q; an explicitly requested model must reach the TUI",
+			cfg.Model, "gpt-4.1-mini")
+	}
+}
+
+// TestNewTUIConfigWithoutModelLeavesItEmpty is the control. Empty must stay
+// empty: it is what lets the remembered model (#1424) and then the daemon
+// default apply. A fix that defaulted to some model would satisfy the test
+// above and silently break both.
+func TestNewTUIConfigWithoutModelLeavesItEmpty(t *testing.T) {
+	cfg := newTUIConfig("http://127.0.0.1:8080", "/tmp/tui-project", "", "")
+
+	if cfg.Model != "" {
+		t.Fatalf("TUIConfig.Model = %q, want empty so the remembered model and daemon default still apply",
+			cfg.Model)
+	}
+}

cmd/harnesscli/main_tui_test.go

@@ -13,7 +13,7 @@ func TestRunTUIRequiresTerminal(t *testing.T) {
 		t.Skip("stdout is a terminal in this environment")
 	}
 
-	err := runTUI("http://localhost:8080", "/tmp/project", "", false)
+	err := runTUI("http://localhost:8080", "/tmp/project", "", "", false)
 	if err == nil {
 		t.Fatal("expected non-terminal runTUI call to fail")
 	}

docs/logs/engineering-log.md

@@ -1,5 +1,33 @@
 # Engineering Log
 
+## 2026-09-08 — Issue #1426 --tui -model reaches the TUI
+
+- Symptom: `harnesscli --tui -model X` parsed the flag and threw it away. The
+  TUI started on the daemon default or, after #1424, on the remembered model —
+  which is precisely what a user passing `-model` is trying to override. No
+  warning, no error: the flag was silently discarded.
+- Cause: `main.go:179` called `runTUI(*baseURL, workspacePath, *resume,
+  *planMode)`. `*model` was never among the arguments, and `newTUIConfig` never
+  set `TUIConfig.Model`. The non-TUI path (`main.go:216`) passed the flag
+  correctly all along, so the defect was confined to the TUI branch.
+- Fix: `model` threaded from the dispatch through `runTUI` into
+  `newTUIConfig`, following the route `planMode` already takes. Nothing in the
+  TUI changed — `selectedModel: cfg.Model` and #1424's `cfg.Model == ""` guard
+  were already correct and simply had no producer of a non-empty value.
+- Precedence, now real: flag, then the model remembered from last session, then
+  the daemon default. The flag deliberately does **not** write to
+  `~/.config/harnesscli/config.json`: a flag is a one-off instruction, not a
+  preference, and silently rewriting the saved model would be a worse bug than
+  the one being fixed.
+- Tests: `TestNewTUIConfigCarriesExplicitModel` and, as its control,
+  `TestNewTUIConfigWithoutModelLeavesItEmpty` — empty must stay empty, or a fix
+  that defaulted to some model would pass the first test while breaking #1424.
+  `runTUI` itself requires a terminal and cannot be unit tested, so
+  `newTUIConfig` is the closest honest seam; the consumer half is already
+  covered by `TestExplicitModelBeatsRememberedModel` in the `tui` package.
+  Neither test alone proves the flag works — producer and consumer are pinned
+  separately and meet only in the live check.
+
 ## 2026-09-08 — Issue #1424 remember the last used model
 
 - Symptom: the TUI forgot the model you picked. `/model`, quit, restart, and you
@@ -36,9 +64,9 @@
   test suite into something that mutates the developer's machine. When making
   anything persistent, check what the tests write before checking what the
   feature reads.
-- Noted, not fixed: `runTUI` never receives the `-model` flag, so
-  `harnesscli --tui -model X` ignores it today. Separate defect; the precedence
-  guard above is written so wiring it needs no further change here.
+- Noted, not fixed here: `runTUI` never receives the `-model` flag, so
+  `harnesscli --tui -model X` ignored it. Filed as #1426 and fixed there; the
+  precedence guard above needed no change, exactly as predicted.
 
 ## 2026-09-08 — Issue #1422 interrupt test flake, and a diagnosis that was wrong twice