fix(pi): pass configured model to launch commands

backend/internal/adapters/agent/pi/pi.go

@@ -74,9 +74,25 @@ func (p *Plugin) Manifest() adapters.Manifest {
 	}
 }
 
+// GetConfigSpec reports the per-project agent config keys Pi understands.
+func (p *Plugin) GetConfigSpec(ctx context.Context) (ports.ConfigSpec, error) {
+	if err := ctx.Err(); err != nil {
+		return ports.ConfigSpec{}, err
+	}
+	return ports.ConfigSpec{
+		Fields: []ports.ConfigField{
+			{
+				Key:         "model",
+				Type:        ports.ConfigFieldString,
+				Description: "Model override passed to `pi --model`.",
+			},
+		},
+	}, nil
+}
+
 // GetLaunchCommand builds the argv to start a new interactive Pi session:
 //
-//	pi [--append-system-prompt <system prompt>] [<prompt>]
+//	pi [--append-system-prompt <system prompt>] [--model <model>] [<prompt>]
 //
 // The prompt is delivered in-command as a trailing positional message. Pi does
 // not honor a `--` options terminator, so the prompt must not begin with "-".
@@ -97,6 +113,7 @@ func (p *Plugin) GetLaunchCommand(ctx context.Context, cfg ports.LaunchConfig) (
 		}
 		cmd = append(cmd, "--append-system-prompt", string(data))
 	}
+	appendModelFlag(&cmd, cfg.Config)
 	if cfg.Prompt != "" {
 		cmd = append(cmd, cfg.Prompt)
 	}
@@ -130,10 +147,17 @@ func (p *Plugin) GetRestoreCommand(ctx context.Context, cfg ports.RestoreConfig)
 		}
 		cmd = append(cmd, "--append-system-prompt", string(data))
 	}
+	appendModelFlag(&cmd, cfg.Config)
 	cmd = append(cmd, "--session", agentSessionID)
 	return cmd, true, nil
 }
 
+func appendModelFlag(cmd *[]string, cfg ports.AgentConfig) {
+	if model := strings.TrimSpace(cfg.Model); model != "" {
+		*cmd = append(*cmd, "--model", model)
+	}
+}
+
 var piBinarySpec = binaryutil.BinarySpec{
 	Label:         "pi",
 	Names:         []string{"pi"},

backend/internal/adapters/agent/pi/pi_test.go

@@ -32,13 +32,20 @@ func TestManifest(t *testing.T) {
 	}
 }
 
-func TestGetConfigSpecEmpty(t *testing.T) {
+func TestGetConfigSpecReportsModelField(t *testing.T) {
 	spec, err := (&Plugin{}).GetConfigSpec(context.Background())
 	if err != nil {
 		t.Fatalf("err: %v", err)
 	}
-	if len(spec.Fields) != 0 {
-		t.Fatalf("expected no fields, got %d", len(spec.Fields))
+	want := []ports.ConfigField{
+		{
+			Key:         "model",
+			Type:        ports.ConfigFieldString,
+			Description: "Model override passed to `pi --model`.",
+		},
+	}
+	if !reflect.DeepEqual(spec.Fields, want) {
+		t.Fatalf("config fields\nwant: %#v\n got: %#v", want, spec.Fields)
 	}
 }
 
@@ -68,6 +75,38 @@ func TestGetLaunchCommandWorkerWithPromptIsInteractive(t *testing.T) {
 	}
 }
 
+func TestGetLaunchCommandAppendsConfiguredModelBeforePrompt(t *testing.T) {
+	p := &Plugin{resolvedBinary: "pi"}
+	cmd, err := p.GetLaunchCommand(context.Background(), ports.LaunchConfig{
+		Config:       ports.AgentConfig{Model: "  openai/gpt-4o  "},
+		SystemPrompt: "follow repo rules",
+		Prompt:       "add a health check",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	want := []string{"pi", "--append-system-prompt", "follow repo rules", "--model", "openai/gpt-4o", "add a health check"}
+	if !reflect.DeepEqual(cmd, want) {
+		t.Fatalf("cmd = %#v, want %#v", cmd, want)
+	}
+}
+
+func TestGetLaunchCommandOmitsBlankConfiguredModel(t *testing.T) {
+	p := &Plugin{resolvedBinary: "pi"}
+	cmd, err := p.GetLaunchCommand(context.Background(), ports.LaunchConfig{
+		Config: ports.AgentConfig{Model: " \t "},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	want := []string{"pi"}
+	if !reflect.DeepEqual(cmd, want) {
+		t.Fatalf("cmd = %#v, want %#v", cmd, want)
+	}
+}
+
 func TestGetLaunchCommandOrchestratorAppendsSystemPromptInteractively(t *testing.T) {
 	p := &Plugin{resolvedBinary: "pi"}
 	cmd, err := p.GetLaunchCommand(context.Background(), ports.LaunchConfig{
@@ -187,6 +226,28 @@ func TestGetRestoreCommand(t *testing.T) {
 	}
 }
 
+func TestGetRestoreCommandAppendsConfiguredModelBeforeSession(t *testing.T) {
+	p := &Plugin{resolvedBinary: "pi"}
+	cmd, ok, err := p.GetRestoreCommand(context.Background(), ports.RestoreConfig{
+		Config: ports.AgentConfig{Model: "  openai/gpt-4o  "},
+		Session: ports.SessionRef{
+			Metadata: map[string]string{ports.MetadataKeyAgentSessionID: "019e950e-52e0-7411-961b-d380ca7e610f"},
+		},
+		SystemPrompt: "follow repo rules",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !ok {
+		t.Fatal("ok=false, want true")
+	}
+
+	want := []string{"pi", "--append-system-prompt", "follow repo rules", "--model", "openai/gpt-4o", "--session", "019e950e-52e0-7411-961b-d380ca7e610f"}
+	if !reflect.DeepEqual(cmd, want) {
+		t.Fatalf("cmd = %#v, want %#v", cmd, want)
+	}
+}
+
 func TestGetRestoreCommandReappendsSystemPromptInteractively(t *testing.T) {
 	p := &Plugin{resolvedBinary: "pi"}
 	cmd, ok, err := p.GetRestoreCommand(context.Background(), ports.RestoreConfig{