feat(templates): add --start-date to templates construct

.surface

@@ -13442,6 +13442,7 @@ FLAG basecamp templates construct --no-stats type=bool
 FLAG basecamp templates construct --profile type=string
 FLAG basecamp templates construct --project type=string
 FLAG basecamp templates construct --quiet type=bool
+FLAG basecamp templates construct --start-date type=string
 FLAG basecamp templates construct --stats type=bool
 FLAG basecamp templates construct --styled type=bool
 FLAG basecamp templates construct --todolist type=string

e2e/templates.bats

@@ -109,6 +109,15 @@ load test_helper
   assert_output_contains "name required"
 }
 
+@test "templates construct with malformed start date shows error" {
+  create_credentials
+  create_global_config '{"account_id": 99999}'
+
+  run basecamp templates construct 123 --name "Project" --start-date someday
+  assert_failure
+  assert_output_contains "Invalid start date"
+}
+
 
 # Construction status errors
 

go.mod

@@ -6,7 +6,7 @@ require (
 	charm.land/bubbles/v2 v2.2.1
 	charm.land/bubbletea/v2 v2.0.9
 	charm.land/lipgloss/v2 v2.0.6
-	github.com/basecamp/basecamp-sdk/go v0.17.0
+	github.com/basecamp/basecamp-sdk/go v0.18.0
 	github.com/basecamp/cli v0.2.2-0.20260828230226-767413fc712d
 	github.com/basecamp/mcp v0.0.0-20260828100356-2d6f44b51e9d
 	github.com/basecamp/surfguard/go v0.1.0

go.sum

@@ -87,8 +87,8 @@ github.com/aymanbagabas/go-udiff v0.4.1 h1:OEIrQ8maEeDBXQDoGCbbTTXYJMYRCRO1fnodZ
 github.com/aymanbagabas/go-udiff v0.4.1/go.mod h1:0L9PGwj20lrtmEMeyw4WKJ/TMyDtvAoK9bf2u/mNo3w=
 github.com/aymerick/douceur v0.2.0 h1:Mv+mAeH1Q+n9Fr+oyamOlAkUNPWPlA8PPGR0QAaYuPk=
 github.com/aymerick/douceur v0.2.0/go.mod h1:wlT5vV2O3h55X9m7iVYN0TBM0NH/MmbLnd30/FjWUq4=
-github.com/basecamp/basecamp-sdk/go v0.17.0 h1:u2kIDtr7bmHXLSkF61HXkLDymQdwoI+pzbT0F6OwHYM=
-github.com/basecamp/basecamp-sdk/go v0.17.0/go.mod h1:Cs9DV8iRJaVT4+IQXGZTeyG2nQAV2kQda7GHuBOeonY=
+github.com/basecamp/basecamp-sdk/go v0.18.0 h1:A6Mu1ugnvvExNdLN4w9th6Tz2fktSdfbqbbDhxYgPPE=
+github.com/basecamp/basecamp-sdk/go v0.18.0/go.mod h1:Cs9DV8iRJaVT4+IQXGZTeyG2nQAV2kQda7GHuBOeonY=
 github.com/basecamp/cli v0.2.2-0.20260828230226-767413fc712d h1:jAzDrCCzDpIwhbFT1xVVs0z2xpXoDEkomHfKB2bUUp8=
 github.com/basecamp/cli v0.2.2-0.20260828230226-767413fc712d/go.mod h1:iTBTaWvsPEFIcZfkxQHEfISyJ6sZ7036K6bNx0RY3EE=
 github.com/basecamp/mcp v0.0.0-20260828100356-2d6f44b51e9d h1:zEQVGq1x1nhKMZ2TudFAcSJ32CHT8richI1vQakIKz4=

internal/commands/templates.go

@@ -12,6 +12,7 @@ import (
 	"github.com/basecamp/basecamp-sdk/go/pkg/basecamp"
 
 	"github.com/basecamp/basecamp-cli/internal/appctx"
+	"github.com/basecamp/basecamp-cli/internal/dateparse"
 	"github.com/basecamp/basecamp-cli/internal/output"
 )
 
@@ -24,7 +25,7 @@ func NewTemplatesCmd() *cobra.Command {
 
 Project templates create projects with predefined structure, tools, and content.
 Library templates copy a reusable to-do list into an existing project.`,
-		Annotations: map[string]string{"agent_notes": "Project construction and to-do list template copies are asynchronous. Poll construction or copy-status until status=completed. Copy grants referenced people project access only with --confirm-adding-people."},
+		Annotations: map[string]string{"agent_notes": "Project construction and to-do list template copies are asynchronous. Poll construction or copy-status until status=completed. construct --start-date anchors the template's relative dates to the Sunday of that week; without it they anchor to the week of construction. Copy grants referenced people project access only with --confirm-adding-people."},
 	}
 
 	cmd.AddCommand(
@@ -629,14 +630,19 @@ func newTemplatesDeleteCmd() *cobra.Command {
 func newTemplatesConstructCmd() *cobra.Command {
 	var projectName string
 	var projectDesc string
+	var startDate string
 
 	cmd := &cobra.Command{
 		Use:   "construct <template_id>",
 		Short: "Create project from template",
 		Long: `Create a new project from a template.
 
 This is an asynchronous operation. The command returns a construction ID
-which can be polled via 'templates construction' until the status is "completed".`,
+which can be polled via 'templates construction' until the status is "completed".
+
+A template's dates are relative to the start of its first week, and template
+weeks start on a Sunday. --start-date anchors them to the Sunday on or before
+the given date; without it they anchor to the week the project is constructed.`,
 		Args: cobra.ExactArgs(1),
 		RunE: func(cmd *cobra.Command, args []string) error {
 			if projectName == "" {
@@ -648,6 +654,14 @@ which can be polled via 'templates construction' until the status is "completed"
 				return output.ErrUsage("Invalid template ID")
 			}
 
+			var parsedStart string
+			if cmd.Flags().Changed("start-date") {
+				parsedStart = dateparse.Parse(startDate)
+				if _, err := time.Parse("2006-01-02", parsedStart); err != nil {
+					return output.ErrUsage(fmt.Sprintf("Invalid start date: %q", startDate))
+				}
+			}
+
 			// Syntactic checks first, then "-", then account and network.
 			projectDesc, err := resolveContentValue(cmd, projectDesc, -1, "--description")
 			if err != nil {
@@ -660,7 +674,8 @@ which can be polled via 'templates construction' until the status is "completed"
 				return err
 			}
 
-			construction, err := app.Account().Templates().CreateProject(cmd.Context(), templateID, projectName, projectDesc)
+			construction, err := app.Account().Templates().CreateProject(cmd.Context(), templateID, projectName, projectDesc,
+				&basecamp.CreateProjectOptions{StartDate: parsedStart})
 			if err != nil {
 				return convertSDKError(err)
 			}
@@ -681,6 +696,7 @@ which can be polled via 'templates construction' until the status is "completed"
 	cmd.Flags().StringVar(&projectName, "name", "", "Project name (required)")
 	cmd.Flags().StringVar(&projectDesc, "description", "", "Project description; use - to read from stdin")
 	cmd.Flags().StringVar(&projectDesc, "desc", "", "Project description (alias)")
+	cmd.Flags().StringVar(&startDate, "start-date", "", "Project start date (YYYY-MM-DD or natural, e.g. \"next monday\"); template dates anchor to the Sunday of that week")
 	_ = cmd.MarkFlagRequired("name")
 
 	allowDash(cmd, "flag:description", "flag:desc")

internal/commands/templates_test.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"net/http"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -228,6 +229,103 @@ func TestTemplatesCopyExplainsPeopleConfirmation(t *testing.T) {
 	assert.True(t, errors.As(err, &confirmationErr), "typed SDK error should remain available")
 }
 
+func TestTemplatesConstructSendsStartDateUnderProjectEnvelope(t *testing.T) {
+	app, transport := setupRecordingTestApp(t,
+		stubRoute{
+			method: http.MethodPost,
+			path:   "/99999/templates/2085958507/project_constructions.json",
+			status: http.StatusCreated,
+			body:   `{"id":598194962,"status":"pending","url":"https://example.test/constructions/598194962.json"}`,
+		},
+	)
+	buf := captureTemplateOutput(app)
+
+	err := executeRecordingCommand(NewTemplatesCmd(), app,
+		"construct", "2085958507", "--name", "Marketing Campaign",
+		"--description", "For Client: Xyz Corp Conference", "--start-date", "2026-09-01")
+	require.NoError(t, err)
+
+	requests := transport.recorded()
+	require.Len(t, requests, 1)
+	assert.Equal(t, http.MethodPost, requests[0].Method)
+	assert.JSONEq(t,
+		`{"project":{"name":"Marketing Campaign","description":"For Client: Xyz Corp Conference","start_date":"2026-09-01"}}`,
+		requests[0].Body,
+	)
+
+	envelope := decodeTemplateEnvelope(t, buf)
+	assert.Equal(t, "Started project construction #598194962 (pending)", envelope.Summary)
+	require.Len(t, envelope.Breadcrumbs, 1)
+	assert.Equal(t, "basecamp templates construction 2085958507 598194962", envelope.Breadcrumbs[0].Cmd)
+}
+
+func TestTemplatesConstructOmitsStartDateWhenUnset(t *testing.T) {
+	app, transport := setupRecordingTestApp(t,
+		stubRoute{
+			method: http.MethodPost,
+			path:   "/99999/templates/2085958507/project_constructions.json",
+			status: http.StatusCreated,
+			body:   `{"id":598194962,"status":"pending","url":"https://example.test/constructions/598194962.json"}`,
+		},
+	)
+	captureTemplateOutput(app)
+
+	err := executeRecordingCommand(NewTemplatesCmd(), app, "construct", "2085958507", "--name", "Marketing Campaign")
+	require.NoError(t, err)
+
+	requests := transport.recorded()
+	require.Len(t, requests, 1)
+	assert.JSONEq(t, `{"project":{"name":"Marketing Campaign"}}`, requests[0].Body)
+}
+
+func TestTemplatesConstructParsesNaturalStartDate(t *testing.T) {
+	app, transport := setupRecordingTestApp(t,
+		stubRoute{
+			method: http.MethodPost,
+			path:   "/99999/templates/2085958507/project_constructions.json",
+			status: http.StatusCreated,
+			body:   `{"id":598194962,"status":"pending","url":"https://example.test/constructions/598194962.json"}`,
+		},
+	)
+	captureTemplateOutput(app)
+
+	before := time.Now()
+	err := executeRecordingCommand(NewTemplatesCmd(), app, "construct", "2085958507", "--name", "Marketing Campaign", "--start-date", "tomorrow")
+	after := time.Now()
+	require.NoError(t, err)
+
+	requests := transport.recorded()
+	require.Len(t, requests, 1)
+	var body struct {
+		Project struct {
+			StartDate string `json:"start_date"`
+		} `json:"project"`
+	}
+	require.NoError(t, json.Unmarshal([]byte(requests[0].Body), &body))
+	tomorrow := func(now time.Time) string { return now.AddDate(0, 0, 1).Format("2006-01-02") }
+	assert.Contains(t, []string{tomorrow(before), tomorrow(after)}, body.Project.StartDate)
+}
+
+func TestTemplatesConstructRejectsBlankStartDate(t *testing.T) {
+	app, transport := setupRecordingTestApp(t)
+	captureTemplateOutput(app)
+
+	err := executeRecordingCommand(NewTemplatesCmd(), app, "construct", "2085958507", "--name", "Marketing Campaign", "--start-date", "")
+	outErr := requireUsageErr(t, err)
+	assert.Contains(t, outErr.Message, "Invalid start date")
+	assert.Empty(t, transport.recorded())
+}
+
+func TestTemplatesConstructRejectsMalformedStartDateBeforeAnyRequest(t *testing.T) {
+	app, transport := setupRecordingTestApp(t)
+	captureTemplateOutput(app)
+
+	err := executeRecordingCommand(NewTemplatesCmd(), app, "construct", "2085958507", "--name", "Marketing Campaign", "--start-date", "someday")
+	outErr := requireUsageErr(t, err)
+	assert.Contains(t, outErr.Message, "Invalid start date")
+	assert.Empty(t, transport.recorded())
+}
+
 func TestTemplatesCopyStatusStates(t *testing.T) {
 	completed := `{
 		"id":5,"status":"completed","source_recording_id":3,"destination_parent_id":9,"url":"https://example.test/copies/5.json",

internal/mcpserver/model/PROVENANCE.json

@@ -1,7 +1,7 @@
 {
   "source": "github.com/basecamp/basecamp-sdk",
-  "commit": "6e73a06f4262062b2c973b2d0787ab0029b08d0d",
-  "ref": "go/v0.17.0",
+  "commit": "400c76ca433d5ae08e1e7d6a561ab113949c70d8",
+  "ref": "go/v0.18.0",
   "files": ["behavior-model.json", "openapi.json"],
   "synced_by": "scripts/sync-mcp-model.sh",
   "patches": "tags assigned to operations the export leaves untagged (PATCHED_TAGS); binary-upload operations dropped (EXCLUDED_OPERATIONS) — see the sync script"

internal/mcpserver/model/openapi.json

@@ -33601,6 +33601,10 @@
           },
           "description": {
             "type": "string"
+          },
+          "start_date": {
+            "type": "string",
+            "description": "Date the new project starts on. Template dates are relative to the start\nof the template's first week, and template weeks start on a Sunday, so\nthe project's dates are anchored to the Sunday on or before this date.\nOmitted, they are anchored to the week in which the construction is\nprocessed."
           }
         },
         "required": [

internal/version/sdk-provenance.json

@@ -1,9 +1,9 @@
 {
   "sdk": {
     "module": "github.com/basecamp/basecamp-sdk/go",
-    "version": "v0.17.0",
-    "revision": "6e73a06f4262",
-    "updated_at": "2026-09-09T22:00:24Z"
+    "version": "v0.18.0",
+    "revision": "400c76ca433d",
+    "updated_at": "2026-09-10T05:31:19Z"
   },
   "api": {
     "repo": "basecamp/bc3",

nix/package.nix

@@ -8,7 +8,7 @@ buildGoModule.override { go = go_1_26; } (finalAttrs: {
   src = lib.cleanSource ./..;
 
   # To update: set to lib.fakeHash, run `nix build`, use the hash from the error.
-  vendorHash = "sha256-GCw7WkPmXDWDAhJrVqbXUfwLa9YzpWdTcSimwovjpcQ=";
+  vendorHash = "sha256-MdVsRrJ3SEEtFFU6X2gP5s414kEhulSkxLqoD9GxiIg=";
 
   subPackages = [ "cmd/basecamp" ];
 

skills/basecamp/SKILL.md

@@ -975,6 +975,7 @@ basecamp templates create "Template Name"         # Create empty project templat
 basecamp templates update <id> --name "New Name"
 basecamp templates delete <id>                    # Trash project template
 basecamp templates construct <id> --name "New Project"  # Create project (async)
+basecamp templates construct <id> --name "New Project" --start-date 2026-09-01  # Anchor template dates to that week
 basecamp templates construction <template_id> <construction_id>  # Check project status
 
 basecamp templates library --json                 # List active to-do list templates
@@ -983,7 +984,10 @@ basecamp templates copy-status <copy_id>          # Check copy status
 ```
 
 **Asynchronous results:** `construct` returns a construction ID; poll `construction`
-until `status="completed"` to get the project. `copy` returns a copy ID; poll
+until `status="completed"` to get the project. A template's dates are relative to its
+first week, and template weeks start on Sunday: `--start-date` (YYYY-MM-DD or natural,
+e.g. `next monday`) anchors them to the Sunday on or before that date; without it they
+anchor to the week of construction. `copy` returns a copy ID; poll
 `copy-status` through `pending` and `processing` until it is `completed` or `failed`.
 
 A copy can report the people who need access to the destination project. Show those