feat(telemetry): attach email + name + signup_date to PostHog Person

Login now passes the API User struct's Email, DisplayName, Username, and
CreatedAt as PostHog Person-level properties via Identify. Mutable fields
(email, name, username) use $set; signup_date uses $set_once so it cannot
be overwritten by subsequent logins.

Person properties go ONLY to PostHog's person record via Identify — they
are NEVER attached to Capture event payloads.

Implementation:
- internal/telemetry/client.go: new SetPersonProperties(props) method;
  RebindIdentity merges them into the Identify event.
- cmd/auth/login.go: bindIdentityAndCapture builds props from User and
  calls SetPersonProperties before RebindIdentity.

Verified end-to-end against PostHog: person record now shows email +
signup_date alongside the existing user_id binding. Events still carry
no email — only user_id.

Author: pratikbin

cmd/auth/login.go

@@ -49,6 +49,7 @@ func captureLoginFailure(method string, err error) {
 // account on this machine would mis-attribute the new login's telemetry.
 func bindIdentityAndCapture(apiClient *api.APIClient, method string) {
 	identityFresh := false
+	var personProps map[string]any
 	if apiClient != nil {
 		if u, err := apiClient.GetUser(); err == nil && u != nil && u.ID != "" {
 			id := config.Identity{UserID: u.ID}
@@ -57,6 +58,7 @@ func bindIdentityAndCapture(apiClient *api.APIClient, method string) {
 			}
 			if saveErr := config.SaveIdentity(id); saveErr == nil {
 				identityFresh = true
+				personProps = userToPersonProps(u)
 			}
 		}
 		// Silent on /me failure — login still succeeds without user_id.
@@ -70,6 +72,7 @@ func bindIdentityAndCapture(apiClient *api.APIClient, method string) {
 
 	if telemetry.Default != nil {
 		if identityFresh {
+			telemetry.Default.SetPersonProperties(personProps)
 			telemetry.Default.RebindIdentity()
 		}
 		telemetry.Default.Capture("auth_event", map[string]any{
@@ -80,6 +83,27 @@ func bindIdentityAndCapture(apiClient *api.APIClient, method string) {
 	}
 }
 
+// userToPersonProps maps the API User struct to PostHog Person-level
+// properties. These go ONLY to the Person record via Identify; they are
+// NOT included in any Capture event payload. Pointer fields are dereferenced
+// only when non-nil.
+func userToPersonProps(u *api.User) map[string]any {
+	p := map[string]any{
+		"email": u.Email,
+	}
+	if u.DisplayName != nil && *u.DisplayName != "" {
+		p["name"] = *u.DisplayName
+	}
+	if u.Username != nil && *u.Username != "" {
+		p["username"] = *u.Username
+	}
+	if u.CreatedAt != "" {
+		// signup_date is immutable — Client uses $set_once for this key.
+		p["signup_date"] = u.CreatedAt
+	}
+	return p
+}
+
 // NewLoginCommand creates the login command.
 func NewLoginCommand() *cli.Command {
 	return &cli.Command{

internal/telemetry/client.go

@@ -28,10 +28,11 @@ type Client struct {
 	machineIDHash string // anonymous distinct_id; never overwritten after Init
 	globalProps   posthog.Properties
 
-	mu         sync.Mutex
-	userID     string // empty pre-login
-	distinctID string // == machineIDHash pre-login, == userID post-login
-	disabled   bool
+	mu          sync.Mutex
+	userID      string // empty pre-login
+	distinctID  string // == machineIDHash pre-login, == userID post-login
+	disabled    bool
+	personProps map[string]any // sent on Identify only; never on Capture events
 }
 
 // silentLogger satisfies posthog.Logger but drops all output. Telemetry must
@@ -120,6 +121,26 @@ func (c *Client) Capture(event string, props map[string]any) {
 	})
 }
 
+// SetPersonProperties stores PostHog Person-level properties (email, name,
+// signup_date, ...) that will be attached to the next Identify event sent
+// by RebindIdentity. The map is held in memory only — it is never persisted
+// to disk and never appears on Capture event payloads.
+//
+// Callers (the login flow) MUST call this BEFORE RebindIdentity for the
+// props to land on the corresponding Identify.
+func (c *Client) SetPersonProperties(props map[string]any) {
+	if c == nil || c.disabled {
+		return
+	}
+	cp := make(map[string]any, len(props))
+	for k, v := range props {
+		cp[k] = v
+	}
+	c.mu.Lock()
+	c.personProps = cp
+	c.mu.Unlock()
+}
+
 // RebindIdentity reads the on-disk Identity and aligns the client state.
 // Idempotent — repeated calls do nothing extra once user is bound.
 //
@@ -154,6 +175,26 @@ func (c *Client) RebindIdentity() {
 	if v, ok := c.globalProps["channel"]; ok {
 		identifyProps.Set("channel", v)
 	}
+	// Attach Person props (email, name, signup_date, ...) supplied by the
+	// login flow. They go ONLY to PostHog's person record via Identify; they
+	// are NOT included in any Capture event payload.
+	c.mu.Lock()
+	personProps := c.personProps
+	c.mu.Unlock()
+	setOnce := map[string]any{}
+	for k, v := range personProps {
+		switch k {
+		case "signup_date", "created_at":
+			// Immutable Person fields — only set on first identify per
+			// person, never overwritten on subsequent logins.
+			setOnce[k] = v
+		default:
+			identifyProps.Set(k, v)
+		}
+	}
+	if len(setOnce) > 0 {
+		identifyProps.Set("$set_once", setOnce)
+	}
 	_ = c.inner.Enqueue(posthog.Identify{
 		DistinctId: id.UserID,
 		Properties: identifyProps,