feat: submission analytics — drop-off, completion rate, median time

[harshtandiya]

Context

No visibility into form funnel today. Need metrics per form:

• Completion rate — submitted / engaged sessions
• Drop-off rate — per-field abandonment
• Median time to submit
• View count vs engaged (first interaction)

Proposed approach

Data model

New doctype FP Submission Session (one row per visit):

field	purpose
form (Link)	parent form
session_id (Data, unique)	uuid from sessionStorage
user (Link, nullable)	logged-in user
guest_hash (Data)	hashed IP+UA for guest dedupe
started_at (Datetime)	first interaction
last_activity_at (Datetime)	rolling
submitted_at (Datetime, nullable)	finalize
submission (Dynamic Link, nullable)	resulting doc
last_field_reached (Data)	last focused field
engaged (Check)	first focus fired
abandoned (Check)	cron-marked after stale
user_agent, referrer (Data)	context

Optional follow-up doctype FP Submission Event (append-only) — session, event_type (focus/blur/submit), field, timestamp. Enables fine-grained drop-off later. Out of scope for first cut.

Lifecycle

1. Page open — frontend generates session_id, stores in sessionStorage. No backend call yet.
2. First field focus — POST /api/method/forms_pro.api.metrics.start_session → creates row with engaged=true.
3. Field blur — throttled beacon updates last_field_reached, last_activity_at. Batch every 5s or on blur.
4. Submit — existing submit_form_response sets submitted_at, links submission.
5. Tab close / navigation — visibilitychange → navigator.sendBeacon() final flush.
6. Stale sweeper — daily cron marks sessions with last_activity_at > 30min and no submitted_at as abandoned=true.

API

New module forms_pro/api/metrics.py:

• start_session(form, session_id) — allow_guest=True, idempotent
• update_session(session_id, last_field, ...) — accepts beacon blob
• get_form_metrics(form) — aggregate query for dashboard

Frontend

• New composable useSubmissionMetrics(formId) in frontend/src/composables/
• Wire into SubmissionPage.vue and PublicEdit.vue (skip edit mode for metrics)
• visibilitychange listener fires sendBeacon with current state
• Display metrics on ManageForm.vue overview

Metric queries

• Completion rate = count(submitted_at) / count(engaged=true)
• Median time = percentile_cont(0.5) within group (order by submitted_at - started_at)
• Drop-off per field = count(last_field_reached=X AND submitted_at IS NULL) / count(reached X)

Edge cases

• Guests — opaque session_id, no user link
• Refresh mid-fill — sessionStorage persists session_id; resume row
• Edit mode — skip logging entirely
• Multi-tab — separate session_ids, accepted
• Bots — engaged=false filters out view-only noise
• Beacon drops (~5%) — cron sweeper backstops
• Write amplification — throttle blur events, no per-keystroke writes
• PII — log field names only, never values

Out of scope

• Per-field event log (FP Submission Event) — follow-up
• External analytics integration (PostHog)
• A/B testing form variants
• Geo / device breakdown