Add goal completion notifications

[skyfallwastaken]

Summary of the problem

Goals track progress but do not tell users when they reach a target.

Closes #1587

Describe your changes

Adds optional email and Slack completion notifications to each goal. Heartbeat activity checks enabled goals and a durable per-period record prevents duplicate notifications. Existing goals remain opted out until a user selects a notification channel.

Screenshots / Media

Not included. The visual change adds email and Slack checkboxes to the existing goal form.

[Copilot]

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[greptile-apps]

Greptile Summary

Adds opt-in email and Slack notifications when programming goals are completed.

• Extends goal settings, persisted channel preferences and Inertia/Svelte form props.
• Schedules completion checks from heartbeat activity and records one completion snapshot per goal period.
• Adds email and Slack delivery jobs, templates, migrations and coverage across controllers, jobs, models, services and system tests.

Confidence Score: 3/5

The PR should not merge until completion checks cannot be silently dropped and delivery retries cannot send duplicate notifications.

Rapid heartbeat activity can discard the threshold-crossing check under the per-user concurrency limit, while interrupted email or Slack delivery can repeat the external side effect because delivery state is only recorded afterwards.

Files Needing Attention: app/jobs/goal_completion_check_job.rb, app/jobs/goal_completion_email_job.rb and app/jobs/goal_completion_slack_job.rb

Important Files Changed

Filename	Overview
app/jobs/goal_completion_check_job.rb	Introduces completion detection and period deduplication, but its total concurrency limit can discard the only check that observes a threshold-crossing heartbeat.
app/jobs/goal_completion_email_job.rb	Sends completion email before persisting delivery state, allowing duplicate delivery after an interruption.
app/jobs/goal_completion_slack_job.rb	Posts directly to Slack before persisting delivery state and has the same retry-idempotency gap as email.
app/services/heartbeat_ingest.rb	Schedules checks after successful direct ingestion while the production historical-import path remains excluded through its existing scheduling flag.
app/javascript/pages/Users/Settings/Goals.svelte	Adds channel controls and notification status to the existing editable goal form with matching server props.
db/migrate/20260820115209_create_goal_completion_notifications.rb	Adds durable per-period notification snapshots with a database uniqueness constraint on goal, period and period start.

Sequence Diagram

sequenceDiagram
  participant HB as Heartbeat ingest
  participant Check as GoalCompletionCheckJob
  participant DB as PostgreSQL
  participant Delivery as Email/Slack job
  participant External as Mail/Slack API
  HB->>Check: schedule_for(user_id)
  Check->>DB: calculate progress
  Check->>DB: create/find period notification
  Check->>Delivery: enqueue selected channels
  Delivery->>External: send completion notification
  Delivery->>DB: set delivered_at

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Prompt To Fix All With AI

### Issue 1
app/jobs/goal_completion_check_job.rb:14-16
**Concurrency drops completion checks**

If heartbeat processing overlaps for one user, the per-user `total_limit` discards later checks while the accepted check can run before the threshold-crossing heartbeat is visible, causing the completed goal to receive no notification until another heartbeat schedules a check.

### Issue 2
app/jobs/goal_completion_email_job.rb:23-24
**Delivery state permits duplicates**

When external delivery succeeds but the subsequent `delivered_at` update fails or the worker stops before it commits, a retry or later completion check sees a nil marker and sends the notification again, causing duplicate email; the Slack job has the same ordering problem.

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (1): Last reviewed commit: "Add goal completion notifications" | Re-trigger Greptile}

[greptile-apps]

Concurrency drops completion checks

If heartbeat processing overlaps for one user, the per-user total_limit discards later checks while the accepted check can run before the threshold-crossing heartbeat is visible, causing the completed goal to receive no notification until another heartbeat schedules a check.

Context Used: AGENTS.md (source)

Knowledge Base Used:

• Background Jobs Infrastructure (GoodJob)
• Heartbeat Ingest

Prompt To Fix With AI

This is a comment left during a code review.
Path: app/jobs/goal_completion_check_job.rb
Line: 14-16

Comment:
**Concurrency drops completion checks**

If heartbeat processing overlaps for one user, the per-user `total_limit` discards later checks while the accepted check can run before the threshold-crossing heartbeat is visible, causing the completed goal to receive no notification until another heartbeat schedules a check.

**Context Used:** AGENTS.md ([source](https://github.com/hackclub/hackatime/blob/main/AGENTS.md))

**Knowledge Base Used:**
- [Background Jobs Infrastructure (GoodJob)](https://app.greptile.com/mahadk/-/custom-context/knowledge-base/hackclub/hackatime/-/docs/background-jobs-infra.md)
- [Heartbeat Ingest](https://app.greptile.com/mahadk/-/custom-context/knowledge-base/hackclub/hackatime/-/docs/heartbeat-ingest.md)

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

[greptile-apps]

Delivery state permits duplicates

When external delivery succeeds but the subsequent delivered_at update fails or the worker stops before it commits, a retry or later completion check sees a nil marker and sends the notification again, causing duplicate email; the Slack job has the same ordering problem.

Context Used: AGENTS.md (source)

Knowledge Base Used: Background Jobs Infrastructure (GoodJob)

Prompt To Fix With AI

This is a comment left during a code review.
Path: app/jobs/goal_completion_email_job.rb
Line: 23-24

Comment:
**Delivery state permits duplicates**

When external delivery succeeds but the subsequent `delivered_at` update fails or the worker stops before it commits, a retry or later completion check sees a nil marker and sends the notification again, causing duplicate email; the Slack job has the same ordering problem.

**Context Used:** AGENTS.md ([source](https://github.com/hackclub/hackatime/blob/main/AGENTS.md))

**Knowledge Base Used:** [Background Jobs Infrastructure (GoodJob)](https://app.greptile.com/mahadk/-/custom-context/knowledge-base/hackclub/hackatime/-/docs/background-jobs-infra.md)

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.