feat(surveys): add FK for linked_insight_id

[adboio]

Problem

step 2 of 4 for this migration....

1. adding int field feat(surveys): add linked_insight_id field #41689
2. [this] adding FK column (no constraint)
3. add FK constraint
4. add index on field

this was previously approved as one big PR (#41574) but i had to split it up due to restrictive migration CI checks :(

this will also likely need a rebase, but just want to get approvals so i can pop it in the queue when ready

Changes

How did you test this code?

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

Changelog: (features only) Is this feature complete?

[adboio]

• feat(surveys): add cross-sell button to funnel insights #41703 : 2 dependent PRs (#41694 , #41873 )
• feat(surveys): add FK for linked_insight_id #41708 👈 (View in Graphite)
• feat(surveys): add linked_insight_id field #41689
• master

This stack of pull requests is managed by Graphite. Learn more about stacking.

[github-actions]

Migration SQL Changes

Hey 👋, we've detected some migrations on this PR. Here's the SQL output for each migration, make sure they make sense:

posthog/migrations/0912_alter_survey_linked_insight_type.py

BEGIN;
--
-- Custom state/database change combination
--
-- (no-op)
COMMIT;

Last updated: 2025-11-19 23:33 UTC (b54e6e3)

[github-actions]

🔍 Migration Risk Analysis

We've analyzed your migrations for potential risks.

Summary: 1 Safe | 0 Needs Review | 0 Blocked

✅ Safe

No contention risk, backwards compatible

posthog.0912_alter_survey_linked_insight_type
  └─ #1 ✅ SeparateDatabaseAndState: Only state operations (no database changes)

Last updated: 2025-11-19 23:33 UTC (b54e6e3)

[greptile-apps]

_{5 files reviewed, no comments}

_{Edit Code Review Agent Settings | Greptile
React with 👍 or 👎 to share your feedback on this new summary format}

[adamleithp]

Low context stamp