chore(tasks): drop the redundant team_id index on sandbox environments

[posthog]

Problem

• Nobody is hurt yet. This is schema hygiene on posthog_sandbox_environment, one row per user-defined sandbox environment per team.
• pganalyze flagged a team_id index on the table that no query has scanned in 35 days.
• The index is redundant, not merely cold: the Meta index on (team, created_by) leads with team_id, so it already serves every team_id lookup and the cascade check when a team row is deleted.
• Cost today is small but permanent: storage plus index maintenance on every insert, update, and delete.

Changes

• Nothing changes for a person using the tasks product. Query plans keep the composite index for the same lookups.
• Mechanism: db_index=False on the team foreign key stops Django from declaring the single-column index, and migration 0118 drops it with DROP INDEX CONCURRENTLY, so no table lock.
• The migration wraps the AlterField in SeparateDatabaseAndState, because the concurrent drop cannot run inside the migration transaction.

Index	Before	After
posthog_sandbox_environment_team_id_d94b6a9a (team_id)	present, 0 scans	dropped
posthog_san_team_id_817c0d_idx (team_id, created_by_id)	present	kept, serves both cases
posthog_sandbox_environment_custom_image_id_a62b5702	present	kept

custom_image_id stays. It also reports no scans, but it serves the on_delete=SET_NULL cascade, and custom images are archived rather than deleted, so the index only looks idle.

How did you test this code?

• No new tests. A dropped redundant index has no behavior to assert that the existing model and API tests do not already cover.
• makemigrations tasks --dry-run reports no state drift.
• sqlmigrate tasks 0118 emits exactly DROP INDEX CONCURRENTLY IF EXISTS "posthog_sandbox_environment_team_id_d94b6a9a".
• analyze_migration_risk classifies the migration as Safe.
• Applied forward and backward against a local dev Postgres and read pg_indexes each time: forward removes the index, backward recreates the same definition.
• Not checked: the product test suites. The sandbox had no ClickHouse or Redis, so products/tasks/backend/tests could not start. CI runs them.

Automatic notifications

• Publish to changelog?

Docs update

None. No user-facing behavior, API, or documented workflow changes.

🤖 Agent context

Autonomy: Fully autonomous

• Written by Claude Code from a PostHog inbox report. Skills invoked: /django-migrations, /writing-pr-descriptions, /writing-code-comments, /writing-simplified-technical-english.
• No duplicate: gh pr list --state open --search found no open PR touching this table. Several merged PRs do the same cleanup on other tables.
• The first draft used a plain RunSQL drop, copying an older merged migration. It now uses the DropIndexConcurrently helper instead, which is idempotent under bin/migrate retries and can rebuild the index on reverse.
• Public artifact: the diff and this description carry only schema facts from this repository and index names read from a local dev database.

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[posthog]

🦔 PostHog Review reviewed this pull request

Nothing worth raising this time, so here's a calming picture instead:

[github-actions]

🤖 CI report

⚠️ Trunk lane — backend Python lane

This PR is assigned to the backend Python lane. It runs backend Python tests and may merge in parallel with PRs in other lanes.

⚠️ Django migration SQL — 1 new migration to review

We've detected new migrations on this PR. Review the SQL output for each migration:

products/tasks/backend/migrations/0118_drop_sandboxenvironment_team_id_idx.py

--
-- Custom state/database change combination
--
SET lock_timeout = 0;
SET statement_timeout = 0;
DROP INDEX CONCURRENTLY IF EXISTS "posthog_sandbox_environment_team_id_d94b6a9a";

Last updated: 2026-09-07 05:53 UTC (807767b)

✅ Django migration risk — migration analysis complete

We've analyzed your migrations for potential risks.

Summary: 1 Safe | 0 Needs Review | 0 Blocked

✅ Safe

Brief or no lock, backwards compatible

tasks.0118_drop_sandboxenvironment_team_id_idx
  └─ #1 ✅ SeparateDatabaseAndState
     Wrapper operation - see nested operations for risk: DropIndexConcurrently
     database_operations: DropIndexConcurrently
     └─ #2 ✅ DropIndexConcurrently
        PostHog concurrent-index helper: idempotent (timeout disabling + invalid-leftover recovery)
        model: None, index: posthog_sandbox_environment_team_id_d94b6a9a

Last updated: 2026-09-07 05:53 UTC (807767b)

[stamphog]

Not approved yet — waiting on the conditions below.

The Migration risk check has not finished for this commit, so stamphog cannot tell a safe migration from a risky one yet. The review runs again on the next push, or you can re-request it once the check reports.

Gate mechanics and policy version

Gate		Result
prerequisites	✓	all clear
deny-list	✗	matches: migrations
size	✓	39L, 2F substantive, 41L/3F incl. docs/generated/snapshots — within ceiling
tier	✗	classified as T2-never: T2-never (41L, 3F, single-area, chore)
stamphog 2.0.0b4		.stamphog/policy.yml @ 807767b · reviewed head 807767b