db: drop duplicate snapshots sandbox_id index

[ValentaTomas]

idx_snapshots_sandbox_id is an exact duplicate of the constraint-backed snapshots_sandbox_id_unique (same key column). The unique twin serves every lookup; the plain copy shows no scans over a multi-month usage window while every snapshot write maintains both. Dropped CONCURRENTLY; uniqueness enforcement is untouched. Fresh, isolated re-roll of the earlier closed draft (#3390).

Schema proof, both definitions in this repo: the dropped index (20250708135400 L3) and the surviving unique constraint (20251009170758 L4-L5) — identical key (sandbox_id). Background on why identical indexes are redundant: PostgreSQL wiki — duplicate indexes.

[cursor]

PR Summary

Low Risk
Schema cleanup only; uniqueness and lookups stay on the constraint-backed index, with standard concurrent-drop operational caveats.

Overview
Removes the redundant non-unique index on snapshots.sandbox_id because snapshots_sandbox_id_unique already indexes that column for lookups and uniqueness. The drop runs CONCURRENTLY with bounded statement_timeout on up and a careful down path that clears invalid indexes before rebuilding.

^{Reviewed by Cursor Bugbot for commit 55899f2. Bugbot is set up for automated code reviews on this repo. Configure here.}

[codecov]

❌ 5 Tests Failed:

Tests completed	Failed	Passed	Skipped
3512	5	3507	9

View the top 3 failed test(s) by shortest run time

github.com/e2b-dev/infra/tests/integration/internal/tests/envd::TestListDir/depth_0_lists_only_root_directory

Stack Traces | 0.01s run time

=== RUN   TestListDir/depth_0_lists_only_root_directory
=== PAUSE TestListDir/depth_0_lists_only_root_directory
=== CONT  TestListDir/depth_0_lists_only_root_directory
    filesystem_test.go:96: 
        	Error Trace:	.../tests/envd/filesystem_test.go:96
        	Error:      	Received unexpected error:
        	            	unavailable: 502 Bad Gateway
        	Test:       	TestListDir/depth_0_lists_only_root_directory
--- FAIL: TestListDir/depth_0_lists_only_root_directory (0.01s)

github.com/e2b-dev/infra/tests/integration/internal/tests/envd::TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory)

Stack Traces | 0.01s run time

=== RUN   TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory)
=== PAUSE TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory)
=== CONT  TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory)
    filesystem_test.go:96: 
        	Error Trace:	.../tests/envd/filesystem_test.go:96
        	Error:      	Received unexpected error:
        	            	unavailable: 502 Bad Gateway
        	Test:       	TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory)
--- FAIL: TestListDir/depth_2_lists_first_level_of_subdirectories_(in_this_case_the_root_directory) (0.01s)

github.com/e2b-dev/infra/tests/integration/internal/tests/envd::TestListDir/depth_1_lists_root_directory

Stack Traces | 0.02s run time

=== RUN   TestListDir/depth_1_lists_root_directory
=== PAUSE TestListDir/depth_1_lists_root_directory
=== CONT  TestListDir/depth_1_lists_root_directory
    filesystem_test.go:96: 
        	Error Trace:	.../tests/envd/filesystem_test.go:96
        	Error:      	Received unexpected error:
        	            	unavailable: 502 Bad Gateway
        	Test:       	TestListDir/depth_1_lists_root_directory
--- FAIL: TestListDir/depth_1_lists_root_directory (0.02s)

github.com/e2b-dev/infra/tests/integration/internal/tests/envd::TestListDir

Stack Traces | 0.48s run time

=== RUN   TestListDir
=== PAUSE TestListDir
=== CONT  TestListDir
--- FAIL: TestListDir (0.48s)

View the full list of 1 ❄️ flaky test(s)

github.com/e2b-dev/infra/tests/integration/internal/tests/envd::TestListDir/depth_3_lists_all_directories_and_files

Flake rate in main: 30.77% (Passed 9 times, Failed 4 times)

Stack Traces | 0.01s run time

=== RUN   TestListDir/depth_3_lists_all_directories_and_files
=== PAUSE TestListDir/depth_3_lists_all_directories_and_files
=== CONT  TestListDir/depth_3_lists_all_directories_and_files
    filesystem_test.go:96: 
        	Error Trace:	.../tests/envd/filesystem_test.go:96
        	Error:      	Received unexpected error:
        	            	unavailable: 502 Bad Gateway
        	Test:       	TestListDir/depth_3_lists_all_directories_and_files
--- FAIL: TestListDir/depth_3_lists_all_directories_and_files (0.01s)

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[claude]

LGTM — straightforward, low-risk migration.

Verified the redundant-index premise directly: idx_snapshots_sandbox_id was created in 20250708135400_snapshots_migrations.sql, and the unique constraint snapshots_sandbox_id_unique (added later in 20251009170758_unique_snapshots.sql) on the same column already provides Postgres's implicit backing index, making the plain index redundant. Checked the migration mechanics — correct timestamp, NO TRANSACTION for the CONCURRENTLY drop/create, statement_timeout bounds and the migrator's 3h baseline restore, and a down path that clears a stranded INVALID index before rebuilding — all consistent with the pattern used in the recent 20260725100500_env_builds_status_group_statistics.sql migration.

Extended reasoning...

Overview

Single new migration file dropping a redundant non-unique index on snapshots.sandbox_id, run CONCURRENTLY with a bounded statement_timeout. Down migration clears any leftover INVALID index and rebuilds it, also CONCURRENTLY.

Security risks

None. This is schema-only cleanup; no auth, crypto, or data-exposure surface is touched. Uniqueness enforcement remains on the constraint-backed index (snapshots_sandbox_id_unique), so there is no correctness regression for duplicate detection.

Level of scrutiny

Low. This is a mechanical DB migration following an established pattern in this repo (see 20260725100500_env_builds_status_group_statistics.sql for the same statement_timeout/NO TRANSACTION structure). I independently verified the redundancy claim against the migration history rather than taking the PR description at face value, and confirmed the down-migration correctly guards against the classic "stranded INVALID index" pitfall of interrupted CONCURRENTLY builds.

Other factors

No CODEOWNERS-sensitive paths, no outstanding reviewer comments to address, and Codecov reports full coverage on the change (trivially, since it's a migration file). This is a fresh re-roll of a previously closed draft PR (#3390) per the description, with no changes needed based on the current diff.