feature flag optimizations part one

[danoswaltCL]

handles 1a, 1b, and 4 from the research spike plan that claude and I spun up #3143

• Removes global exclude logic from getKeys() (if we can't do that, then we'll need to cache the global exclude lists, because it isn't happening currently so gets called every time... not a problem current as clc and mathia-student-ui don't have global exclude lists currently, but if someone added a big one today, it would cause problems)

• Guards against include-list data being used in segment lookups when INCLUDE_ALL (this is one part of a two part fix in another pr)

• Fixes issues in exposure save:

  • wasn't actually fire-and-forget because the transaction is awaited
  • was doing a full SELECT on every call with .save because of how typeorm treats full object as param vs an id, however:
  • ignore on conflict makes that work the way we'd actually want, which is to do a blind insert and bail if it exists without erroring

[Copilot]

Pull request overview

This PR targets backend feature-flag performance by streamlining FeatureFlagService.getKeys() execution: it removes a per-request global-exclusion check, prevents irrelevant inclusion-segment data from being used for INCLUDE_ALL flags, and makes exposure recording a true fire-and-forget bulk insert with conflict ignore.

Changes:

• Removed global exclusion logic from getKeys() to avoid repeated expensive checks per request.
• Adjusted segment resolution inputs to ignore inclusion segments when filterMode === INCLUDE_ALL.
• Reworked exposure persistence to use a repository bulk insert with orIgnore() and to avoid awaiting a transaction; added unit tests for the new behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
packages/backend/src/api/services/FeatureFlagService.ts	Removes global exclusion check, guards inclusion segment IDs for INCLUDE_ALL, and switches exposure recording to fire-and-forget via repository insert.
packages/backend/src/api/repositories/FeatureFlagExposureRepository.ts	Adds recordExposureIfNotExists() bulk insert using orIgnore() to avoid duplicate-write overhead.
packages/backend/test/unit/services/FeatureFlagService.test.ts	Adds unit coverage for removed global exclusion call, exposure recording behavior, and segment handling by filterMode.
packages/backend/test/unit/repositories/FeatureFlagExposureRepository.test.ts	Adds unit coverage asserting the repository insert path uses orIgnore() and correct values.

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