chore: deprecate TokenBalancesController

[Prithpal-Sooriya]

Explanation

TokenBalancesController already supports an optional isDeprecated constructor callback (added in #9033) so hosts can disable it when AssetsController supersedes legacy balance state under the assets-unify-state feature flag.

This PR completes deprecation coverage on the remaining entry points that could still start polling or schedule balance fetches after the flag toggles at runtime:

• startPolling / _startPolling
• updateChainPollingConfigs
• TransactionController:transactionConfirmed

When isDeprecated() returns true, these paths now call #enforceDisabledState() and return early, matching the behavior of updateBalances, _executePoll, and the other messenger-driven handlers.

References

• ASSETS-3335
• Prior art: #9033, #9186 (TokensController), #9182 (CurrencyRateController)
• Extension consumer: metamask-extension#43108

Manual testing steps

N/A — behavior-preserving unless isDeprecated() returns true.

Screenshots/Recordings

N/A

Changed files

File	Change	Verification
packages/assets-controllers/src/TokenBalancesController.ts	Guard _startPolling, updateChainPollingConfigs, and #onTransactionConfirmed with isDeprecated	ESLint
packages/assets-controllers/src/TokenBalancesController.test.ts	Add 3 runtime-toggle tests for the new entry points	yarn workspace @metamask/assets-controllers run jest --no-coverage src/TokenBalancesController.test.ts -t "isDeprecated"
packages/assets-controllers/CHANGELOG.md	Document extended isDeprecated entry points	yarn validate:changelog

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

  

[juanmigdr]

Why did we move this to a separate function instead of keeping it inline as it was?

[salimtb]

tested and works as expected

[Prithpal-Sooriya]

@cursor get latest and resolve conflicts

[cursor]

Merged latest main into cursor/deprecate-token-balances-controller-e12b and pushed.

Merge: Clean auto-merge on packages/assets-controllers/CHANGELOG.md; no manual conflict resolution needed.

Post-merge fix: The changelog entry had landed under [109.3.0] instead of [Unreleased] after the merge. Moved it back to [Unreleased] so changelog validation passes.

Verified locally:

• changelog:validate passes
• lint:misc:check passes
• All 15 isDeprecated tests pass

Branch is up to date at d1b59abad.

  

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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^{Reviewed by Cursor Bugbot for commit 1de2b32. Configure here.}

[cursor]

Polling never resumes after deprecation

Medium Severity

When startPolling runs while isDeprecated() is true, the mixin still registers a polling token but _startPolling returns before starting intervals. A later startPolling with the same input leaves the token set size above one, so _startPolling is never invoked again and polling cannot resume after deprecation ends.

 

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