feat(assets-controllers): add isDeprecated to MultichainAssetsController

[Prithpal-Sooriya]

Explanation

MultichainAssetsController is being superseded by the unified AssetsController (feature flag assets-unify-state). To allow it to be turned off without tearing down the controller, this PR adds an optional isDeprecated constructor callback, following the same pattern already introduced for TokenListController (#8945) and the sibling multichain controllers MultichainAssetsRatesController / MultichainBalancesController (#9044).

When isDeprecated() returns true:

• No Snap requests are issued.
• accountsAssets, assetsMetadata, and allIgnoredAssets are reset to {} at construction and re-enforced at every entry point (addAssets, ignoreAssets, _executePoll, and the AccountsController:accountAdded / accountRemoved / accountAssetListUpdated subscriptions), so no stale asset data remains in state.

The callback is re-evaluated on each entry point, so deprecation can be toggled at runtime without reconstructing the controller. The default (() => false) preserves existing behavior, so this is a non-breaking, additive change.

References

• https://consensyssoftware.atlassian.net/browse/ASSETS-3333
• Follows #9044 and #8945

Manual testing steps

N/A — behavior-preserving by default (the new option defaults to disabled). New behavior is covered by unit tests.

Changed files

• packages/assets-controllers/src/MultichainAssetsController/MultichainAssetsController.ts — Added the optional isDeprecated constructor option, a private #enforceDisabledState() helper that clears the three state maps, and guards at every entry point. Verified with lint (eslint, clean), typecheck (yarn build, clean), and unit tests.
• packages/assets-controllers/src/MultichainAssetsController/MultichainAssetsController.test.ts — Added an isDeprecated describe block (construction, runtime-toggle, and no-Snap-request guarantees) and threaded the option through the setupController helper. Verified via jest (59/59 passing).
• packages/assets-controllers/CHANGELOG.md — Added an entry under Unreleased > Added. Verified with yarn workspace @metamask/assets-controllers run changelog:validate.

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

  

[Prithpal-Sooriya]

@cursor fetch latest and resolve merge conflicts

[cursor]

Done. I fetched the latest origin/main and resolved the merge conflict.

• Conflict: Only packages/assets-controllers/CHANGELOG.md conflicted (both main and this branch added entries under Unreleased > Added). I kept my isDeprecated entry at the top of Added and preserved all of main's new entries (Robinhood chain support, getAssetId, the Changed/Removed/Fixed items, and the released-version sections). All other files auto-merged cleanly.
• Verified after merge: reinstalled dependencies (the merge updated lockfile/manifests), changelog validation passes, and the MultichainAssetsController test suite is green (59/59).
• Pushed: merge commit 37e709e is on cursor/deprecate-multichain-assets-controller-ace6, so PR feat(assets-controllers): add isDeprecated to MultichainAssetsController #9310 is now up to date with main and conflict-free.

  

[Prithpal-Sooriya]

Slop generated UTs... This is fine since we are deprecating. Otherwise I'd do a quick cleanup.