feat(assets-controller): add getAsset

[Kriys94]

Explanation

WPN-1472 centralizes the Assets domain in @metamask/assets-controller so consumers (including Snaps) can read controller-owned balances, metadata, prices, and fiat values instead of tracking them independently. Today the controller exposes getAssets (bulk, per-account map), getAssetMetadata (metadata only), and getAssetsPrice, but there is no way to read a single combined asset for a specific account/asset pair.

This PR adds a getAsset read API to AssetsController:

• getAsset(accountId, assetId): Asset | undefined returns the combined Asset (balance + metadata + price + computed fiatValue) for a single account/asset pair from current controller state, or undefined when a complete renderable asset is not available.
• Exposed as the AssetsController:getAsset messenger action so it can be called through the messenger (e.g. by preinstalled Snaps once WPC-1017 lands).

Behavior details:

• Reuses the same state-composition and filtering logic as getAssets (via the private #getAssetsFromState) so the returned shape never drifts: balance and metadata are required; a missing price falls back to { price: 0, lastUpdated: 0 } with fiatValue: 0; hidden/filtered assets resolve to undefined.
• Reads from current state only — it does not trigger a data-source refresh.
• Validates inputs and throws (rather than silently returning undefined) on an empty accountId or a malformed CAIP-19 assetId, so consumers can distinguish bad requests from absent data.
• Normalizes the assetId (checksums EVM ERC-20 addresses) before lookup, consistent with how state is keyed.
• #getAssetsFromState's accounts parameter was widened to Pick<InternalAccount, 'id'>[] (it only reads account.id) so getAsset can reuse it without constructing a full account object.

The generated messenger action types (AssetsControllerGetAssetAction) were regenerated and exported from index.ts, and a ### Added changelog entry was added.

References

• Jira: WPN-1473 — [AssetsController] Add getAsset read API for Snap consumers
• Part of the Assets migration epic (WPN-1472); sibling controller-side stories are WPN-1489 (stage-gated ingestion) and WPN-1490 (stage-gated ignoring of Snap events)
• Consumer-side exposure to Snaps is blocked by WPC-1017 (messenger API exposure); the controller-side method in this PR is independent of that work

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

---

Note

Low Risk
Additive read-only API with tests and aligned with existing getAssets composition; no fetch or state-write behavior changes beyond the new method signature tweak on #getAssetsFromState.

Overview
Adds getAsset(accountId, assetId) and the AssetsController:getAsset messenger action so consumers can read one fully composed Asset (balance, metadata, price, fiatValue) from current state without calling bulk getAssets.

Implementation routes through #getAssetsFromState with the same filtering as getAssets (requires balance + metadata, zero price fallback, hidden assets excluded), normalizes CAIP-19 IDs, validates inputs (throws on empty account or invalid asset id), and does not trigger fetches. #getAssetsFromState now accepts Pick<InternalAccount, 'id'>[] so single-asset lookups do not need full account objects.

Exports AssetsControllerGetAssetAction, registers/unregisters the messenger handler, documents the API in generated action types, and adds changelog + unit tests.

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Skips enabled-chain filtering

Medium Severity

getAsset passes only the asset’s own chain into #getAssetsFromState, while default getAssets filters with #enabledChains. A balance on a disabled network can be returned by getAsset but omitted from getAssets, breaking the documented parity between the two APIs.

 

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[Kriys94]

Well this function will be used by Snaps independently from the enabledChains

[Prithpal-Sooriya]

nit - A tad nuts that we are calculating all assets, only to return a single asset here.

This is okay for now, we can raise/improve moving forward.

[Prithpal-Sooriya]

Very good! Keep interface minimal!
Easier to test and use.

[Prithpal-Sooriya]

🌶️ this test file is too big, impossible to read!

Thoughts on:

1. Making this spec more dry. I think we can leverage test tables (it.each)
2. spicer -- separate test for each method, truly isolated, easy to read 😈

[Prithpal-Sooriya]

I'm fine keeping this as is... but I'd like to pencil in test cleanup.

[Prithpal-Sooriya]

Approving with comments