fix(host-api): tear down subscriptions on transport disposal

[cuteWarmFrog]

Description

Fixes the uncaught Error: Transport is disposed thrown from a subscription producer after a transport is destroyed (seen in Sentry when a product/container is closed — e.g. statement-store flush after navigating away).

handleSubscription tracks each producer's unsubscribe per requestId, but only runs them via the cleanup it returns. transport.destroy() never calls that cleanup, and host-container's subscription slot discards it. So a disposed transport leaves producers running; their next (often batched/async) emission calls send() → postMessage() → throwIfDisposed() and throws, unhandled.

Changes Made

In packages/host-api/src/transport.ts, handleSubscription:

• Drain on destroy: register the existing teardown via transport.onDestroy(...), so destroy() tears down every active producer subscription regardless of what the caller does with the returned cleanup. The returned cleanup also unregisters the destroy listener.
• No-op late emissions: guard the receive/interrupt callbacks with the disposed flag, so an emission already queued at the moment of disposal is dropped silently instead of throwing.
• Avoid double-unsub: the stop handler now deletes its map entry, so a subscription that was already stopped isn't unsubscribed again when destroy() drains the map.

One place, fixes every consumer (statement-store, theme, accounts, preimage, chat, payments).

Tests

Added two tests in transport.spec.ts:

• destroy() runs the producer's unsubscribe.
• a producer emission after destroy() does not throw and is not delivered.

Both fail on the current code and pass with this change.

Verification

• nx typecheck host-api: pass
• nx lint host-api: 0 errors (pre-existing any warnings only)
• host-api/transport.spec.ts: 9/9 pass

Note: 3 tests in __tests__/hostApi/theme.spec.ts fail on the clean release/0.8 tip (the published 0.8.0 commit) independent of this change — pre-existing, unrelated to this fix.

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[cuteWarmFrog]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

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