Fix: subEntityId not passed to app when deeplink clicked from within target channel

[Copilot]

On Teams desktop/web, clicking a deeplink (with subEntityId in context) from within the same channel where the tab is already open causes the host to send a load message to the running tab rather than doing a full reload. The SDK's LoadContext interface lacked a subEntityId field, so the value was silently dropped — leaving context.page.subPageId undefined. Mobile always does a full reload, so it was unaffected.

Main changes in the PR:

1. ResumeContext — added subPageId?: string so apps using registerOnResumeHandler receive the sub-page navigation target
2. LoadContext (deprecated) — added subEntityId?: string for parity; documented to point consumers toward ResumeContext.subPageId
3. convertToResumeContext (handlers.ts) — maps loadContext.subEntityId → resumeContext.subPageId

Before / after (app using registerOnResumeHandler):

// Deeplink clicked from within the same channel — previously subPageId was undefined
app.lifecycle.registerOnResumeHandler((context: ResumeContext) => {
  console.log(context.subPageId); // Before: undefined  |  After: "some-value"
  app.notifySuccess();
});

Validation

Validation performed:

1. Ran full test suite (9249 tests pass; only pre-existing umdExportParity failures due to missing build artifact)

Unit Tests added:

Yes — added tests in teamsAPIs.spec.ts and app.spec.ts covering:

• registerOnLoadHandler receives subEntityId from the load message
• registerOnResumeHandler receives subPageId mapped from subEntityId (framed and frameless)
• subPageId is undefined when subEntityId is absent from the load context

End-to-end tests added:

No

Additional Requirements

Change file added:

No

Next/remaining steps:

• The Teams desktop/web host must actually include subEntityId in the load message payload when resuming a tab via a deeplink. This SDK change is a necessary precondition, but the fix is only effective once the host sends the field.

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