fix(tangle): preserve native session events

[drewstone]

What changed

• Preserve the harness-native chat identifier on execution-bound session.updated events.
• Continue to reject mismatched execution identifiers and lifecycle session identifiers.
• Normalize only documented optional Sandbox result fields that the SDK materializes as undefined.
• Reject unknown undefined fields and unsolicited context receipts.

Proof

• Tangle provider tests: 58 passed.
• Tangle provider typecheck: passed.
• Tangle provider build: passed.

[tangletools]

✅ Auto-approved drewstone PR — d1022fd4

This PR was opened by the trusted drewstone account.
The full PR reviewer audit still runs separately and will publish findings if it detects issues.

This approval is provisional. It rests on the audit running. If the audit cannot run — for example the CLI bridge rejects it — this approval is dismissed rather than left standing, so an unrun check never reads as a passing one.

_{tangletools · auto-approval · reason: drewstone_author · 2026-08-13T20:52:27Z}