#17337: fix(delivery): keep route fields paired to channel during context merge

Fixes #13332 ## Problem When Telegram and webchat share the same session (`agent:main:main`), `mergeDeliveryContext()` would inherit route fields (`to`, `accountId`, `threadId`) from the fallback context even when the primary and fallback contexts named **different channels**. This caused a Telegram-originated reply to pick up webchat's `to`/`accountId` values, mis-routing the response to the webchat UI instead of back to Telegram. ## Fix Added a `channelsConflict` guard in `mergeDeliveryContext()` — when both primary and fallback specify different channel names, route fields (`to`, `accountId`, `threadId`) are **not** inherited from the fallback. They remain paired to the selected channel. This is a 13-line logic change in `src/utils/delivery-context.ts`. ## Changed files - **`src/utils/delivery-context.ts`** — added channel-conflict check before fallback inheritance - **`src/utils/delivery-context.test.ts`** — 3 new test cases: - Cross-channel fields are NOT inherited (telegram vs discord) - Same-channel fields ARE inherited normally - Missing channel in fallback still merges normally - Updated `normalizeSessionDeliveryFields` test to verify cross-channel carryover is blocked ## Tests All 3 new unit tests pass. Existing delivery-context tests updated and passing. <!-- greptile_comment --> <h3>Greptile Summary</h3> Adds cross-channel conflict detection to `mergeDeliveryContext()` to prevent route field mis-pairing when Telegram and webchat share the same session. When primary and fallback contexts specify different channels, route fields (`to`, `accountId`, `threadId`) are not inherited from fallback, keeping them paired to the selected channel. - Fixes mis-routing issue where Telegram replies inherited webchat's route fields - Logic change is minimal (13 lines) and well-tested with 3 new test cases - Preserves existing behavior when channels match or when either context lacks a channel - Updated integration test verifies cross-channel carryover is blocked <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk - The fix is targeted, well-tested, and solves a specific cross-channel routing bug. The logic is sound: it only blocks route field inheritance when both contexts explicitly specify different channels, preserving all existing behavior for same-channel and missing-channel scenarios. Three new unit tests directly validate the fix, and an integration test confirms the end-to-end behavior. - No files require special attention _{Last reviewed commit: 4248f11} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->