#17527: fix(gateway): allow WebChat to attach to main session regardless of deliveryContext channel

Fixes #15189 ## Problem When WebChat connects to the main session, `recordInboundSession` updates the session's `lastChannel` and `deliveryContext` fields to `webchat`. This breaks announce, heartbeat, and cron delivery because those systems route replies through `deliveryContext` — and WebChat uses WebSocket, not deliveryContext routing. **Example:** User chats via Telegram, opens WebChat to check something, and suddenly all cron/heartbeat announcements try to route through `webchat` (which has no external delivery path) instead of Telegram. ## Fix Skip the `updateLastRoute` call when the inbound channel is an internal message channel (WebChat). The existing `isInternalMessageChannel()` utility already identifies these channels — we just gate the route update behind it. ### Changed files - **`src/channels/session.ts`** — Early return before `updateLastRoute` when channel is internal (8 lines) - **`src/channels/session.test.ts`** — New test file with 2 cases: WebChat preserves existing delivery context; external channels update normally (125 lines) ## Tests ``` ✓ src/channels/session.test.ts (2 tests) ✓ skips updateLastRoute when channel is webchat (internal) ✓ updates lastRoute normally for external channels ``` <!-- greptile_comment --> <h3>Greptile Summary</h3> This PR fixes a bug where WebChat connections to the main session would overwrite the session's `deliveryContext` and `lastChannel` to "webchat", breaking announce/heartbeat/cron delivery for the external channel (e.g., Telegram) that actually owns the conversation. The fix adds an early return in `recordInboundSession` that skips the `updateLastRoute` call when the inbound channel is an internal message channel (webchat), using the existing `isInternalMessageChannel()` utility. - **`src/channels/session.ts`**: Gates `updateLastRoute` behind `isInternalMessageChannel()` check — webchat skips route updates while still recording session metadata via `recordSessionMetaFromInbound` - **`src/channels/session.test.ts`**: New test file with two integration tests verifying webchat preserves existing delivery context and external channels update normally - Minor: unused `vi` import in the test file <h3>Confidence Score: 5/5</h3> - This PR is safe to merge — it's a targeted, well-scoped bug fix with proper test coverage - The change is minimal (one guard clause using an existing utility), correctly addresses a real routing bug, and has two passing integration tests covering both the fix and the happy path. The fix is applied at the right layer — `recordSessionMetaFromInbound` (origin metadata) is still called, only `updateLastRoute` (delivery routing) is skipped for internal channels. No risk of regression for external channels. - No files require special attention _{Last reviewed commit: cb87e1e} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->