Summary

• When dmScope is set to per-channel-peer (or per-peer, per-account-channel-peer), WhatsApp DM sessions receive isolated session keys that differ from mainSessionKey.
• However, updateLastRouteInBackground was unconditionally called with mainSessionKey for all DM routes, corrupting the main session's delivery context with the isolated DM's routing info.
• Gate the updateLastRouteInBackground call on params.route.sessionKey === params.route.mainSessionKey, so it only fires when the DM session is not isolated by dmScope.

This is the same fix pattern as PR #13580 (Telegram), now applied to WhatsApp.

Fixes #24912
Related: #13580

Changes

• src/web/auto-reply/monitor/process-message.ts: Added params.route.sessionKey === params.route.mainSessionKey guard to the updateLastRouteInBackground call for DM routes.
• src/web/auto-reply/monitor/process-message.inbound-contract.test.ts: Added two test cases verifying that updateLastRouteInBackground is called when sessionKey === mainSessionKey and skipped when they differ (dmScope isolation).

Test plan

• Verify existing tests pass (vitest run src/web/auto-reply/monitor/process-message.inbound-contract.test.ts)
• New test: calls updateLastRouteInBackground for DMs when sessionKey equals mainSessionKey (no dmScope isolation - existing behavior preserved)
• New test: skips updateLastRouteInBackground for DMs when dmScope isolates session key (dmScope active - bug fix verified)
• Manual: configure dmScope: per-channel-peer on a WhatsApp account, send DMs from different peers, verify the main session's last-route is not overwritten

🤖 Generated with Claude Code

Greptile Summary

Fixes session corruption bug in WhatsApp DM routing when dmScope isolation is active. When dmScope is configured (e.g., per-channel-peer), isolated DM sessions receive different session keys from the main session, but the code was unconditionally calling updateLastRouteInBackground with mainSessionKey for all DMs, overwriting the main session's delivery context with isolated session routing data.

• Adds guard condition checking sessionKey === mainSessionKey before updating last route for DMs
• Preserves existing behavior for non-isolated DMs (when dmScope is not set or set to "main")
• Mirrors the fix pattern from PR fix(telegram): skip updateLastRoute when dmScope isolates DM sessions #13580 (Telegram)
• Includes comprehensive test coverage for both isolated and non-isolated scenarios

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• Surgical bug fix with clear logic, comprehensive test coverage, and follows established pattern from previous fix. The change is minimal (adding a single condition check), well-tested, and addresses a specific corruption issue without introducing new complexity or side effects.
• No files require special attention

_{Last reviewed commit: 67ba9d6}

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