#8507: fix: preserve accountId for multi-account agent-to-agent messaging

## Problem When using `sessions_send` for agent-to-agent communication in a multi-account Telegram setup, announces from the target agent fail with: ``` Telegram bot token missing. Set TELEGRAM_BOT_TOKEN or channels.telegram.botToken. ``` This happens even when the account-level token is correctly configured at `channels.telegram.accounts.<id>.botToken`. ## Root Cause When an agent runs via `sessions_send` (or other internal channel operations), `runAgentStep` calls the `agent` gateway method with `channel: INTERNAL_MESSAGE_CHANNEL` and `deliver: false`. In `resolveAgentDeliveryPlan`, the `resolvedAccountId` was only being set from: 1. Explicit `params.accountId` (not passed by runAgentStep) 2. `baseDelivery.accountId` (only for implicit delivery mode) Since internal channel operations don't use implicit delivery mode, the session's `lastAccountId` was lost, causing tools like `message` to not have the correct `agentAccountId` context. ## Fix - Modified `resolveAgentDeliveryPlan` to fall back to `baseDelivery.lastAccountId` before checking delivery mode - Updated Telegram token error messages to mention the account-level config path ## Testing This fix enables multi-account announces where each agent has its own Telegram bot token: ```json5 { channels: { telegram: { accounts: { wren: { botToken: "wren-token" }, mogger: { botToken: "mogger-token" } } } } } ``` With this fix, when Mogger sends a `sessions_send` to Wren, Wren's announce will correctly use `wren-token` to post to Telegram. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR fixes multi-account agent-to-agent messaging by preserving an account context when resolving an agent’s delivery plan, and it improves Telegram error messaging to include the account-scoped bot token config path. The key behavioral change is in `resolveAgentDeliveryPlan` (`src/infra/outbound/agent-delivery.ts`), which now falls back to the session’s `lastAccountId` when no explicit `accountId` is provided, even for internal-channel operations where `deliver: false` is used. The Telegram tool updates (`src/agents/tools/telegram-actions.ts`) are purely user-facing error text changes to guide users toward `channels.telegram.accounts.<id>.botToken`. <h3>Confidence Score: 3/5</h3> - This PR is likely safe to merge, but the accountId fallback change may unintentionally affect explicit-target sends. - The change is small and addresses a real missing-context bug, but `resolvedAccountId` now prefers `lastAccountId` even when `explicitTo` is provided, which appears to contradict an existing e2e test expectation and could change routing/account selection for explicit sends. - src/infra/outbound/agent-delivery.ts <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->