#3182: fix(gateway): use canonical session key in chat.send

Fixes session key mismatch where `chat.send` used raw key (e.g. `"main"`) but `chat.history` used canonical key (e.g. `"agent:main:main"`), causing messages to be written to one session but read from another. This affected: - iOS app chat (messages not appearing in history) - TUI chat output (no assistant responses shown) The fix uses `canonicalKey` from `loadSessionEntry()` instead of the raw `p.sessionKey` when building the `MsgContext`. Fixes #2493 <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR fixes a session key mismatch in `chat.send` by using the canonical session key returned by `loadSessionEntry()` when constructing the `MsgContext`. This aligns `chat.send` with `chat.history`/session storage behavior so messages written during send are appended to the same session that history reads from. The change is localized to the gateway RPC handler (`src/gateway/server-methods/chat.ts`) and affects how inbound chat messages are attributed to a session when dispatched into the auto-reply pipeline. <h3>Confidence Score: 4/5</h3> - This PR is likely safe to merge; the change is small and fixes a real session key mismatch, with a remaining risk of inconsistent use of raw vs canonical keys in adjacent control-plane logic. - The core fix (using `canonicalKey` for `MsgContext.SessionKey`) matches the session store’s canonicalization behavior and should resolve the reported history mismatch. Remaining concern is that other parts of `chat.send` still use the raw session key (send policy evaluation, abort/broadcast bookkeeping), which can lead to edge-case inconsistencies if callers mix alias and canonical keys. - src/gateway/server-methods/chat.ts <!-- greptile_other_comments_section --> _{(3/5) Reply to the agent's comments like "Can you suggest a fix for this @greptileai?" or ask follow-up questions!} **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 -->