#22951: feat(discord): make thread session isolation configurable

## Summary - Adds `threadSessionSuffix` boolean to `DiscordAccountConfig` - When `true`, thread messages get a `:thread:<threadId>` suffix on their session key, giving each thread its own isolated conversation session - Defaults to `false` (existing behavior — threads share the parent channel's session) ### Motivation Without this, all threads under a parent channel share the same session. This means conversation context from one thread bleeds into another — the bot may reference messages from a different thread, confusing users. With `threadSessionSuffix: true`, each thread gets its own session and the bot maintains separate conversation context per thread. Note: `resolveThreadSessionKeys()` already supports the `useSuffix` parameter and defaults to `true` internally — this PR simply exposes the choice to operators via config rather than hardcoding `false`. ### Config ```json { "channels": { "discord": { "threadSessionSuffix": true } } } ``` ## Test plan - [ ] With `threadSessionSuffix: false` (default): verify threads share parent session (existing behavior unchanged) - [ ] With `threadSessionSuffix: true`: verify each thread gets its own session key (`:thread:<id>` suffix) - [ ] Verify no impact on DM sessions - [ ] Verify no impact on forum channel sessions 🤖 Generated with [Claude Code](https://claude.com/claude-code) <!-- greptile_comment --> <h3>Greptile Summary</h3> Adds configurable thread session isolation for Discord via `threadSessionSuffix` boolean (defaults to `false` for backward compatibility). When enabled, each thread gets its own session key with `:thread:<threadId>` suffix, preventing conversation context from bleeding across threads. **Key changes:** - New `threadSessionSuffix?: boolean` field in `DiscordAccountConfig` - Inbound message handler now respects config via `useSuffix: discordConfig?.threadSessionSuffix ?? false` - Exposes existing `resolveThreadSessionKeys()` behavior that was previously hardcoded **Issue found:** - Outbound session resolution (`src/infra/outbound/outbound-session.ts:277`) still hardcodes `useSuffix: false`, creating a session key mismatch when the new config is enabled — inbound and outbound messages for the same thread would use different session keys, breaking conversation continuity <h3>Confidence Score: 2/5</h3> - This PR has a logic issue that breaks the feature when enabled - Score reflects incomplete implementation — the inbound path correctly reads the new config, but the outbound path still hardcodes the old behavior, causing session key mismatches that would break conversation state when `threadSessionSuffix: true` is configured - Pay close attention to `src/infra/outbound/outbound-session.ts` — needs updating to respect the new config _{Last reviewed commit: 2fc51d1} <!-- greptile_other_comments_section --> _{(4/5) You can add custom instructions or style guidelines for the agent [here](https://app.greptile.com/review/github)!} <!-- /greptile_comment -->