Bug Description

Discord thread starter context (ThreadStarterBody) is re-injected into the agent's input on every turn of a thread conversation, causing echo contamination. The agent receives [Thread starter - for context] repeatedly, which can leak into outbound messages.

Root Cause

The Discord adapter in finalizeInboundContext sets ThreadStarterBody: threadStarterBody unconditionally on every inbound message. Unlike Slack (fixed in #32133) and iMessage (fixed in #33295), Discord has no guard to limit this to the first turn.

Layer 1 — Discord Adapter (no guard):

// Current (broken):
ThreadStarterBody: threadStarterBody,

// Fixed (matches Slack pattern):
ThreadStarterBody: !previousTimestamp ? threadStarterBody : void 0,

Layer 2 — Session Handler (no guard):

// Current (broken):
const threadStarterBody = ctx.ThreadStarterBody?.trim();

// Fixed:
const threadStarterBody = isNewSession ? ctx.ThreadStarterBody?.trim() : void 0;

Impact

• Thread starter text is prepended to every agent turn
• Agent may echo back metadata markers like [Thread starter - for context]
• Increases token usage on every turn
• Affects all Discord thread conversations

Affected Files

All compiled bundles containing the Discord adapter and session handler:

• dist/reply-*.js
• dist/pi-embedded-*.js
• dist/compact-*.js
• dist/plugin-sdk/reply-*.js
• dist/plugin-sdk/dispatch-*.js

Workaround

Set includeThreadStarter: false per-channel in config:

{
  "channels": {
    "discord": {
      "guilds": {
        "<guild-id>": {
          "channels": {
            "*": {
              "includeThreadStarter": false
            }
          }
        }
      }
    }
  }
}

This disables thread starter context entirely (including the useful first-turn context).

Related PRs

• fix(slack): reduce token bloat by skipping thread context on existing sessions #32133 — Slack thread context fix (same pattern, Discord not included)
• fix(imessage): prevent echo loop from leaking internal metadata and amplifying NO_REPLY into queue overflow #33295 — iMessage echo loop hardening

Suggested Fix

Apply the same !previousTimestamp guard pattern from the Slack fix (#32133) to the Discord adapter, and add a redundant isNewSession guard in the session handler.