fix(agent-chat): guard integration lookup in manualPosting modal

[giladresisi]

Problem

Opening the agent-chat "populated modal" (the manualPosting CopilotKit action) can white-screen the whole chat with:

TypeError: Cannot read properties of undefined (reading 'picture')
  at OpenModal.useCallback[startModal] (agent.chat.tsx:305)

manualPosting builds the modal from properties — the channels the user has selected in the agent-chat sidebar (PropertiesContext, fed by AgentList). It looked up the integration with properties.find(...).picture and no null guard. Whenever the action references an integration that isn't in the selected list, find returns undefined and .picture throws.

This is reachable any time the agent opens the modal for a channel the user hasn't selected in the sidebar — e.g. asking the agent to open a modal for an existing post's channel.

Fix

One-character defensive guard — properties.find(...)?.picture || '' — so the modal degrades to an empty picture instead of crashing. No behavior change when the integration is present.

Notes

Pre-existing latent crash, independent of any specific feature. Small and self-contained.

🤖 Generated with Claude Code

[postiz-contribution]

Contribution-checker quality warning
Heuristic score: 16/100 (low). This is a non-blocking warning surfaced by the project's quality settings.

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[postiz-agent]

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