Track source attribution for individual context parts

[copyberry]

Track source attribution for individual context parts

What changed

• Add ContentItemMetadata to distinguish user input, developer instructions, AGENTS.md, skills, harness context, and tool-supplied context independently of message role and content classification.
• Keep attribution attached to content through prompt assembly, history processing, and hook-output spilling. Distinguish command hooks from MCP hooks and retain tool namespaces when known.
• Treat missing historical attribution as unknown and send per-content metadata only to Responses Lite.

Testing

Update request and history assertions to cover attribution persistence and Responses Lite metadata handling.

[chatgpt-codex-connector]

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