Proof-of-Time provenance example (PR #2597): timestamp receipts via MCP, zero adapter code

[axcpeter]

Opened #2597 (examples/mcp_tttps_provenance.py) a little while back and wanted to add some context here in case anyone runs into it.

The example shows a CodeAgent attaching a cryptographic timestamp receipt to its own output using ToolCollection.from_mcp() against an already-published MCP server (@helm-protocol/ttt-mcp, npm, MIT license). It doesn't add any new smolagents capability, from_mcp() already does everything needed. The example just wires it to a Proof-of-Time backend so the agent can seal a tamper-evident "this output existed at time T" receipt for its own result. Worth being precise about what that receipt claims: it attests to when a content hash was seen and that it hasn't been altered since. It says nothing about whether the output itself is correct.

Tested it locally against a real MCP server round trip and a real CodeAgent run, including a fail-open check (PoT backend unreachable, agent still completes normally, no exception surfaces). If anyone wants to see the shape of a receipt without wiring up an agent, there's a small interactive verifier here: https://huggingface.co/spaces/Pittro/tttps-proof-explorer

For anyone who'd rather skip MCP entirely, we also built a plain step_callbacks version (no MCP server, no smolagents import at the package level, just a function wired directly into step_callbacks) and verified it locally. It's not on PyPI yet though, only langchain-openttt is actually published right now (pip install langchain-openttt); the smolagents, LiteLLM and LlamaIndex equivalents are still local only while we finish packaging them.

Open to feedback on the PR itself, or on whether "attach a signed timestamp to agent output" is worth documenting more formally somewhere in the examples tree.