feat(contract): clean-chat-output-v1 — codify M287 cascade sanitization invariants#1859
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…on invariants Author the provable contract behind `clean_chat_output` so the six invariants established by the M287 → #1852 → #1853 cascade are falsifier-backed instead of merely tested. ## Why The cascade fixed three things in concert: - #1852: EOS stop-token detection (`<|im_end|>` / `<|endoftext|>`) - #1853: leading "Human:"/"User:"/"Assistant:" prefix strip - M287 surface: 'Human: I need to...' runaway pattern post-EOS-miss The implementation (`crates/aprender-serve/src/api/realize_handlers.rs::clean_chat_output`) already lives; this contract retroactively codifies its guarantees so future stop-sequence changes require a contract bump alongside the code change. Hooks `pv lint` / contract-coverage audits onto a previously-uncontracted sanitization layer. ## Six falsifiers - V1_001: leading "Human:" / "User:" / "Assistant:" stripped - V1_002: stop sequence inside body truncates at first occurrence - V1_003: earliest stop sequence wins when multiple are present - V1_004: clean text passes through (trim-only) - V1_005: empty / whitespace / stop-only collapses to "" - V1_006: STOP_SEQUENCES code constant ↔ contract YAML stay synced (manual audit for now; could be pv-lint check later) ## Evidence All six are already covered by existing unit tests in `crates/aprender-serve/src/api/realize_handlers_clean_chat.rs` and `crates/aprender-serve/src/api/tests/format_chat_02.rs`. ## Validation `pv validate contracts/clean-chat-output-v1.yaml` → "Contract is valid." 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Summary
Authors the provable contract behind `clean_chat_output` so the six invariants established by the M287 → #1852 → #1853 cascade are falsifier-backed instead of merely tested.
Why
The cascade fixed three things in concert:
The implementation (`crates/aprender-serve/src/api/realize_handlers.rs::clean_chat_output`) already lives; this contract retroactively codifies its guarantees so future stop-sequence changes require a contract bump alongside the code change. Hooks `pv lint` / contract-coverage audits onto a previously-uncontracted sanitization layer.
Six falsifiers
All six are already covered by existing unit tests in `crates/aprender-serve/src/api/realize_handlers_clean_chat.rs` and `crates/aprender-serve/src/api/tests/format_chat_02.rs`.
Validation
```bash
$ cargo run -p aprender-contracts-cli --bin pv -- validate contracts/clean-chat-output-v1.yaml
0 error(s), 0 warning(s)
Contract is valid.
```
🤖 Generated with Claude Code