pearl th-01c714: bracketed-paste + flatten prompt so multi-line task arrives as one TUI submission

[brentrager]

Summary

After PR #57 (pearl th-7fdfa9) fixed the literal-`j` newline encoding bug in `tmux_driver::send`, newlines correctly survive into the TUI's input box — but the `smooth-code` TUI submits on every `\n`. A 13-line task prompt was therefore arriving as 13 separate `You:` submissions instead of one cohesive task (evidence: `~/.smooth/bench-runs/80c092b0/python-affine-cipher.pane.log`).

Two-pronged fix:

• tmux_driver::send — added `-p` to `tmux paste-buffer` for bracketed-paste mode. Bracketed-paste-aware TUIs treat embedded newlines as soft newlines (insert), not Enter (submit). For applications that don't enable bracketed-paste mode, tmux strips the markers — safe upgrade.
• lib::build_prompt + human_driver::flatten_for_tui — reformatted the bench task prompt to a single line (semicolon-joined), and added `flatten_for_tui` (collapses `\n` to ` | `) applied to the seed prompt and every driver-model follow-up before `driver.send`. Belt-and-suspenders so the harness doesn't depend on the receiver honoring bracketed paste.

Tests added

• `lib::build_prompt_is_single_line` — asserts no `\n`/`\r` in the bench task prompt.
• `human_driver::flatten_for_tui_*` (5 cases) — passthrough, trimming, empty input, blank-line dropping, multi-line → pipe-separated.

Verification (single-task smoke)

`cargo run --release -p smooai-smooth-bench -- score-tui --pr --th-binary $(which th) --task-limit 1 --debug --output /tmp/bench/smoke3.json --budget-usd 2`

New pane log (`~/.smooth/bench-runs/83791c18/python-affine-cipher.pane.log`) shows the seeded prompt landing as one `You:` block containing the full prompt:

```
System:
Type a message to get started. /help for commands.

You:
You are solving Aider Polyglot task `affine-cipher` (python). Working directory: the current directory. Files present: INSTRUCTIONS.md, affine_cipher.py, affine_cipher_test.py. Your job: read
INSTRUCTIONS.md and the test file to understand the requirements; edit the source file(s) so `python3 -m pytest -q` passes every test; do not modify test files; stop once the tests pass — do not keep
iterating. Constraints: use only the standard library for the language; keep the implementation idiomatic and concise.
```

(The visual line-wrapping above is just the pane width — it's a single TUI submission. The previous buggy run had 13 separate `You:` blocks for the same prompt.)

The task itself still failed (affine-cipher under single-shot constraints is hard), but the harness is now sending what we intend.

Which strategy did the heavy lifting?

Hard to say in isolation — both shipped together. The flattened prompt is the load-bearing fix because it makes the question moot regardless of whether the TUI honors bracketed paste. The `-p` flag is the cleaner long-term fix if/when smooth-code adds bracketed-paste handling; for now it's a free safety belt.

Test plan

• `cargo fmt -- --check`
• `cargo clippy -p smooai-smooth-bench --all-targets` (0 errors)
• `cargo build` (clean)
• `cargo test -p smooai-smooth-bench --lib` (130 passed)
• Single-task `score-tui --pr --task-limit 1 --debug` smoke — pane log shows one `You:` block per submission

🤖 Generated with Claude Code

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Latest commit: d045c8a

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