Ignore chats/ in scaffolded projects

[EiffL]

Summary

• Adds chats/ to the managed .gitignore template, as its last entry.
• jupyter-ai writes agent chat transcripts into chats/ at the project root, so every exchange with an agent dirtied the tree and lc materialize refused to start. A chat is neither a result nor an input.
• Existing projects pick the entry up through lc init's entry-wise repair, which appends only the missing line.

Test plan

• uv run pytest tests/test_templates.py tests/test_project.py tests/test_cli.py (126 passed)
• uv run ruff check src/ tests/

🤖 Generated with Claude Code

[github-actions]

✅ Eval

Metric	Value
Outputs check	success
Agent run	success
Turns	47
Tool calls	45
Cost	$0.78
Agent wall time	3m32s
Model	claude-sonnet-5

lc status

  mode:    direct
  sandbox: landlock (fs: declared, network: allowed)
  crate:   up to date with the outputs

  · current  baseline/best_fit        21005ce
  · current  baseline/hubble_diagram  21005ce
  · current  baseline/residuals       21005ce

3 current

Confusion & pain points (Claude analysis)

Confusion & pain points

• Data format required manual reverse-engineering. astra.yaml and the scaffold docs gave no schema for data/SCPUnion2.1_mu_vs_z.txt, so the agent spent ~8 tool calls (awk/sort/grep probes on column ranges, unique values, zero counts) inferring that column 4 is statistical σ_μ and column 5 is systematic error — only confirmed indirectly by checking that a stat-only fit produced reduced χ²≈1. This is detour work the task/data should have documented (a header comment or data/README.md note describing columns) rather than leaving to empirical guesswork.
• Initial ls -la command exited nonzero despite producing output. The combined ls/cat/head one-liner reported "Exit code 2" with no visible error, likely because one of the chained commands (cat pyproject.toml 2>/dev/null or similar) failed silently inside the &&/; chain — the agent didn't investigate the nonzero code further and just moved on, suggesting the failure was cosmetic but still noise in the trace.
• Numerical instability in the optimizer required a fix mid-run. The l_bfgs_b optimizer path drove Omega_L outside (0,1) during line search, making E(z) imaginary (RuntimeWarning: invalid value encountered in sqrt) and triggering IntegrationWarning. This wasn't a lightcone-cli/spec issue but a modeling gap in the agent's own first draft of cosmo.py/fit.py — it had to add physical bounds after discovering the failure via a test lc run, rather than anticipating it.
• Stale file-state warning after a manual edit. Editing pyproject.toml a second time triggered a tool note that "the file had been modified on disk since you last read it," forcing an extra git diff sanity check to confirm no unexpected changes had crept in — minor friction from interleaving uv add (which rewrites pyproject.toml/uv.lock) with manual edits without re-reading first.
• Otherwise the run was clean: skill loading, spec validation, lc run probes, lc materialize, and RO-Crate publication all worked on the first or second try with no CLI misunderstandings.

Full trace: agent-trace artifact on this run.