sabela: Instructions file for Codex

Agent tool surface

Guidance for anyone shaping the tools an agent sees. It applies to the siza client's tool list, the product chat catalogue, and the JSON those tools return. Repo-wide coding rules live in CLAUDE.md.

The principle

Parsimony, of the surface and of the returned message. Both spend the same budget: the model's context is the scarcest resource in the loop, and every tool name, parameter and returned field is drawn from it before any work happens.

The lens is the one in what category theory teaches us about dataframes: find the core abstraction, express operations as compositions over it, and resist the urge to add a new primitive for every new use. A surface with a few composable operations beats a surface with one operation per task, for the same reason a small algebra beats a catalogue of special cases.

Rules

• Fold, do not accrete. Before adding a tool, ask which existing tool should grow a parameter instead. A new name costs every future caller the reading of it.

• Audit call counts, but read them against the corpus.

  grep -ho '^- `[a-z_]*`' docs/discover/live/*_verbose.md | sort | uniq -c | sort -rn
  

  Zero calls is evidence ONLY when the recorded episodes exercise the capability. A corpus of write-one-cell tasks cannot condemn read_cell, execute_cell or delete_cell: driving a real notebook needs all three, and their absence measures the tasks, not the tools. Before folding a tool away, name the episode that needed it and did something worse instead.

• A tool the harness itself uses is load-bearing at zero model calls. Deletion and re-execution complete the write algebra (insert, replace, delete, run); the recovery paths depend on them whether or not a model ever types the name.

• A separate lookup is a lookup that will not happen. If answering one question reliably requires a second call, carry the answer on the first result. A search hit now carries a haddock synopsis, because a type alone does not say which of describeColumns, summarize and mean answers "summary statistics". The full documentation stays available on demand: carrying the synopsis and offering the detail are complements, not alternatives.

• Check a tool is on the surface before concluding it is unwanted. describe_function recorded zero calls across every episode because the siza catalogue never offered it, not because any model declined it.

• The return value is part of the surface. Return what the caller needs in order to decide, not everything that is known. A field nobody acts on is a field that displaced one they would have.

• Measure the spend. Context cost per call is a design fact. Prefer a bounded synopsis to a full document, a ranked few to an exhaustive list, and say what was omitted rather than silently truncating.

• Manage the context, not just the message. A tool surface is only half the budget; the conversation carrying it is the other half, and it grows without anyone deciding to grow it. Seeding each prompt with the whole prior transcript took a three-part task from 3K characters before its first prompt to 250K before its third, and the work done per prompt fell away with it (live_test52-54).