# Traps Bugs this project has **already** shipped into a branch, what let them through, and the guard that now catches them. Read before writing tests; each entry is a class of mistake, not a one-off. The pattern in almost all of them: **the test passed, and the test was wrong.** A green suite is evidence only if the test can fail. --- ## 1. A regression test that cannot fail against the bug is not a regression test **M4-a.** `LogPlayer.new()` changed from `(name, class_id, luck_descriptor)` to `(name, race_id, calling_id, luck_descriptor)`. Three callers kept the old 3-argument shape. The fix added a test — which constructed its *own* correct `LogPlayer` and asserted the constructor worked. You could revert the broken call site and the suite stayed green. **The guard:** a regression test must assert on **the thing that was broken**, not on a fresh correct instance of the same type. Here, that meant asserting on the seed log the *call site* builds (`test_main_window_shell.gd`), not on a `LogPlayer` the test made. **Prove it.** Before accepting a fix, re-break the code, run the suite, and *watch the new test fail*. If it doesn't, the test is decoration. This is now the standard for any fix that claims to guard a regression. --- ## 2. GDScript default parameters turn an arity change into a silent miscompile **M4-a.** Every parameter of `LogPlayer._init` has a default, so `LogPlayer.new("Vexcca", "sellsword", "Fortune spits on you")` — the *old* 3-arg call — compiled without a warning against the *new* 4-arg signature. `"sellsword"` bound to `race_id` (rejected → `""`), the Luck descriptor bound to `calling_id` (rejected → `""`), and `luck_descriptor` defaulted to `""`. The live shell and both proving scenes emitted a player block of four empty strings — which fails the very JSON Schema that migration had just tightened. Two `push_error`s fired into a log nobody was reading. **Why it survived review:** the migration was verified with `grep -rn "class_id" client api docs content`, which came back clean. **Grep cannot see positional arguments.** The field name was gone; the *call sites* were not. **The guard:** when changing a function's arity or parameter order, grep for the **callers** (`grep -rn "LogPlayer.new("`), never for the field name. And if the type is constructed in a scene or harness that no unit test touches, that is exactly where the bug will live — write the test that loads it. --- ## 3. A determinism test that compares two runs tests nothing **M4-a.** Character creation is seeded: the same seed must always produce the same character (charter §10). The test built the character twice and asserted the two were equal. Both runs change *together* — so reordering `Attributes.IDS` from `str,dex,con,fth,mag` to anything else would have silently rewritten **every seeded character in every future save**, with the suite fully green. **The guard:** pin the **stream**, not the symmetry. `test_golden_vector_pins_the_rng_stream` hardcodes the exact five attribute values *and the exact hidden Luck* for a fixed seed. It was proven to fail against a reordered `Attributes.IDS`. Any RNG-order contract (creation now; combat seeding at M5; saves at M9) needs a golden vector. Two-runs-agree is not a determinism test. --- ## 4. A closed vocabulary is not bounded if the model can repeat a tag **Currency.** Charter §6 gives NPCs eight moves and *no quantity argument*, deliberately: the model picks from a closed vocabulary and never invents a number (§2). But `TagExtractor` returns **every** occurrence of a tag, `MoveValidator` is a pure membership test, and `MoveApplier` looped and applied each one. So a model emitting `[MOVE: accept_item(copper)]` forty-seven times drained a 47-copper purse, and ten `[MOVE: give_item(gold)]` tags minted 100,000c. **The model chose the amount, in unary.** Rejecting a quantity argument bought nothing; repetition smuggled the integer back in. **The guard:** a move applies **at most once per reply**, keyed on `name(id)`. And `adjust_disposition`'s `MAX_DELTA` now caps the reply's **net** swing — it used to clamp per *tag*, so three `+15`s moved standing by 45, the exact "wholesale swing" its own comment forbids. **The general lesson:** when the defence is "the model can only pick from a list," ask what happens if it picks the *same item N times*. Validation that is a membership test is not a rate limit. --- ## 5. One fact, two homes — and only one of them is guarded **M4-a.** The calling roster (`sellsword`, `reaver`, …) needs to be known by the client (`Callings.IDS`), the JSON Schema the API validates against, the *origin* schema, and the content blurb files. A parity test guarded code ↔ canon-log schema. It did **not** guard: - `docs/canon-log.md` — *the* cross-boundary contract doc, still documenting `class_id`. - `.claude/skills/world-building/references/schema.md` — a **shipped authoring tool** whose job is to emit content in the exact format the build consumes. It still told authors to write `allowed_classes`. Any origin authored with it would have been rejected by the schema, and at runtime `NewGame` would have read `allowed_callings` → `[]` → **every calling forbidden.** **The guard:** when a roster or enum exists in more than one place, enumerate **every** copy — including prose docs and tooling — and add a parity test per machine-readable copy. Ask specifically: *is there a doc, a skill, or a template that also writes this down?* --- ## 6. Generated content has a client consumer **Duncarrow purge.** `content/world/**` is emitted by `content_build`, but it is also **read by the client** (`content_db.gd` via the harnesses, plus `test_content_db.gd`). Deleting generated content is therefore a *client* change, not a content change, and will break client tests. **The guard:** after any content change, run `PYTHONPATH=tools python3 -m content_build --check`, then `git diff --stat dev...HEAD -- content/world content/server` and confirm nothing changed that you did not intend. --- ## The checklist this all reduces to - Can the new test **fail**? Re-break the code and watch it. If it can't fail, it isn't a test. - Changed an **arity or parameter order**? Grep the *callers*, not the field name. - Anything **seeded**? Pin the stream with a golden vector. - Anything the **model can emit**? Ask what happens if it emits it *twice*. - Any fact written down **twice**? Guard every copy — including docs and tooling. - Touched **content**? Check the generated tree and the build.