/old-coder

name: old-coder
description: Evidence-first development — surround the implementation with an executable spec and a gauntlet of constraints (tests, types, coverage, mutation) so line-by-line review becomes optional. Use when the user explicitly asks for high-assurance or evidence-first work ("reliable", "TDD", "prove it works", "I won't read the code"), or when the change touches high-stakes domains (money, auth, data loss, concurrency, public API). For routine changes where the user just wants normal tests, write good tests directly instead of invoking this loop.

Old Coder: Reliable Coding Under Constraint and Test

The human will NOT read your implementation. Their confidence comes entirely from two artifacts you produce: (1) an **executable specification** they approve before you write code, and (2) an **evidence report** proving the code ran the gauntlet. Your job is to make those two artifacts trustworthy enough that line-by-line review becomes optional within the spec's boundaries.

This inverts the normal review model: **trust moves from inspection to constraints.** Be honest about what that buys: the gauntlet turns the constraints the spec expresses into executable evidence — it cannot show the spec expresses everything that matters, and it is not self-authenticating, because a checker can be unsound and a mapping can claim more than it demonstrates. That is exactly why the human approves the SPEC (the one artifact that breaks the everything-authored-by-the-same-agent correlation), and why EVIDENCE reports layered, auditable confidence, never absolute proof. Every shortcut you take against the gauntlet destroys the only basis of trust.

**Composition with `old-coder-api`:** when both skills apply, this skill owns workflow order, SPEC approval, the gauntlet, and EVIDENCE; `old-coder-api` owns the HTTP/JSON contract. Run its scope check and API gates while drafting SPEC, turn the surviving constraints and risks into acceptance criteria and checks, then map those checks into EVIDENCE. Do not run two parallel workflows.

The Loop

SPEC → (human approves spec, not code) → RED → GREEN → REFACTOR → GAUNTLET → EVIDENCE
                                          ↑_____________________|
                                              repeat per behavior

1. SPEC — the only thing the human reads before code

Turn the request into **executable acceptance criteria** before touching implementation files:

• Write behaviors as Gherkin-style scenarios or a named test list — concrete

inputs, concrete expected outputs, edge cases, and error cases. "Handles bad input" is not a spec; `divide(1, 0) raises ZeroDivisionError with message X` is.

• Include what the change must NOT do (invariants that must survive: existing

tests, public API signatures, performance budgets if stated). These negative constraints are contract clauses like any scenario: each must end up mapped in EVIDENCE to a test, a gauntlet layer, or an explicit skipped-with-reason line — never silently absent from the mapping.

• The spec doubles as the authorization point: include the **setup plan** —

tools to install, git usage (init? checkpoint commit cadence?), files the gauntlet will add **by path**, and **every new dependency with a one-line justification** (prefer the standard library and deps already present; an unjustified package is a spec defect) — so approving the spec authorizes the environment changes in one step instead of N interruptions, and the human can veto a risky package before it is ever installed.

• Show the spec to the human in plain language and get approval **before writing

implementation**. In autonomous mode, state the spec in your response and proceed — but the correlation-breaking review never happened, so EVIDENCE must record `spec approval: not obtained (autonomous run)` and claim correspondingly lower confidence; the spec becomes the artifact the human reviews after the fact.

• **An answer to a question is not an approval.** If you asked the human to

decide something, they answered that question and nothing else. Their answer is an INPUT to the spec, and it CHANGES the spec — so any approval you held before the question is approval of a document that no longer exists. Questions and approval are two exchanges, in that order: fold the answers in, say what changed, show the revised spec, ask again. If you cannot quote the words that approved THIS spec, you do not have approval — an answer to your question, a "go ahead" about some other step, silence, and the request that started the task are none of them approval. The recommended-option shape makes this easy to get wrong: when the human picks the options you recommended, the spec looks unchanged and consent looks implied, and neither is true.

• The spec is append-only during the task. If implementation reveals the spec was

wrong, say so explicitly and revise it visibly — never silently drift.

• **Write the spec to a file and name it by absolute path.** A relative path is

not clickable in a terminal, so the human cannot open the one artifact they are being asked to approve. Same for EVIDENCE when you get there. The SPEC and Gherkin templates are in `references/templates.md`.

• **Commit the spec at approval** where the repo's git conventions allow it —

the setup plan is where that was authorized. Once the approved spec is a commit, later drift is literally a `git diff`. Without a durable spec, a compaction loses the approved contract while the code it authorized remains, and nobody can check whether a scenario was quietly dropped from the EVIDENCE mapping.

2. RED — prove each test can fail

Write the test for one behavior. **Run it and watch it fail** before writing the implementation. A test you never saw fail proves nothing — it may be testing nothing. Details that matter in practice:

• If the module under test doesn't exist yet, create a stub that raises

(